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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..d7b82bc --- /dev/null +++ b/.gitattributes @@ -0,0 +1,4 @@ +*.txt text eol=lf +*.htm text eol=lf +*.html text eol=lf +*.md text eol=lf diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..6bf4440 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #69061 (https://www.gutenberg.org/ebooks/69061) diff --git a/old/69061-0.txt b/old/69061-0.txt deleted file mode 100644 index 839be3f..0000000 --- a/old/69061-0.txt +++ /dev/null @@ -1,2042 +0,0 @@ -The Project Gutenberg eBook of Precision locating and dividing -methods, by Anonymous - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world at no cost and with almost no restrictions -whatsoever. You may copy it, give it away or re-use it under the terms -of the Project Gutenberg License included with this eBook or online at -www.gutenberg.org. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: Precision locating and dividing methods - -Author: Anonymous - -Release Date: September 28, 2022 [eBook #69061] - -Language: English - -Produced by: deaurider and the Online Distributed Proofreading Team at - https://www.pgdp.net (This file was produced from images - generously made available by The Internet Archive) - -*** START OF THE PROJECT GUTENBERG EBOOK PRECISION LOCATING AND -DIVIDING METHODS *** - - - - - -Transcriber’s Notes: - - Underscores “_” before and after a word or phrase indicate _italics_ - in the original text. - Equal signs “=” before and after a word or phrase indicate =bold= - in the original text. - Small capitals have been converted to SOLID capitals. - Illustrations have been moved so they do not break up paragraphs. - Typographical and punctuation errors have been silently corrected. - - - - - =MACHINERY’S REFERENCE SERIES= - - EACH NUMBER IS ONE UNIT IN A COMPLETE LIBRARY OF - MACHINE DESIGN AND SHOP PRACTICE REVISED AND - REPUBLISHED FROM MACHINERY - - NUMBER 135 - PRECISION LOCATING AND - DIVIDING METHODS - - CONTENTS - Precision Locating Methods 3 - Accurate Dividing and Spacing Methods 21 - Locating Work for Boring on Milling Machine 32 - - Copyright, 1914, The Industrial Press, - Publishers of MACHINERY, - 140-148 Lafayette Street, New York City - - Other books in this series dealing with - the subjects of Toolmaking and kindred - topics are as follows: - - No. 31—THREAD TOOLS AND GAGES - No. 64—GAGE MAKING AND LAPPING - No. 107—DROP FORGING DIE SINKING - No. 130—GAGING TOOLS AND METHODS - -[Illustration: MACHINERY] - - MACHINERY - - The Leading - Mechanical Journal - - MACHINE DESIGN - CONSTRUCTION - SHOP PRACTICE - - THE INDUSTRIAL PRESS - 140-148 Lafayette St. - New York City - 51-52 Chancery Lane, London - - - - -CHAPTER I - -PRECISION LOCATING METHODS - - -The degree of accuracy that is necessary in the construction of -certain classes of machinery and tools, has made it necessary for -toolmakers and machinists to employ various methods and appliances -for locating holes or finished surfaces to given dimensions and -within the prescribed limits of accuracy. In this treatise, various -approved methods of locating work, such as are used more particularly -in tool-rooms, are described and illustrated. These are not given, in -every case, as being the best possible method under all conditions, -because, as every mechanical man knows, the best way may be dependent -upon the element of accuracy with little regard for the time required -to do the work, or this order may be reversed; therefore, one method is -seldom, if ever, the best under all circumstances, and it is necessary -for the workman to consider the conditions in each case and then be -guided by his judgment and experience in determining just how the work -should be done. - - -Button Method of Accurately Locating Work - -Among the different methods employed by toolmakers for accurately -locating work such as jigs, etc., on the faceplate of a lathe, one of -the most commonly used is known as the “button method.” This method is -so named because cylindrical bushings or buttons are attached to the -work in positions corresponding to the holes to be bored, after which -they are used in locating the work. These buttons which are ordinarily -about ½ or ⅝ inch in diameter, are ground and lapped to the same size, -and the ends are finished perfectly square. The outside diameter -should preferably be such that the radius can easily be determined, -and the hole through the center should be about ⅛ inch larger than the -retaining screw so that the button can be adjusted laterally. - -As a simple example of the practical application of the button method, -suppose three holes are to be bored in a jig-plate according to the -dimensions given in Fig. 1. A common method of procedure would be as -follows: First lay out the centers of all holes to be bored, by the -usual method. Mark these centers with a prick-punch and then drill -holes for the machine screws which are used to clamp the buttons. After -the buttons are clamped lightly in place, set them in correct relation -with each other and with the jig-plate. The proper location of the -buttons is very important, as their positions largely determine the -accuracy of the work. The best method of locating a number of buttons -depends, to some extent, upon their relative positions, the instruments -available, and the accuracy required. When buttons must be located at -given distances from the finished sides of a jig, a surface plate and -vernier height gage are often used. The method is to place that side -from which the button is to be set, upon an accurate surface plate and -then set the button by means of the height gage, allowance being made, -of course, for the radius of the button. The center-to-center distance -between the different buttons can afterwards be verified by taking -direct measurements with a micrometer. - -[Illustration: Fig. 1. Simple Example of Work Illustrating Application -of Button Method] - -Figs. 2 and 3 illustrate a method which requires only a micrometer. Two -of the buttons are set at the correct distance from one edge of the -plate by measuring from a parallel strip. Obviously, the micrometer -reading will exceed the distance from the center of a button to the -edge of the plate, by the amount equal to the thickness of the parallel -strip plus the radius of the button. The center-to-center distance -between each pair of buttons is also tested as indicated in Fig. 3, by -measuring the overall distance and deducting the diameter of one button. - -After the buttons have been set and the screws are tightened, all -measurements should be carefully checked. The work is then mounted -on the faceplate of the lathe and one of the buttons is set true by -the use of a test indicator as shown in Fig. 4. When the dial of the -indicator ceases to vibrate, thus showing that the button runs true, -the latter should be removed so that the hole can be drilled and bored -to the required size. In a similar manner other buttons are indicated -and the holes bored, one at a time. It is evident that if each button -is correctly located and set perfectly true in the lathe, the various -holes will be located the required distance apart within very close -limits. - -[Illustration: Fig. 2. Determining Distance from Button to Edge of -Plate] - -Another example of work illustrating the application of the button -method is shown in Fig. 5. The disk-shaped part illustrated is a flange -templet which formed a part of a fixture for drilling holes in flanged -plates, the holes being located on a circle 6 inches in diameter. -It was necessary to space the six holes equi-distantly so that the -holes in the flanges would match in any position, thus making them -interchangeable. First a plug was turned so that it fitted snugly in -the 1¼-inch central hole of the plate and projected above the top -surface about ¾ inch. A center was located in this plug and from it -a circle of three inches radius was drawn. This circle was divided -into six equal parts and then small circles ⅝ inch in diameter were -drawn to indicate the outside circumference of the bushings to be -placed in the holes. These circles served as a guide when setting the -button and enabled the work to be done much more quickly. The centers -of the holes were next carefully prick-punched and small holes were -drilled and tapped for No. 10 machine screws. After this the six -buttons were attached in approximately the correct positions and the -screws tightened enough to hold the buttons firmly, but allow them to -be moved by tapping lightly. As the radius of the circle is 3 inches, -the radius of the central plug, ⅝ inch, and that of each button, ⁵/₁₆ -inch, the distance from the outside of the central plug to the outside -of any button, when correctly set, must be 3 ¹⁵/₁₆ inches. Since there -are six buttons around the circle, the center-to-center distance is -equal to the radius, and the distance between the outside or any two -buttons should be 3⅝ inches. Having determined these dimensions, each -button is set equi-distant from the central plug and the required -distance apart, by using a micrometer. As each button is brought into -its correct position, it should be tightened down a little so that it -will be located firmly when finally set. The work is then strapped to -the faceplate of a lathe and each button is indicated for boring the -different holes by means of an indicator, as previously described. When -the buttons are removed it will be found that in nearly all cases the -small screw holes will not run exactly true; therefore, it is advisable -to form a true starting point for the drill by using a lathe tool. - -[Illustration: Fig. 3. Testing Location of Buttons] - -Fig. 7 shows a method of locating buttons from the finished sides of a -plate, and this same plate with the five buttons attached is shown in -Fig. 6. As the dimensions in Fig. 7 indicate, the holes must not only -be accurate with relation to each other, but also with reference to -the edges of the templet; therefore, it is necessary to work from the -sides as well as the center. The width of the plate was first measured -carefully and found to be 5 inches. As the center-to-center distance -between buttons _B_ and _C_ and also buttons _D_ and _E_, is 2½ inches, -the distance from the center of each outside button to the edge of the -plate is 1¼ inch. A ¼-inch parallel was clamped against the side, as -shown in the illustration, and then the distance from the outside of -each button to the outside of the parallel (1 ¹³/₁₆ inch) was measured -in conjunction with the distance _L_ from the central button. The -distance _L_ was obtained by first determining the center-to-center -distance _M_ which represents the hypotenuse of a right-angled triangle. - - _M_² = 1.25² + 1.625² - ______________ _____ - or _M_ = √1.25² + 1.625² = √4.024 = 2.050 inches. - -Therefore, _L_ = 2.050 + 0.625 = 2.675 inches. - -In this case, the center button was first located correctly from the -sides and end and then the other buttons were set. When doing precision -work of this kind, the degree of accuracy obtained will depend upon -the instruments used, the judgment and skill of the workman, and the -care exercised. A good general rule to follow when locating bushings -or buttons is to use the method which is the most direct and which -requires the least number of measurements, in order to prevent an -accumulation of errors. - - -Locating Work by the Disk Method - -Comparatively small precision work is sometimes located by the disk -method, which is the same in principle as the button method, the chief -difference being that disks are used instead of buttons. These disks -are made to such diameters that when their peripheries are in contact, -each disk center will coincide with the position of the hole to be -bored; the centers are then used for locating the work. To illustrate -this method, suppose that the master-plate shown at the left in Fig. 8 -is to have three holes _a_, _b_, and _c_ bored into it, to the center -distances given. - -[Illustration: Fig. 4. Testing Concentricity of Button Preparatory to -Boring Hole in Lathe] - -It is first necessary to determine the diameters of the disks. If -the center distances between all the holes were equal, the diameters -would, of course, equal this dimension. When, however, the distances -between the centers are unequal, the diameters may be found as follows: -Subtract, say, dimension _y_ from _x_, thus obtaining the difference -between the radii of disks _C_ and _A_ (see right-hand sketch); add -this difference to dimension _z_, and the result will be the diameter -of disk _A_. Dividing this diameter by 2 gives the radius, which, -subtracted from center distance _x_ equals the radius of _B_; similarly -the radius of _B_ subtracted from dimension _y_ equals the radius of -_C_. - -For example, 0.930-0.720 = 0.210 or the difference between the radii -of disks _C_ and _A_. Then the diameter of _A_ = 0.210 + 0.860 = 1.070 -inch, and the radius equals 1.070 ÷ 2 = 0.535 inch. The radius of _B_ = -0.930-0.535 = 0.395 inch and 0.395 × 2 = 0.790, or the diameter of _B_. -The center distance 0.720-0.395 = 0.325, which is the radius of _C_; -0.325 × 2 = 0.650 or the diameter of _C_. - -[Illustration: Fig. 5. Flange Templet with Buttons Attached] - -[Illustration: Fig. 6. Hinge Jig Templet with Buttons Attached] - -After determining the diameters, the disks should be turned nearly to -size and finished, preferably in a bench lathe. First insert a solder -chuck in the spindle, face it perfectly true, and attach the disk by a -few drops of solder, being careful to hold the work firmly against the -chuck while soldering. Face the outer side and cut a sharp V-center -in it; then grind the periphery to the required diameter. Next fasten -the finished disks onto the work in their correct locations with their -peripheries in contact, and then set one of the disks exactly central -with the lathe spindle by applying a test indicator to the center in -the disk. After removing the disk and boring the hole, the work is -located for boring the other holes in the same manner. - -[Illustration: Fig. 7. Hinge Jig Templet Illustrated in Fig. 6] - -Small disks may be secured to the work by means of jeweler’s wax. -This is composed of common rosin and plaster of paris and is made as -follows: Heat the rosin in a vessel until it flows freely, and then add -plaster of paris and keep stirring the mixture. Care should be taken -not to make the mixture too stiff. When it appears to have the proper -consistency, pour some of it onto a slate or marble slab and allow it -to cool; then insert the point of a knife under the flattened cake thus -formed and try to pry it off. If it springs off with a slight metallic -ring, the proportions are right, but if it is gummy and ductile, -there is too much rosin. On the other hand, if it is too brittle and -crumbles, this indicates that there is too much plaster of paris. The -wax should be warmed before using. A mixture of beeswax and shellac, or -beeswax and rosin in about equal proportions, is also used for holding -disks in place. When the latter are fairly large, it may be advisable -to secure them with small screws, provided the screw holes are not -objectionable. - - -Disk-and-Button Method of Locating Holes - -The accuracy of work done by the button method previously described -is limited only by the skill and painstaking care of the workman, -but setting the buttons requires a great deal of time. By a little -modification, using what is sometimes called the “disk-and-button -method,” a large part of this time can be saved without any sacrifice -of accuracy. The disk-and-button method is extensively used in many -shops. Buttons are used, but they are located in the centers of disks -of whatever diameters are necessary to give the required locations. -As three disks are used in each step of the process, it is sometimes -called the “three-disk method.” - -To illustrate the practical application of this method, suppose six -equally-spaced holes are to be located in the circumference of a -circle six inches in diameter. To locate these, one needs, besides the -buttons, three disks three inches in diameter, each having a central -hole exactly fitting the buttons. It is best to have, also, a bushing -of the same diameter as the buttons, which has a center-punch fitted -to slide in it. First the center button is screwed to the templet, and -one of the disks _A_, Fig. 9, is slipped over it; then a second disk -_B_ carrying a bushing and center-punch is placed in contact with disk -_A_ and a light blow on the punch marks the place to drill and tap for -No. 2 button, which is kept in its proper place while tightening the -screw by holding the two disks _A_ and _B_ in contact. Next the third -disk _C_ is placed in contact with disks _A_ and _B_ and locates No. 3 -button, and so on until the seven buttons are secured in position. The -templet is then ready to be strapped to the lathe faceplate for boring. - -[Illustration: Fig. 8. An Example of Precision Work, and Method of -Locating Holes by Use of Disks in Contact] - -Of course, it is not possible to use disks of “standard” sizes for -many operations, but making a special disk is easy, and its cost -is insignificant as compared with the time saved by its use. One -who employs this method, especially if he also uses disks to lay -out angles, soon accumulates a stock of various sizes. While it is -desirable to have disks of tool steel, hardened and ground, or, in the -larger sizes, of machine steel, case-hardened and ground, a disk for -occasional use will be entirely satisfactory if left soft. - -Another example of work is shown in Fig. 10. This is a jig templet -similar to the one illustrated in Figs. 6 and 7. Sketch _A_ gives its -dimensions and sketch _B_ shows the disk-and-button way of locating the -holes. A steel square is clamped with its stock against the right-hand -edge of the templet and its blade extending across the top. The lower -edge of the blade should be located 0.250 inch from the upper edge of -the templet by the use of size blocks. A 2½-inch disk, touching both -blade and stock, locates hole _C_. Another 2½-inch disk, touching the -first disk and the square blade, locates hole _B_. Next a disk 1.600 -inch diameter is placed in contact with the two upper disks and -locates the center hole _A_; and, finally, the disks for holes _B_ and -_C_ are used to locate holes _D_ and _E_. - -[Illustration: Fig. 9. Locating Holes on a Circle and Equi-distant by -using Disks and Buttons in Combination] - -Two other jobs that illustrate this method may be of interest. -The first one, shown in Fig. 11, required the locating of nine -equally-spaced holes on a circumference of 7⅜ inches diameter. In any -such case, the size of the smaller disks is found by multiplying the -diameter of the circle upon which the centers of the disks are located -by the sine of half the angle between two adjacent disks. The angle -between the centers of adjacent disks equals 360 ÷ number of disks. 360 -÷ 9 = 40; hence, in this case, the diameter of the smaller disks equals -7⅜ multiplied by the sine of 20 degrees, or 7⅜ × 0.34202 = 2.5224 -inches. 7⅜-2.5224 = 4.8526 inches, which is the diameter of the central -disk. - -The templet shown in Fig. 12 required two holes on a circumference 6½ -inches diameter, with their centers 37 degrees 20 minutes apart. To -find the diameter of the smaller disks, multiply the diameter of the -large circle by the sine of one-half the required angle, as in the -preceding example; thus 6½ × sin 18 degrees 40 minutes = 2.0804 inches, -which is the diameter of the two smaller disks. The diameter of the -larger disk equals 6½-2.0804 = 4.4196 inches. - -Very accurate results can be obtained by the disk-and-button method. -Of course, absolute exactness is equally unattainable with buttons and -a micrometer, or any other method; the micrometer does not show the -slight inaccuracy in any one chordal measurement, while in using the -disks the error is accumulative and the insertion of the last disk in -the series shows the sum of the errors in all the disks. It is only in -cases like the one illustrated in Fig. 9 that we note this, and then, -though in correcting the error, we may change the diameter of the -circle a very slight amount, an exceedingly accurate division of the -circumference is secured. - - -Use of Two- and Three-Diameter Disks - -Fig. 13 illustrates, on an enlarged scale, a piece of work requiring -great accuracy, which was successfully handled by an extension of the -three-disk method. Fourteen holes were required in a space hardly -larger than a silver half-dollar, and, although the drawing gave -dimensions from the center of the circle, the actual center could not -be used in doing the work, as there was to be no hole there; moreover, -a boss slightly off center prevented the use of a central disk, unless -the bottom of the disk were bored out to receive this boss, which was -not thought expedient. Hence, the method adopted was to make the plate -thicker than the dimension given on the drawing, and then bore it out -to leave a rim of definite diameter, this rim to be removed after it -had served its purpose as a locating limit for the disks. - -[Illustration: Fig. 10. (A) Layout of Jig-Plate. (B) Disk-and-Button -Method of Locating Holes] - -As the holes _A_ and _B_, which were finished first, were 0.600 inch -apart and 0.625 inch from the center, the rim was bored to 1.850 inch -and two 0.600-inch disks, in contact with the rim and with each other, -located these holes. As hole _C_ was to be equi-distant from holes -_A_ and _B_, and its distance from the center was given, the size of -the disk for this hole was readily determined. The disks for holes -_A_, _B_ and _C_ have two diameters; the upper diameters are made to -whatever size is required for locating the disks of adjacent holes, and -they also form a hub which can be used when setting the disks with an -indicator. Hole _D_ was 0.4219 inch from _B_, and calculations based -on this dimension and its distance from the center showed that it was -0.4375 inch from hole _C_. - -A “three-story” disk or button was made for hole _D_. The diameter of -the large part was 0.46875 inch and it overlapped disks _C_ and _B_ -(the upper sections of which were made 0.375 inch and 0.4062 inch, -respectively), thus locating _D_. Then hole _F_ and all the remaining -holes were located in a similar manner. The upper diameters of disks -_E_ and _D_ were used in locating disks for other adjacent holes, -as well as a hub for the indicator; for instance, to locate a hole -with reference to holes _C_ and _D_, the diameter of the new disk and -the diameter of the upper part of disk _D_, were varied to give the -required location. The relation between the disks _B_, _D_ and _F_ is -shown by the side view. - -[Illustration: Fig. 11. Example of Circular Spacing requiring a Large -Central Disk] - -It had been decided that no screws should be used in attaching the -buttons or disks to the work, as it was feared that the tapped holes -would introduce inaccuracy by deflecting the boring-tools; therefore -the following method was employed. After all the disks were fastened -in place by clamps, a soft solder of low melting point was flowed -about them, filling the work to the top of the rim. When the solder -had cooled, the clamps were removed, the work transferred to the lathe -faceplate, indicated in the usual way, and the holes bored by a “_D_” -or “hog-nose” drill, guided by an axial hole in each disk, which had -been provided for that purpose when the disks were made. It was thought -that the unequal contraction of the solder and the plate in cooling -might throw the holes “out of square;” however, careful measurements -failed to show any appreciable lack of parallelism in test-bars -inserted in the holes. - -[Illustration: Fig. 12. Locating Holes at an Angle by use of Disks and -Buttons] - -[Illustration: Fig. 13. Locating Holes by Means of Two- and -Three-Diameter Disks in Contact] - - -Accurate Angular Measurements with Disks - -For setting up a piece of work on which a surface is to be planed or -milled at an exact angle to a surface already finished, disks provide -an accurate means of adjustment. One method of using disks for angular -work is illustrated at _A_ in Fig. 14. Let us assume that the lower -edge of plate shown is finished and that the upper edge is to be -milled at an angle _a_ of 32 degrees with the lower edge. If the two -disks _x_ and _y_ are to be used for locating the work, how far apart -must they be set in order to locate it at the required angle? The -center-to-center distance can be determined as follows: Subtract the -radius of the larger disk from the