56 H. J. Grayson : 



1.— The Screw. 



Embracing : — 



1. Cutting the screw tliread and (i.) the grinding nut. 



2. Process of grinding the screw, including : — 



(i.) Preliminary separation of Emery or other abrasives. 



(ii.) Method of Refining crudely separated abrasives, 

 (iii.) Preliminary grinding of the screw by hand, 

 (iv.) Grinding Avith fine abrasives and semi-automatic control. 



(v.) Mode of operating the mechanical grinder. 



3. Method of testing the screw and its bearings during final 

 correction and adjustment. 



I. — Cutting the Screiv Thread. 



The method of cutting the screw thread hereunder described 

 differed but little from that adopted by Rowland and others, but 

 the process of grinding it varied in important particulars. The 

 Rowland screw appears to have been ground between the regular 

 lathe centres by means of a specially constructed brass nut, described 

 in the article on " Screws " in the Encyclopaedia Britannica. The 

 process of grinding followed by the writer varied materially, and is 

 described below. With respect, first, to the operation of cutting the 

 thread. 



A suitable bar of mild steel was selected and carefully annealed 

 by slow heating and cooling. Its diameter permitted of the removal 

 of several heavy cuts from end to end of its length, after v.hich it 

 was again annealed, accurately centied in the lathe, and turned 

 down to about | in. diameter with repeated light cuts. Later 

 experience with other screws has shown that fine grinding may be 

 preferable to turning as a preparation of the surface for threading, 

 as it is not so likely to warp and compress the rod, and leaves its 

 surface more uniform and true. 



The cutting of the thread on the prepared bar differed in no wise 

 from the routine usually followed in the cutting of a good thread. 

 The lathe was run slowly with an abundant supply of potash soap 

 solution continually playing on the threading tool. The advance 

 or forward " feed " of the cutting tool should never result in a 

 heavy cut;, and as the work proceeds the cuts sliould l>e reduced until 

 those finally taken are apj^roximately only .0005 (if an inch. It is, 

 however, important that the last cuts taken should be continuous 

 and even throughout the threaded length of the bar, even though 



