PRECISION TOOL MAKING 



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are of fine construction, may be readily replaced in case of breakage 

 or wear. In this case it is necessary that the parts be made accurately 

 where they fit together, in order to insure interchangeability of the 

 tool parts, without afifecting the satisfactory operation of the tool 

 or the accuracy of the parts being produced. The shaving punch and 

 die for the message register pinion previously referred to and shown in 

 Fig. 5 is a typical example, the construction and limits being so that 

 parts such as the punch, die, gage bushing, and pilot may be easily 

 replaced. For instance, in order to insure interchangeability of the 

 punch, the dimensions of the plunger and punch at A are held within 

 a limit of .0002 in., and other parts to correspondingly close limits. 



Feeding of Material and Properly Formed Part in '^Tandem" or 

 '^Follow" Type of Dies. In this type of tool the operation is a pro- 

 gressive one. While one part of the die notches, embosses, forms, or 



Fig. 10 — Multiple perforating, blanking, and clipping punch and die 

 for 3/8" brass hexagon nuts. 



perforates the stock, another part blanks out the parts at a place 

 where, at a former stroke, the preceding operations have been per- 

 formed, so that complete parts result from each stroke of the press, 

 although, of course, more than one operation has been performed on 

 the parts before completion. This is illustrated in Fig. 10, which shows 

 a multiple perforating, blanking, and clipping punch and die for 

 making 3/8 in. brass hexagon nuts. As will be noted from the con- 

 struction of the tool and the sequence of operations shown in Fig. 11, 

 seven nuts are made with no scrap skeleton remaining at each stroke 



