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diff --git a/31756.txt b/31756.txt new file mode 100644 index 0000000..82b0c54 --- /dev/null +++ b/31756.txt @@ -0,0 +1,1081 @@ +The Project Gutenberg EBook of Screw-Thread Cutting by the Master-Screw +Method since 1480, by Edwin A. Battison + +This eBook is for the use of anyone anywhere 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 + + +Title: Screw-Thread Cutting by the Master-Screw Method since 1480 + +Author: Edwin A. Battison + +Release Date: March 24, 2010 [EBook #31756] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK SCREW-THREAD CUTTING SINCE 1480 *** + + + + +Produced by Colin Bell, Joseph Cooper, Louise Pattison and +the Online Distributed Proofreading Team at +https://www.pgdp.net + + + + + +[Transcriber's Notes: + +This is Paper 37 from the Smithsonian Institution United States National +Museum Bulletin 240, comprising Papers 34-44, which will also be +available as a complete e-book. + +The front material, introduction and relevant index entries from the +Bulletin are included in each single-paper e-book. + +Typographical errors have been corrected as follows: + + Page 110: "... the spindle, to prevent ..." (had "pindle") + Page 120: "... servants a l'intelligence de plusieurs choses difficiles, + & necessaires ..." (had "a," "plusiers," "necessaires")] + + + + +SMITHSONIAN INSTITUTION + +UNITED STATES NATIONAL MUSEUM + +BULLETIN 240 + + +[Illustration] + +SMITHSONIAN PRESS + + +MUSEUM OF HISTORY AND TECHNOLOGY + + CONTRIBUTIONS + FROM THE + MUSEUM + OF HISTORY AND + TECHNOLOGY + + _Papers 34-44_ + _On Science and Technology_ + +SMITHSONIAN INSTITUTION . WASHINGTON, D.C. 1966 + + + + +_Publications of the United States National Museum_ + + +The scholarly and scientific publications of the United States National +Museum include two series, _Proceedings of the United States National +Museum_ and _United States National Museum Bulletin_. + +In these series, the Museum publishes original articles and monographs +dealing with the collections and work of its constituent museums--The +Museum of Natural History and the Museum of History and +Technology--setting forth newly acquired facts in the fields of +anthropology, biology, history, geology, and technology. Copies of each +publication are distributed to libraries, to cultural and scientific +organizations, and to specialists and others interested in the different +subjects. + +The _Proceedings_, begun in 1878, are intended for the publication, in +separate form, of shorter papers from the Museum of Natural History. +These are gathered in volumes, octavo in size, with the publication date +of each paper recorded in the table of contents of the volume. + +In the _Bulletin_ series, the first of which was issued in 1875, appear +longer, separate publications consisting of monographs (occasionally in +several parts) and volumes in which are collected works on related +subjects. _Bulletins_ are either octavo or quarto in size, depending on +the needs of the presentation. Since 1902 papers relating to the +botanical collections of the Museum of Natural History have been +published in the _Bulletin_ series under the heading _Contributions from +the United States National Herbarium_, and since 1959, in _Bulletins_ +titled "Contributions from the Museum of History and Technology," have +been gathered shorter papers relating to the collections and research of +that Museum. + +The present collection of Contributions, Papers 34-44, comprises +Bulletin 240. Each of these papers has been previously published in +separate form. The year of publication is shown on the last page of each +paper. + + FRANK A. TAYLOR + _Director, United States National Museum_ + + + + +CONTRIBUTIONS FROM +THE MUSEUM OF HISTORY AND TECHNOLOGY: +PAPER 37 + +SCREW-THREAD CUTTING BY THE +MASTER-SCREW METHOD SINCE 1480 + +_Edwin A. Battison_ + + + + +_Edwin A. Battison_ + +SCREW-THREAD CUTTING BY THE MASTER-SCREW METHOD SINCE 1480 + + _Among the earliest known examples of screw-thread cutting machines + are the screw-cutting lathe of 1483, known only in pictures and + drawings, and an instrument of the traverse-spindle variety for + threading metal, now in the Smithsonian Institution, dating from the + late 17th or early 18th century. The author shows clearly their + evolution from something quite specialized to the present-day tool. + He has traced the patents for these instruments through the