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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: ISO-8859-1
+
+*** 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 à l'intelligence de plusieurs choses difficiles,
+            & nécessaires ..." (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 Fürsten von
+Waldburg-Wolfegg-Waldsee, im Auftrage des Deutschen Vereins für
+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'Encyclopédie, ou dictionnaire raisonné des
+sciences, des arts et des métiers ... receuil de planches sur les
+sciences, les arts libéraux, et les arts méchaniques, 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'Encyclopédie_, 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'Encyclopédie_, 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'Encyclopédie_,
+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'Encyclopédie_, 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'Encyclopédie_, 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 mathématiques, et méchaniques,
+servants à l'intelligence de plusiers choses difficiles, & necessaires à
+toutes républiques_, 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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+<body>
+
+
+<pre>
+
+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: ISO-8859-1
+
+*** 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
+
+
+
+
+
+
+</pre>
+
+<div class="tnote">
+<p>Transcriber&rsquo;s Notes:</p>
+
+<p>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.</p>
+
+<p>The front material, introduction and relevant index entries from
+the Bulletin are included in each single-paper e-book.</p>
+
+<p><a href="#corrections_37">Corrections</a> to typographical errors are underlined
+<ins class="mycorr" title="Original: like thsi">like this</ins>. Mouse over to view the original text.</p>
+
+</div>
+
+
+<hr style="width: 65%;" />
+
+<h1>SMITHSONIAN INSTITUTION<br />
+UNITED STATES NATIONAL MUSEUM<br />
+BULLETIN 240</h1>
+
+<div class="figright">
+  <img src="images/i_002.png" alt="Smithsonian Press Logo" title=" " />
+</div>
+
+<p class="right" style="clear:both;">SMITHSONIAN PRESS<br /></p>
+
+<p>MUSEUM OF HISTORY AND TECHNOLOGY</p>
+
+<p style="font-size: 2em; font-weight: bold;" class="smcap">Contributions<br />
+From the<br />
+Museum<br />
+of History and<br />
+Technology</p>
+
+<p style="font-size: 1.25em;"><em>Papers 34-44<br />
+On Science and Technology</em></p>
+
+<p>SMITHSONIAN INSTITUTION &middot; WASHINGTON, D.C. 1966</p>
+
+<hr style="width: 65%;" />
+
+<p class="center" style="font-size: 1.25em;"><em>Publications of the United States National Museum</em></p>
+
+<p>The scholarly and scientific publications of the United States National Museum
+include two series, <cite>Proceedings of the United States National Museum</cite> and <cite>United States
+National Museum Bulletin</cite>.</p>
+
+<p>In these series, the Museum publishes original articles and monographs dealing
+with the collections and work of its constituent museums&mdash;The Museum of Natural
+History and the Museum of History and Technology&mdash;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.</p>
+
+<p>The <cite>Proceedings</cite>, 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.</p>
+
+<p>In the <cite>Bulletin</cite> 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. <cite>Bulletins</cite> 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 <cite>Bulletin</cite> series under the heading <cite>Contributions from the United States
+National Herbarium</cite>, and since 1959, in <cite>Bulletins</cite> titled &ldquo;Contributions from the Museum
+of History and Technology,&rdquo; have been gathered shorter papers relating to the collections
+and research of that Museum.</p>
+
+<p>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.</p>
+
+<p class="right"><span class="smcap">Frank A. Taylor</span><br />
+<em>Director, United States National Museum</em></p>
+
+<hr style="width: 65%;" />
+
+<p><span class="pagenum"><a name="Page_105" id="Page_105">[Pg 105]</a></span></p>
+<h1><a name="Paper_37" id="Paper_37"></a><span class="smcap">Contributions from<br />
