MACHINE-SHOP PRACTICE 433 



The operation of a slotter is similar to that of a shaper with 

 the difference that as the ram works vertically instead of 

 horizontally, the tool cuts on the down stroke, and the ram 

 is counterbalanced to return easily. The slotter is used on 

 irregular shapes and especially on all kinds of heavy work. 

 Such work requires only an ordinary machinist, although 

 specialists*are sometimes employed. 



500. Drilling Machines. Probably the first power ma- 

 chine that every machinist runs is the drilling machine or 

 drill press. Sometimes it is simply called the drill, although 

 this term usually refers to the small drill that actually does 

 the work. 



The different parts of all drilling machines have practi- 

 cally the same names, so that by becoming familiar with 

 the parts of one type, the student will have learned the es- 

 sential features of all. The drilling machine consists of a 

 revolving spindle carrying a socket for holding the tool, a 

 table for supporting or holding the work, and an arrangement 

 for feeding the tool into the work either by hand or power. 

 Different speeds for running the drill in different kinds of 

 metal are provided for by cone pulleys and back gears, the 

 back gears giving the slower speeds. 



In all drilling machines the work is held stationary while 

 the tool turns. This order is reversed in the action of a 

 lathe, where the work turns and the tool remains stationary. 



501. Milling Machines. The milling machine (Fig. 

 199) is not so generally used as its worth merits, because 

 comparatively few machinists know how to operate it. This 

 machine is not limited to plane milling, but will mill irregular 

 shapes by the use of formed cutters. The work is done by 



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