early + 1930's and from this research we see the part played by such devices + in the development of the machine-tool industry._ + + THE AUTHOR: _Edwin A. Battison is associate curator of mechanical + and civil engineering in the Smithsonian Institution's Museum of + History and Technology._ + + +Directness and simplicity characterize pioneer machine tools because +they were intended to accomplish some quite specialized task and the +need for versatility was not apparent. History does not reveal the +earliest forms of any primitive machines nor does it reveal much about +the various early stages in evolution toward more complex types. At best +we have discovered and dated certain developments as existing in +particular areas. Whether these forms were new at the time they were +first found or how widely dispersed such forms may have been is unknown. +Surviving evidence is in the form of pictures or drawings, such as the +little-known screw-cutting lathe of 1483 (fig. 1) shown in _Das +mittelalterliche Hausbuch_. + +This lathe shows that its builder had a keen perception of the necessary +elements, reduced to bare essentials, required to accomplish the object. +Present are the coordinate slides often credited to Henry Maudslay. His +slides are not, of course, associated with the spindle; neither is there +any natural law which compels them to guide the tool exactly parallel +with the axis of revolution. In this sense the screw-cutting lathe in +the _Hausbuch_ is superior because it is in harmony with natural law and +can generate a true cylinder, whereas Maudslay's lathe can only transfer +to the work whatever accuracy is built into it. + +In principle this machine shown in the _Hausbuch_ is very advanced as we +see when we follow the design through to the present time. The artist, +whose drawings give us our only knowledge of the machine, himself was +obviously not very familiar with the details of its function. Reference +to figure 1 shows that the threads on the lead screw and on the work, +wind in opposite directions. This must be an error in delineation since +the two are closely coupled together without any intervening mechanism +so that the only possible result on the work must be a thread winding in +the same direction as on the original screw. The work also is shown +threaded for its entire length; this cannot be accomplished with any one +location of the cross-slide. We are left with the question of whether +this slide was used in two locations or whether the artist, possibly +working from notes or an earlier rough sketch, failed to show an +unthreaded portion on one end or the other of the work. + +[Illustration: Figure 1.--EARLIEST REPRESENTATION FOUND OF A +MASTER-SCREW TYPE of thread-cutting machine. From the inconsistencies, +such as right- and left-hand threads on master and work, it appears that +the artist had scant insight into actual function. From plate 62 of _Das +mittelalterliche Hausbuch, nach dem Originale im Besitze des Fuersten von +Waldburg-Wolfegg-Waldsee, im Auftrage des Deutschen Vereins fuer +Kunstwissenschaft, herausgegeben von Helmuth Th. Bossert und Willy F. +Storck_ (Leipzig: E. A. Seemann, 1912).] + +Of at least equal importance with the lead screw and work and their +relationship to each other is the tool-support with its screw-adjusted +cross-slide (fig. 2). Just how this was attached to the frame of the +machine so that it placed the tool at a suitable radius is again a +questionable point. The very well-developed cutting tool is sharpened to +a thin, keen edge totally unsuited for cutting metal but ideal for use +on a softer, fibrous substance: undoubtedly wood, in this instance. +Unfortunately, the angle at which the artist chose to show us this +cutter is not a view from which it is possible to judge whether or not +the tool has been made to conform to the helix angle of the thread to be +cut. This cross-slide, in conjunction with the traversing work spindle, +gives us a machine having two coordinate slides yielding the same effect +as the slide rest usually attributed to Henry Maudslay at the end of the +18th century. Actually, an illustration of coordinate slides independent +of the spindle had been published as early as 1569 by Besson[1] and +knowledge of them widely disseminated by his popular work on mechanics. +These slides are shown as part of a screw-cutting machine with a +questionably adequate connection, by means of cords, between