radius of the smaller disk, and -divide the difference by the sine of one-half the required angle. - -[Illustration: Fig. 14. Obtaining Accurate Angular Measurements with -Disks] - - _Example_: If the required angle _a_ is 32 degrees, - the radius of the large disk, 2 inches, and the radius of the - small disk, 1 inch, what is the center-to-center distance? - - The sine of one-half the required angle, or 16 degrees, is - 0.27564. The difference between the radii of the disks equals - 2 - 1 = 1, and 1 ÷ 0.27564 = 3.624 inches. Therefore, for an - angle of 32 degrees, disks of the sizes given should be set so - that the distance between their centers is 3.624 inches. - -Another method of accurately locating angular work is illustrated at -_B_ in Fig. 14. In this case, two disks are also used, but they are -placed in contact with each other and changes for different angles -are obtained by varying the diameter of the larger disk. The smaller -disk is a standard 1-inch size, such as is used for setting a 2-inch -micrometer. By this method any angle up to about 40 degrees can be -obtained within a very close limit of accuracy. The following rule may -be used for determining the diameter of the larger disk, when both -disks are in contact and the diameter of the small disk is known: - -Multiply twice the diameter of the small disk by the sine of one-half -the required angle; divide this product by 1 minus the sine of one-half -the required angle; add the quotient to the diameter of the small disk -to obtain the diameter of the large disk. - - _Example_: The required angle a is 15 degrees. - Find the diameter of the large disk to be in contact - with the standard 1-inch reference disk. - - The sine of 7 degrees 30 minutes is 0.13053. - Multiplying twice the diameter of the small disk - by the sine of 7 degrees 30 minutes, we have - 2 × 1 × 0.13053 = 0.26106. This product divided by - 1 minus the sine of 7 degrees 30 minutes - - 0.26106 - = ——————————— = 3.002. - 1 - 0.13053 - - This quotient added to the diameter of the small - disk equals 1 + 0.3002 = 1.3002 inch, which is the - diameter of the large disk. - -[Illustration: Fig. 15. Disk-and-Square Method of Accurately Setting -Angular Work] - -The accompanying table gives the sizes of the larger disks to the -nearest 0.0001 inch for whole degrees ranging from 5 to 40 degrees -inclusive. Incidentally, the usefulness of these disks can be increased -by stamping on each one its diameter and also the angle which it -subtends when placed in contact with the standard 1-inch disk. - -DISK DIAMETERS FOR ANGULAR MEASUREMENT - - +------+---------++------+---------++------+---------++ - | Deg. | Inch || Deg. | Inch || Deg. | Inch || - +------+---------++------+---------++------+---------++ - | 5 | 1.0912 || 17 | 1.3468 || 29 | 1.6680 || - | 6 | 1.1104 || 18 | 1.3708 || 30 | 1.6983 || - | 7 | 1.1300 || 19 | 1.3953 || 31 | 1.7294 || - | 8 | 1.1499 || 20 | 1.4203 || 32 | 1.7610 || - | 9 | 1.1702 || 21 | 1.4457 || 33 | 1.7934 || - | 10 | 1.1909 || 22 | 1.4716 || 34 | 1.8262 || - | 11 | 1.2120 || 23 | 1.4980 || 35 | 1.8600 || - | 12 | 1.2334 || 24 | 1.5249 || 36 | 1.8944 || - | 13 | 1.2553 || 25 | 1.5524 || 37 | 1.9295 || - | 14 | 1.2775 || 26 | 1.5805 || 38 | 1.9654 || - | 15 | 1.3002 || 27 | 1.6090 || 39 | 2.0021 || - | 16 | 1.3234 || 28 | 1.6382 || 40 | 2.0396 || - +------+---------++------+---------++------+---------++ - | _Machinery_ || - +----------------------------------------------------++ - - -Disk-and-Square Method of Determining Angles - -The method shown in Fig. 15 for determining angles for setting up -work on a milling machine or planer, possesses several advantages. No -expensive tools are required, the method can be applied quickly, and -the results obtained are quite accurate enough for any but the most -exacting requirements. As will be seen, an ordinary combination square -is used in connection with a disk, the head of the square being set at -different points on the blade according to the angle that is desired. -Theoretically, a one-inch disk could be used for all angles from about -6 degrees up to a right angle, but in practice it is more convenient -and accurate to employ larger disks for the larger angles. - -The only inaccuracy resulting from this method is due to setting the -square at the nearest “scale fraction” instead of at the exact point -determined by calculation. This error is very small, however, and is -negligible in practically all cases. The dimension _x_ required for any -desired angle _a_ can be found by multiplying the radius of the disk, -by the cotangent of one-half the desired angle, and adding to this -product the radius of the disk. - - _Example_: The square blade is to be set to an - angle of 15 degrees 10 minutes, using a 2-inch disk. - At what distance _x_ (see Fig. 15) should the - head of the square be set? - - Cot 7 degrees 35 minutes = 7.5113, - and 7.5113 × 1 + 1 = 8.5113 inches. - - By setting the square to 8½ inches “full,” the - blade would be set very close to the required angle - of 15 degrees 10 minutes. - -Locating Work by means of Size Blocks - -The size-block method of locating a jig-plate or other part, in -different positions on a lathe faceplate, for boring holes accurately -at given center-to-center distances, is illustrated in Fig. 16. The way -the size blocks are used in this particular instance is as follows: A -pair of accurate parallels are attached to a faceplate at right angles -to each other and they are so located that the center of one of the -holes to be bored will coincide with the lathe spindle. The hole which -is aligned in this way should be that one on the work which is nearest -the outer corner, so that the remaining holes can be set in a central -position by adjusting the work away from the parallels. After the -first hole is bored, the work is located for boring each additional -hole by placing size blocks of the required width between the edges of -the work and the parallels. For instance, to set the plate for boring -hole _D_, size blocks (or a combination of blocks or gages) equal in -width to dimension _A_₁ would be inserted at _A_, and other blocks -equal in width to dimension _B_₁ beneath the work as at _B_. As will be -seen, the dimensions of these blocks equal the horizontal and vertical -distances between holes _C_ and _D_. With the use of other combinations -of gage blocks, any additional holes that might be required are located -in the central position. While only two holes are shown in this case, -it will be understood that the plate could be located accurately for -boring almost any number of holes by this method. - -[Illustration: Fig. 16. Method of setting Work on Faceplate with Size -Blocks or Gages] - -Incidentally, such gages as the Johansson combination gages are -particularly suited for work of this kind, as any dimension within -the minimum and maximum limits of a set can be obtained by simply -placing the required sizes together. Sometimes when such gages are not -available, disks which have been ground to the required diameter are -interposed between the parallels and the work for securing accurate -locations. Another method of securing a positive adjustment of the -work is to use parallels composed of two tapering sections, which -can be adjusted to vary the width and be locked together by means of -screws. Each half has the same taper so that outer edges are parallel -for any position, and the width is measured by using a micrometer. The -size-block method is usually applied to work having accurately machined -edges, although a part having edges which are of a rough or irregular -shape can be located by this method, if it is mounted on an auxiliary -plate having accurately finished square edges. For instance, if holes -were to be bored in the casting for a jig templet which had simply been -planed on the top and bottom, the casting could be bolted to a finished -plate having square edges and the latter be set in the different -positions required, by means of size blocks. Comparatively large jig -plates are sometimes located for boring in this way and the milling -machine is often used instead of a lathe. - - -The Master-plate Method - -When it is necessary to machine two or more plates so that they are -duplicates as to the location of holes, circular recesses, etc., what -is known as a master-plate is often used for locating the work on the -lathe faceplate. This master-plate _M_ (see Fig. 17) contains holes -which correspond to those wanted in the work, and which accurately fit -a central plug _P_ in the lathe spindle, so that by engaging first one -hole and then another with the plug, the work is accurately positioned -for the various operations. - -When making the master-plate, great care should be taken to have the -sides parallel and the holes at right angles to the sides, as well as -accurately located with reference to one another. The various holes -may be located with considerable precision by the use of buttons as -previously described. Of course, it is necessary to have a hole in the -master-plate for each different position in which the work will have to -be placed on the faceplate; for example, if a circular recess _r_ were -required, a hole _r_₁ exactly concentric with it would be needed in -the master-plate. The method of holding the work and locating it with -reference to the holes in the master-plate will depend largely on its -shape. The cylindrical blank _B_ illustrated, is positioned by a recess -in the master-plate in which it fits. The work is commonly held to the -master-plate by means of clamps and tap bolts or by screws which pass -through the work and into the master-plate. Solder is sometimes used -when it is not convenient to hold the work by clamps or screws. - -[Illustration: Fig. 17. Master-plate applied to a Bench Lathe Faceplate] - -The plug _P_ which locates the master-plate, is first turned to fit -the spindle or collet of the lathe and the outer or projecting end -is roughturned for the holes in the master-plate, which should all -be finished to exactly the same diameter. The plug is then inserted -in the spindle and ground and lapped to a close fit for the holes in -the master-plate. The latter, with the work attached to it, is next -clamped to the faceplate by the straps shown, which engage a groove -around the edge of the master-plate. The first hole is finished by -drilling to within, say, 0.005 or 0.006 inch of the size, and then -boring practically to size, a very small amount being left for reaming -or grinding. The remaining holes can then be finished in the same -way, the work being positively located in each case by loosening the -master-plate and engaging the proper hole in it with the central plug. -It is apparent that by the use of this same master-plate, a number of -pieces _B_ could be made which would be practically duplicates. - -The master-plate method of locating work can be applied in many -different ways. It is used for making duplicate dies, for accurately -locating the various holes in watch movements, and for many other -operations requiring great precision. Master-plates are quite -frequently used by toolmakers when it is necessary to produce a number -of drill jigs which are to be used for drilling holes in different -parts having the same relative locations, thus requiring jigs that are -duplicates within very close limits. - -When a master-plate is required, that is to be used in making -duplicates of an existing model, the holes are bored in the -master-plate by reversing the process illustrated in Fig. 17. That is, -the central plug _P_ is turned to fit the largest hole in the model and -the latter with the attached master-plate blank is clamped to lathe -faceplate. The first hole is then bored to within say 0.002 inch of the -finish diameter, to allow for grinding, provided the master-plate is -to be hardened. The central plug is then turned down to fit the next -largest hole and the second hole is bored in the master-plate. This -method is continued until all the holes are bored. In order to prevent -any change in the position of the master-plate relative to the model, -it may be secured by inserting dowel-pins through both parts, the work -being held to the lathe faceplate by ordinary screw clamps. If the -holes in the model do not extend clear through, a flat plate having -parallel sides may be interposed between the model and master-plate to -provide clearance between the two and prevent cutting into the model -when boring the master-plate. - - - - -CHAPTER II - -ACCURATE DIVIDING AND SPACING METHODS - - -Toolmakers and machinists occasionally find it necessary to locate a -number of equally-spaced holes on a straight line between two points, -or to divide a circle with holes which are equi-distant within a very -small limit of accuracy. Several dividing and spacing methods are -described in this chapter; some of these methods can, with slight -modification, be applied in various ways. - -[Illustration: Fig. 18. Method of Drilling Small Equally-spaced Holes -in Rows] - - -Locating Small Equally-spaced Holes in Rows - -It is sometimes necessary to drill one or more rows of small -equally-spaced holes. The best method of doing this work naturally -depends, to some extent, upon the accuracy required, but even when a -high degree of accuracy is not necessary, if an attempt is made to lay -out the holes and drill them in the ordinary way, considerable time -is usually required and the results are liable to be unsatisfactory. -For example, suppose a row of holes ¹/₁₆ inch in diameter and ⅛ inch -center-to-center distance were to be drilled in a flat plate. Some -machinists would proceed by first scribing a center-line and then -laying out the centers of the holes by means of dividers. A much easier -and accurate method is illustrated in Fig. 18, and is as follows: -Lay out the first hole and drill it; then secure a small piece of -flat steel for a drill guide, drill a hole through it, bevel one -corner and scribe a fine line on the beveled section, as shown in the -illustration. Align the hole drilled in the guide with the hole in the -work, by inserting a close-fitting plug, and clamp a scale against one -edge of the drill guide so that one of the graduation marks exactly -matches with the line on the guide. The edge of the scale must also be -located parallel to the center-line of the row of holes to be drilled. -Now proceed to drill the holes, setting the drill guide each time, to -whatever graduation line represents the required spacing or pitch of -the holes. - -It is advisable to use a magnifying glass to accurately align the -graduation mark on the scale with the line on the drill guide. If two -or more rows of holes are to be drilled parallel, the guide block can -be drilled accordingly, so that the different rows of holes can be -finished at the same time. The drill guide block should be relieved -slightly in the center so as to insure the ends of the block bearing -against the edge of the scale. A toolmaker or machinist can drill a row -of holes accurately by this simple method, in the time required to lay -them out in the usual way, and even though accuracy is not necessary, -it is quicker to drill holes by this method than by the one more -commonly employed. - - -Use of Disks for Locating Equally-Spaced Holes - -A simple method of spacing holes that are to be drilled in a straight -line is illustrated in Fig. 19. Two disks are made, each having a -diameter equal to the center-to-center distance required between the -holes. These disks must also have holes which are exactly central -with the outside to act as a guide for the drill or reamer. The first -two holes are drilled in the work while the disks are clamped so that -they are in contact with each other and also with the straightedge as -shown. One disk is then placed on the opposite side of the other, as -indicated by the dotted line, and a third hole is drilled; this process -of setting one disk against the opposite side of the other is continued -until all the holes are drilled. When it is necessary to drill a -parallel row of “staggered” holes, the second row can be located by -placing disks of the proper size in contact with the first row of disks. - -[Illustration: Fig. 19. Locating Equi-distant Holes in a Straight Line -by Means of Disks and Straightedge] - -A method of using disks, which is preferable for very accurate work, is -shown in Fig. 20. The disks are clamped against each other and along -straightedge _A_ by the screws shown, and if the outside diameters are -correct and the guide holes concentric with the outside, very accurate -work can be done. With this device there may be as many disks as there -are holes to be drilled, if the number of holes is comparatively small, -but if it is necessary to drill a long row of holes, the disks and -frame are shifted along an auxiliary straightedge _B_, the hole in one -of the end disks being aligned with the last hole drilled by inserting -a close-fitting plug through the disk and hole. - - -Adjustable Jig for Accurate Hole Spacing - -An adjustable jig for accurately spacing small holes is shown in Fig. -21. - -[Illustration: Fig. 20. Special Disk-jig for Precision Drilling] - -This form is especially adapted for locating a number of equally -spaced holes between two previously drilled or bored holes, and the -accuracy of the method lies in the fact that a slight error in the -original spacing of the guide bushing is multiplied, and, therefore, -easily detected. There are two of these guide bushings _A_ and _B_ -which are carried by independent slides. These slides can be shifted -along a dovetail groove after loosening the screws of clamp-gib _C_. To -illustrate the method of using this jig, suppose five equally spaced -holes are to be located between two holes that are 12 inches apart. -As the center-to-center distance between adjacent holes is 2 inches, -slides _A_ and _B_ would be set so that the dimension _x_ equals 2 -inches plus the radii of the bushings. A straightedge is then clamped -to the work in such position that a close-fitting plug can be inserted -through the end holes which were previously drilled or bored. Then with -a plug inserted through, say, bushing _B_ and one of the end holes, the -first hole is drilled and reamed through bushing _A_; the jig is then -shifted to the left until the plug in _B_ enters the hole just made. -The second hole is then drilled and reamed through bushing _A_ and -this drilling and shifting of the jig is continued until the last hole -is finished. The distance between the last hole and the original end -hole at the left is next tested by attempting to insert close-fitting -plugs through both bushings. Evidently, if there were any inaccuracy in -the spacing of the bushings, this would be multiplied as many times as -the jig was shifted, the error being accumulative. To illustrate how -the error accumulates, suppose that the bushings were 0.001 inch too -far apart; then the distance to the first hole would be 2.001 inch, to -the second hole, 4.002 inch, and finally the distance from the first -to the sixth hole would be 10.005 inches; consequently, the distance -between the sixth and seventh holes would equal 12-10.005 = 1.995 inch, -or 0.005 inch less than the required spacing, assuming, for the sake -of illustration, that the first and last holes were exactly 12 inches -apart. In case of an error of 0.005 inch, the bushings would be set -closer together an amount equal to one-fifth of this error, as near as -could be determined with a micrometer, and all of the holes would then -be re-reamed. - -[Illustration: Fig. 21. Adjustable Jig for Accurate Hole Spacing] - - -Methods of Accurately Dividing a Circle - -Sometimes it is necessary to machine a number of holes in a plate so -that all the holes are on a circle or equi-distant from a central -point, and also the same distance apart, within very small limits. A -simple method of spacing holes equally is illustrated at _A_, Fig. -22. A number of buttons equal to the number of holes required are -ground and lapped to exactly the same diameter, preferably by mounting -them all on an arbor and finishing them at the same time. The ends -should also be made square with the cylindrical surface of the button. -When these buttons are finished, the diameter is carefully measured -and this dimension is subtracted from the diameter of the circle on -which the holes are to be located, in order to obtain the diameter -_d_ (see illustration). A narrow shoulder is then turned on the plate -to be bored, the diameter being made exactly equal to dimension -_d_. By placing the buttons in contact with this shoulder, they are -accurately located radially and can then be set equi-distant from -each other by the use of a micrometer. In this particular case, it -would be advisable to begin by setting the four buttons which are 90 -degrees apart and then the remaining four. The buttons are next used -for setting the work preparatory to boring. (See “Button Method of -Accurately Locating Work.”) - -[Illustration: Fig. 22. Four Methods of Accurately Dividing a Circle] - - -Correcting Spacing Errors by Split Ring Method - -Another method of securing equal spacing for holes in indexing wheels, -etc., is illustrated at _B_, Fig. 22. This method, however, is not to -be recommended if the diameter of the circle on which the holes are -to be located, must be very accurate. The disk or ring in which the -holes are required, is formed of two sections _e_ and _f_, instead -of being one solid piece. The centers for the holes are first laid -out as accurately as possible on ring _e_. Parts _e_ and _f_ are then -clamped together and the holes are drilled through these two sections. -Obviously, when the holes are laid out and drilled in this way, there -will be some error in the spacing, and, consequently, all of the holes -would not match, except when plate _e_ is in the position it occupied -when being drilled. Whatever errors may exist in the spacing can be -eliminated, however, by successively shifting plate _e_ to different -positions and re-reaming the holes for each position. A taper reamer -is used and two pins should be provided having the same taper as the -reamer. Ring _e_ is first located so that a hole is aligned quite -accurately with one in the lower plate. The ring is then clamped and -the hole is partly reamed, the reamer being inserted far enough to -finish the hole in plate _e_ and also cut clear around in the upper -part of plate _f_. One of the taper pins is then driven into this hole -and then a hole on the opposite side is partly reamed, after which the -other pin is inserted. The remaining holes are now reamed in the same -way, and the reamer should be fed in to the same depth in each case. If -a pair of holes is considerably out of alignment, it may be necessary -to run the reamer in to a greater depth than was required for the first -pair reamed, and in such a case all the holes should be re-reamed to -secure a uniform size. - -The next step in this operation is to remove the taper pins and clamps -or turn index plate _e_ one hole and again clamp it in position. The -reaming process just described is then repeated; the holes on opposite -sides of the plate are re-reamed somewhat deeper, the taper pins are -inserted, and then all of the remaining holes are re-reamed to secure -perfect alignment for the new position of the plate. By repeating this -process of shifting plate _e_ and re-reaming the holes, whatever error -that may have existed originally in the spacing of the holes, will -practically be eliminated. It would be very difficult, however, to have -these holes located with any great degree of accuracy, on a circle of -given diameter. - - -Circular Spacing by Contact of Uniform Disks - -When an accurate indexing or dividing wheel is required on a machine, -the method of securing accurate divisions of the circle illustrated -at _C_, Fig. 22, is sometimes employed. There is a series of circular -disks or bushings equal in number to the divisions required, and these -disks are all in contact with each other and with a circular boss or -shoulder on the plate to which they are attached. The space between -adjacent disks is used to accurately locate the dividing wheel, -engagement being made with a suitable latch or indexing device. When -making a dividing wheel of this kind, all of the disks are ground and -lapped to the same diameter and then the diameter of the central boss -or plate is gradually reduced until all of the disks are in contact -with each other and with the boss. For an example of the practical -application of this method see “Originating a Precision Dividing Wheel.” - - -Spacing by Correcting the Accumulated Error - -Another indexing method of spacing holes equi-distant, is illustrated -by the diagram at _D_, Fig. 22. An accurately fitting plug is inserted -in the central hole of the plate in which holes are required. Two -arms _h_ are closely fitted to this plug but are free to rotate -and are provided with a fine-pitch screw and nut at the outer ends -for adjusting the distance between the arms. Each arm contains an -accurately made, hardened steel bushing _k_ located at the same radial -distance from the center of the plate. These bushings are used as a -guide for the drill and reamer when machining the holes in the plate. - -To determine the center-to-center distance between the bushings, -divide 360 by twice the number of holes required; find the sine -corresponding to the angle thus obtained, and multiply it by the -diameter of the circle upon which the holes are located. For example, -if there were to be eleven holes on a circle 8 inches in diameter, the -distance between the centers of the bushings would equal - - 360 - ——————— = 16.36 degrees. - 2 × 11 - -The sine of 16.36 degrees is 0.2815, and 0.2815 × 8 = 2.252 inches. The -arms are adjusted to locate the centers of the bushings this distance -apart, by placing closely fitting plugs in the bushings and measuring -from one plug to another with a micrometer or vernier caliper. Of -course, when taking this measurement, allowance is made for the -diameter of the plugs. - -After the arms are set, a hole is drilled and reamed; an accurately -fitting plug is then inserted through the bushing and hole to secure -the arms when drilling and reaming the adjacent hole. The radial arms -are then indexed one hole so that the plug can be inserted through one -of the arms and the last hole reamed. The third hole is then drilled -and reamed, and this operation is repeated for all of the holes. -Evidently, if the center-to-center distance between the bushings is -not exactly right, the error will be indicated by the position of the -arms relative to the last hole and the first one reamed; moreover, -this error will be multiplied as many times as there are holes. For -instance, if the arms were too far apart, the difference between -the center-to-center distance of the last pair of holes and the -center-to-center distance of the bushings in the arms, would equal, in -this particular case, eight times the error, and the arms should be -re-adjusted accordingly. Larger bushings would then be inserted in the -arms and the holes re-reamed, this operation being repeated until the -holes were all equi-distant. - -As will be seen, the value of this method lies in the fact that it -shows the accumulated error. Thus, if the arms were 0.0005 inch too far -apart, the difference between the first and last hole would equal 8 × -0.0005 = 0.004 inch. This same principle of dividing can be applied in -various ways. For instance, the radial arms if slightly modified, could -be used for drilling equally-spaced holes in the periphery or disk of a -plate, or, if a suitable marking device were attached, a device of this -kind could be used for accurately dividing circular parts. - - -Originating a Precision Dividing Wheel - -There are various methods employed for making accurate indexing wheels -for a definite number of divisions. One of these methods, suitable -particularly for small numbers of divisions, employs a split wheel with -a series of taper holes reamed through the two divisions. By shifting -the two divisions from point to point (as explained in connection with -sketch _B_, Fig. 22) and reaming and re-reaming the taper holes at each -shifting, they may finally be brought very accurately into position. -Another method that has been employed consists in clamping about the -rim of the dividing wheel a number of precisely similar blocks, fitting -close to each other and to the wheel itself. These blocks are then used -for locating the wheel in each of its several positions in actual work. -A third and simpler method (a modification of the one last described) -consists in grinding a series of disks and clamping them around a -rim of such diameter that the disks all touch each other and the rim -simultaneously, as explained in connection with sketch _C_, Fig. 22. -The wheel described in the following, which is illustrated in Fig. 23, -was made in this way. - -[Illustration: Fig. 23. Precision Dividing Wheel] - -Disks _A_ are clamped against an accurately ground face of the wheel -_B_ and are supposed to just touch each other all around, and to be -each of them in contact with the ground cylindrical surface at _x_. -They are held in proper position by bolts _C_ and nuts _D_. The bolts -fit loosely in the holes of the disks or bushings _A_ so that the -latter are free to be located as may be desired with reference to the -bolts. - -One or two improvements in the construction of this type of dividing -wheel may be noted before proceeding to a description of the way in -which it is made. For one thing, instead of having an indexing bolt -enter the V-space between two adjoining disks, a smaller diameter _y_ -is ground on each of them, over which locking finger or pawl passes, -holding the wheel firmly from movement in either direction. This -construction has the advantage of a probable lessening of error by -locating on each bushing instead of between two bushings; moreover, it -gives a better holding surface and better holding angles than would be -the case if this smaller diameter were not provided. - -A second improvement lies in the method of clamping the bushings _A_ in -place. Instead of providing each bolt with a separate washer, a ring -_F_ is used. This ring fits closely on a seat turned to receive it on -the dividing wheel _B_. When one bushing _A_ has been clamped in place, -the disk is locked from movement so that there is no possibility, in -clamping the remaining bushings, of having their location disturbed in -the slightest degree by the turning of the nuts in fastening them in -place. - -The bushings _A_, of which there were in this case 24, were all ground -exactly to the required diameters on their locating and locking -surfaces. The important things in this operation are, first, that the -large or locating diameter of the bushing should be exactly to size; -and second, that this surface should be in exact alignment with the -diameter in which the locking is done; and, finally, that the face of -the bushing should be squared with the cylindrical surfaces. A refined -exactness for the diameter of the locking surfaces is not so important, -as the form of locking device provided allows slight variations at this -point without impairment of accuracy. This dimension was kept within -very close limits, however. The truth of the two cylindrical surfaces -and the face of the bushing was assured by finishing all these surfaces -in one operation on the grinding machine. - -The sizing of the outer diameter of the bushing, which was 1.158 inch, -must be done so accurately that it was not thought wise to trust to -the ordinary micrometer caliper. An indexing device was therefore made -having a calipering lever with a long end, in the ratio of 10 to 1, -which actuated the plunger of a dial test indicator of the well-known -type made by the Waltham Watch Tool Co. The thousandth graduations -on the dial of this indicator would then read in ten-thousandths, -permitting readings to be taken to one-half or one-quarter of this -amount. The final measurements with this device were all taken after -dipping the bushings in water of a certain temperature, long enough to -give assurance that this temperature was universal in all the parts -measured. It will be understood, of course, in this connection, that -getting the diameter of these bushings absolutely to 1.158 inch was -not so important as getting them all exactly alike, whether slightly -over or slightly under this dimension; hence, the precaution taken in -measurement. - -Wheel _B_ was next ground down nearly to size, great care being taken -that it should run exactly concentric with the axis. As soon as -the diameter of the surface _x_ was brought nearly to the required -dimension as obtained by calculation, the disks were tried in place. -The first one was put in position with its loose hole central on the -bolt and clamped in place under ring _F_. The next bushing was then -pressed up against it and against the surface _x_ of the wheel and -clamped in place. The third one was similarly clamped in contact with -its neighboring bushing and the wheel, and so on, until the whole -circle was completed. It was then found that the last disk would not -fill the remaining space. This required the grinding off of some stock -from surface _x_, and a repetition of the fitting of the bushings _A_ -until they exactly filled the space provided for them. - -[Illustration: Fig. 24. Precision Dividing Wheel and its Indexing -Mechanism] - -This operation required, of course, considerably more skill than a -simple description of the job would indicate. One of the points that -had to be carefully looked out for was the cleaning of all the surfaces -in contact. A bit of dust or lint on one of the surfaces would throw -the fitting entirely out. The temperature of the parts was another -important consideration. As an evidence of the accuracy with which the -work was done, it might be mentioned that it was found impossible to -do this fitting on a bench on the southern or sunny side of the shop, -the variations of temperature between morning and noon, and between -bright sunshine and passing clouds, being such that the disks would -not fit uniformly. The variation from these minute temperature changes -resulted from the different coefficients of expansion of the iron -wheel and the steel bushings. The obvious thing to do would be to build -a room for this work kept at a constant temperature and preferably that -of the body, so that the heat of the body would make no difference in -the results. It was found sufficient in this case, however, to do the -work on the northern side of the shop where the temperature was more -nearly constant, not being affected by variations in sunshine. - -The dividing wheel, the construction of which has just been described, -was made by the Fellows Gear Shaper Co. It is used for indexing the -Fellows gear cutters in the machine in which the teeth are ground. The -indexing mechanism of this machine is shown in Fig. 24. It is operated -by a handle or lever pinned to rock-shaft _H_, to which is keyed arm -_J_. Pivoted to _J_ is a pawl _K_ engaging the teeth of ratchet _L_, -which revolves loosely on shaft _H_. This ratchet _L_ controls the -movement of locking finger _E_. The parts are shown in their normal or -locked position in the engraving. - -As the handle on shaft _H_ is pulled in the direction indicated by the -arrow, arm _J_ is raised, carrying the ratchet wheel around to the -right. This allows flat spring _M_ to drop off of the ratchet tooth, -permitting helical spring _O_ to raise latch _E_ and thus leave the -wheel free. The continued movement of the hand-lever and of rock-shaft -_H_, by means of gear _N_, intermediate pinion _P_ and gear _Q_, causes -the indexing pawl _R_, which is pivoted to gear _Q_ and acts on the -head of one of the bolts _C_ (see Fig. 23), to index the wheel one -step. Just before reaching its new location the new tooth of ratchet -wheel _L_ coming up, bears down on the top of spring _M_, pressing -latch _E_ into place against the tension of coil spring _O_. By this -means the wheel is locked in position. - -When the operator pushes the handle on shaft _H_ back again to its -position of rest, the pawl _R_ is retracted into position to act on the -next bolt head for the next indexing. Star-wheel _L_ remains stationary -on this backward movement, being prevented from revolving by the notch -on the top of the tooth into which spring _M_ fits. Pawl _K_ on its -return engages with the next tooth of this wheel, ready for the next -indexing operation. - -A slight rotary adjustment of dividing wheel _B_, independent of this -indexing mechanism, is required for the feeding of the machine. This -is accomplished by the end movement of latch _E_, which is pivoted in -slide _S_. This slide is pressed to the right by spring plunger _T_, -and is adjusted positively in the other direction by feed-screw _U_, -which is finely graduated to permit accurate adjustment. The accuracy -in indexing obtained by the use of a wheel thus made was required to -bring the finished cutters within the very narrow limits allowed for -them in the final inspection. - - - - -CHAPTER III - -LOCATING WORK FOR BORING ON MILLING MACHINE - - -It is often desirable to perform boring operations on the milling -machine, particularly in connection with jig work. Large jigs, which -because of their size or shape could not be conveniently handled in -the lathe, and also a variety of smaller work, can often be bored -to advantage on the milling machine. When such a machine is in good -condition, the necessary adjustments of the work in both vertical and -horizontal planes, can be made with considerable accuracy by the direct -use of the graduated feed-screw dials. It is good practice, however, -when making adjustments in this way, to check the accuracy of the -setting by measuring the center distances between the holes directly. -For the purpose of obtaining fine adjustments when boring on the -milling machine, the Brown & Sharpe Mfg. Co. makes special scales -and verniers that are attached to milling machines, so that the table -may be set by direct measurement. By attaching a scale and vernier to -the table and saddle, respectively, and a second scale to the column -with a vernier on the knee, both longitudinal and vertical measurements -can be made quickly and accurately, and the chance of error resulting -from inaccuracy of the screw, or from lost motion between the screw and -nut, is eliminated. - - -Checking Location of Holes by Micrometer-and-plug Method - -One method of checking the accuracy of the location of holes bored in -the milling machine, is to insert closely fitting ground plugs into -the bored holes and then determine the center-to-center distance by -taking a direct measurement across the plugs with a micrometer or -vernier caliper. For example, if holes were to be bored in a jig-plate, -as shown in Fig. 1, assuming that hole _A_ were finished first, the -platen would then be moved two inches, as shown by the feed dial; hole -_B_ would then be bored slightly under size. Plugs should then be -accurately fitted to these holes, having projecting ends, preferably of -the same size. By measuring from one of these plugs to the other with a -vernier or micrometer caliper, the center distance between them can be -accurately determined, allowance being made, of course, for the radii -of each plug. If this distance is incorrect, the work can be adjusted -before finishing _B_ to size, by using the feed-screw dial. After hole -_B_ is finished, the knee could be dropped 1.5 inch, as shown by the -vertical feed dial, and hole _C_ bored slightly under size; then by the -use of plugs, as before, the location of this hole could be tested by -measuring center distances between _C-B_ and _C-A_. - -An example of work requiring the micrometer-and-plug test, is shown -set up in the milling machine in Fig. 25. The large circular plate -shown has a central hole and it was necessary to bore the outer holes -in correct relation with the center hole within a limit of 0.0005 inch. -The center hole was first bored and reamed to size; then an accurately -fitting plug was inserted and the distances to all the other holes -were checked by measuring from this plug. This method of testing with -the plugs is intended to prevent errors which might occur because of -wear in the feed-screws or nuts, that would cause the graduated dials -to give an incorrect reading. On some jig work, sufficient accuracy -could be obtained by using the feed-screw dials alone, that is, without -testing with the plugs, in which case the accuracy would naturally -depend largely on the condition of the machine. - -[Illustration: Fig. 25. Example of Precision Boring on Milling Machine] - -A method that is a modification of the one in which plugs are used -to test the center distance is as follows: All the holes are first -drilled with suitable allowance for boring, the location being obtained -directly by the feed-screw dials. A special boring-tool, the end of -which is ground true with the shank, is then inserted in the spindle -and the first hole, as at _A_ in Fig. 1 is finished, after which -the platen is adjusted for hole _B_ by using the dial as before. A -close-fitting plug is then inserted in hole _A_ and the accuracy of the -setting is obtained by measuring the distance between this plug and the -end of the boring-tool, which is a combination tool and test plug. In -a similar manner, the tool is moved from one position to another, and, -as all the holes have been previously drilled, all are bored without -removing the tool from the spindle. - -Another modification of the micrometer-and-plug method is illustrated -in Figs. 26 and 27. It is assumed that the plate to be bored is -finished on the edges, and that it is fastened to an angle-plate, which -is secured to the table of the milling machine and set square with the -spindle. A piece of cold-rolled steel or brass is first fastened in the -chuck (which is mounted on the spindle) and turned off to any diameter. -This diameter should preferably be an even number of thousandths, to -make the calculations which are to follow easier. The turning can be -done either by holding the tool in the milling machine vise, or by -securing it to the table with clamps. In either case, the tool should -be located near the end of the table, so as to be out of the way when -not in use. - -[Illustration: Fig. 26. Obtaining Vertical Adjustment by Means of Depth -Gage and turned Plug in Chuck] - -After the piece in the chuck is trued, the table and knee are adjusted -until the center of the spindle is in alignment with the center of the -first hole to be machined. This setting of the jig-plate is effected -by measuring with a micrometer depth gage from the top and sides of -the work, to the turned plug, as illustrated in Fig. 26. When taking -these measurements, the radius of the plug in the chuck is, of course, -deducted. When the plate is set the plug is removed from the chuck -and the first hole drilled and bored or reamed to its proper size. We -shall assume that the holes are to be located as shown by the detail -view, Fig. 26, and that hole _A_ is the first one bored. The plug is -then again inserted in the chuck and trued with the tool, after which -it is set opposite the place where the second hole _B_ is to be bored; -this is done by inserting an accurately fitting plug in hole _A_ and -measuring from this plug to the turned piece in the chuck, with an -outside micrometer as indicated in Fig. 27. Allowance is, of course, -again made for the radii of the two plugs. The horizontal measurement -can be taken from the side of the work with a depth gage as before. The -plug is then removed and the hole drilled and bored to the proper size. -The plug is again inserted in the chuck and turned true; the table is -then moved vertically to a position midway between _A_ and _B_, and -then horizontally to the proper position for hole _C_, as indicated by -the depth gage from the side of the work. The location can be verified -by measuring the center distances _x_ with the micrometer. In a similar -manner holes _D_, _E_, _F_ and _G_ are accurately located. - -[Illustration: Fig. 27. Adjusting for Center-to-center Distance by use -of Plugs and Micrometer] - -If the proper allowances are made for the variation in the size of the -plug, which, of course, is made smaller each time it is trued, and if -no mistakes are made in the calculations, this method is very accurate. -Care should be taken to have the gibs on all sides fairly tight at the -beginning, and these should not be tightened after each consecutive -alignment, as this generally throws the work out a few thousandths. -If the reductions in the size of the plug, each time it is turned, -are confusing, new plugs can be used each time a test is made, or the -end of the original plug can be cut off so that it can be turned to -the same diameter for every test. If the center distances _x_ are not -given, it is, of course, far more convenient to make all the geometric -calculations before starting to work. - - -The Button-and-plug Method - -The use of the button method as applied to the milling machine, is -illustrated in Fig. 28, where a plain jig-plate is shown set up for -boring. The jig, with buttons _B_ accurately located in positions -corresponding to the holes to be bored, is clamped to the angle-plate -_A_ that is set at right angles to the spindle. Inserted in the spindle -there is a plug _P_, the end of which is ground to the exact size of -the indicating buttons. A sliding sleeve _S_ is accurately fitted -to this plug and when the work is to be set for boring a hole, the -table and knee of the machine are adjusted until the sleeve _S_ will -pass over the button representing the location of the hole, which -brings the button and spindle into alignment. When setting the button -in alignment, all lost motion or backlash should be taken up in the -feed-screws. For instance, if the button on the jig should be a little -higher than the plug in the spindle, do not lower the knee until the -bushing slips over the button, but lower the knee more than is required -and then raise it until the bushing will pass over the button. This -same rule should be followed for longitudinal adjustments. - -[Illustration: Fig. 28. Accurate Method of Aligning Spindle with Button -on Jig-Plate] - -After the button is set by this method, it is removed and the plug in -the spindle is replaced by a drill and then by a boring-tool or reamer -for finishing the hole to size. In a similar manner the work is set for -the remaining holes. The plug _P_ for the spindle must be accurately -made so that the outer end is concentric with the shank, and the latter -should always be inserted in the spindle in the same relative position. -With a reasonable degree of care, work can be set with considerable -precision by this method, providing, of course, the buttons are -properly set. - -Some toolmakers use, instead of the plug and sleeve referred to, a test -indicator for setting the buttons concentric with the machine spindle. -This indicator is attached to and revolves with the spindle, while the -point is brought into contact with the button to be set. The difficulty -of seeing the pointer as it turns is a disadvantage, but with care -accurate results can be obtained. - - -Size Block and Gage Method - -Another method which can at times be employed for accurately locating -a jig-plate in different positions on an angle-plate, is shown in -Fig. 29. The angle-plate is, of course, set at right angles to the -spindle and depth gages and size blocks are used for measuring directly -the amount of adjustment. Both the angle-plate and work should have -finished surfaces on two sides at right angles to each other, from -which measurements can be taken. After the first hole has been bored, -the plate is adjusted the required distance both horizontally and -vertically, by using micrometer depth gages, which should preferably be -clamped to the angle-plate. If the capacity of the gages is exceeded, -measurements may be taken by using standard size blocks in conjunction -with the depth gages. - -[Illustration: Fig. 29. Locating Work from Edges of Angle-Plate by -means of Depth Gages and Size Blocks] - -It is frequently necessary to bore holes in cast jig-plates or machine -parts, which either have irregularly shaped or unfinished edges. A good -method of locating such work is illustrated in Fig. 30. The part to be -bored is attached to an auxiliary plate _A_ which should have parallel -sides and at least two edges which are straight and at right angles -to each other. This auxiliary plate with the work, is clamped against -an accurate angle-plate _B_, which should be set square with the axis -of the machine spindle. A parallel strip is bolted to the angle-plate -and the inner edge is set square with the machine table. After the -first hole is bored, the work is located for boring the other to the -edge of the auxiliary plate, and horizontal measurements _y_ between -the parallel and the plate. These measurements, if quite large, might -be taken with micrometer gages, whereas, for comparatively small -adjustments, size blocks might be more convenient. - - -Vernier Height Gage and Plug Method - -When a vernier height gage is available, it can often be used to -advantage for setting work preparatory to boring in a milling