+The Museum of History and Technology</span>:<br />
+<span class="smcap">Paper</span> 37<br />
+<br /><br />
+<span class="smcap">Screw-Thread Cutting by the<br />
+Master-Screw Method Since 1480</span><br />
+</h1>
+<p><span class="rnum" style="font-size: larger;"><em>Edwin A. Battison</em></span><br />
+</p>
+
+<hr style="width: 65%;" />
+<p><span class="pagenum"><a name="Page_106" id="Page_106">[Pg 106]</a></span></p>
+
+<p><em>Edwin A. Battison</em></p>
+
+<h2>SCREW-THREAD CUTTING BY THE <br />MASTER-SCREW METHOD SINCE 1480</h2>
+<div class="blockquotn">
+<p><i>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&rsquo;s and from this research we see
+the part played by such devices in the development of the machine-tool
+industry.</i></p>
+
+<p><span class="smcap">The Author</span>: <i>Edwin A. Battison is associate curator of mechanical and
+civil engineering in the Smithsonian Institution&rsquo;s Museum of History and
+Technology.</i></p>
+</div>
+
+<p><span class="smcap">Directness and simplicity</span> 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 <i>Das
+mittelalterliche Hausbuch</i>.</p>
+
+<p>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 <i>Hausbuch</i> is superior because it is in harmony with natural law and
+can generate a true cylinder, whereas Maudslay&rsquo;s lathe can only transfer
+to the work whatever accuracy is built into it.</p>
+
+<p>In principle this machine shown in the <i>Hausbuch</i> is very advanced as we
+see when we follow the design<span class="pagenum"><a name="Page_107" id="Page_107">[Pg 107]</a></span> 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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_107.png" style="width:600px;" alt="Figure 1.&mdash; Earliest representation found of a
+master-screw type of thread-cutting machine"
+title="Figure 1." />
+<p class="caption2">Figure 1.&mdash;<span class="smcap">Earliest representation found of a
+master-screw type</span> 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 <i>Das
+mittelalterliche Hausbuch, nach dem Originale im Besitze des F&uuml;rsten von
+Waldburg-Wolfegg-Waldsee, im Auftrage des Deutschen Vereins f&uuml;r
+Kunstwissenschaft, herausgegeben von Helmuth Th. Bossert und Willy F.
+Storck</i> (Leipzig: E. A. Seemann, 1912).</p></div>
+
+<p>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<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a> 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.</p>
+
+<p>It was the author&rsquo;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&rsquo;s tool (fig. 3).<span class="pagenum"><a name="Page_108" id="Page_108">[Pg 108]</a></span> This proved to be
+an instrument of the traverse-spindle variety for threading metal.
+Fortunately, all essential details were present including a cutter (<span class="smcap">A</span> in
+figure 4); this instrument was identified by the signature &ldquo;Manuel
+Wetschgi, Augspurg.&rdquo; 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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_108a.png" style="width:400px;" alt="Figure 2.&mdash; 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."
+title="Figure 2." />
+<p class="caption2">Figure 2.&mdash;<span class="smcap">Cross-slide</span> for the thread-cutting lathe of
+<i>Das mittelalterliche Hausbuch</i>, 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.</p></div>
+
+<p>In several respects this little machine differs from its predecessor of
+the <i>Hausbuch</i>, 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 &ldquo;tailstock&rdquo; 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 &ldquo;tailstock&rdquo; spindle to prevent
+its rotation.</p>
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_108.png" style="width:600px;" alt="Figure 3.&mdash; 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.)" title="Figure 3." />
+<p class="caption2">Figure 3.&mdash;<span class="smcap">Small thread-cutting lathe</span> 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.)</p></div>
+
+<p>Figure 6 shows the traversing spindle and nut removed from the machine.
