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.) 



stable form dictated that attention be dedicated to 

 improved accuracy of the threaded components. 



An attack on this problem, which interestingly 

 reverts to the fundamental principle of motion de- 

 rived from a master screw without the intervention 

 of oilier mechanism (fig. 19), is covered by a patent 5 

 issued to Charles Yandcr Woerd, one-time superin- 

 tendent of the Waltham Watch Company. The 

 problem is well stated in the patent 



I hu invention relates to the manufacture of leading 

 screws i" I " used foi purposes requiring the highest 

 attainable degree of correctness in the cutting of the 



1 S patent 193930 issued to Charles Vander Woerd of 

 Waltham, Massachusetts, February 19, 1884 



screw-threads of said screw ... as. lor 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 l>v a 

 marking device which is reciprocated over the ula^s 

 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 

 Othei purposes, in which the thread is so nearly correct 

 as to produce no perceptible variation in the micro- 

 scopic sp.tces between the ruled lines 01 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 ol temperature from time to time, the 



116 



BULLETIN 240: CONTRIBUTIONS FROM THE MUSEUM OF HISTORY AND TECHNOLOGY 



