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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. - -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. 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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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