Jin- ii Details 01 rw phreading lathi seen in the right foreground of figure g showing the 

 method of drive and support foi the work From J / , vol. g, plate i . 



dl work. This can be realized from figure 16 which 

 shows .1 traverse-spindle lathe headstock typical oi the 

 mid- 19th century. During the years intervening be- 

 tween the machines of figures 12 and 16, the gem raJ 

 design was greatly improved b) removing the lead 

 screws from the centei of the spindle. This made pos- 

 sible a shorter, much stiffer spindle and supported both 

 ol the spindle in one frame or headstock rather 

 than in separate pieces attached to the bed. The 

 screws were now mounted outside oi the spindle- 

 bearings, one .it .i time, while the mating nuts were cut 

 parti. illy into the circumference ol a disk which could 

 lie turned to bring an) particular nut into working 

 position as required. With this arrangement, a wide 

 variety of leads either right or left hand could be pro- 

 sided and additional leads could he lilted at an\ hum e 

 time. Screw-cutting lathes of this design were popu- 

 lar foi a \ei\ long time with instrument makeis .md 

 opticians who had little need to cut screws of great 

 length. 



The demands of expanding i i id i ist i \ lor greater 

 versatility in the production of engineering elements 

 late in the Kith century set the stage for the evolution 

 of more complex machines tending to place the 

 threaded spindle lathes in eclipse. Maudslay's lathe 

 of 17'J7 Willi) ill-. 13) appeared at this time when 

 industry was receptive to rapid innovation. Un- 

 fortunately, 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 \ ai i<t\ 



of ratios, as was true of slightl) latei Maudsla^ latins. 

 or a fixed ratio. The plausibility ol the fixed ratio 

 theor) is supported b) the ver) convenient means, 

 i figure 1 5, for removing the lead screvi in prep- 

 aration for substitution of one of another pitch. 

 All that is required is to hack oil its suppoi ting centei 



at the tailstock (lid and withdraw the screw from its 



spin nut- 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 sci ew in order to gel the tool 

 back to the point ol beginning preliminary to taking 

 anothei int. 1 )a\ id Wilkinson's lathe of 1 798 (fig. 1 7) 

 which was developed in Rhode Island at th( 

 time shows the same method of mounting and driving 

 the master screw. At least in the United States, tins 

 method of changing the lead screw instead of using 

 change gears remained populai lor many years. 

 Examples of this changeable screw feature are to be 

 found in the lathes constructed lor the pump factory 

 of W. & R. Douglas Company, Middletown, 

 nei in ni. in the I830's. Middletown. at that time 

 one of the leading metal-working centers in one ol 

 the chief industrial States, had been for many years 



•J. Fo ii Petree, introduction, Henry Maudday, 1771- 

 1831, and M midday Sons and Field, Lid. (London: The Maudslay 

 Sot iety, 1949 . 



i i : (September -'•''. 1911 no. 13, 



pp. 529 531. 



PAPER 37: SCREW-THR) \l> CI tTTNG HY THE MASTER-SCREW Ml HUH) 



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