machine. -One advantage of this method is that it requires little in the way of -special equipment. The work is mounted on an angle-plate or directly -on the platen, depending on its form, and at one end an angle-plate is -set up with its face parallel to the spindle. An accurately finished -plug is inserted in the spindle and this plug is set vertically from -the platen and horizontally from the end angle-plate, by measuring with -the vernier height gage. After the plug is set for each hole, it is, of -course, removed and the hole drilled and bored or reamed. - -[Illustration: Fig. 30. Method of Holding and Locating Casting of -Irregular Shape, for Boring Holes] - -The way the plug and height gage is used is clearly illustrated in -Figs. 31 and 32. The work, in this particular case, is a small jig. -This is clamped directly to the machine table and at one end an -angle-plate is also bolted to the table. This angle-plate is first set -parallel with the traverse of the saddle or in line with the machine -spindle. To secure this alignment, an arbor is inserted in the spindle -and a test indicator is clamped to it by gripping the indicator between -bushings placed on the arbor. The table is then moved longitudinally -until the contact point of the indicator is against the surface plate; -then by traversing the saddle crosswise, any lack of parallelism -between the surface of the angle-plate and the line of saddle traverse -will be shown by the indicator. - -[Illustration: Fig. 31. Making a Vertical Adjustment by Measuring to -Ground Plug in Spindle] - -[Illustration: Fig. 32. Making a Horizontal Adjustment by measuring -from Angle-Plate to Ground Plug] - -When the work is to be adjusted horizontally, the vernier height gage -is used as shown in Fig. 32, the base of the gage resting on the -angle-plate and the measurement being taken to an accurately ground and -lapped plug in the spindle. For vertical adjustments, the measurements -are taken between this ground plug and the machine platen as in Fig. 31. - - -Locating Holes to be Bored from Center-punch Marks - -The problem of accurately locating holes to be bored on the milling -machine has received much attention, and the method generally used when -accuracy has been required is the button method, which was previously -described. So much time is required for doing the work by this method, -however, that numerous efforts have been made to obtain equally good -results in other ways. - -[Illustration: Fig. 33. Diagram Illustrating Rapid but Accurate Method -of Locating Holes to be bored on Milling Machine] - -The increasing demand for rapidity combined with accuracy and a minimum -liability of error, led to the development of the system described in -the following: A center-punch mark takes the place of the button, from -which to indicate the work into the proper position for boring. The -fundamental principle involved is to lay out, accurately, two lines -at right angles to each other, and correctly center-punch the point -where they intersect. With proper care, lines may be drawn with a -vernier height gage at right angles, with extreme accuracy, the chief -difficulty being to accurately center the lines where they cross. For -semi-accurate work this may be done with a common center-punch but -where extreme accuracy is required this method is not applicable, as -the average man is incapable of marking the point of intersection -accurately. - -The diagram, Fig. 33, illustrates, in a simple way, the procedure -adopted in laying out work by this system. The base _E_ is in contact -with a surface plate while the line _BB_ is drawn with a height gage; -then with side _F_ on the plate the line _AA_ is drawn. It will be -seen that these lines will be at right angles to each other, if the -bases _E_ and _F_ are square. Work done by this method must have two -working surfaces or base lines, and these must be at right angles -to each other. There is no difficulty in drawing the locating lines -_AA_ and _BB_ correctly, either with a vernier height gage or with a -special micrometer gage reading to 0.0001 inch, the only difficult -element being to accurately center-punch the lines where they intersect -as at _D_. It is assumed that two holes are to be bored, so that the -intersection at _C_ would also be center-punched. - -The scriber point of the height gage should be ground so that it will -make a V-shaped line, as shown by the enlarged sketch _G_, rather than -one which would resemble a saw-tooth, as at _H_, if a cross-section of -it were examined with a microscope. This is important because when the -lines are V-shaped, an accurate point of intersection is obtained. - -[Illustration: Fig. 34. Center Locating Punch] - -[Illustration: Fig. 35. Center Enlarging Punch] - -As it is quite or almost impossible to accurately center-punch the -intersection of even two correctly drawn lines, by ordinary means, the -punch shown in Figs. 34 and 36 was designed and an extended experience -with it on a very high grade of work has demonstrated its value for -the purpose. It consists essentially of a small center-punch _O_ (Fig. -36) held in vertical position by a holder _P_ which is knurled to -facilitate handling. Great care should be exercised in making this -tool to have the body of the punch straight, and to have it stand at -right angles to the surface to be operated upon, for the slightest -inclination will cause the finished hole to be incorrect, no matter -how carefully the lines are drawn. The 60-degree point must be ground -true with the axis. The holder for the punch stands on three legs, -located as indicated, and ground accurately to a taper fit in the -holder, where they are secured by watch screws bearing on their tops. -The lower ends are hardened, and terminate in an angular point of 55 -degrees (the point of the vernier scriber being 60 degrees). The edges -are sharp, and slightly rounded at the ends, so that the legs will -slide along a line smoothly. The points _V_ and _U_ (Fig. 36) have -edges that are in line with each other, while the point _T_ has an edge -at right angles to the other two. The center of the punch is located at -equal distances from all the legs, and is held off the work normally by -a leather friction acted upon by a set-screw in the side of holder _P_. - -[Illustration: Fig. 36. Section of Center Locating Punch] - -[Illustration: Fig. 37. Section of Center Enlarging Punch] - -If this tool is placed upon lines of the form shown at _G_, Fig. 33, -the legs _V_ and _U_ may be slid along horizontal line _B-B_, Fig. 33, -until the sharp edge of leg _T_ drops into line _A-A_. When this occurs -the punch _O_ is lightly tapped with a hammer, and the resulting mark -will be accurately located in the center of the intersection of the -lines. It is good practice to make the work very smooth before drawing -the lines, and after laying them out, to stone them so as to remove the -slight burr raised in drawing them. A drop of oil is then rubbed into -the lines, and the surplus wiped off. This procedure permits points -_V_ and _U_ to run very smoothly along the line, and the burr having -been removed, the edge of leg _T_ drops into the line very readily with -a slight click. As it is not advisable to strike punch _O_ more than a -very light blow, it marks the work but slightly, and a more distinct -indentation is made with the follower punch shown in Figs. 35 and 37. -This punch is made like the previous one, so that it will stand at -right angles to the work. The sectional view (Fig. 37) shows the punch -_A_ supported by the holder _E_ which has four legs cut away on the -sides so that the point of the punch may be seen. When this punch is in -position, it is struck a sufficiently heavy blow to make a distinctly -visible mark. The work is now ready to be placed upon the work table of -the milling machine, and indicated for boring the holes, an indicator -being used in the milling machine spindle. - -[Illustration: Fig. 38. Indicator used for Aligning Punch Marks with -Machine Spindle] - -An indicator which has been found especially valuable for this purpose -is shown in Figs. 38 and 39. It is of the concentric centering type, -and with it the work is brought concentric with the axis of the -spindle. The arbor _I_ is provided with a threaded nose on which disk -_D_ is screwed. This disk has four holes in its rim, equally-spaced -from each other. Hardened, ground, and lapped bushings _b_ are put into -these holes to receive plug _A_ which is made a gage-fit both in these -holes and in hole _B_ in the outer end of sector _C_. This sector is -held by a split sleeve to the barrel _L_ which carries the 60-degree -centering-rod _K_ that comes into contact with the work to be bored. -The spherical base of barrel _L_ fits into a corresponding concave seat -in the nose of the arbor at _H_, and is held in place by a spring _E_ -which connects at one end to the cylindrical stud in the base of the -barrel, and at the other to the axial rod _M_ by which it and the other -connecting parts may be drawn into place, and held by the headless -set-screw _J_, bearing on a flat spot on the tang end of the rod. - -Now, if plug _A_ is removed from bushing _b_ the point of the -centering-rod _K_ may be made to describe a circle. At some point -within this circle is located the center-punch mark on the work to -be bored. The holes in the rim of the faceplate all being exactly -the same distance from an axial line through both the arbor _I_ and -centering-rod _K_, it follows that the center mark on the work must -be so located by horizontal and vertical movements of the work table -that pin _A_ may be freely entered in all the four holes in the rim of -disk _D_. When that occurs, the center coincides with the axis of the -spindle. - -The point of the center-punch _A_ (Fig. 37) should have an angle -slightly greater than the angle on the centering-rod _K_, as it is -impossible to locate the work in the preliminary trials so that the -center of the work will be coincident with the axis of the spindle, and -unless the precaution mentioned is taken, the true center on the work -is liable to be drawn from its proper location when trying to bring the -work into such a position that the plug will enter all the holes in the -disk. As the work being operated on is brought nearer to the proper -location by the movements of the milling machine table, spring _G_ will -be compressed, the center rod sliding back into barrel _L_. This spring -is made so that it will hold the center against the work firmly, but -without interfering with the free rotation of the sector _C_ around -disk _D_. When the work is located so that the plug enters the holes, -the gibs of the machine should be tightened up and the plug tried -once more, to make sure that the knee of the machine has not moved -sufficiently to cause the work on the table to be out of line. The work -table is now clamped to prevent accidental horizontal shifting, and the -work is drilled and bored. - -[Illustration: Fig. 39. Sectional View of Indicator shown in Fig. 38] - -In using this indicator the milling machine spindle is not rotated -together with arbor _I_, only the sector being turned around the disk. -The tool is set, however, in the beginning, so that the axes of two -of the bushings _b_ are at right angles to the horizontal plane of -the machine table, while the axes of the other holes in the disk -are parallel with the top of the work table. The centering-rods are -made interchangeable and of various lengths, to reach more or less -accessible centers. Fig. 38 shows the indicator with one of the long -center-rods in the foreground. - -The only part of the milling machine on which dependence must be placed -for accuracy is the hole in the spindle, and this is less liable to get -out of truth, from wear such as would impair the accuracy, than are the -knee, table, or micrometer screws. The only moving part is the sector, -and this, being light, is very sensitive. - -A series of 24 holes was laid out and bored in one and one-half day by -the method described in the foregoing. Measurements across accurately -lapped plugs in the holes, showed the greatest deviation from truth -to be 0.0002 inch, and running from that to accuracy so great that no -error was measurable. This same work with buttons would have required -considerably more time. - - - - -[Illustration: MACHINERY] - - -Machinery is the leading journal in the machine-building field and -meets the requirements of the mechanical engineer, superintendent, -designer, toolmaker and machinist, as no other journal does. -MACHINERY deals exclusively with machine design, tool design, machine -construction, shop practice, shop systems and shop management. The -reading matter in MACHINERY is written by practical men and edited by -mechanical men of long practical training. - -Each number of MACHINERY contains a variety of articles on machine shop -practice. These articles include carefully prepared descriptions of -manufacturing methods and current mechanical developments. Shop systems -and shop managements are ably handled by the foremost writers. Every -number contains the most extensive and complete record published by any -journal, or in any form, of new machinery and tools and accessories -for the machine shop. A special department is devoted to “Letters on -Practical Subjects,” to which practical mechanics contribute their -experiences. There is a department of Shop Kinks—brief, concise little -contributions which contain ideas of value to the man in the shop or at -the drafting table. - -The mechanical engineer, machine designer and draftsman are also well -provided for in MACHINERY. Every number contains articles on the theory -and practice of machine design, on the properties of materials, and -on labor-saving methods and systems. There are reviews of research -work in the mechanical field, and valuable results of carefully made -experiments are recorded. - -The supremacy of MACHINERY in the mechanical field is due to the -care with which all matter offered for publication in its pages is -scrutinized. Only the _best_ of the material offered by mechanical -writers is published, and, as a result, its pages contain the most -authoritative, practical and up-to-date mechanical information. - - MACHINERY, 140-148 Lafayette Street, - New York City 51 and 52, - CHANCERY LANE, LONDON, W. C. - -Heat-Treatment of Steel - -[Illustration] - -is one of a series of high-class authoritative, attractive and -well-bound books published by MACHINERY. - -The strongest claim that can be made for these books is that they have -all the characteristics of MACHINERY itself. - -These books cover comprehensively, and in a thoroughly practical -manner, the most important subjects in the metal-working field. - -Each book comprises about 300 pages, printed on high-grade paper, -with engravings of the same superior type that has made MACHINERY -distinctive in its field. - -The price of each book is $2.50. Special combination offers on a -monthly payment plan will be sent upon request. - - MACHINERY - 140-148 Lafayette St. New York City - 51 and 52, Chancery Lane, London, W. C. - -The Five New Books - -Brought Out by MACHINERY - -SPUR AND BEVEL GEARING - -A treatise on the principles, dimensions, calculation, design and -strength of spur and bevel gearing, together with chapters on special -tooth forms and methods of cutting gear teeth. - -SPIRAL AND WORM GEARING - -A treatise on the principles, dimensions, calculation and design of -spiral and worm gearing, together with chapters on the methods of -cutting the teeth in these types of gears. - -TURNING AND BORING - -By FRANKLIN D. JONES Associate Editor of MACHINERY - -A specialized treatise for machinists, students in industrial and -engineering schools, and apprentices on turning and boring methods, -including modern practice with engine lathes, turret lathes, vertical -and horizontal boring machines. - -PLANING AND MILLING - -By FRANKLIN D. JONES Associate Editor of MACHINERY - -A treatise on the use of planers, shapers, slotters and various types -of horizontal and vertical milling machines and their attachments. - -HEAT-TREATMENT OF STEEL - -A comprehensive treatise on the hardening, tempering, annealing and -case-hardening of various kinds of steel, including high-speed, -high-carbon, alloy and low-carbon steels, together with chapters on -heat-treating furnaces and on hardness testing. - -Price of each book $2.50. Special combination offers on a monthly -payment plan will be sent upon request. - - MACHINERY - 140-148 Lafayette St. New York City - 51 and 52, Chancery Lane, London, W. 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If you -are not located in the United States, you will have to check the laws of the -country where you are located before using this eBook. -</div> - -<p style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: Precision locating and dividing methods</p> -<p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em'>Author: Anonymous</p> -<p style='display:block; text-indent:0; margin:1em 0'>Release Date: September 28, 2022 [eBook #69061]</p> -<p style='display:block; text-indent:0; margin:1em 0'>Language: English</p> - <p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em; text-align:left'>Produced by: deaurider and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)</p> -<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK PRECISION LOCATING AND DIVIDING METHODS ***</div> -<hr class="chap" /> -<p class="f150"><b>MACHINERY’S REFERENCE SERIES</b></p> - -<p class="center">EACH NUMBER IS ONE UNIT IN A COMPLETE LIBRARY OF<br /> -MACHINE DESIGN AND SHOP PRACTICE REVISED AND<br /> -REPUBLISHED FROM MACHINERY</p> - -<p class="f150 space-above2"><b>NUMBER 135</b></p> -<h1>PRECISION LOCATING AND<br />DIVIDING METHODS</h1> - -<p class="f150 space-above2"><b>CONTENTS</b></p> - -<table class="fontsize_120 no-wrap" border="0" cellspacing="0" summary="TOC" cellpadding="0" > - <tbody><tr> - <td class="tdl">Precision Locating Methods</td> - <td class="tdr"><a href="#Page_3"> 3</a></td> - </tr><tr> - <td class="tdl">Accurate Dividing and Spacing Methods</td> - <td class="tdr"><a href="#Page_21">21</a></td> - </tr><tr> - <td class="tdl">Locating Work for Boring on Milling Machine  </td> - <td class="tdr"><a href="#Page_32">32</a></td> - </tr> - </tbody> -</table> - -<p class="f110 space-above2 space-below2">Copyright, 1914, The Industrial Press,<br /> -Publishers of <span class="smcap">Machinery</span>,<br /> -140-148 Lafayette Street, New York City</p> - -<hr class="chap" /> -<table class="fontsize_110 no-wrap" border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl">Other books in this series dealing with</td> - </tr><tr> - <td class="tdl">the subjects of Toolmaking and kindred</td> - </tr><tr> - <td class="tdl">topics are as follows:<br /> </td> - </tr><tr> - <td class="tdl">No. 31—<span class="smcap">Thread Tools and Gages</span></td> - </tr><tr> - <td class="tdl">No. 64—<span class="smcap">Gage Making and Lapping</span></td> - </tr><tr> - <td class="tdl">No. 107—<span class="smcap">Drop Forging Die Sinking</span></td> - </tr><tr> - <td class="tdl">No. 130—<span class="smcap">Gaging Tools and Methods</span></td> - </tr> - </tbody> -</table> - -<p class="space-above3"> </p> -<div class="figcenter space-above3"> - <img src="images/i_02.jpg" alt="" width="300" height="412" /> -</div> - -<p class="f150 space-above2"><b><span class="smcap">Machinery</span></b></p> - -<p class="center">The Leading<br />Mechanical Journal</p> - -<p class="f110"><span class="smcap">Machine Design</span><span class="ws2"> </span><br /> -<span class="smcap">Construction</span><br /> -<span class="ws2"> </span><span class="smcap">Shop Practice</span></p> - -<p class="f110 space-above2">THE INDUSTRIAL PRESS</p> -<p class="center">140-148 Lafayette St. New York City<br />51-52 Chancery Lane, London</p> - -<hr class="chap" /> - -<div class="chapter"> -<p><span class="pagenum" id="Page_3">[Pg 3]</span></p> - -<h2 class="nobreak">CHAPTER I<br /> -<span class="h_subtitle">PRECISION LOCATING METHODS</span></h2> -</div> - -<p>The degree of accuracy that is necessary in the construction of -certain classes of machinery and tools, has made it necessary for -toolmakers and machinists to employ various methods and appliances -for locating holes or finished surfaces to given dimensions and -within the prescribed limits of accuracy. In this treatise, various -approved methods of locating work, such as are used more particularly -in tool-rooms, are described and illustrated. These are not given, in -every case, as being the best possible method under all conditions, -because, as every mechanical man knows, the best way may be dependent -upon the element of accuracy with little regard for the time required -to do the work, or this order may be reversed; therefore, one method is -seldom, if ever, the best under all circumstances, and it is necessary -for the workman to consider the conditions in each case and then be -guided by his judgment and experience in determining just how the work -should be done.</p> - -<h3 id="BUTTON">Button Method of Accurately<br /> Locating Work</h3> - -<p>Among the different methods employed by toolmakers for accurately -locating work such as jigs, etc., on the faceplate of a lathe, one of -the most commonly used is known as the “button method.” This method is -so named because cylindrical bushings or buttons are attached to the -work in positions corresponding to the holes to be bored, after which -they are used in locating the work. These buttons which are ordinarily -about ½ or ⅝ inch in diameter, are ground and lapped to the same size, -and the ends are finished perfectly square. The outside diameter -should preferably be such that the radius can easily be determined, -and the hole through the center should be about ⅛ inch larger than the -retaining screw so that the button can be adjusted laterally.</p> - -<p>As a simple example of the practical application of the button method, -suppose three holes are to be bored in a jig-plate according to the -dimensions given in <a href="#FIG_1">Fig. 1</a>. A common method of procedure would -be as follows: First lay out the centers of all holes to be bored, by the -usual method. Mark these centers with a prick-punch and then drill -holes for the machine screws which are used to clamp the buttons. After -the buttons are clamped lightly in place, set them in correct relation -with each other and with the jig-plate. The proper location of the -buttons is very important, as their positions largely determine the -accuracy of the work. The best method of locating a number of buttons -depends, to some extent, upon their relative positions, the instruments -available, and the accuracy required. When buttons must be located at -<span class="pagenum" id="Page_4">[Pg 4]</span> -given distances from the finished sides of a jig, a surface plate and -vernier height gage are often used. The method is to place that side -from which the button is to be set, upon an accurate surface plate and -then set the button by means of the height gage, allowance being made, -of course, for the radius of the button. The center-to-center distance -between the different buttons can afterwards be verified by taking -direct measurements with a micrometer.</p> - -<div class="figcenter space-above3"> - <img id="FIG_1" src="images/i_04.jpg" alt="" width="600" height="285" /> - <p class="center space-below2"><b>Fig. 1</b>. Simple Example of Work - Illustrating Application of Button Method</p> -</div> - -<p>Figs. <a href="#FIG_2">2</a> and <a href="#FIG_3">3</a> -illustrate a method which requires only a micrometer. -Two of the buttons are set at the correct distance from one edge of the -plate by measuring from a parallel strip. Obviously, the micrometer -reading will exceed the distance from the center of a button to the -edge of the plate, by the amount equal to the thickness of the parallel -strip plus the radius of the button. The center-to-center distance -between each pair of buttons is also tested as indicated in <a href="#FIG_3">Fig. 3</a>, -by measuring the overall distance and deducting the diameter of one button.</p> - -<p>After the buttons have been set and the screws are tightened, all -measurements should be carefully checked. The work is then mounted -on the faceplate of the lathe and one of the buttons is set true by -the use of a test indicator as shown in <a href="#FIG_4">Fig. 4</a>. -When the dial of the indicator ceases to vibrate, thus showing that the -button runs true, the latter should be removed so that the hole can -be drilled and bored to the required size. In a similar manner other -buttons are indicated and the holes bored, one at a time. It is evident -that if each button is correctly located and set perfectly true in the -lathe, the various holes will be located the required distance apart -within very close limits.