CHAPTER XXXV 

 MACHINE-SHOP PRACTICE 



478. Operations on Castings. Castings and forgings are 

 usually taken to a machine-shop, where the surplus metal 

 and rough parts are removed to make the castings conform 

 to the design of the machine for which they are intended. 

 This process is known as machining. They go next to the 

 fitting shop for the necessary handwork, and finally to the 

 erecting shop where the parts are assembled into a finished 

 machine. The machine is then tested, taken apart, crated, 

 and shipped to the customer; it is again set up by men 

 called erectors. 



The parts of a machine are finished to the exact dimensions 

 called for in the blue-print by removing, when necessary, a 

 certain portion called a cut or turning. There is a limit to 

 the speed of tools made from ordinary steel because of the 

 friction and heat generated. If too great a speed is used, 

 the heat may take the temper out of the steel, render it 

 useless, and cause the casting to expand. A mixture of soap 

 and water is used to lubricate the casting and tool, and 

 reduce the heat as much as possible. High-speed steel, 

 which has already been described, has a cutting capacity 

 four or five times that of tool steel and for this reason is 

 used extensively. 



479. Work of Machinists. The work of the machinist 

 is to shape metal to a definite form, size, and finish by the 



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