Rollins — Riding Concave Gratings. 



51 



machines. The size of the curved ways is such that the blank 

 moves under the diamond in an arc whose radius is the same 

 as the curvature of the grating. This causes the cuts made by 

 the diamond to all have the same angle with the surface and 

 their sides to be of equal widths. It does not make the spac- 

 ing equal, but this may be compensated for as already men- 

 tioned. The plan of compensation shown in figure 2 was 



devised by Mr. William Gaertner, to whom and to Captain 

 Khotinsky I am indebted for working out the drawings shown 

 in figures 2, 3, 4. The nut in this machine is not rigidly 

 attached to the carriage carrying the grating, but motion is 

 imparted to the carriage by means of a projecting arm, which, 

 sliding on a curved way, allows the nut to turn sufficiently to 

 equalize the spacing. 



In figure 5 another way of carrying out the principle is 

 illustrated diagram matically, the curvature of the grating being 

 made very short to show the idea more clearly. The block, 

 BK, to be ruled is mounted on the carriage, C, which moves 

 in an arc on curved ways, motion being imparted to it from 

 the long nut, SN, by a band of thin, tempered steel attached 

 at W and N ;// . As the nut SN is moved to the left, in the 

 direction of the arrow 1, the carriage, C, turns in the direc- 



