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+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. Battison
+
+*** END OF THIS PROJECT GUTENBERG EBOOK SCREW-THREAD CUTTING SINCE 1480 ***
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