+Provision has been<span class="pagenum"><a name="Page_109" id="Page_109">[Pg 109]</a></span> 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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_109.png" style="width:600px;" alt="Figure 4.&mdash;The working area of figure 3, showing the tool
+and signature. (Smithsonian photo 46525A.)" title="Figure 4." />
+<p  class="caption2">Figure 4.&mdash;<span class="smcap">The working area</span> of figure 3, showing the tool
+and signature. (Smithsonian photo 46525A.)</p></div>
+
+<p>Perhaps the most startling feature of this machine when compared with
+the machine of the <i>Hausbuch</i>, 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 <span class="smcap">A</span> in fig. 3) by gradually releasing
+the pressure<span class="pagenum"><a name="Page_110" id="Page_110">[Pg 110]</a></span> necessary to keep the tool cutting as the end of the
+thread was approached.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_110.png" style="width:600px;" alt="Figure 5.&mdash;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.)" title="Figure 5." />
+<p  class="caption2">Figure 5.&mdash;<span class="smcap">Spring for keeping the follower spindle</span>
+against the work, showing the method and range of adjustment. Note the
+rectangular projection to engage a mating socket in the <ins class="mycorr"
+title="Original: pindle"><a name="corr_37_1" id="corr_37_1"></a>spindle</ins>, to
+prevent spindle rotation. (Smithsonian photo 46525.)</p></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_110a.png" style="width:600px;" alt="Figure 6.&mdash;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.)" title="Figure 6." />
+<p  class="caption2">Figure 6.&mdash;<span class="smcap">Work spindle and its nut</span> removed from the
+machine to illustrate how easily another spindle and nut of different
+pitch could be substituted. (Smithsonian photo 46525C.)</p></div>
+
+<p>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 <i>Das
+mittelalterliche Hausbuch</i> of 1483. The double work-support is, of
+course, a great improvement, while the tool-support is regressive since
+it lacks a feed screw.</p>
+
+<p>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.<span class="pagenum"><a name="Page_111" id="Page_111">[Pg 111]</a></span> 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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_111a.png" style="width:400px;" alt="Figure 7.&mdash;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.)" title="Figure 7." />
+<p  class="caption2">Figure 7.&mdash;<span class="smcap">Thread of modern form</span> recently cut, using the
+old screw and nut but with a new tool. The material threaded is
+carbon-steel drill rod. (Smithsonian photo 49276A.)</p></div>
+
+<p>Figure 12, the headstock of another and more advanced lathe than shown
+in figures 9 and 11 but of the same type, shows &ldquo;keys&rdquo; (<span class="smcap">D</span>), 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, <span class="smcap">C</span>. At <span class="smcap">D</span> 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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_111.png" style="width:600px;" alt="Figure 8.&mdash;Binding screw seen at A in figure 3, showing
+the long smooth fadeout of the thread below the shoulder. (Smithsonian
+photo 49276.)" title="Figure 8." />
+<p  class="caption2">Figure 8.&mdash;<span class="smcap">Binding screw</span> seen at <span class="smcap">A</span> in figure 3, showing
+the long smooth fadeout of the thread below the shoulder. (Smithsonian
+photo 49276.)</p></div>
+
+<div class="figcenter" style="width: 600px;"><span class="pagenum"><a name="Page_112" id="Page_112">[Pg 112]</a></span>
+<img src="images/i_112.png" style="width:600px;" alt="Figure 9.&mdash;Making screws in France in the third quarter
+of the 18th century. From L&rsquo;Encyclop&eacute;die, ou dictionnaire raisonn&eacute; des
+sciences, des arts et des m&eacute;tiers ... receuil de planches sur les
+sciences, les arts lib&eacute;raux, et les arts m&eacute;chaniques, avec leur
+explication (Paris: 1762-1772), vol. 9, plate 1." title="Figure 9." />
+<p  class="caption2">Figure 9.&mdash;<span class="smcap">Making screws in France</span> in the third quarter
+of the 18th century. From <i>L&rsquo;Encyclop&eacute;die, ou dictionnaire raisonn&eacute; des
+sciences, des arts et des m&eacute;tiers ... receuil de planches sur les
+sciences, les arts lib&eacute;raux, et les arts m&eacute;chaniques, avec leur
+explication</i> (Paris: 1762-1772), vol. 9, plate 1.</p></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_112a.png" style="width:600px;" alt="Figure 10.&mdash;Details of the machine in the left foreground
+of figure 9, showing the crude tool-support without screw adjustment.