</p> - -<div class="figcenter space-above3"> - <img id="FIG_2" src="images/i_05.jpg" alt="" width="500" height="405" /> - <p class="center space-below2"><b>Fig. 2</b>. Determining Distance - from Button to Edge of Plate</p> -</div> - -<p>Another example of work illustrating the application of the button -method is shown in <a href="#FIG_5">Fig. 5</a>. The disk-shaped part illustrated is -a flange templet which formed a part of a fixture for drilling holes in flanged -plates, the holes being located on a circle 6 inches in diameter. -It was necessary to space the six holes equi-distantly so that the -holes in the flanges would match in any position, thus making them -interchangeable. First a plug was turned so that it fitted snugly in the -<span class="pagenum" id="Page_5">[Pg 5]</span> -1¼-inch central hole of the plate and projected above the top surface -about ¾ inch. A center was located in this plug and from it a circle -of three inches radius was drawn. This circle was divided into six -equal parts and then small circles ⅝ inch in diameter were drawn to -indicate the outside circumference of the bushings to be placed in -the holes. These circles served as a guide when setting the button -and enabled the work to be done much more quickly. The centers of the -holes were next carefully prick-punched and small holes were drilled -and tapped for No. 10 machine screws. After this the six buttons -were attached in approximately the correct positions and the screws -tightened enough to hold the buttons firmly, but allow them to be -moved by tapping lightly. As the radius of the circle is 3 inches, -the radius of the central plug, ⅝ inch, and that of each button, ⁵/₁₆ -inch, the distance from the outside of the central plug to the outside -of any button, when correctly set, must be 3 ¹⁵/₁₆ inches. Since there -are six buttons around the circle, the center-to-center distance is -equal to the radius, and the distance between the outside or any two -buttons should be 3⅝ inches. Having determined these dimensions, each -button is set equi-distant from the central plug and the required -distance apart, by using a micrometer. As each button is brought into -its correct position, it should be tightened down a little so that it -will be located firmly when finally set. The work is then strapped to -the faceplate of a lathe and each button is indicated for boring the -different holes by means of an indicator, as previously described. When -the buttons are removed it will be found that in nearly all cases the -<span class="pagenum" id="Page_6">[Pg 6]</span> -small screw holes will not run exactly true; therefore, it is advisable -to form a true starting point for the drill by using a lathe tool.</p> - -<div class="figcenter space-above3"> - <img id="FIG_3" src="images/i_06.jpg" alt="" width="500" height="511" /> - <p class="center space-below2"><b>Fig. 3</b>. Testing Location of Buttons</p> -</div> - -<p><a href="#FIG_7">Fig. 7</a> shows a method of locating buttons -from the finished sides of a plate, and this same plate with the five -buttons attached is shown in <a href="#FIG_6">Fig. 6</a>. As the -dimensions in <a href="#FIG_7">Fig. 7</a> indicate, the holes must not -only be accurate with relation to each other, but also with reference -to the edges of the templet; therefore, it is necessary to work from -the sides as well as the center. The width of the plate was first -measured carefully and found to be 5 inches. As the center-to-center -distance between buttons <i>B</i> and <i>C</i> and also buttons -<i>D</i> and <i>E</i>, is 2½ inches, the distance from the center of -each outside button to the edge of the plate is 1¼ inch. A ¼-inch -parallel was clamped against the side, as shown in the illustration, -and then the distance from the outside of each button to the outside -of the parallel (1 ¹³/₁₆ inch) was measured in conjunction with the -distance <i>L</i> from the central button. The distance <i>L</i> was -obtained by first determining the center-to-center distance <i>M</i> -which represents the hypotenuse of a right-angled triangle.</p> - -<p class="f120"><i>M</i>² = 1.25² + 1.625²</p> - -<p class="f120 no-wrap">or <i>M</i> = √<span class="over">1.25² + 1.625²</span> - = √<span class="over">4.024</span> = 2.050 inches.</p> - -<p class="f120">Therefore, <i>L</i> = 2.050 + 0.625 = 2.675 inches.</p> - -<p><span class="pagenum" id="Page_7">[Pg 7]</span> -In this case, the center button was first located correctly from the -sides and end and then the other buttons were set. When doing precision -work of this kind, the degree of accuracy obtained will depend upon -the instruments used, the judgment and skill of the workman, and the -care exercised. A good general rule to follow when locating bushings -or buttons is to use the method which is the most direct and which -requires the least number of measurements, in order to prevent an -accumulation of errors.</p> - -<h3>Locating Work by the Disk Method</h3> - -<p>Comparatively small precision work is sometimes located by the disk -method, which is the same in principle as the button method, the chief -difference being that disks are used instead of buttons. These disks -are made to such diameters that when their peripheries are in contact, -each disk center will coincide with the position of the hole to be -bored; the centers are then used for locating the work. To illustrate -this method, suppose that the master-plate shown at the left in <a href="#FIG_8">Fig. 8</a> -is to have three holes <i>a</i>, <i>b</i>, and <i>c</i> bored into it, -to the center distances given.</p> - -<div class="figcenter"> - <img id="FIG_4" src="images/i_07.jpg" alt="" width="600" height="421" /> - <p class="center space-below2"><b>Fig. 4</b>. Testing Concentricity - of Button Preparatory to Boring Hole in Lathe</p> -</div> - -<p>It is first necessary to determine the diameters of the disks. If -the center distances between all the holes were equal, the diameters -would, of course, equal this dimension. When, however, the distances -between the centers are unequal, the diameters may be found as follows: -Subtract, say, dimension <i>y</i> from <i>x</i>, thus obtaining the -difference between the radii of disks <i>C</i> and <i>A</i> (<a href="#FIG_8">see -right-hand sketch</a>); add this difference to dimension <i>z</i>, and the -result will be the diameter of disk <i>A</i>. Dividing this diameter -by 2 gives the radius, which, subtracted from center distance <i>x</i> -equals the radius of <i>B</i>; similarly the radius of <i>B</i> -subtracted from dimension <i>y</i> equals the radius of <i>C</i>. -<span class="pagenum" id="Page_8">[Pg 8]</span></p> - -<p class="blockquot">For example, 0.930-0.720 = 0.210 or the difference -between the radii of disks <i>C</i> and <i>A</i>. Then the diameter of -<i>A</i> = 0.210 + 0.860 = 1.070 inch, and the radius equals 1.070 ÷ -2 = 0.535 inch. The radius of <i>B</i> = 0.930-0.535 = 0.395 inch and -0.395 × 2 = 0.790, or the diameter of <i>B</i>. The center distance -0.720-0.395 = 0.325, which is the radius of <i>C</i>; 0.325 × 2 = 0.650 -or the diameter of <i>C</i>.</p> - -<div class="figcenter"> - <img id="FIG_5" src="images/i_08a.jpg" alt="" width="600" height="319" /> - <p class="center space-below2"><b>Fig. 5</b>. Flange Templet with Buttons Attached</p> - <img id="FIG_6" src="images/i_08b.jpg" alt="" width="600" height="319" /> - <p class="center space-below2"><b>Fig. 6</b>. Hinge Jig Templet with Buttons Attached</p> -</div> - -<p>After determining the diameters, the disks should be turned nearly to -size and finished, preferably in a bench lathe. First insert a solder -chuck in the spindle, face it perfectly true, and attach the disk by a -few drops of solder, being careful to hold the work firmly against the -chuck while soldering. Face the outer side and cut a sharp V-center -in it; then grind the periphery to the required diameter. Next fasten -the finished disks onto the work in their correct locations with their -peripheries in contact, and then set one of the disks exactly central -with the lathe spindle by applying a test indicator to the center in -the disk. After removing the disk and boring the hole, the work is -located for boring the other holes in the same manner. -<span class="pagenum" id="Page_9">[Pg 9]</span></p> - -<div class="figcenter"> - <img id="FIG_7" src="images/i_09.jpg" alt="" width="600" height="439" /> - <p class="center space-below2"><b>Fig. 7</b>. Hinge Jig Templet Illustrated - in <a href="#FIG_6">Fig. 6</a></p> -</div> - -<p>Small disks may be secured to the work by means of jeweler’s wax. -This is composed of common rosin and plaster of paris and is made as -follows: Heat the rosin in a vessel until it flows freely, and then add -plaster of paris and keep stirring the mixture. Care should be taken -not to make the mixture too stiff. When it appears to have the proper -consistency, pour some of it onto a slate or marble slab and allow it -to cool; then insert the point of a knife under the flattened cake thus -formed and try to pry it off. If it springs off with a slight metallic -ring, the proportions are right, but if it is gummy and ductile, -there is too much rosin. On the other hand, if it is too brittle and -crumbles, this indicates that there is too much plaster of paris. The -wax should be warmed before using. A mixture of beeswax and shellac, or -beeswax and rosin in about equal proportions, is also used for holding -disks in place. When the latter are fairly large, it may be advisable -to secure them with small screws, provided the screw holes are not -objectionable.</p> - -<h3>Disk-and-Button Method of<br /> Locating Holes</h3> - -<p>The accuracy of work done by the button method previously described -is limited only by the skill and painstaking care of the workman, -but setting the buttons requires a great deal of time. By a little -modification, using what is sometimes called the “disk-and-button -method,” a large part of this time can be saved without any sacrifice -of accuracy. The disk-and-button method is extensively used in many -shops. Buttons are used, but they are located in the centers of disks -of whatever diameters are necessary to give the required locations. -As three disks are used in each step of the process, it is sometimes -called the “three-disk method.”</p> - -<p>To illustrate the practical application of this method, suppose six -<span class="pagenum" id="Page_10">[Pg 10]</span> -equally-spaced holes are to be located in the circumference of a -circle six inches in diameter. To locate these, one needs, besides the -buttons, three disks three inches in diameter, each having a central -hole exactly fitting the buttons. It is best to have, also, a bushing -of the same diameter as the buttons, which has a center-punch fitted -to slide in it. First the center button is screwed to the templet, and -one of the disks <i>A</i>, <a href="#FIG_9">Fig. 9</a>, is slipped over -it; then a second disk <i>B</i> carrying a bushing and center-punch -is placed in contact with disk <i>A</i> and a light blow on the punch -marks the place to drill and tap for No. 2 button, which is kept in -its proper place while tightening the screw by holding the two disks -<i>A</i> and <i>B</i> in contact. Next the third disk <i>C</i> is -placed in contact with disks <i>A</i> and <i>B</i> and locates No. 3 -button, and so on until the seven buttons are secured in position. -The templet is then ready to be strapped to the lathe faceplate for boring.</p> - -<div class="figcenter"> - <img id="FIG_8" src="images/i_10.jpg" alt="" width="600" height="294" /> - <p class="center space-below2"><b>Fig. 8</b>. An Example of Precision Work, - and Method<br /> of Locating Holes by Use of Disks in Contact</p> -</div> - -<p>Of course, it is not possible to use disks of “standard” sizes for -many operations, but making a special disk is easy, and its cost -is insignificant as compared with the time saved by its use. One -who employs this method, especially if he also uses disks to lay -out angles, soon accumulates a stock of various sizes. While it is -desirable to have disks of tool steel, hardened and ground, or, in the -larger sizes, of machine steel, case-hardened and ground, a disk for -occasional use will be entirely satisfactory if left soft.</p> - -<p>Another example of work is shown in <a href="#FIG_10">Fig. 10</a>. -This is a jig templet similar to the one illustrated in Figs. -<a href="#FIG_6">6</a> and <a href="#FIG_7">7</a>. Sketch <i>A</i> gives -its dimensions and sketch <i>B</i> shows the disk-and-button way of -locating the holes. A steel square is clamped with its stock against -the right-hand edge of the templet and its blade extending across the -top. The lower edge of the blade should be located 0.250 inch from the -upper edge of the templet by the use of size blocks. A 2½-inch disk, -touching both blade and stock, locates hole <i>C</i>. Another 2½-inch -disk, touching the first disk and the square blade, locates hole -<i>B</i>. Next a disk 1.600 inch diameter is placed in contact with the -<span class="pagenum" id="Page_11">[Pg 11]</span> -two upper disks and locates the center hole <i>A</i>; and, finally, the -disks for holes <i>B</i> and <i>C</i> are used to locate holes <i>D</i> -and <i>E</i>.</p> - -<div class="figcenter"> - <img id="FIG_9" src="images/i_11.jpg" alt="" width="500" height="467" /> - <p class="center space-below2"><b>Fig. 9</b>. Locating Holes on a Circle - and Equi-distant<br /> by using Disks and Buttons in Combination</p> -</div> - -<p>Two other jobs that illustrate this method may be of interest. -The first one, shown in <a href="#FIG_11">Fig. 11</a>, required the locating -of nine equally-spaced holes on a circumference of 7⅜ inches diameter. In any -such case, the size of the smaller disks is found by multiplying the -diameter of the circle upon which the centers of the disks are located -by the sine of half the angle between two adjacent disks. The angle -between the centers of adjacent disks equals 360 ÷ number of disks. -360 ÷ 9 = 40; hence, in this case, the diameter of the smaller disks -equals 7⅜ multiplied by the sine of 20 degrees, or 7⅜ × 0.34202 = -2.5224 inches. 7⅜-2.5224 = 4.8526 inches, which is the diameter of -the central disk.</p> - -<p>The templet shown in <a href="#FIG_12">Fig. 12</a> required two holes on a -circumference 6½ inches diameter, with their centers 37 degrees 20 minutes apart. -To find the diameter of the smaller disks, multiply the diameter of the -large circle by the sine of one-half the required angle, as in the -preceding example; thus 6½ × sin 18 degrees 40 minutes = 2.0804 inches, -which is the diameter of the two smaller disks. The diameter of the -larger disk equals 6½-2.0804 = 4.4196 inches.</p> - -<p>Very accurate results can be obtained by the disk-and-button method. Of -course, absolute exactness is equally unattainable with buttons and a -micrometer, or any other method; the micrometer does not show the slight -<span class="pagenum" id="Page_12">[Pg 12]</span> -inaccuracy in any one chordal measurement, while in using the disks the -error is accumulative and the insertion of the last disk in the series -shows the sum of the errors in all the disks. It is only in cases like -the one illustrated in <a href="#FIG_9">Fig. 9</a> that we note this, -and then, though in correcting the error, we may change the diameter of -the circle a very slight amount, an exceedingly accurate division of -the circumference is secured.</p> - -<p>Use of Two- and Three-Diameter Disks</p> - -<p><a href="#FIG_13">Fig. 13</a> illustrates, on an enlarged scale, a piece -of work requiring great accuracy, which was successfully handled by -an extension of the three-disk method. Fourteen holes were required -in a space hardly larger than a silver half-dollar, and, although the -drawing gave dimensions from the center of the circle, the actual -center could not be used in doing the work, as there was to be no hole -there; moreover, a boss slightly off center prevented the use of a -central disk, unless the bottom of the disk were bored out to receive -this boss, which was not thought expedient. Hence, the method adopted -was to make the plate thicker than the dimension given on the drawing, -and then bore it out to leave a rim of definite diameter, this rim to -be removed after it had served its purpose as a locating limit for the -disks.</p> - -<div class="figcenter"> - <img id="FIG_10" src="images/i_12.jpg" alt="" width="600" height="439" /> - <p class="center space-below2"><b>Fig. 10</b>. (A) Layout of Jig-Plate.<br /> - (B) Disk-and-Button Method of Locating Holes</p> -</div> - -<p>As the holes <i>A</i> and <i>B</i>, which were finished first, were -0.600 inch apart and 0.625 inch from the center, the rim was bored -to 1.850 inch and two 0.600-inch disks, in contact with the rim and -with each other, located these holes. As hole <i>C</i> was to be -equi-distant from holes <i>A</i> and <i>B</i>, and its distance from -the center was given, the size of the disk for this hole was readily -determined. The disks for holes <i>A</i>, <i>B</i> and <i>C</i> have -<span class="pagenum" id="Page_13">[Pg 13]</span> -two diameters; the upper diameters are made to whatever size is -required for locating the disks of adjacent holes, and they also form -a hub which can be used when setting the disks with an indicator. Hole -<i>D</i> was 0.4219 inch from <i>B</i>, and calculations based on this -dimension and its distance from the center showed that it was 0.4375 -inch from hole <i>C</i>.</p> - -<p>A “three-story” disk or button was made for hole <i>D</i>. The diameter -of the large part was 0.46875 inch and it overlapped disks <i>C</i> -and <i>B</i> (the upper sections of which were made 0.375 inch and -0.4062 inch, respectively), thus locating <i>D</i>. Then hole <i>F</i> -and all the remaining holes were located in a similar manner. The -upper diameters of disks <i>E</i> and <i>D</i> were used in locating -disks for other adjacent holes, as well as a hub for the indicator; -for instance, to locate a hole with reference to holes <i>C</i> and -<i>D</i>, the diameter of the new disk and the diameter of the upper -part of disk <i>D</i>, were varied to give the required location. The -relation between the disks <i>B</i>, <i>D</i> and <i>F</i> is shown by -the side view.</p> - -<div class="figcenter"> - <img id="FIG_11" src="images/i_13.jpg" alt="" width="500" height="431" /> - <p class="center space-below2"><b>Fig. 11</b>. Example of Circular - Spacing<br /> requiring a Large Central Disk</p> -</div> - -<p>It had been decided that no screws should be used in attaching the -buttons or disks to the work, as it was feared that the tapped holes -would introduce inaccuracy by deflecting the boring-tools; therefore -the following method was employed. After all the disks were fastened -in place by clamps, a soft solder of low melting point was flowed -about them, filling the work to the top of the rim. When the solder -had cooled, the clamps were removed, the work transferred to the -lathe faceplate, indicated in the usual way, and the holes bored by a -“<i>D</i>” or “hog-nose” drill, guided by an axial hole in each disk, -which had been provided for that purpose when the disks were made. It -was thought that the unequal contraction of the solder and the plate -in cooling might throw the holes “out of square;” however, careful -measurements failed to show any appreciable lack of parallelism in -test-bars inserted in the holes. -<span class="pagenum" id="Page_14">[Pg 14]</span></p> - -<div class="figcenter"> - <img id="FIG_12" src="images/i_14a.jpg" alt="" width="500" height="405" /> - <p class="center space-below2"><b>Fig. 12</b>.Locating Holes at - an Angle by use of Disks and Buttons</p> - <img id="FIG_13" src="images/i_14b.jpg" alt="" width="500" height="521" /> - <p class="center space-below2"><b>Fig. 13</b>. Locating Holes by - Means of Two- and<br /> Three-Diameter Disks in Contact</p> -</div> -<p><span class="pagenum" id="Page_15">[Pg 15]</span></p> - -<h3>Accurate Angular Measurements with Disks</h3> - -<p>For setting up a piece of work on which a surface is to be planed -or milled at an exact angle to a surface already finished, disks provide -an accurate means of adjustment. One method of using disks for -angular work is illustrated at <i>A</i> in <a href="#FIG_14">Fig. 14</a>. -Let us assume that the lower edge of plate shown is finished and that -the upper edge is to be milled at an angle <i>a</i> of 32 degrees with -the lower edge. If the two disks <i>x</i> and <i>y</i> are to be used -for locating the work, how far apart must they be set in order to -locate it at the required angle? The center-to-center distance can be -determined as follows: Subtract the radius of the larger disk from the -radius of the smaller disk, and divide the difference by the sine of -one-half the required angle.</p> - -<div class="figcenter"> - <img id="FIG_14" src="images/i_15.jpg" alt="" width="600" height="276" /> - <p class="center space-below2"><b>Fig. 14</b>. Obtaining Accurate - Angular Measurements with Disks</p> -</div> - -<div class="blockquot"> -<p><i>Example</i>: If the required angle <i>a</i> is 32 degrees, the -radius of the large disk, 2 inches, and the radius of the small disk, 1 -inch, what is the center-to-center distance?</p> - -<p>The sine of one-half the required angle, or 16 degrees, is 0.27564. -The difference between the radii of the disks equals 2 - 1 = 1, and 1 -÷ 0.27564 = 3.624 inches. Therefore, for an angle of 32 degrees, disks -of the sizes given should be set so that the distance between their -centers is 3.624 inches.</p> -</div> - -<p>Another method of accurately locating angular work is illustrated at -<i>B</i> in <a href="#FIG_14">Fig. 14</a>. In this case, two disks are -also used, but they are placed in contact with each other and changes -for different angles are obtained by varying the diameter of the larger -disk. The smaller disk is a standard 1-inch size, such as is used for -setting a 2-inch micrometer. By this method any angle up to about 40 -degrees can be obtained within a very close limit of accuracy. The -following rule may be used for determining the diameter of the larger -disk, when both disks are in contact and the diameter of the small disk -is known: -<span class="pagenum" id="Page_16">[Pg 16]</span></p> - -<p>Multiply twice the diameter of the small disk by the sine of one-half -the required angle; divide this product by 1 minus the sine of one-half -the required angle; add the quotient to the diameter of the small disk -to obtain the diameter of the large disk.</p> - -<div class="blockquot"> -<p><i>Example</i>: The required angle a is 15 degrees. -Find the diameter of the large disk to be in contact -with the standard 1-inch reference disk.</p> - -<p>The sine of 7 degrees 30 minutes is 0.13053. -Multiplying twice the diameter of the small disk by the sine of 7 -degrees 30 minutes, we have 2 × 1 × 0.13053 = 0.26106. This product -divided by 1 minus the sine of 7 degrees 30 minutes</p> -</div> - -<table class="fontsize_120 no-wrap" border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdl" rowspan="2">= </td> - <td class="tdc">0.26106</td> - <td class="tdl" rowspan="2"> = 3.002.</td> - </tr><tr> - <td class="tdc over">1 - 0.13053</td> - </tr> - </tbody> -</table> - -<p class="blockquot no-indent">This quotient added to the diameter of -the small disk equals 1 + 0.3002 = 1.3002 inch, which is the diameter -of the large disk.</p> - -<div class="figcenter"> - <img id="FIG_15" src="images/i_16.jpg" alt="" width="600" height="313" /> - <p class="center space-below2"><b>Fig. 15</b>. Disk-and-Square Method - of Accurately Setting Angular Work</p> -</div> - -<p>The accompanying table gives the sizes of the larger disks to the -nearest 0.0001 inch for whole degrees ranging from 5 to 40 degrees -inclusive. Incidentally, the usefulness of these disks can be increased -by stamping on each one its diameter and also the angle which it -subtends when placed in contact with the standard 1-inch disk.