384 BELL SYSTEM TECHNICAL JOURNAL 



Another tool of this kind is the second operation perforating punch 

 and die shown in Fig. 8, which perforates the slots in the rack for 

 elevator apparatus shown in Fig. 9, and also in the illustration of 

 the tool. The requirements of this part specify that all of the 107 

 slots 1/16 in. wide and spaced on .125 in. centers must be within 

 d= .003 in. of their proper location from the beveled end, which is a 

 difificult requirement to meet on account of the nature and thickness 

 of the stock, and, like the multiple bank strip, there must be practically 

 no accumulated error. The tool has fifty perforators, fifty-one die 

 and fifty-two shedder sections which are made with a degree of 

 accuracy comparable to that of the multiple bank strip tool. 



Insuring Accurate Gaging in Subsequent Operations. This is a reason 

 which sometimes requires the tool maker to work to closer limits or 

 to hold certain dimensions to closer limits than would be otherwise 

 required. In such cases the tool must produce piece parts which are 

 sufficiently accurate at certain gaging points used later in other tools 

 or in the apparatus assembly fixtures, to insure the proper results 

 from the subsequent tools and in assembly. This may require an 

 accuracy of from .0005 in. to .001 in. An example is the bank contact 

 for step-by-step type banks. In order that the parts may be made 

 sufficiently accurate at certain points so that proper bank assembly 

 may be obtained with the assembly fixtures, the blanking die openings 

 are made to a limit of -+- .001 in. — .000 in. for the width at the ends, 

 the length, and the offset dimension, although the apparatus require- 

 ments for the piece part do not necessitate this degree of accuracy. 



Production of Satisfactory Blanks from Thin Stock. Typical piece 

 parts of this kind are the mica diaphragm .0017 in. to .002 in. thick 

 used in transmitters, and the oiled red rope paper insulator .007 in. 

 thick for coil spool assemblies which are shown in Fig. 4. In order to 

 obtain clean-cut blanks, with practically no rough edges or burrs, 

 from thin material of this kind, it is necessary that the clearance 

 between the blanking punch and the die for the insulator does not 

 exceed .0002 in. and the diaphragm .0001 in. all around, and the 

 perforators nearly the same. In fact, these die parts are made to 

 fit so closely that they will cut wet tissue paper. Accurate working 

 fits are necessary between the other moving members, such as shedder, 

 liner pins, etc., which mean that it must be possible to just push the 

 parts together with no perceptible shake or clearance. The general 

 construction of these tools is of the standard compound liner pin 

 type similar to Fig. 1. 



Interchangeability of Tool Parts. Some tools are so designed that 

 certain parts, which on account of the design of the part being produced 