the master +screw and the work. + +It was the author's pleasure recently to obtain for the Smithsonian +Institution and identify a small, nicely made, brass instrument which +had been in two collections in this country and one collection in +Germany as an unidentified locksmith's tool (fig. 3). This proved to be +an instrument of the traverse-spindle variety for threading metal. +Fortunately, all essential details were present including a cutter (A in +figure 4); this instrument was identified by the signature "Manuel +Wetschgi, Augspurg." The Wetschgis were a well-known family of gunsmiths +and mechanics in Augsburg through several generations. Two bore the +given name Emanuel: the earlier was born in 1678 and died in 1728. He +was quite celebrated in his field of rifle making and became chief of +artillery to the Landgrave of Hesse-Kassel shortly before his death in +his 51st year. Little is known of the later Emanuel Wetschgi except that +he was at Augsburg in 1740. Tentative attribution of the instrument has +been made to the earlier Emanuel, chiefly on the basis of his recognized +position as an outstanding craftsman. + +[Illustration: Figure 2.--CROSS-SLIDE for the thread-cutting lathe of +_Das mittelalterliche Hausbuch_, shown in figure 1. It is remarkable not +only for its early date, but also for its high state of development with +a crossfeed screw which had not become universally accepted 300 years +later. The cutter, shown out of its socket, is obviously sharpened for +use on wood.] + +In several respects this little machine differs from its predecessor of +the _Hausbuch_, as might be expected when allowance is made for the +generations of craftsmen who undoubtedly worked with such tools over the +roughly 200 years of time separating them. Another factor to consider +when comparing these two machines is that one was used on metal, the +other probably only on wood. Therefore, it is not surprising to find on +the later machine an outboard or "tailstock" support for the work. The +spindle of this support has to travel in unison with the work-driving +spindle so that it is not an unexpected discovery to find that it is +spring-loaded. Figure 5 shows how this spring may be adjusted to +accommodate various lengths of work by moving the attachment screw to +various holes in both the spring and in the frame. Also visible in the +same illustration is a rectangular projection at the other end of the +spring which engages a mating hole in the "tailstock" spindle to prevent +its rotation. + +[Illustration: Figure 3.--SMALL THREAD-CUTTING LATHE which was made to +be held in a vise during use. It was found as shown here, with only the +operating crank missing. The overall length is approximately 12 inches, +depending on the adjustment of parts. (Smithsonian photo 46525B.)] + +Figure 6 shows the traversing spindle and nut removed from the machine. +Provision has been made for doing this so easily that there is every +reason to believe that, originally, there were various different spindle +and nut units which could be interchangeably used in the machine. +Additional evidence tending to support this concept exists in the +cutting tool (fig. 4), which must have been intended for serious work as +it has been carefully fitted in its unsymmetrical socket. The cutting +blade of this tool, which works with a scraping rather than a true +cutting action, is too wide to form a properly proportioned thread when +used with the existing lead screw. This may well indicate that the tool +was made for use with a lead of coarser pitch, now lost. + +[Illustration: Figure 4.--THE WORKING AREA of figure 3, showing the tool +and signature. (Smithsonian photo 46525A.)] + +Perhaps the most startling feature of this machine when compared with +the machine of the _Hausbuch_, is the absence of a cross-slide for +adjusting the tool. Possibly this can be explained by the blunt scraping +edge on the tool. In actual use, recently, to cut a sample screw, using +a tool similar to the one found in the machine (fig. 7), it was found +advantageous to be free of a cross-slide and thus be able to feed the +tool into the work by feel rather than by rule, as would be done with a +slide rest. In this way, it was possible to thread steel without +tearing, as the cutting pressure could readily be felt and the tool +could release itself from too heavy a cut. Size on several screws could +be repeated by setting the