</p> - -<p class="f120 space-above2"><b>DISK DIAMETERS FOR ANGULAR MEASUREMENT</b></p> - -<table class="fontsize_120 no-wrap" border="0" cellspacing="0" summary=" " cellpadding="0" rules="cols" > - <thead><tr> - <th class="tdc bb"> Deg. </th> - <th class="tdc bb br2">Inch</th> - <th class="tdc bb"> Deg. </th> - <th class="tdc bb br2">Inch</th> - <th class="tdc bb"> Deg. </th> - <th class="tdc bb">Inch</th> - </tr> - </thead> - <tbody><tr> - <td class="tdc"> 5</td> - <td class="tdc br2"> 1.0912 </td> - <td class="tdc">17</td> - <td class="tdc br2"> 1.3468 </td> - <td class="tdc">29</td> - <td class="tdc"> 1.6680 </td> - </tr><tr> - <td class="tdc"> 6</td> - <td class="tdc br2">1.1104</td> - <td class="tdc">18</td> - <td class="tdc br2">1.3708</td> - <td class="tdc">30</td> - <td class="tdc">1.6983</td> - </tr><tr> - <td class="tdc"> 7</td> - <td class="tdc br2">1.1300</td> - <td class="tdc">19</td> - <td class="tdc br2">1.3953</td> - <td class="tdc">31</td> - <td class="tdc">1.7294</td> - </tr><tr> - <td class="tdc"> 8</td> - <td class="tdc br2">1.1499</td> - <td class="tdc">20</td> - <td class="tdc br2">1.4203</td> - <td class="tdc">32</td> - <td class="tdc">1.7610</td> - </tr><tr> - <td class="tdc"> 9</td> - <td class="tdc br2">1.1702</td> - <td class="tdc">21</td> - <td class="tdc br2">1.4457</td> - <td class="tdc">33</td> - <td class="tdc">1.7934</td> - </tr><tr> - <td class="tdc">10</td> - <td class="tdc br2">1.1909</td> - <td class="tdc">22</td> - <td class="tdc br2">1.4716</td> - <td class="tdc">34</td> - <td class="tdc">1.8262</td> - </tr><tr> - <td class="tdc">11</td> - <td class="tdc br2">1.2120</td> - <td class="tdc">23</td> - <td class="tdc br2">1.4980</td> - <td class="tdc">35</td> - <td class="tdc">1.8600</td> - </tr><tr> - <td class="tdc">12</td> - <td class="tdc br2">1.2334</td> - <td class="tdc">24</td> - <td class="tdc br2">1.5249</td> - <td class="tdc">36</td> - <td class="tdc">1.8944</td> - </tr><tr> - <td class="tdc">13</td> - <td class="tdc br2">1.2553</td> - <td class="tdc">25</td> - <td class="tdc br2">1.5524</td> - <td class="tdc">37</td> - <td class="tdc">1.9295</td> - </tr><tr> - <td class="tdc">14</td> - <td class="tdc br2">1.2775</td> - <td class="tdc">26</td> - <td class="tdc br2">1.5805</td> - <td class="tdc">38</td> - <td class="tdc">1.9654</td> - </tr><tr> - <td class="tdc">15</td> - <td class="tdc br2">1.3002</td> - <td class="tdc">27</td> - <td class="tdc br2">1.6090</td> - <td class="tdc">39</td> - <td class="tdc">2.0021</td> - </tr><tr> - <td class="tdc bb">16</td> - <td class="tdc br2 bb">1.3234</td> - <td class="tdc bb">28</td> - <td class="tdc br2 bb">1.6382</td> - <td class="tdc bb">40</td> - <td class="tdc bb">2.0396</td> - </tr><tr> - <td class="tdr bb" colspan="6"><big><b><i>Machinery</i></b></big> </td> - </tr><tr> - <td class="tdc" colspan="6"> </td> - </tr> - </tbody> -</table> - -<p><span class="pagenum" id="Page_17">[Pg 17]</span></p> - -<h3>Disk-and-Square Method of Determining Angles</h3> - -<p>The method shown in <a href="#FIG_15">Fig. 15</a> for determining -angles for setting up work on a milling machine or planer, possesses -several advantages. No expensive tools are required, the method can be -applied quickly, and the results obtained are quite accurate enough for -any but the most exacting requirements. As will be seen, an ordinary -combination square is used in connection with a disk, the head of the -square being set at different points on the blade according to the -angle that is desired. Theoretically, a one-inch disk could be used for -all angles from about 6 degrees up to a right angle, but in practice it -is more convenient and accurate to employ larger disks for the larger angles.</p> - -<p>The only inaccuracy resulting from this method is due to setting the -square at the nearest “scale fraction” instead of at the exact point -determined by calculation. This error is very small, however, and is -negligible in practically all cases. The dimension <i>x</i> required -for any desired angle <i>a</i> can be found by multiplying the radius -of the disk, by the cotangent of one-half the desired angle, and adding -to this product the radius of the disk.</p> - -<div class="blockquot"> -<p><i>Example</i>: The square blade is to be set to an angle of 15 -degrees 10 minutes, using a 2-inch disk. At what distance <i>x</i> -(<a href="#FIG_15">see Fig. 15</a>) should the head of the square be set?</p> - -<p class="f110">Cot 7 degrees 35 minutes = 7.5113,<br /> and 7.5113 × 1 -+ 1 = 8.5113 inches.</p> - -<p class="no-indent">By setting the square to 8½ inches “full,” the -blade would be set very close to the required angle of 15 degrees 10 -minutes.</p> -</div> - -<h3>Locating Work by means of Size Blocks</h3> - -<p><span class="pagenum" id="Page_18">[Pg 18]</span> -The size-block method of locating a jig-plate or other part, in -different positions on a lathe faceplate, for boring holes accurately -at given center-to-center distances, is illustrated in <a href="#FIG_16">Fig. 16</a>. -The way the size blocks are used in this particular instance is as follows: -A pair of accurate parallels are attached to a faceplate at right angles -to each other and they are so located that the center of one of the -holes to be bored will coincide with the lathe spindle. The hole which -is aligned in this way should be that one on the work which is nearest -the outer corner, so that the remaining holes can be set in a central -position by adjusting the work away from the parallels. After the first -hole is bored, the work is located for boring each additional hole by -placing size blocks of the required width between the edges of the -work and the parallels. For instance, to set the plate for boring hole -<i>D</i>, size blocks (or a combination of blocks or gages) equal in -width to dimension <i>A</i>₁ would be inserted at <i>A</i>, and other -blocks equal in width to dimension <i>B</i>₁ beneath the work as at -<i>B</i>. As will be seen, the dimensions of these blocks equal the -horizontal and vertical distances between holes <i>C</i> and <i>D</i>. -With the use of other combinations of gage blocks, any additional holes -that might be required are located in the central position. While only -two holes are shown in this case, it will be understood that the plate -could be located accurately for boring almost any number of holes by -this method.</p> - -<div class="figcenter"> - <img id="FIG_16" src="images/i_18.jpg" alt="" width="600" height="308" /> - <p class="center space-below2"><b>Fig. 16</b>. Method of setting Work on Faceplate<br /> - with Size Blocks or Gages</p> -</div> - -<p>Incidentally, such gages as the Johansson combination gages are -particularly suited for work of this kind, as any dimension within -the minimum and maximum limits of a set can be obtained by simply -placing the required sizes together. Sometimes when such gages are not -available, disks which have been ground to the required diameter are -interposed between the parallels and the work for securing accurate -locations. Another method of securing a positive adjustment of the -work is to use parallels composed of two tapering sections, which -can be adjusted to vary the width and be locked together by means of -screws. Each half has the same taper so that outer edges are parallel -for any position, and the width is measured by using a micrometer. The -size-block method is usually applied to work having accurately machined -edges, although a part having edges which are of a rough or irregular -shape can be located by this method, if it is mounted on an auxiliary -plate having accurately finished square edges. For instance, if holes -were to be bored in the casting for a jig templet which had simply been -planed on the top and bottom, the casting could be bolted to a finished -plate having square edges and the latter be set in the different -positions required, by means of size blocks. Comparatively large jig -plates are sometimes located for boring in this way and the milling -machine is often used instead of a lathe.</p> - -<h3>The Master-plate Method</h3> - -<p>When it is necessary to machine two or more plates so that they are -duplicates as to the location of holes, circular recesses, etc., -what is known as a master-plate is often used for locating the work -on the lathe faceplate. This master-plate <i>M</i> (<a href="#FIG_17">see Fig. 17</a>) -contains holes which correspond to those wanted in the work, and which -accurately fit a central plug <i>P</i> in the lathe spindle, so that -by engaging first one hole and then another with the plug, the work is -accurately positioned for the various operations.</p> - -<p>When making the master-plate, great care should be taken to have the -sides parallel and the holes at right angles to the sides, as well as -<span class="pagenum" id="Page_19">[Pg 19]</span> -accurately located with reference to one another. The various holes -may be located with considerable precision by the use of buttons as -previously described. Of course, it is necessary to have a hole in the -master-plate for each different position in which the work will have to -be placed on the faceplate; for example, if a circular recess <i>r</i> -were required, a hole <i>r</i>₁ exactly concentric with it would be -needed in the master-plate. The method of holding the work and locating -it with reference to the holes in the master-plate will depend largely -on its shape. The cylindrical blank <i>B</i> illustrated, is positioned -by a recess in the master-plate in which it fits. The work is commonly -held to the master-plate by means of clamps and tap bolts or by screws -which pass through the work and into the master-plate. Solder is sometimes -used when it is not convenient to hold the work by clamps or screws.</p> - -<div class="figcenter"> - <img id="FIG_17" src="images/i_19.jpg" alt="" width="600" height="321" /> - <p class="center space-below2"><b>Fig. 17</b>. Master-plate applied - to a Bench Lathe Faceplate</p> -</div> - -<p>The plug <i>P</i> which locates the master-plate, is first turned to -fit the spindle or collet of the lathe and the outer or projecting end -is roughturned for the holes in the master-plate, which should all be -finished to exactly the same diameter. The plug is then inserted in -the spindle and ground and lapped to a close fit for the holes in -the master-plate. The latter, with the work attached to it, is next -clamped to the faceplate by the straps shown, which engage a groove -around the edge of the master-plate. The first hole is finished by -drilling to within, say, 0.005 or 0.006 inch of the size, and then -boring practically to size, a very small amount being left for reaming -or grinding. The remaining holes can then be finished in the same -way, the work being positively located in each case by loosening the -master-plate and engaging the proper hole in it with the central plug. -It is apparent that by the use of this same master-plate, a number of -pieces <i>B</i> could be made which would be practically duplicates.</p> - -<p>The master-plate method of locating work can be applied in many -different ways. It is used for making duplicate dies, for accurately -locating the various holes in watch movements, and for many other -operations requiring great precision. Master-plates are quite frequently -<span class="pagenum" id="Page_20">[Pg 20]</span> -used by toolmakers when it is necessary to produce a number of drill -jigs which are to be used for drilling holes in different parts having -the same relative locations, thus requiring jigs that are duplicates -within very close limits.</p> - -<p>When a master-plate is required, that is to be used in making -duplicates of an existing model, the holes are bored in the -master-plate by reversing the process <a href="#FIG_17">illustrated in Fig. 17</a>. -That is, the central plug <i>P</i> is turned to fit the largest hole in -the model and the latter with the attached master-plate blank is -clamped to lathe faceplate. The first hole is then bored to within say -0.002 inch of the finish diameter, to allow for grinding, provided -the master-plate is to be hardened. The central plug is then turned -down to fit the next largest hole and the second hole is bored in the -master-plate. This method is continued until all the holes are bored. -In order to prevent any change in the position of the master-plate -relative to the model, it may be secured by inserting dowel-pins -through both parts, the work being held to the lathe faceplate by -ordinary screw clamps. If the holes in the model do not extend clear -through, a flat plate having parallel sides may be interposed between -the model and master-plate to provide clearance between the two and -prevent cutting into the model when boring the master-plate.</p> - -<hr class="chap" /> -<p><span class="pagenum" id="Page_21">[Pg 21]</span></p> - -<div class="chapter"> -<h2 class="nobreak">CHAPTER II<br /> -<span class="h_subtitle">ACCURATE DIVIDING AND<br /> SPACING METHODS</span></h2> -</div> - -<p>Toolmakers and machinists occasionally find it necessary to locate a -number of equally-spaced holes on a straight line between two points, -or to divide a circle with holes which are equi-distant within a very -small limit of accuracy. Several dividing and spacing methods are -described in this chapter; some of these methods can, with slight -modification, be applied in various ways.</p> - -<div class="figcenter"> - <img id="FIG_18" src="images/i_21.jpg" alt="" width="500" height="435" /> - <p class="center space-below2"><b>Fig. 18</b>. Method of Drilling - Small Equally-spaced Holes in Rows</p> -</div> - -<h3>Locating Small Equally-spaced<br /> Holes in Rows</h3> - -<p>It is sometimes necessary to drill one or more rows of small -equally-spaced holes. The best method of doing this work naturally -depends, to some extent, upon the accuracy required, but even when a -high degree of accuracy is not necessary, if an attempt is made to lay -out the holes and drill them in the ordinary way, considerable time -is usually required and the results are liable to be unsatisfactory. -For example, suppose a row of holes ¹/₁₆ inch in diameter and ⅛ inch -center-to-center distance were to be drilled in a flat plate. Some -machinists would proceed by first scribing a center-line and then -laying out the centers of the holes by means of dividers. A much easier -and accurate method is <a href="#FIG_18">illustrated in Fig. 18</a>, and is as follows: -<span class="pagenum" id="Page_22">[Pg 22]</span> -Lay out the first hole and drill it; then secure a small piece of flat -steel for a drill guide, drill a hole through it, bevel one corner -and scribe a fine line on the beveled section, as shown in the -illustration. Align the hole drilled in the guide with the hole in the -work, by inserting a close-fitting plug, and clamp a scale against one -edge of the drill guide so that one of the graduation marks exactly -matches with the line on the guide. The edge of the scale must also be -located parallel to the center-line of the row of holes to be drilled. -Now proceed to drill the holes, setting the drill guide each time, to -whatever graduation line represents the required spacing or pitch of -the holes.</p> - -<p>It is advisable to use a magnifying glass to accurately align the -graduation mark on the scale with the line on the drill guide. If two -or more rows of holes are to be drilled parallel, the guide block can -be drilled accordingly, so that the different rows of holes can be -finished at the same time. The drill guide block should be relieved -slightly in the center so as to insure the ends of the block bearing -against the edge of the scale. A toolmaker or machinist can drill a row -of holes accurately by this simple method, in the time required to lay -them out in the usual way, and even though accuracy is not necessary, -it is quicker to drill holes by this method than by the one more -commonly employed.</p> - -<h3>Use of Disks for Locating<br /> Equally-Spaced Holes</h3> - -<p>A simple method of spacing holes that are to be drilled in a -straight line is illustrated in <a href="#FIG_19">Fig. 19</a>. Two -disks are made, each having a diameter equal to the center-to-center -distance required between the holes. These disks must also have holes -which are exactly central with the outside to act as a guide for the -drill or reamer. The first two holes are drilled in the work while the -disks are clamped so that they are in contact with each other and also -with the straightedge as shown. One disk is then placed on the opposite -side of the other, as indicated by the dotted line, and a third hole -is drilled; this process of setting one disk against the opposite side -of the other is continued until all the holes are drilled. When it is -necessary to drill a parallel row of “staggered” holes, the second row -can be located by placing disks of the proper size in contact with the -first row of disks.</p> - -<div class="figcenter"> - <img id="FIG_19" src="images/i_22.jpg" alt="" width="600" height="297" /> - <p class="center space-below2"><b>Fig. 19</b>. Locating Equi-distant Holes - in a Straight Line<br /> by Means of Disks and Straightedge</p> -</div> - -<p><span class="pagenum" id="Page_23">[Pg 23]</span> -A method of using disks, which is preferable for very accurate work, is -shown in <a href="#FIG_20">Fig. 20</a>. The disks are clamped against -each other and along straightedge <i>A</i> by the screws shown, and if -the outside diameters are correct and the guide holes concentric with -the outside, very accurate work can be done. With this device there -may be as many disks as there are holes to be drilled, if the number -of holes is comparatively small, but if it is necessary to drill a -long row of holes, the disks and frame are shifted along an auxiliary -straightedge <i>B</i>, the hole in one of the end disks being aligned -with the last hole drilled by inserting a close-fitting plug through -the disk and hole.</p> - -<h3>Adjustable Jig for Accurate Hole Spacing</h3> - -<p>An adjustable jig for accurately spacing small holes is shown in -<a href="#FIG_21">Fig. 21</a>.</p> - -<div class="figcenter"> - <img id="FIG_20" src="images/i_23.jpg" alt="" width="600" height="299" /> - <p class="center space-below2"><b>Fig. 20</b>. Special Disk-jig - for Precision Drilling</p> -</div> - -<p>This form is especially adapted for locating a number of equally -spaced holes between two previously drilled or bored holes, and the -accuracy of the method lies in the fact that a slight error in the -original spacing of the guide bushing is multiplied, and, therefore, -easily detected. There are two of these guide bushings <i>A</i> and -<i>B</i> which are carried by independent slides. These slides can be -shifted along a dovetail groove after loosening the screws of clamp-gib -<i>C</i>. To illustrate the method of using this jig, suppose five -equally-spaced holes are to be located between two holes that are 12 -inches apart. As the center-to-center distance between adjacent holes -is 2 inches, slides <i>A</i> and <i>B</i> would be set so that the -dimension <i>x</i> equals 2 inches plus the radii of the bushings. -A straightedge is then clamped to the work in such position that a -close-fitting plug can be inserted through the end holes which were -previously drilled or bored. Then with a plug inserted through, say, -bushing <i>B</i> and one of the end holes, the first hole is drilled -and reamed through bushing <i>A</i>; the jig is then shifted to the -left until the plug in <i>B</i> enters the hole just made. The second -hole is then drilled and reamed through bushing <i>A</i> and this -<span class="pagenum" id="Page_24">[Pg 24]</span> -drilling and shifting of the jig is continued until the last hole is -finished. The distance between the last hole and the original end hole -at the left is next tested by attempting to insert close-fitting plugs -through both bushings. Evidently, if there were any inaccuracy in the -spacing of the bushings, this would be multiplied as many times as the -jig was shifted, the error being accumulative. To illustrate how the -error accumulates, suppose that the bushings were 0.001 inch too far -apart; then the distance to the first hole would be 2.001 inch, to the -second hole, 4.002 inch, and finally the distance from the first to the -sixth hole would be 10.005 inches; consequently, the distance between -the sixth and seventh holes would equal 12-10.005 = 1.995 inch, or -0.005 inch less than the required spacing, assuming, for the sake of -illustration, that the first and last holes were exactly 12 inches -apart. In case of an error of 0.005 inch, the bushings would be set -closer together an amount equal to one-fifth of this error, as near as -could be determined with a micrometer, and all of the holes would then -be re-reamed.</p> - -<div class="figcenter"> - <img id="FIG_21" src="images/i_24.jpg" alt="" width="600" height="251" /> - <p class="center space-below2"><b>Fig. 21</b>. Adjustable Jig - for Accurate Hole Spacing</p> -</div> - -<h3>Methods of Accurately Dividing<br /> a Circle</h3> - -<p>Sometimes it is necessary to machine a number of holes in a plate so -that all the holes are on a circle or equi-distant from a central -point, and also the same distance apart, within very small limits. A -simple method of spacing holes equally is illustrated at <i>A</i>, -<a href="#FIG_22">Fig. 22</a>. A number of buttons equal to the number of holes -required are ground and lapped to exactly the same diameter, preferably by -mounting them all on an arbor and finishing them at the same time. The ends -should also be made square with the cylindrical surface of the button. -When these buttons are finished, the diameter is carefully measured and -this dimension is subtracted from the diameter of the circle on which -the holes are to be located, in order to obtain the diameter <i>d</i> -(see illustration). A narrow shoulder is then turned on the plate to be -bored, the diameter being made exactly equal to dimension <i>d</i>. By -placing the buttons in contact with this shoulder, they are accurately -located radially and can then be set equi-distant from each other by -the use of a micrometer. In this particular case, it would be advisable -<span class="pagenum" id="Page_25">[Pg 25]</span> -to begin by setting the four buttons which are 90 degrees apart and -then the remaining four. The buttons are next used for setting the work -preparatory to boring. (See “<a href="#BUTTON">Button Method of Accurately -Locating Work</a>.”)</p> - -<div class="figcenter"> - <img id="FIG_22" src="images/i_25.jpg" alt="" width="500" height="449" /> - <p class="center space-below2"><b>Fig. 22</b>. Four Methods - of Accurately Dividing a Circle</p> -</div> - -<h3>Correcting Spacing Errors<br /> by Split Ring Method</h3> - -<p>Another method of securing equal spacing for holes in indexing wheels, -etc., is illustrated at <i>B</i>, <a href="#FIG_22">Fig. 22</a>. This method, -however, is not to be recommended if the diameter of the circle on which the -holes are to be located, must be very accurate. The disk or ring in -which the holes are required, is formed of two sections <i>e</i> and -<i>f</i>, instead of being one solid piece. The centers for the holes -are first laid out as accurately as possible on ring <i>e</i>. Parts -<i>e</i> and <i>f</i> are then clamped together and the holes are -drilled through these two sections. Obviously, when the holes are -laid out and drilled in this way, there will be some error in the -spacing, and, consequently, all of the holes would not match, except -when plate <i>e</i> is in the position it occupied when being drilled. -Whatever errors may exist in the spacing can be eliminated, however, -by successively shifting plate <i>e</i> to different positions and -re-reaming the holes for each position. A taper reamer is used and -two pins should be provided having the same taper as the reamer. Ring -<i>e</i> is first located so that a hole is aligned quite accurately -with one in the lower plate. The ring is then clamped and the hole is -<span class="pagenum" id="Page_26">[Pg 26]</span> -partly reamed, the reamer being inserted far enough to finish the hole -in plate <i>e</i> and also cut clear around in the upper part of plate -<i>f</i>. One of the taper pins is then driven into this hole and then -a hole on the opposite side is partly reamed, after which the other pin -is inserted. The remaining holes are now reamed in the same way, and -the reamer should be fed in to the same depth in each case. If a pair -of holes is considerably out of alignment, it may be necessary to run -the reamer in to a greater depth than was required for the first pair -reamed, and in such a case all the holes should be re-reamed to secure -a uniform size.</p> - -<p>The next step in this operation is to remove the taper pins and clamps -or turn index plate <i>e</i> one hole and again clamp it in position. -The reaming process just described is then repeated; the holes on -opposite sides of the plate are re-reamed somewhat deeper, the taper -pins are inserted, and then all of the remaining holes are re-reamed -to secure perfect alignment for the new position of the plate. By -repeating this process of shifting plate <i>e</i> and re-reaming -the holes, whatever error that may have existed originally in the -spacing of the holes, will practically be eliminated. It would be very -difficult, however, to have these holes located with any great degree -of accuracy, on a circle of given diameter.