+From L&rsquo;Encyclop&eacute;die, vol. 9, plate 2." title="Figure 10." />
+<p  class="caption2">Figure 10.&mdash;<span class="smcap">Details of the machine</span> in the left foreground
+of figure 9, showing the crude tool-support without screw adjustment.
+From <i>L&rsquo;Encyclop&eacute;die</i>, vol. 9, plate 2.</p></div>
+
+<p><span class="pagenum"><a name="Page_113" id="Page_113">[Pg 113]</a></span>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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_113.png" style="width:600px;" alt="Figure 11.&mdash;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&rsquo;Encyclop&eacute;die, vol. 9, plate 1." title="Figure 11." />
+<p  class="caption2">Figure 11.&mdash;<span class="smcap">Details of the threading lathe</span> seen in the
+right foreground of figure 9 showing the method of drive and support for
+the work. From <i>L&rsquo;Encyclop&eacute;die</i>, vol. 9, plate 1.</p></div>
+
+
+<p>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&rsquo;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<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> 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&rsquo;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. &amp; B. Douglas Company,
+Middletown, Connecticut,<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a> in the 1830&rsquo;s. Middletown, at that time one
+of the leading metal-working centers in one of the chief industrial
+States, had been for many years<span class="pagenum"><a name="Page_114" id="Page_114">[Pg 114]</a></span> the site of the Simeon North arms
+factory which rivaled Whitney&rsquo;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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_114a.png" style="width:600px;" alt="Figure 12.&mdash;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&rsquo;Encyclop&eacute;die,
+vol. 10, plate 13." title="Figure 12." />
+<p  class="caption2">Figure 12.&mdash;<span class="smcap">Well-developed example</span> 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 <i>L&rsquo;Encyclop&eacute;die</i>,
+vol. 10, plate 13.</p></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_114b.png" style="width:300px;" alt="Figure 13.&mdash;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&rsquo;Encyclop&eacute;die, vol. 10, plate
+13." title="Figure 13." />
+<p  class="caption2">Figure 13.&mdash;<span class="smcap">End view of the headstock</span> seen in figure 12,
+showing the keys or half nuts which engage the threaded spindle, in
+engaged and disengaged positions. From <i>L&rsquo;Encyclop&eacute;die</i>, vol. 10, plate
+13.</p></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_114c.png" style="width:600px;" alt="Figure 14.&mdash;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&rsquo;Encyclop&eacute;die, vol. 10, plate 16." title="Figure 14." />
+<p  class="caption2">Figure 14.&mdash;<span class="smcap">Spindle of figures 12 and 13</span>, showing the
+several leads and the many-sided seat for the driving pulley. Note the
+scale of feet. From <i>L&rsquo;Encyclop&eacute;die</i>, vol. 10, plate 16.</p></div>
+
+<p>Roughly twenty years later, Joseph Nason of New York patented<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a> the
+commercially very important &ldquo;Fox&rdquo; brassworker&rsquo;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:</p>
+
+<div class="blockquot"><p>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.</p></div>
+
+<p>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.<span class="pagenum"><a name="Page_115" id="Page_115">[Pg 115]</a></span></p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_115.png" style="width:600px;" alt="Figure 15.&mdash;Maudslay&rsquo;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.)" title="Figure 15." />
+<p  class="caption2">Figure 15.&mdash;<span class="smcap">Maudslay&rsquo;s well-known</span> screw-cutting lathe of
+1797-1800, showing the method of mounting and driving changeable master
+screws. (<i>Photo courtesy of The Science Museum, London.</i>)</p></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_116a.png" style="width:600px;" alt="Figure 16.&mdash;Headstock of a German instrument-maker&rsquo;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.)" title="Figure 16." />
+<p  class="caption2">Figure 16.&mdash;<span class="smcap">Headstock of a German instrument-maker&rsquo;s
+lathe</span>, 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.)</p></div>