tool to produce the desired diameter when its +supporting arm came to rest against the frame of the machine. The screws +used in the machine itself were apparently made in just such a way. They +were not cut with a die as the thread blends very gradually into the +body of the screw without the characteristic marks left by the cutting +edges of a die. Threads cut with a single-point tool controlled by a +cross-slide usually end even more abruptly than those cut by a die, +while it would be quite simple with a machine of the nature we are +considering to bring the thread to a gentle tapering end as seen in +figure 8 (another view of the screw A in fig. 3) by gradually releasing +the pressure necessary to keep the tool cutting as the end of the +thread was approached. + +[Illustration: Figure 5.--SPRING FOR KEEPING THE FOLLOWER SPINDLE +against the work, showing the method and range of adjustment. Note the +rectangular projection to engage a mating socket in the spindle, to +prevent spindle rotation. (Smithsonian photo 46525.)] + +[Illustration: Figure 6.--WORK SPINDLE AND ITS NUT removed from the +machine to illustrate how easily another spindle and nut of different +pitch could be substituted. (Smithsonian photo 46525C.)] + +That machines of this general type having the lead screw on the axis of +the work were competitive with other methods and other types of machines +over a long period of time may be seen from figures 9 and 10. The +machine, left front in figure 9 and in more intimate detail in figure +10, can be seen to differ little from that shown in _Das +mittelalterliche Hausbuch_ of 1483. The double work-support is, of +course, a great improvement, while the tool-support is regressive since +it lacks a feed screw. + +The development of engineering theory, coupled with the rising needs of +industry, particularly with the advent of the Industrial Revolution, +brought about accelerated development of screw-cutting lathes through +the combination of screw-cutting machines with simple lathes as seen in +figure 9 and in detail in figure 11. One important advance shown here +is driving the machine by means of a cord or band so that any means of +rotary power could be applied, not just hand or foot power. Of greater +interest and technical importance to this study is the provision, seen +to better advantage in figure 11, for readily changing from one master +lead screw to another. This had already been achieved in the Manuel +Wetschgi machine, as far as versatility is concerned, although not in +quite such a convenient way. + +[Illustration: Figure 7.--THREAD OF MODERN FORM recently cut, using the +old screw and nut but with a new tool. The material threaded is +carbon-steel drill rod. (Smithsonian photo 49276A.)] + +Figure 12, the headstock of another and more advanced lathe than shown +in figures 9 and 11 but of the same type, shows "keys" (D), each of +which is a partial nut of different pitch to engage with a thread of +mating pitch. The dotted lines in figure 13 show the engaged and +disengaged positions of one of these keys, and figure 14 shows the +spindle with the various leads, C. At D is a grooved collar to be +engaged by the narrow key shown in operating position at the left in +figure 12 for the purpose of controlling the endwise movement of the +spindle when used for ordinary turning instead of thread-cutting. In +return for greater convenience and freedom from the expense of the many +separate spindles, as typified by the Wetschgi machine, a sacrifice has +been made in the length of the thread which can be cut without +interruption. + +[Illustration: Figure 8.--BINDING SCREW seen at A in figure 3, showing +the long smooth fadeout of the thread below the shoulder. (Smithsonian +photo 49276.)] + +[Illustration: Figure 9.--MAKING SCREWS IN FRANCE in the third quarter +of the 18th century. From _L'Encyclopedie, ou dictionnaire raisonne des +sciences, des arts et des metiers ... receuil de planches sur les +sciences, les arts liberaux, et les arts mechaniques, avec leur +explication_ (Paris: 1762-1772), vol. 9, plate 1.] + +[Illustration: Figure 10.