</p> - -<h3>Circular Spacing by Contact<br /> of Uniform Disks</h3> - -<p>When an accurate indexing or dividing wheel is required on a machine, -the method of securing accurate divisions of the circle illustrated -at <i>C</i>, <a href="#FIG_22">Fig. 22</a>, is sometimes employed. There is a -series of circular disks or bushings equal in number to the divisions required, -and these disks are all in contact with each other and with a circular -boss or shoulder on the plate to which they are attached. The space -between adjacent disks is used to accurately locate the dividing wheel, -engagement being made with a suitable latch or indexing device. When -making a dividing wheel of this kind, all of the disks are ground and -lapped to the same diameter and then the diameter of the central boss -or plate is gradually reduced until all of the disks are in contact -with each other and with the boss. For an example of the practical -application of this method see “<a href="#ORIGIN">Originating a Precision Dividing Wheel</a>.”</p> - -<h3>Spacing by Correcting the<br /> Accumulated Error</h3> - -<p>Another indexing method of spacing holes equi-distant, is illustrated -by the diagram at <i>D</i>, <a href="#FIG_22">Fig. 22</a>. An accurately fitting -plug is inserted in the central hole of the plate in which holes are required. -Two arms <i>h</i> are closely fitted to this plug but are free to -rotate and are provided with a fine-pitch screw and nut at the outer -ends for adjusting the distance between the arms. Each arm contains an -accurately made, hardened steel bushing <i>k</i> located at the same -radial distance from the center of the plate. These bushings are used -as a guide for the drill and reamer when machining the holes in the plate.</p> - -<p>To determine the center-to-center distance between the bushings, divide -<span class="pagenum" id="Page_27">[Pg 27]</span> -360 by twice the number of holes required; find the sine corresponding -to the angle thus obtained, and multiply it by the diameter of the -circle upon which the holes are located. For example, if there were to -be eleven holes on a circle 8 inches in diameter, the distance between -the centers of the bushings would equal</p> - -<table class="fontsize_120 no-wrap" border="0" cellspacing="0" summary=" " cellpadding="0" > - <tbody><tr> - <td class="tdc">360</td> - <td class="tdl" rowspan="2"> = 16.36 degrees.</td> - </tr><tr> - <td class="tdc over">2 × 11</td> - </tr> - </tbody> -</table> - -<p class="no-indent">The sine of 16.36 degrees is 0.2815, and 0.2815 × -8 = 2.252 inches. The arms are adjusted to locate the centers of the -bushings this distance apart, by placing closely fitting plugs in the -bushings and measuring from one plug to another with a micrometer or -vernier caliper. Of course, when taking this measurement, allowance is -made for the diameter of the plugs.</p> - -<p>After the arms are set, a hole is drilled and reamed; an accurately -fitting plug is then inserted through the bushing and hole to secure -the arms when drilling and reaming the adjacent hole. The radial arms -are then indexed one hole so that the plug can be inserted through one -of the arms and the last hole reamed. The third hole is then drilled -and reamed, and this operation is repeated for all of the holes. -Evidently, if the center-to-center distance between the bushings is -not exactly right, the error will be indicated by the position of the -arms relative to the last hole and the first one reamed; moreover, -this error will be multiplied as many times as there are holes. For -instance, if the arms were too far apart, the difference between -the center-to-center distance of the last pair of holes and the -center-to-center distance of the bushings in the arms, would equal, in -this particular case, eight times the error, and the arms should be -re-adjusted accordingly. Larger bushings would then be inserted in the -arms and the holes re-reamed, this operation being repeated until the -holes were all equi-distant.</p> - -<p>As will be seen, the value of this method lies in the fact that it -shows the accumulated error. Thus, if the arms were 0.0005 inch too far -apart, the difference between the first and last hole would equal 8 × -0.0005 = 0.004 inch. This same principle of dividing can be applied in -various ways. For instance, the radial arms if slightly modified, could -be used for drilling equally-spaced holes in the periphery or disk of a -plate, or, if a suitable marking device were attached, a device of this -kind could be used for accurately dividing circular parts.</p> - -<h3 id="ORIGIN">Originating a Precision Dividing Wheel</h3> - -<p>There are various methods employed for making accurate indexing wheels -for a definite number of divisions. One of these methods, suitable -particularly for small numbers of divisions, employs a split wheel with -a series of taper holes reamed through the two divisions. By shifting -the two divisions from point to point (as explained in connection with -sketch <i>B</i>, <a href="#FIG_22">Fig. 22</a>) and reaming and re-reaming the -taper holes at each shifting, they may finally be brought very accurately into -position. Another method that has been employed consists in clamping -<span class="pagenum" id="Page_28">[Pg 28]</span> -about the rim of the dividing wheel a number of precisely similar -blocks, fitting close to each other and to the wheel itself. These -blocks are then used for locating the wheel in each of its several -positions in actual work. A third and simpler method (a modification -of the one last described) consists in grinding a series of disks and -clamping them around a rim of such diameter that the disks all touch -each other and the rim simultaneously, as explained in connection with -sketch <i>C</i>, <a href="#FIG_22">Fig. 22</a>. The wheel described in -the following, which is illustrated in <a href="#FIG_23">Fig. 23</a>, -was made in this way.</p> - -<div class="figcenter"> - <img id="FIG_23" src="images/i_28.jpg" alt="" width="500" height="518" /> - <p class="center space-below2"><b>Fig. 23</b>. Precision Dividing Wheel</p> -</div> - -<p>Disks <i>A</i> are clamped against an accurately ground face of the -wheel <i>B</i> and are supposed to just touch each other all around, -and to be each of them in contact with the ground cylindrical surface -at <i>x</i>. They are held in proper position by bolts <i>C</i> and -nuts <i>D</i>. The bolts fit loosely in the holes of the disks or -bushings <i>A</i> so that the latter are free to be located as may be -desired with reference to the bolts.</p> - -<p>One or two improvements in the construction of this type of dividing -wheel may be noted before proceeding to a description of the way in -which it is made. For one thing, instead of having an indexing bolt -enter the V-space between two adjoining disks, a smaller diameter -<i>y</i> is ground on each of them, over which locking finger or pawl -passes, holding the wheel firmly from movement in either direction. -This construction has the advantage of a probable lessening of error by -<span class="pagenum" id="Page_29">[Pg 29]</span> -locating on each bushing instead of between two bushings; moreover, it -gives a better holding surface and better holding angles than would be -the case if this smaller diameter were not provided.</p> - -<p>A second improvement lies in the method of clamping the bushings -<i>A</i> in place. Instead of providing each bolt with a separate -washer, a ring <i>F</i> is used. This ring fits closely on a seat -turned to receive it on the dividing wheel <i>B</i>. When one bushing -<i>A</i> has been clamped in place, the disk is locked from movement so -that there is no possibility, in clamping the remaining bushings, of -having their location disturbed in the slightest degree by the turning -of the nuts in fastening them in place.</p> - -<p>The bushings <i>A</i>, of which there were in this case 24, were all -ground exactly to the required diameters on their locating and locking -surfaces. The important things in this operation are, first, that the -large or locating diameter of the bushing should be exactly to size; -and second, that this surface should be in exact alignment with the -diameter in which the locking is done; and, finally, that the face of -the bushing should be squared with the cylindrical surfaces. A refined -exactness for the diameter of the locking surfaces is not so important, -as the form of locking device provided allows slight variations at this -point without impairment of accuracy. This dimension was kept within -very close limits, however. The truth of the two cylindrical surfaces -and the face of the bushing was assured by finishing all these surfaces -in one operation on the grinding machine.</p> - -<p>The sizing of the outer diameter of the bushing, which was 1.158 inch, -must be done so accurately that it was not thought wise to trust to -the ordinary micrometer caliper. An indexing device was therefore made -having a calipering lever with a long end, in the ratio of 10 to 1, -which actuated the plunger of a dial test indicator of the well-known -type made by the Waltham Watch Tool Co. The thousandth graduations -on the dial of this indicator would then read in ten-thousandths, -permitting readings to be taken to one-half or one-quarter of this -amount. The final measurements with this device were all taken after -dipping the bushings in water of a certain temperature, long enough to -give assurance that this temperature was universal in all the parts -measured. It will be understood, of course, in this connection, that -getting the diameter of these bushings absolutely to 1.158 inch was -not so important as getting them all exactly alike, whether slightly -over or slightly under this dimension; hence, the precaution taken in -measurement.</p> - -<p>Wheel <i>B</i> was next ground down nearly to size, great care being -taken that it should run exactly concentric with the axis. As soon as -the diameter of the surface <i>x</i> was brought nearly to the required -dimension as obtained by calculation, the disks were tried in place. -The first one was put in position with its loose hole central on the -bolt and clamped in place under ring <i>F</i>. The next bushing was -then pressed up against it and against the surface <i>x</i> of the -wheel and clamped in place. The third one was similarly clamped in -contact with its neighboring bushing and the wheel, and so on, until -<span class="pagenum" id="Page_30">[Pg 30]</span> -the whole circle was completed. It was then found that the last disk -would not fill the remaining space. This required the grinding off of -some stock from surface <i>x</i>, and a repetition of the fitting of the -bushings <i>A</i> until they exactly filled the space provided for them.</p> - -<div class="figcenter"> - <img id="FIG_24" src="images/i_30.jpg" alt="" width="500" height="578" /> - <p class="center space-below2"><b>Fig. 24</b>. Precision Dividing - Wheel and its Indexing Mechanism</p> -</div> - -<p>This operation required, of course, considerably more skill than a -simple description of the job would indicate. One of the points that -had to be carefully looked out for was the cleaning of all the surfaces -in contact. A bit of dust or lint on one of the surfaces would throw -the fitting entirely out. The temperature of the parts was another -important consideration. As an evidence of the accuracy with which the -work was done, it might be mentioned that it was found impossible to do -this fitting on a bench on the southern or sunny side of the shop, the -variations of temperature between morning and noon, and between bright -sunshine and passing clouds, being such that the disks would not fit -uniformly. The variation from these minute temperature changes resulted -<span class="pagenum" id="Page_31">[Pg 31]</span> -from the different coefficients of expansion of the iron wheel and the -steel bushings. The obvious thing to do would be to build a room for -this work kept at a constant temperature and preferably that of the -body, so that the heat of the body would make no difference in the -results. It was found sufficient in this case, however, to do the work -on the northern side of the shop where the temperature was more nearly -constant, not being affected by variations in sunshine.</p> - -<p>The dividing wheel, the construction of which has just been described, -was made by the Fellows Gear Shaper Co. It is used for indexing the -Fellows gear cutters in the machine in which the teeth are ground. The -indexing mechanism of this machine is shown in <a href="#FIG_24">Fig. 24</a>. -It is operated by a handle or lever pinned to rock-shaft <i>H</i>, to -which is keyed arm <i>J</i>. Pivoted to <i>J</i> is a pawl <i>K</i> -engaging the teeth of ratchet <i>L</i>, which revolves loosely on shaft -<i>H</i>. This ratchet <i>L</i> controls the movement of locking finger -<i>E</i>. The parts are shown in their normal or locked position in the -engraving.</p> - -<p>As the handle on shaft <i>H</i> is pulled in the direction indicated by -the arrow, arm <i>J</i> is raised, carrying the ratchet wheel around to -the right. This allows flat spring <i>M</i> to drop off of the ratchet -tooth, permitting helical spring <i>O</i> to raise latch <i>E</i> and -thus leave the wheel free. The continued movement of the hand-lever -and of rock-shaft <i>H</i>, by means of gear <i>N</i>, intermediate -pinion <i>P</i> and gear <i>Q</i>, causes the indexing pawl <i>R</i>, -which is pivoted to gear <i>Q</i> and acts on the head of one of the -bolts <i>C</i> (<a href="#FIG_23">see Fig. 23</a>), to index the wheel -one step. Just before reaching its new location the new tooth of -ratchet wheel <i>L</i> coming up, bears down on the top of spring -<i>M</i>, pressing latch <i>E</i> into place against the tension of -coil spring <i>O</i>. By this means the wheel is locked in position.</p> - -<p>When the operator pushes the handle on shaft <i>H</i> back again to -its position of rest, the pawl <i>R</i> is retracted into position to -act on the next bolt head for the next indexing. Star-wheel <i>L</i> -remains stationary on this backward movement, being prevented from -revolving by the notch on the top of the tooth into which spring -<i>M</i> fits. Pawl <i>K</i> on its return engages with the next tooth -of this wheel, ready for the next indexing operation.</p> - -<p>A slight rotary adjustment of dividing wheel <i>B</i>, independent of -this indexing mechanism, is required for the feeding of the machine. -This is accomplished by the end movement of latch <i>E</i>, which is -pivoted in slide <i>S</i>. This slide is pressed to the right by spring -plunger <i>T</i>, and is adjusted positively in the other direction -by feed-screw <i>U</i>, which is finely graduated to permit accurate -adjustment. The accuracy in indexing obtained by the use of a wheel -thus made was required to bring the finished cutters within the very -narrow limits allowed for them in the final inspection.</p> - -<hr class="chap x-ebookmaker-drop" /> -<p><span class="pagenum" id="Page_32">[Pg 32]</span></p> - -<div class="chapter"> -<h2 class="nobreak">CHAPTER III<br /> -<span class="h_subtitle">LOCATING WORK FOR BORING<br /> - ON MILLING MACHINE</span></h2> -</div> - -<p>It is often desirable to perform boring operations on the milling -machine, particularly in connection with jig work. Large jigs, which -because of their size or shape could not be conveniently handled in -the lathe, and also a variety of smaller work, can often be bored -to advantage on the milling machine. When such a machine is in good -condition, the necessary adjustments of the work in both vertical and -horizontal planes, can be made with considerable accuracy by the direct -use of the graduated feed-screw dials. It is good practice, however, -when making adjustments in this way, to check the accuracy of the -setting by measuring the center distances between the holes directly. -For the purpose of obtaining fine adjustments when boring on the -milling machine, the Brown & Sharpe Mfg. Co. makes special scales and -verniers that are attached to milling machines, so that the table may -be set by direct measurement. By attaching a scale and vernier to the -table and saddle, respectively, and a second scale to the column with -a vernier on the knee, both longitudinal and vertical measurements can -be made quickly and accurately, and the chance of error resulting from -inaccuracy of the screw, or from lost motion between the screw and nut, -is eliminated.</p> - -<h3>Checking Location of Holes by<br /> Micrometer-and-plug Method</h3> - -<p>One method of checking the accuracy of the location of holes bored in -the milling machine, is to insert closely fitting ground plugs into the -bored holes and then determine the center-to-center distance by taking -a direct measurement across the plugs with a micrometer or vernier -caliper. For example, if holes were to be bored in a jig-plate, as -shown in <a href="#FIG_1">Fig. 1</a>, assuming that hole <i>A</i> were finished -first, the platen would then be moved two inches, as shown by the feed dial; -hole <i>B</i> would then be bored slightly under size. Plugs should then be -accurately fitted to these holes, having projecting ends, preferably of -the same size. By measuring from one of these plugs to the other with a -vernier or micrometer caliper, the center distance between them can be -accurately determined, allowance being made, of course, for the radii -of each plug. If this distance is incorrect, the work can be adjusted -before finishing <i>B</i> to size, by using the feed-screw dial. After -hole <i>B</i> is finished, the knee could be dropped 1.5 inch, as shown -by the vertical feed dial, and hole <i>C</i> bored slightly under size; -then by the use of plugs, as before, the location of this hole could be -tested by measuring center distances between <i>C-B</i> and <i>C-A</i>.</p> - -<p>An example of work requiring the micrometer-and-plug test, is shown set -<span class="pagenum" id="Page_33">[Pg 33]</span> -up in the milling machine in <a href="#FIG_25">Fig. 25</a>. The large circular -plate shown has a central hole and it was necessary to bore the outer holes in -correct relation with the center hole within a limit of 0.0005 inch. -The center hole was first bored and reamed to size; then an accurately -fitting plug was inserted and the distances to all the other holes -were checked by measuring from this plug. This method of testing with -the plugs is intended to prevent errors which might occur because of -wear in the feed-screws or nuts, that would cause the graduated dials -to give an incorrect reading. On some jig work, sufficient accuracy -could be obtained by using the feed-screw dials alone, that is, without -testing with the plugs, in which case the accuracy would naturally -depend largely on the condition of the machine.</p> - -<div class="figcenter"> - <img id="FIG_25" src="images/i_33.jpg" alt="" width="600" height="488" /> - <p class="center space-below2"><b>Fig. 25</b>. Example of Precision - Boring on Milling Machine</p> -</div> - -<p>A method that is a modification of the one in which plugs are used -to test the center distance is as follows: All the holes are first -drilled with suitable allowance for boring, the location being obtained -directly by the feed-screw dials. A special boring-tool, the end of -which is ground true with the shank, is then inserted in the spindle -and the first hole, as at <i>A</i> in <a href="#FIG_1">Fig. 1</a> is finished, -after which the platen is adjusted for hole <i>B</i> by using the dial as before. -A close-fitting plug is then inserted in hole <i>A</i> and the accuracy -of the setting is obtained by measuring the distance between this plug -and the end of the boring-tool, which is a combination tool and test -plug. In a similar manner, the tool is moved from one position to -another, and, as all the holes have been previously drilled, all are -bored without removing the tool from the spindle. -<span class="pagenum" id="Page_34">[Pg 34]</span></p> - -<p>Another modification of the micrometer-and-plug method is illustrated -in Figs. <a href="#FIG_26">26</a> and <a href="#FIG_27">27</a>. -It is assumed that the plate to be bored is finished on the edges, and -that it is fastened to an angle-plate, which is secured to the table -of the milling machine and set square with the spindle. A piece of -cold-rolled steel or brass is first fastened in the chuck (which is -mounted on the spindle) and turned off to any diameter. This diameter -should preferably be an even number of thousandths, to make the -calculations which are to follow easier. The turning can be done either -by holding the tool in the milling machine vise, or by securing it to -the table with clamps. In either case, the tool should be located near -the end of the table, so as to be out of the way when not in use.</p> - -<div class="figcenter"> - <img id="FIG_26" src="images/i_34.jpg" alt="" width="500" height="415" /> - <p class="center space-below2"><b>Fig. 26</b>. Obtaining Vertical - Adjustment by Means of<br /> Depth Gage and turned Plug in Chuck</p> -</div> - -<p>After the piece in the chuck is trued, the table and knee are adjusted -until the center of the spindle is in alignment with the center of the -first hole to be machined. This setting of the jig-plate is effected -by measuring with a micrometer depth gage from the top and sides of -the work, to the turned plug, as illustrated in <a href="#FIG_26">Fig. 26</a>. -When taking these measurements, the radius of the plug in the chuck is, of course, -deducted. When the plate is set the plug is removed from the chuck and -the first hole drilled and bored or reamed to its proper size. We shall -assume that the holes are to be located as shown by the detail view, -<a href="#FIG_26">Fig. 26</a>, and that hole <i>A</i> is the first one bored. -The plug is then again inserted in the chuck and trued with the tool, after which -<span class="pagenum" id="Page_35">[Pg 35]</span> -it is set opposite the place where the second hole <i>B</i> is to be -bored; this is done by inserting an accurately fitting plug in hole -<i>A</i> and measuring from this plug to the turned piece in the chuck, -with an outside micrometer as indicated in <a href="#FIG_27">Fig. 27</a>. -Allowance is, of course, again made for the radii of the two plugs. The -horizontal measurement can be taken from the side of the work with a -depth gage as before. The plug is then removed and the hole drilled and -bored to the proper size. The plug is again inserted in the chuck and -turned true; the table is then moved vertically to a position midway -between <i>A</i> and <i>B</i>, and then horizontally to the proper -position for hole <i>C</i>, as indicated by the depth gage from the -side of the work. The location can be verified by measuring the center -distances <i>x</i> with the micrometer. In a similar manner holes -<i>D</i>, <i>E</i>, <i>F</i> and <i>G</i> are accurately located.</p> - -<div class="figcenter"> - <img id="FIG_27" src="images/i_35.jpg" alt="" width="600" height="438" /> - <p class="center space-below2"><b>Fig. 27</b>. Adjusting for - Center-to-center Distance<br /> by use of Plugs and Micrometer</p> -</div> - -<p>If the proper allowances are made for the variation in the size of the -plug, which, of course, is made smaller each time it is trued, and if -no mistakes are made in the calculations, this method is very accurate. -Care should be taken to have the gibs on all sides fairly tight at the -beginning, and these should not be tightened after each consecutive -alignment, as this generally throws the work out a few thousandths. If -the reductions in the size of the plug, each time it is turned, are -confusing, new plugs can be used each time a test is made, or the end -of the original plug can be cut off so that it can be turned to the -same diameter for every test. If the center distances <i>x</i> are not -given, it is, of course, far more convenient to make all the geometric -calculations before starting to work. -<span class="pagenum" id="Page_36">[Pg 36]</span></p> - -<h3>The Button-and-plug Method</h3> - -<p>The use of the button method as applied to the milling machine, is -illustrated in <a href="#FIG_28">Fig. 28</a>, where a plain jig-plate -is shown set up for boring. The jig, with buttons <i>B</i> accurately -located in positions corresponding to the holes to be bored, is clamped -to the angle-plate <i>A</i> that is set at right angles to the spindle. -Inserted in the spindle there is a plug <i>P</i>, the end of which is -ground to the exact size of the indicating buttons. A sliding sleeve -<i>S</i> is accurately fitted to this plug and when the work is to be -set for boring a hole, the table and knee of the machine are adjusted -until the sleeve <i>S</i> will pass over the button representing -the location of the hole, which brings the button and spindle into -alignment. When setting the button in alignment, all lost motion or -backlash should be taken up in the feed-screws. For instance, if the -button on the jig should be a little higher than the plug in the -spindle, do not lower the knee until the bushing slips over the button, -but lower the knee more than is required and then raise it until the -bushing will pass over the button. This same rule should be followed -for longitudinal adjustments.