+
+<div class="figcenter" style="width: 600px;"><span class="pagenum"><a name="Page_116" id="Page_116">[Pg 116]</a></span>
+<img src="images/i_116.png" style="width:600px;" alt="Figure 17.&mdash;David Wilkinson&rsquo;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.)" title="Figure 17." />
+<p  class="caption2">Figure 17.&mdash;<span class="smcap">David Wilkinson&rsquo;s screw-cutting lathe</span>,
+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.)</p></div>
+
+<p>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<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a>
+issued to Charles Vander Woerd, one-time superintendent of the Waltham
+Watch Company. The problem is well stated in the patent:</p>
+
+<div class="blockquot"><p>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<span class="pagenum"><a name="Page_117" id="Page_117">[Pg 117]</a></span>
+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.</p></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_117a.png" style="width:600px;" alt="Figure 18.&mdash;Nason&rsquo;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." title="Figure 18." />
+<p  class="caption2">Figure 18.&mdash;<span class="smcap">Nason&rsquo;s lathe</span>, 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.</p></div>
+
+<p>It is interesting to note in figure 19 that Vander Woerd&rsquo;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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_117.png" style="width:300px;" alt="Figure 19.&mdash;Vander Woerd&rsquo;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." title="Figure 19." />
+<p  class="caption2">Figure 19.&mdash;<span class="smcap">Vander Woerd&rsquo;s patent</span>, 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.</p></div>
+
+<p>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<span class="pagenum"><a name="Page_118" id="Page_118">[Pg 118]</a></span> 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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_118.png" style="width:600px;" alt="Figure 20.&mdash;A hob-grinding machine patented in 1932 and
+incorporating the master-screw principle. Carl G. Olson&rsquo;s U.S. patent
+1874592." title="Figure 20." />
+<p  class="caption2">Figure 20.&mdash;<span class="smcap">A hob-grinding machine</span> patented in 1932 and
+incorporating the master-screw principle. Carl G. Olson&rsquo;s U.S. patent
+1874592.</p></div>
+
+<p>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.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a> In speaking of the
+spindle-driving mechanism disclosed in earlier patents, the patent goes
+on to say:</p>
+
+<div class="blockquot"><p>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.</p></div>
+
+<p>Claim 8 which concludes the descriptive portion of the patent states in
+part:</p>
+
+<div class="blockquot"><p>In a hob grinding machine of the class described, a rotary work
+supporting spindle, means for effecting<span class="pagenum"><a name="Page_119" id="Page_119">[Pg 119]</a></span> 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, ...</p></div>
+
+<p>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.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_119.png" style="width:600px;" alt="Figure 21.&mdash;A hob-grinding machine of 1933, showing use
+of the master screw with a modifier but without change gears. Carl G.
+Olson&rsquo;s U.S. patent 1901926." title="Figure 21." />
+<p  class="caption2">Figure 21.&mdash;<span class="smcap">A hob-grinding machine of</span> 1933, showing use
+of the master screw with a modifier but without change gears. Carl G.
+Olson&rsquo;s U.S. patent 1901926.</p></div>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_119a.png" style="width:400px;" alt="Figure 22.&mdash;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&rsquo;s (1933) U.S. patent 1901926." title="Figure 22." />
+<p  class="caption2">Figure 22.&mdash;<span class="smcap">A sine-bar device</span> 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&rsquo;s (1933) U.S. patent 1901926.</p></div>
+
+<p>Figure 21 shows a plan view<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> 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:</p>
+
+<div class="blockquot"><p>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.<span class="pagenum"><a name="Page_120" id="Page_120">[Pg 120]</a></span></p>
+
+<p>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.</p></div>
+