--DETAILS OF THE MACHINE in the left foreground +of figure 9, showing the crude tool-support without screw adjustment. +From _L'Encyclopedie_, vol. 9, plate 2.] + +This reduction in the length that could conveniently be threaded was no +great drawback on many classes of work. This can be realized from figure +16 which shows a traverse-spindle lathe headstock typical of the +mid-19th century. During the years intervening between the machines of +figures 12 and 16, the general design was greatly improved by removing +the lead screws from the center of the spindle. This made possible a +shorter, much stiffer spindle and supported both ends of the spindle in +one frame or headstock rather than in separate pieces attached to the +bed. The screws were now mounted outside of the spindle-bearings, one at +a time, while the mating nuts were cut partially into the circumference +of a disk which could be turned to bring any particular nut into working +position as required. With this arrangement, a wide variety of leads +either right or left hand could be provided and additional leads could +be fitted at any future time. Screw-cutting lathes of this design were +popular for a very long time with instrument makers and opticians who +had little need to cut screws of great length. + +[Illustration: Figure 11.--DETAILS OF THE THREADING LATHE seen in the +right foreground of figure 9 showing the method of drive and support for +the work. From _L'Encyclopedie_, vol. 9, plate 1.] + +The demands of expanding industry for greater versatility in the +production of engineering elements late in the 18th century set the +stage for the evolution of more complex machines tending to place the +threaded spindle lathes in eclipse. Maudslay's lathe of 1797-1800 (fig. +15) appeared at this time when industry was receptive to rapid +innovation. Unfortunately, the gearing which once existed to connect the +headstock spindle with the lead screw has long been lost. At this time +it is quite difficult to say with certainty whether the original gear +set offered a variety of ratios, as was true of slightly later Maudslay +lathes, or a fixed ratio. The plausibility of the fixed ratio theory is +supported by the very convenient means, seen in figure 15, for removing +the lead screw in preparation for substitution of one of another pitch. +All that is required is to back off its supporting center at the +tailstock end and withdraw the screw from its split nut[2] and from the +driving clutch near the headstock. This split nut also would have to be +changed to one of a pitch corresponding to that of the screw. While more +expensive than a solid nut, it neatly circumvents the need (and saves +the time involved) to reverse the screw in order to get the tool back to +the point of beginning preliminary to taking another cut. David +Wilkinson's lathe of 1798 (fig. 17) which was developed in Rhode Island +at the same time shows the same method of mounting and driving the +master screw. At least in the United States, this method of changing the +lead screw instead of using change gears remained popular for many +years. Examples of this changeable screw feature are to be found in the +lathes constructed for the pump factory of W. & B. Douglas Company, +Middletown, Connecticut,[3] in the 1830's. Middletown, at that time one +of the leading metal-working centers in one of the chief industrial +States, had been for many years the site of the Simeon North arms +factory which rivaled Whitney's. In this atmosphere, it is reasonable to +expect that machinery constructed by local mechanics, as was the custom +in those days, would reflect the most accepted refinements in machine +design. + +[Illustration: Figure 12.--WELL-DEVELOPED EXAMPLE of lathe headstock +having several leads on the spindle and provision for mounting the work +or a work-holding chuck on the spindle. Adapted from _L'Encyclopedie_, +vol. 10, plate 13.] + +[Illustration: Figure 13.--END VIEW OF THE HEADSTOCK seen in figure 12, +showing the keys or half nuts which engage the threaded spindle, in +engaged and disengaged positions. From _L'Encyclopedie_, vol. 10, plate +13.] + +[Illustration: Figure 14.