</p> - -<div class="figcenter"> - <img id="FIG_28" src="images/i_36.jpg" alt="" width="600" height="443" /> - <p class="center space-below2"><b>Fig. 28</b>. Accurate Method - of Aligning Spindle with Button on Jig-Plate</p> -</div> - -<p>After the button is set by this method, it is removed and the plug in -the spindle is replaced by a drill and then by a boring-tool or reamer -for finishing the hole to size. In a similar manner the work is set -for the remaining holes. The plug <i>P</i> for the spindle must be -accurately made so that the outer end is concentric with the shank, -and the latter should always be inserted in the spindle in the same -relative position. With a reasonable degree of care, work can be set -with considerable precision by this method, providing, of course, the -buttons are properly set. -<span class="pagenum" id="Page_37">[Pg 37]</span></p> - -<p>Some toolmakers use, instead of the plug and sleeve referred to, a test -indicator for setting the buttons concentric with the machine spindle. -This indicator is attached to and revolves with the spindle, while the -point is brought into contact with the button to be set. The difficulty -of seeing the pointer as it turns is a disadvantage, but with care -accurate results can be obtained.</p> - -<h3>Size Block and Gage Method</h3> - -<p>Another method which can at times be employed for accurately -locating a jig-plate in different positions on an angle-plate, is shown -in <a href="#FIG_29">Fig. 29</a>. The angle-plate is, of course, set at -right angles to the spindle and depth gages and size blocks are used -for measuring directly the amount of adjustment. Both the angle-plate -and work should have finished surfaces on two sides at right angles -to each other, from which measurements can be taken. After the first -hole has been bored, the plate is adjusted the required distance both -horizontally and vertically, by using micrometer depth gages, which -should preferably be clamped to the angle-plate. If the capacity of the -gages is exceeded, measurements may be taken by using standard size -blocks in conjunction with the depth gages.</p> - -<div class="figcenter"> - <img id="FIG_29" src="images/i_37.jpg" alt="" width="600" height="345" /> - <p class="center space-below2"><b>Fig. 29</b>. Locating Work from - Edges of Angle-Plate<br /> by means of Depth Gages and Size Blocks</p> -</div> - -<p>It is frequently necessary to bore holes in cast jig-plates or machine -parts, which either have irregularly shaped or unfinished edges. A good -method of locating such work is illustrated in <a href="#FIG_30">Fig. 30</a>. -The part to be bored is attached to an auxiliary plate <i>A</i> which should -have parallel sides and at least two edges which are straight and at right -angles to each other. This auxiliary plate with the work, is clamped -against an accurate angle-plate <i>B</i>, which should be set square -with the axis of the machine spindle. A parallel strip is bolted to the -angle-plate and the inner edge is set square with the machine table. -After the first hole is bored, the work is located for boring the other -<span class="pagenum" id="Page_38">[Pg 38]</span> -to the edge of the auxiliary plate, and horizontal measurements -<i>y</i> between the parallel and the plate. These measurements, -if quite large, might be taken with micrometer gages, whereas, for -comparatively small adjustments, size blocks might be more convenient.</p> - -<h3>Vernier Height Gage and Plug Method</h3> - -<p>When a vernier height gage is available, it can often be used to -advantage for setting work preparatory to boring in a milling machine. -One advantage of this method is that it requires little in the way of -special equipment. The work is mounted on an angle-plate or directly -on the platen, depending on its form, and at one end an angle-plate is -set up with its face parallel to the spindle. An accurately finished -plug is inserted in the spindle and this plug is set vertically from -the platen and horizontally from the end angle-plate, by measuring with -the vernier height gage. After the plug is set for each hole, it is, of -course, removed and the hole drilled and bored or reamed.</p> - -<div class="figcenter"> - <img id="FIG_30" src="images/i_38.jpg" alt="" width="600" height="384" /> - <p class="center space-below2"><b>Fig. 30</b>. Method of Holding and - Locating Casting<br /> of Irregular Shape, for Boring Holes</p> -</div> - -<p>The way the plug and height gage is used is clearly illustrated in -Figs. <a href="#FIG_31">31</a> and <a href="#FIG_32">32</a>. -The work, in this particular case, is a small jig. This is clamped -directly to the machine table and at one end an angle-plate is also -bolted to the table. This angle-plate is first set parallel with -the traverse of the saddle or in line with the machine spindle. To -secure this alignment, an arbor is inserted in the spindle and a test -indicator is clamped to it by gripping the indicator between bushings -placed on the arbor. The table is then moved longitudinally until the -contact point of the indicator is against the surface plate; then by -traversing the saddle crosswise, any lack of parallelism between the -surface of the angle-plate and the line of saddle traverse will be -shown by the indicator. -<span class="pagenum" id="Page_39">[Pg 39]</span></p> - -<div class="figcenter"> - <img id="FIG_31" src="images/i_39a.jpg" alt="" width="600" height="489" /> - <p class="center space-below2"><b>Fig. 31</b>. Making a Vertical Adjustment - by Measuring to Ground Plug in Spindle</p> - <img id="FIG_32" src="images/i_39b.jpg" alt="" width="600" height="486" /> - <p class="center space-below2"><b>Fig. 32</b>. Making a Horizontal Adjustment - by measuring from Angle-Plate to Ground Plug</p> -</div> - -<p><span class="pagenum" id="Page_40">[Pg 40]</span> -When the work is to be adjusted horizontally, the vernier height gage -is used as shown in <a href="#FIG_32">Fig. 32</a>, the base of the gage resting -on the angle-plate and the measurement being taken to an accurately ground and -lapped plug in the spindle. For vertical adjustments, the measurements -are taken between this ground plug and the machine platen as in <a href="#FIG_31">Fig. 31</a>.</p> - -<h3>Locating Holes to be Bored<br /> from Center-punch Marks</h3> - -<p>The problem of accurately locating holes to be bored on the milling -machine has received much attention, and the method generally used when -accuracy has been required is the button method, which was previously -described. So much time is required for doing the work by this method, -however, that numerous efforts have been made to obtain equally good -results in other ways.</p> - -<div class="figcenter"> - <img id="FIG_33" src="images/i_40.jpg" alt="" width="600" height="375" /> - <p class="center space-below2"><b>Fig. 33</b>. Diagram Illustrating Rapid - but Accurate Method of<br /> Locating Holes to be bored on Milling Machine</p> -</div> - -<p>The increasing demand for rapidity combined with accuracy and a minimum -liability of error, led to the development of the system described in -the following: A center-punch mark takes the place of the button, from -which to indicate the work into the proper position for boring. The -fundamental principle involved is to lay out, accurately, two lines -at right angles to each other, and correctly center-punch the point -where they intersect. With proper care, lines may be drawn with a -vernier height gage at right angles, with extreme accuracy, the chief -difficulty being to accurately center the lines where they cross. For -semi-accurate work this may be done with a common center-punch but -where extreme accuracy is required this method is not applicable, as -the average man is incapable of marking the point of intersection -accurately.</p> - -<p>The diagram, <a href="#FIG_33">Fig. 33</a>, illustrates, in a simple way, the -procedure adopted in laying out work by this system. The base <i>E</i> is in -contact with a surface plate while the line <i>BB</i> is drawn with a -<span class="pagenum" id="Page_41">[Pg 41]</span> -height gage; then with side <i>F</i> on the plate the line <i>AA</i> is -drawn. It will be seen that these lines will be at right angles to each -other, if the bases <i>E</i> and <i>F</i> are square. Work done by this -method must have two working surfaces or base lines, and these must -be at right angles to each other. There is no difficulty in drawing -the locating lines <i>AA</i> and <i>BB</i> correctly, either with a -vernier height gage or with a special micrometer gage reading to 0.0001 -inch, the only difficult element being to accurately center-punch the -lines where they intersect as at <i>D</i>. It is assumed that two holes -are to be bored, so that the intersection at <i>C</i> would also be -center-punched.</p> - -<p>The scriber point of the height gage should be ground so that it -will make a V-shaped line, as shown by the enlarged sketch <i>G</i>, -rather than one which would resemble a saw-tooth, as at <i>H</i>, if a -cross-section of it were examined with a microscope. This is important -because when the lines are V-shaped, an accurate point of intersection -is obtained.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_34" src="images/i_41a.jpg" alt="" width="230" height="429" /> - <p class="center"><b>Fig. 34</b>. Center Locating Punch</p> - </div> - <div class="figsub"> - <img id="FIG_35" src="images/i_41b.jpg" alt="" width="200" height="415" /> - <p class="center"><b>Fig. 35</b>. Center Enlarging Punch</p> - </div> -</div> - -<p>As it is quite or almost impossible to accurately center-punch the -intersection of even two correctly drawn lines, by ordinary means, the -punch shown in Figs. <a href="#FIG_34">34</a> and <a href="#FIG_36">36</a> -was designed and an extended experience with it on a very high grade -of work has demonstrated its value for the purpose. It consists -essentially of a small center-punch <i>O</i> (<a href="#FIG_36">Fig. -36</a>) held in vertical position by a holder <i>P</i> which is knurled -to facilitate handling. Great care should be exercised in making this -tool to have the body of the punch straight, and to have it stand at -right angles to the surface to be operated upon, for the slightest -inclination will cause the finished hole to be incorrect, no matter how -<span class="pagenum" id="Page_42">[Pg 42]</span> -carefully the lines are drawn. The 60-degree point must be ground true -with the axis. The holder for the punch stands on three legs, located -as indicated, and ground accurately to a taper fit in the holder, where -they are secured by watch screws bearing on their tops. The lower ends -are hardened, and terminate in an angular point of 55 degrees (the -point of the vernier scriber being 60 degrees). The edges are sharp, -and slightly rounded at the ends, so that the legs will slide along -a line smoothly. The points <i>V</i> and <i>U</i> (<a href="#FIG_36">Fig. 36</a>) -have edges that are in line with each other, while the point <i>T</i> has an edge -at right angles to the other two. The center of the punch is located at -equal distances from all the legs, and is held off the work normally by -a leather friction acted upon by a set-screw in the side of holder <i>P</i>.</p> - -<div class="figcontainer"> - <div class="figsub"> - <img id="FIG_36" src="images/i_42a.jpg" alt="" width="250" height="455" /> - <p class="center"><b>Fig. 36</b>. Section of<br /> Center Locating Punch</p> - </div> - <div class="figsub"> - <img id="FIG_37" src="images/i_42b.jpg" alt="" width="215" height="462" /> - <p class="center"><b>Fig. 37</b>. Section of<br /> Center Enlarging Punch</p> - </div> -</div> - -<p>If this tool is placed upon lines of the form shown at <i>G</i>, <a href="#FIG_33">Fig. 33</a>, -the legs <i>V</i> and <i>U</i> may be slid along horizontal line -<i>B-B</i>, <a href="#FIG_33">Fig. 33</a>, until the sharp edge of leg <i>T</i> -drops into line <i>A-A</i>. When this occurs the punch <i>O</i> is lightly tapped -with a hammer, and the resulting mark will be accurately located in the -center of the intersection of the lines. It is good practice to make -the work very smooth before drawing the lines, and after laying them -out, to stone them so as to remove the slight burr raised in drawing -them. A drop of oil is then rubbed into the lines, and the surplus -<span class="pagenum" id="Page_43">[Pg 43]</span> -wiped off. This procedure permits points <i>V</i> and <i>U</i> to run -very smoothly along the line, and the burr having been removed, the -edge of leg <i>T</i> drops into the line very readily with a slight -click. As it is not advisable to strike punch <i>O</i> more than a -very light blow, it marks the work but slightly, and a more distinct -indentation is made with the follower punch shown in Figs. -<a href="#FIG_35">35</a> and <a href="#FIG_37">37</a>. -This punch is made like the previous one, so that it will stand at -right angles to the work. The sectional view (<a href="#FIG_37">Fig. 37</a>) shows -the punch <i>A</i> supported by the holder <i>E</i> which has four legs cut away -on the sides so that the point of the punch may be seen. When this -punch is in position, it is struck a sufficiently heavy blow to make a -distinctly visible mark. The work is now ready to be placed upon the -work table of the milling machine, and indicated for boring the holes, -an indicator being used in the milling machine spindle.</p> - -<div class="figcenter"> - <img id="FIG_38" src="images/i_43.jpg" alt="" width="600" height="393" /> - <p class="center space-below2"><b>Fig. 38</b>. Indicator used for - Aligning Punch Marks with Machine Spindle</p> -</div> - -<p>An indicator which has been found especially valuable for this purpose -is shown in Figs. <a href="#FIG_38">38</a> and <a href="#FIG_39">39</a>. -It is of the concentric centering type, and with it the work is -brought concentric with the axis of the spindle. The arbor <i>I</i> -is provided with a threaded nose on which disk <i>D</i> is screwed. -This disk has four holes in its rim, equally-spaced from each other. -Hardened, ground, and lapped bushings <i>b</i> are put into these -holes to receive plug <i>A</i> which is made a gage-fit both in these -holes and in hole <i>B</i> in the outer end of sector <i>C</i>. This -sector is held by a split sleeve to the barrel <i>L</i> which carries -the 60-degree centering-rod <i>K</i> that comes into contact with the -work to be bored. The spherical base of barrel <i>L</i> fits into a -corresponding concave seat in the nose of the arbor at <i>H</i>, and -is held in place by a spring <i>E</i> which connects at one end to the -cylindrical stud in the base of the barrel, and at the other to the -axial rod <i>M</i> by which it and the other connecting parts may be -drawn into place, and held by the headless set-screw <i>J</i>, bearing -on a flat spot on the tang end of the rod.</p> - -<p>Now, if plug <i>A</i> is removed from bushing <i>b</i> the point of the -centering-rod <i>K</i> may be made to describe a circle. At some point -<span class="pagenum" id="Page_44">[Pg 44]</span> -within this circle is located the center-punch mark on the work to be -bored. The holes in the rim of the faceplate all being exactly the -same distance from an axial line through both the arbor <i>I</i> and -centering-rod <i>K</i>, it follows that the center mark on the work -must be so located by horizontal and vertical movements of the work -table that pin <i>A</i> may be freely entered in all the four holes in -the rim of disk <i>D</i>. When that occurs, the center coincides with -the axis of the spindle.</p> - -<p>The point of the center-punch <i>A</i> (<a href="#FIG_37">Fig. 37</a>) should -have an angle slightly greater than the angle on the centering-rod <i>K</i>, as it -is impossible to locate the work in the preliminary trials so that the -center of the work will be coincident with the axis of the spindle, and -unless the precaution mentioned is taken, the true center on the work -is liable to be drawn from its proper location when trying to bring the -work into such a position that the plug will enter all the holes in the -disk. As the work being operated on is brought nearer to the proper -location by the movements of the milling machine table, spring <i>G</i> -will be compressed, the center rod sliding back into barrel <i>L</i>. -This spring is made so that it will hold the center against the work -firmly, but without interfering with the free rotation of the sector -<i>C</i> around disk <i>D</i>. When the work is located so that the -plug enters the holes, the gibs of the machine should be tightened up -and the plug tried once more, to make sure that the knee of the machine -has not moved sufficiently to cause the work on the table to be out of -line. The work table is now clamped to prevent accidental horizontal -shifting, and the work is drilled and bored.</p> - -<div class="figcenter"> - <img id="FIG_39" src="images/i_44.jpg" alt="" width="600" height="407" /> - <p class="center space-below2"><b>Fig. 39</b>. Sectional View of - Indicator shown in Fig. 38</p> -</div> - -<p>In using this indicator the milling machine spindle is not rotated -together with arbor <i>I</i>, only the sector being turned around the -disk. The tool is set, however, in the beginning, so that the axes of -two of the bushings <i>b</i> are at right angles to the horizontal -plane of the machine table, while the axes of the other holes in the -<span class="pagenum" id="Page_45">[Pg 45]</span> -disk are parallel with the top of the work table. The centering-rods -are made interchangeable and of various lengths, to reach more or less -accessible centers. <a href="#FIG_38">Fig. 38</a> shows the indicator -with one of the long center-rods in the foreground.</p> - -<p>The only part of the milling machine on which dependence must be placed -for accuracy is the hole in the spindle, and this is less liable to get -out of truth, from wear such as would impair the accuracy, than are the -knee, table, or micrometer screws. The only moving part is the sector, -and this, being light, is very sensitive.</p> - -<p>A series of 24 holes was laid out and bored in one and one-half day by -the method described in the foregoing. Measurements across accurately -lapped plugs in the holes, showed the greatest deviation from truth -to be 0.0002 inch, and running from that to accuracy so great that no -error was measurable. This same work with buttons would have required -considerably more time.</p> - -<hr class="chap" /> - -<div class="figleft"> - <img src="images/i_02.jpg" alt="" width="300" height="412" /> -</div> - -<p><big><b>Machinery</b></big> is the leading journal in the machine-building -field and meets the requirements of the mechanical engineer, superintendent, -designer, toolmaker and machinist, as no other journal does. <span -class="smcap">Machinery</span> deals exclusively with machine design, -tool design, machine construction, shop practice, shop systems and shop -management. The reading matter in <span class="smcap">Machinery</span> -is written by practical men and edited by mechanical men of long -practical training.</p> - -<p>Each number of <span class="smcap">Machinery</span> contains a -variety of articles on machine shop practice. These articles include -carefully prepared descriptions of manufacturing methods and current -mechanical developments. Shop systems and shop managements are ably -handled by the foremost writers. Every number contains the most -extensive and complete record published by any journal, or in any -form, of new machinery and tools and accessories for the machine shop. -A special department is devoted to “Letters on Practical Subjects,” -to which practical mechanics contribute their experiences. There is -a department of Shop Kinks—brief, concise little contributions which -contain ideas of value to the man in the shop or at the drafting table.</p> - -<p>The mechanical engineer, machine designer and draftsman are also -well provided for in <span class="smcap">Machinery</span>. Every number -contains articles on the theory and practice of machine design, on the -properties of materials, and on labor-saving methods and systems. There -are reviews of research work in the mechanical field, and valuable -results of carefully made experiments are recorded.</p> - -<p>The supremacy of <span class="smcap">Machinery</span> in the -mechanical field is due to the care with which all matter offered for -publication in its pages is scrutinized. Only the <i>best</i> of the -material offered by mechanical writers is published, and, as a result, -its pages contain the most authoritative, practical and up-to-date -mechanical information.</p> - -<hr class="r65" /> - -<p class="f200"><b><span class="smcap">Machinery</span>, 140-148 <small>Lafayette Street,<br /> -New York City</small></b></p> -<p class="f120">51 and 52, CHANCERY LANE, LONDON, W. C.</p> - -<hr class="chap" /> - -<p class="f200"><b>Heat-Treatment of Steel</b></p> - -<div class="figleft"> - <img src="images/i_47.jpg" alt="" width="300" height="439" /> -</div> - -<p class="no-indent">is one of a series of high-class authoritative, attractive -and well-bound books published by <span class="smcap">Machinery</span>.</p> - -<p>The strongest claim that can be made for these books is that they have -all the characteristics of <span class="smcap">Machinery</span> itself.</p> - -<p>These books cover comprehensively, and in a thoroughly practical -manner, the most important subjects in the metal-working field.</p> - -<p>Each book comprises about 300 pages, printed on high-grade paper, with -engravings of the same superior type that has made <span class="smcap">Machinery</span> -distinctive in its field.</p> - -<p>The price of each book is $2.50. Special combination offers on a -monthly payment plan will be sent upon request.</p> - -<p class="f200"><b><span class="smcap">Machinery</span> 140-148 <small>Lafayette St.<br /> -New York City</small></b></p> -<p class="f120">51 and 52, CHANCERY LANE, LONDON, W. C.</p> - -<hr class="chap" /> - -<p class="f200"><b>The Five New Books</b></p> - -<p class="f150"><b>Brought Out by <span class="smcap">Machinery</span></b></p> - -<hr class="r5" /> - -<p><span class="fontsize_120"><b>SPUR AND BEVEL GEARING</b></span></p> - -<p>A treatise on the principles, dimensions, calculation, design and -strength of spur and bevel gearing, together with chapters on special -tooth forms and methods of cutting gear teeth.</p> - -<p><span class="fontsize_120"><b>SPIRAL AND WORM GEARING</b></span></p> - -<p>A treatise on the principles, dimensions, calculation and design of -spiral and worm gearing, together with chapters on the methods of -cutting the teeth in these types of gears.</p> - -<p><span class="fontsize_120"><b>TURNING AND BORING</b></span></p> - -<p>By <span class="smcap">Franklin D. Jones</span> Associate Editor -of <span class="smcap">Machinery</span></p> - -<p>A specialized treatise for machinists, students in industrial and -engineering schools, and apprentices on turning and boring methods, -including modern practice with engine lathes, turret lathes, vertical -and horizontal boring machines.</p> - -<p><span class="fontsize_120"><b>PLANING AND MILLING</b></span></p> - -<p>By <span class="smcap">Franklin D. Jones</span> Associate Editor -of <span class="smcap">Machinery</span></p> - -<p>A treatise on the use of planers, shapers, slotters and various types -of horizontal and vertical milling machines and their attachments.</p> - -<p><span class="fontsize_120"><b>HEAT-TREATMENT OF STEEL</b></span></p> - -<p>A comprehensive treatise on the hardening, tempering, annealing and -case-hardening of various kinds of steel, including high-speed, -high-carbon, alloy and low-carbon steels, together with chapters on -heat-treating furnaces and on hardness testing.</p> - -<p class="space-above2">Price of each book $2.50. Special combination -offers on a monthly payment plan will be sent upon request.</p> - -<p class="f200"><b><span class="smcap">Machinery</span> 140-148 <small>Lafayette St.<br /> -New York City</small></b></p> -<p class="f120">51 and 52, CHANCERY LANE, LONDON, W. 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