422 APPLIED SCIENCE 



class, the power is subject to great fluctuations because, in 

 addition to the friction of the work, friction and loss of energy 

 are caused by the retardation, return, and acceleration of 

 the machine. The work of shapers, slotters, and other 

 machines, is done by t'he stroke of a reciprocating tool in 

 one direction During the working stroke the tool must 

 move at a suitable cutting speed, while on the return stroke, 

 when no work is performed, it is desirable that it should 

 travel as rapidly as possible. 



484. The Cutting Capacity of a Machine. To save ex- 

 pense and labor, a casting should be cut in the most eco- 

 nomical way and in the shortest possible time. To do this, 

 the cutting tool should attain the highest possible speed 

 without injuring the metal or casting. The amount of metal 

 removed in a given time represents the cutting capacity of 

 the machine. This depends upon three factors: (1) the 

 speed of the cut; (2) the distance covered by the tool in 

 passing from one cutting part to the next; and (3) the depth 

 of the cut, that is, the thickness of the strip removed from 

 the casting. 



The cutting feed of a tool is the thickness of the chip or the travel 

 of the tool sideways during one revolution of the .work. Thus, if 

 the feed of a lathe is vc in. for each revolution of the work, the 

 tool moves along the lathe bed re in. and cuts a chip j\ in. wide. 

 Sometimes the feed is given as the number of turns which the work 

 makes while the tool advances 1 in., as 50 or 60 turns to the inch. 

 This is, of course, the same as saying ^V or A in. feed per rev- 

 olution. The feed is occasionally stated as so many inches per 

 minute, but this is not the common practice. The cut or depth 

 of cut is not the feed; it is the distance the tool enters the work 

 when feeding. Twice the depth of the cut subtracted from the 

 original diameter of the work will give the new diameter after 

 turning. 