--SPINDLE OF FIGURES 12 AND 13, showing the +several leads and the many-sided seat for the driving pulley. Note the +scale of feet. From _L'Encyclopedie_, vol. 10, plate 16.] + +Roughly twenty years later, Joseph Nason of New York patented[4] the +commercially very important "Fox" brassworker's lathe (fig. 18). While +this does have a ratio in the pair of gears connecting the work spindle +and master screw, it is clear from the patent that various pitches are +to be obtained by changing screws, not by changing gears. The patent +sums it up as follows: + + A nut upon the end of the stud ... is unscrewed when the guide + screw is to be removed or changed. The two wheels ... should have + in their number of teeth a common multiple. They are seldom or + never removed and their diameters are made dissimilar only for the + purpose of giving to the guide screw a slower rate of motion than + that of the mandrel whereby it may be made of coarser pitch than + that of the screw to be cut and its wear materially lessened. + +The introduction of gearing between the spindle and the lead screw, for +whatever purpose, could not help but introduce variable factors caused +by inaccuracies in the gears themselves and in their mounting. These +were of little consequence for common work, particularly when coupled to +a screw which, itself, was of questionable accuracy. The increasing +refinements demanded in scientific instruments and in machine tools +themselves after they had reached a relatively stable form dictated that +attention be dedicated to improved accuracy of the threaded components. + +[Illustration: Figure 15.--MAUDSLAY'S WELL-KNOWN screw-cutting lathe of +1797-1800, showing the method of mounting and driving changeable master +screws. (_Photo courtesy of The Science Museum, London._)] + +[Illustration: Figure 16.--HEADSTOCK OF A GERMAN INSTRUMENT-MAKER'S +LATHE, typical of the mid-19th century, showing the traverse spindle, +interchangeable lead screws, and semicircumferential nut containing +several leads. The nut may be brought into engagement by the lever at +top rear of the headstock. This releases the end thrust control on the +spindle simultaneously with engagement of the nut. (Smithsonian photo +49839.)] + +[Illustration: Figure 17.--DAVID WILKINSON'S SCREW-CUTTING LATHE, +patented in the United States in 1798. Note the ready facility with +which the lead screw may be exchanged for another and the same means of +supporting and driving as in figure 15. (U.S. National Archives photo.)] + +An attack on this problem, which interestingly reverts to the +fundamental principle of motion derived from a master screw without the +intervention of other mechanism (fig. 19), is covered by a patent[5] +issued to Charles Vander Woerd, one-time superintendent of the Waltham +Watch Company. The problem is well stated in the patent: + + This invention relates to the manufacture of leading screws to be + used for purposes requiring the highest attainable degree of + correctness in the cutting of the screw-threads of said screw ... + as, for example, in machines for ruling lines in glass plates to + produce refraction [sic] gratings for the resolution of the lines + of the solar spectrum, such machines being required to rule many + thousands of lines on an inch of space by a marking device which is + reciprocated over the glass plate and is fed by the action of a + leading screw after the formation of each line. Great difficulty + has been experienced in constructing a leading screw for this and + other purposes, in which the thread is so nearly correct as to + produce no perceptible variation in the microscopic spaces between + the ruled lines or gratings.... Various causes prevent the + formation of a thread on the rod or blank, which is absolutely + uniform and accurate from end to end of the rod. Among other causes + are the variations of temperature from time to time, the + imperfections of the operating leading screw, the springing of the + leading screw and of the rod that is being threaded, and other + unavoidable causes, all of which, although apparently trivial and + producing only slight variations in the thread at different parts + of the rod or blank, are of sufficient moment to be seriously + considered when a screw of absolute accuracy is desired. + +[Illustration: Figure 18.--NASON'S LATHE, patented in 1854, showing a +master lead screw driven at less than work speed so that the master +could be of a coarser and more durable pitch than the work. U.S. patent +10383.] + +It is interesting to note in figure 19 that Vander Woerd's machine, to +avoid the problems outlined in his patent, has returned to a starkly +simple design. We are not told, however, how he originated this master +screw which is used to produce the accurately threaded work pieces. +Later generations, in the search for ever-greater accuracy, also +returned to the fundamental simplicity of a master screw as we shall see +when we consider the refinements in mechanism necessary to the extended +development of the automobile and the airplane. + +[Illustration: Figure 19.