GRAPHIC RECORDING INSTRUMENTS 553 



the piece which is being turned. Corresponding points in the 

 two figures bear the same letter. 



The variation of power with depth of cut and the time required 

 for each operation are clearly shown. 



A simple form of recording ammeter which has been in use 

 for many years is shown in Fig. 338. The current flows through 

 the coil A giving rise to an attraction on the soft iron disc B 



FIG. 336. Piece to which cycle ghown in Fig. 337 applies. 



10:00 A.M. 9:45 A.M. 9:30 A.M. 9:15 A.M. 



FIG. 337. Curve showing typical cycle on a roughing lathe. 



carried by the rod CD which passes freely along the axis of the 

 coil. The rod is supported on knife edges by two flat springs 

 CC and DD which are fixed at their lower ends; DD carries the 

 pointer E to which the pen is attached. The record is made on 

 a circular sheet of paper which is rotated at a uniform rate by 

 the clockwork. Ordinarily for central station work the records 

 are for a 24-hour period. For special work this may be varied 

 by using the appropriate clockwork. The pen, which rests on 

 the paper continuously, is a little V-shaped trough cut away at 

 one end so that only a fine point at the apex of the V drags on 



