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BELL SYSTEM TECHNICAL JOURNAL 



that it can be adapted to standardized housings, which are stocked, 

 and especially where the tool is to be operated on high speed presses. 



In order that a better appreciation may be obtained of some of 

 the more exacting requirements which are being met in building tools 

 of this kind, several of the important reasons for accurate workmanship 

 to limits as close as a few ten-thousandths of an inch or less on some of 

 the tool parts, together with typical examples, will first be considered. 



Meeting the Accuracy Required of Piece Part, In order to obtain the 

 correct functioning of the apparatus or equipment and also to insure 

 interchangeability in assembly, many piece parts must be made with a 



Fig. 5 — Shaving and perforating punch and die for impulse wheel. 



considerable degree of accuracy, often within limits of ± .001 in. or 

 less for some of the dimensions. This is one of the most important 

 and common reasons for accurately built tools, especially in the case 

 of parts made in sufficiently large quantities to require a number of 

 similar tools producing the same part, as the product of each tool 

 must be interchangeable with that of any other provided for the same 

 operation, and also for subsequent operations. 



The bronze impulse wheel for No. 2 type dials and the pinion used 

 in message registers. Fig. 4, are typical examples. Both of these 

 parts are given shaving operations — the wheel after being blanked, 

 and the pinion after being cut to length and swaged — in order to 

 secure the required accuracy and smoothness of contour. Fig. 5 