--VANDER WOERD'S PATENT, seen here, covered the +combination of a master screw, toolslide and work in a rigid frame to be +supported and driven by outside means of no required precision. U.S. +patent 293930 dated February 1884.] + +As the power and speed of automobiles and aircraft increased, critical +parts became more highly stressed. Gears and threaded parts were +particularly troublesome details of the mechanism because of the +stresses concentrated in them, and, in the case of gears, because of the +internal and external stresses originating in minute deviations from the +ideal of tooth form and spacing. The problems were not entirely new but +had hitherto been solved by increasing the size of the parts, an avenue +of limited utility to designers in these fields where total weight as +well as the effects of mass and inertia are so important. By making +these parts of heat-treated steel, the strength could be made suitable +while the size and mass of the parts were kept within bounds. The +necessary processes of heat-treating were not always applicable to +finished parts as they sometimes destroyed both finish and accuracy. +Grinding, which was well developed for the simple plane, cylindrical, +and conical surfaces so widely used in mechanisms, had to be extended to +threads and gears so that they could be finished after heat-treating. +Sometimes the gear teeth themselves were ground; for other applications +it was sufficient to improve the accuracy of the gear cutters. + +[Illustration: Figure 20.--A HOB-GRINDING MACHINE patented in 1932 and +incorporating the master-screw principle. Carl G. Olson's U.S. patent +1874592.] + +Attempts to produce gear hobs free of the imperfections and distortions +introduced by heat treatment led to another return to the use of the +master lead screw. Figure 20 illustrates a machine having this feature +which was patented in 1932 by Carl G. Olson.[6] In speaking of the +spindle-driving mechanism disclosed in earlier patents, the patent goes +on to say: + + This driving mechanism includes an integral spindle 20, one + extremity thereof being designed for supporting a hob 22 and the + other extremity thereof being formed so as to present a lead screw + 24. The spindle 20 is mounted between a bearing 26 and a bearing + 28, the latter bearing providing a nut in which the lead screw 24 + rotates.... From the description thus far given it will be apparent + that the rotation of the lead screw 24 within the bearing or nut 28 + will cause the hob to be moved axially, the lead of the screw 24 + being equal to the lead of the thread in the hob. + +Claim 8 which concludes the descriptive portion of the patent states in +part: + + In a hob grinding machine of the class described, a rotary work + supporting spindle, means for effecting longitudinal movement of + the spindle, a tool holder for supporting a grinding wheel in + operative position with respect to the work supported by the + spindle during the rotary and longitudinal movement thereof, ... + +Even before this patent was applied for, another patent was pending for +the purpose of modifying the pitch of the lead screw without the use of +change gears in spite of the wide acceptance of such gear mechanisms for +over a hundred years. + +[Illustration: Figure 21.--A HOB-GRINDING MACHINE OF 1933, showing use +of the master screw with a modifier but without change gears. Carl G. +Olson's U.S. patent 1901926.] + +[Illustration: Figure 22.--A SINE-BAR DEVICE to modify the effective +lead of a master lead screw without introducing a complex mechanism +which would be both difficult to make and to operate within the required +close limits. Carl G. Olson's (1933) U.S. patent 1901926.] + +Figure 21 shows a plan view[7] of the machine, and figure 22 a detailed +view of the sine-bar mechanism actuated by the master screw, 6, to +modify the effective pitch of the lead screw in accordance with the +realities of practice as stated in the preamble of the patent: + + This invention relates to material working machines, and + particularly to machines such as hob grinders and the like, wherein + the work is reciprocated through the agency of a lead screw. + + In the manufacture of hobs it is common practice to employ the same + machine for grinding hobs of varied diameters, and in order to + employ such a machine in this manner the pitch of the lead