I v Maudslay's well-known screw-cutting lathe 



of 1797 1800, showing the method of mountii 

 driving changeable mastei screws {Photo com 

 \! . I ■ ion.) 



Figure 16.— Headstock of a German instri mi nt-maker's i \nu . typical of the mid- 19th century, showing 

 the traverse spindle, interchangeable lead screws, and semicircumferential nul containing several leads. 

 I he nul in. iv be brought into engagement by the leva at top reai ol the headstoi k. I his releases the end 

 thrust control on the spindle simultaneously with engagement ol the nut. (Smithsonian photo }'i 8 39-) 



PAPER 37: SCREW-THREAD CITI'INO BY II IJ MASTER-SCREW MM HOD 115 