+<p>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.<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a> That part of
+the invention pertaining to the use of a master screw, &ldquo;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, ...&rdquo; is shown in figure 23.</p>
+
+<div class="figcenter" style="width: 600px;">
+<img src="images/i_120.png" style="width:600px;" alt="Figure 23.&mdash;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&rsquo;s
+worm-grinding machine." title="Figure 23." />
+<p  class="caption2">Figure 23.&mdash;<span class="smcap">Details of a work spindle with work</span>, 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&rsquo;s
+worm-grinding machine.</p></div>
+
+<p>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 <i>Das mittelalterliche Hausbuch</i> of 1483, the earliest
+such machine now known.</p>
+
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> <span class="smcap">Jacques Besson</span>, <i>Des instruments math&eacute;matiques, et
+m&eacute;chaniques, <ins class="mycorr" title="Original: servants a l'intelligence de plusiers choses difficiles, &amp; necessaires"><a name="corr_37_2" id="corr_37_2"></a>servants &agrave; l&rsquo;intelligence de plusieurs choses difficiles, &amp;
+n&eacute;cessaires</ins> &agrave; toutes r&eacute;publiques</i>, 1st ed. (Orleans, 1569). [Also
+available in later editions in French, German, and Spanish.]</p></div>
+
+<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> <span class="smcap">J. Foster Petree</span>, introduction, <i>Henry Maudslay, 1771-1831,
+and Maudslay Sons and Field, Ltd.</i> (London: The Maudslay Society,
+1949).</p></div>
+
+<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> <i>American Machinist</i> (September 28, 1916), vol. 45, no. 13,
+pp. 529-531.</p></div>
+
+<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> U.S. patent 10383 issued to Joseph Nason of New York,
+January 3, 1854.</p></div>
+
+<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> U.S. patent 293930 issued to Charles Vander Woerd of
+Waltham, Massachusetts, February 19, 1884.</p></div>
+
+<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> 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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> 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.</p></div>
+
+<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> 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.</p></div></div>
+
+
+<p class="center" style="font-size:0.8em"><br /><br /><br />
+U.S. GOVERNMENT PRINTING OFFICE: 1964</p>
+<hr style="width: 45%;" />
+<p class="center">For sale by the Superintendent of Documents, U.S. Government Printing Office<br />
+Washington, D.C. 20402&mdash;Price 20 cents</p>
+<hr style="width: 45%;" />
+
+<h3>Index</h3>
+
+<p>Besson, Jacques, <a href="#Page_107">107</a><br /><br /></p>
+<p>Douglas, W. &amp; B., Company, <a href="#Page_113">113</a><br /><br /></p>
+<p>Maudslay, Henry, <a href="#Page_106">106</a>, <a href="#Page_113">113</a><br /><br /></p>
+<p>Nason, Joseph, <a href="#Page_114">114</a></p>
+<p>North, Simeon, arms factory, <a href="#Page_114">114</a><br /><br /></p>
+<p>Olson, Carl G., <a href="#Page_118">118</a><br /><br /></p>
+<p>Vander Woerd, Charles, <a href="#Page_116">116</a>, <a href="#Page_117">117</a><br /><br /></p>
+<p>Ward, Frederick A., <a href="#Page_120">120</a></p>
+<p>Wetschgi, Emanuel, <a href="#Page_108">108</a></p>
+<p>Wetschgi, Manuel, <a href="#Page_108">108</a>, <a href="#Page_111">111</a></p>
+<p>Whitney arms factory, <a href="#Page_114">114</a></p>
+<p>Wilkinson, David, <a href="#Page_113">113</a><br /><br /></p>
+
+<div class="tnote">
+<a id="corrections_37" name="corrections_37"></a>
+<h3>Transcriber&rsquo;s corrections</h3>
+<p>Page <a href="#corr_37_1">110</a>: &ldquo;... the spindle, to prevent ...&rdquo; (had &ldquo;pindle&rdquo;)</p>
+<p>Page <a href="#corr_37_2">120</a>: &ldquo;... servants &agrave; l'intelligence de plusieurs choses difficiles,
+&amp; n&eacute;cessaires ...&rdquo; (had &ldquo;a,&rdquo; &ldquo;plusiers,&rdquo; &ldquo;necessaires&rdquo;)</p>
+</div>
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of Screw-Thread Cutting by the
+Master-Screw Method since 1480, by Edwin A. Battison
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@@ -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. Battison
+
+*** END OF THIS PROJECT GUTENBERG EBOOK SCREW-THREAD CUTTING SINCE 1480 ***
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