screw, + thereof, which actuates the work carrier, must conform to the axial + pitch of the hob to be ground. This will be readily apparent when + it is understood that the helix angles of hobs vary in accordance + with their diameters and, consequently, the difference between the + normal pitch and the axial pitch correspondingly varies. While the + requirement for the normal pitch may be the same for hobs of + different diameters, it is necessary to change the axial pitch in + accordance with a change in the hob diameter, and this axial pitch + of the hob is equal to the pitch of the lead screw which actuates + the work carrier in grinding machines heretofore used. Hence, in + order to adapt such machines to cover a wide range of leads, it is + necessary to provide a large number of interchangeable lead screws + and obviously this represents a large investment, and the + interchanging of these screws requires the expenditure of + considerable time in setting up the machine for each job. + +Thread-grinding machines were being designed concurrent with the +development of hob-grinding machines. Many were entirely concerned with +features peculiar to the problems of wheel-dressing and to automatic +characteristics. An invention to embody the use of a master screw and +concerned with the precision grinding of worm threads, for use in +gearing, was patented by Frederick A. Ward in this era.[8] That part of +the invention pertaining to the use of a master screw, "a rotary work +holder mounted on said carriage and provided with a driving spindle, an +exchangeable master screw and stationary nut detachably secured to said +spindle and head,..." is shown in figure 23. + +[Illustration: Figure 23.--DETAILS OF A WORK SPINDLE WITH WORK, showing +the use of a master lead screw to control the pitch of a precision worm +thread being ground. From the 1933 U.S. patent 1899654, of F. A. Ward's +worm-grinding machine.] + +Machines embodying the principle of the master lead screw are found in +constant use by industry at the present time for specialized +application. Whenever technological changes again reopen the topic of +thread-cutting to a new degree of accuracy or call for a reevaluation of +popular methods for any other reason, we may expect to see another +resurgence of the master-screw method, for no other design eliminates so +many variables or rests on such firm and fundamental natural principles +as the machine of _Das mittelalterliche Hausbuch_ of 1483, the earliest +such machine now known. + + +FOOTNOTES: + +[1] JACQUES BESSON, _Des instruments mathematiques, et mechaniques, +servants a l'intelligence de plusiers choses difficiles, & necessaires a +toutes republiques_, 1st ed. (Orleans, 1569). [Also available in later +editions in French, German, and Spanish.] + +[2] J. FOSTER PETREE, introduction, _Henry Maudslay, 1771-1831, and +Maudslay Sons and Field, Ltd._ (London: The Maudslay Society, 1949). + +[3] _American Machinist_ (September 28, 1916), vol. 45, no. 13, pp. +529-531. + +[4] U.S. patent 10383 issued to Joseph Nason of New York, January 3, +1854. + +[5] U.S. patent 293930 issued to Charles Vander Woerd of Waltham, +Massachusetts, February 19, 1884. + +[6] U.S. patent 1874592, filed June 8, 1929, issued to C. G. Olson of +Chicago, Illinois, August 30, 1932, and assigned to the Illinois Tool +Works, also of Chicago. + +[7] U.S. patent 1901926, filed February 16, 1928, issued to C. G. Olson +of Chicago, Illinois, March 21, 1933, and assigned to the Illinois Tool +Works, also of Chicago. + +[8] U.S. patent 1899654, filed August 31, 1931, issued to F. A. Ward of +Detroit, Michigan, February 28, 1933, and assigned to the Gear Grinding +Company of Detroit, Michigan. + + * * * * * + +U.S. GOVERNMENT PRINTING OFFICE: 1964 + +For sale by the Superintendent of Documents, U.S. Government Printing Office +Washington, D.C. 20402--Price 20 cents + + +INDEX + + + Besson, Jacques, 107 + + + Douglas, W. & B., Company, 113 + + + Maudslay, Henry, 106, 113 + + + Nason, Joseph, 114 + + North, Simeon, arms factory, 114 + + + Olson, Carl G., 118 + + + Vander Woerd, Charles, 116, 117 + + + Ward, Frederick A., 120 + + Wetschgi, Emanuel, 108 + + Wetschgi, Manuel, 108, 111 + + Whitney arms factory, 114 + + Wilkinson, David, 113 + + + + + +End of the Project Gutenberg EBook of Screw-Thread Cutting by the +Master-Screw Method since 1480, by Edwin A. 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