392 BELL SYSTEM TECHNICAL JOURNAL 



After the boring of the holes in the die block is completed, the 

 die openings are worked out roughly by drilling a series of holes 

 corresponding to the shape required and brought to about .001 in. 

 of the nominal by means of the lathe filing attachment, as shown in 

 Fig. 18, or a standard bench filing machine. The perforating and 

 blanking contour which is the one being filed in the illustration con- 

 forms only partially to the finished openings on the die as shown in Fig. 

 12, and the correct outline is obtained by means of an insert indicated on 

 the die layout in Fig. 15. This construction is necessary because the two 

 blanking openings are close together and could not be satisfactorily heat 

 treated without considerable distortion. Also, it facilitates considerably 

 the work of the tool maker in working out the die openings. The insert 

 is heat treated before assembly in the die. The forming dies are 

 also made separately and inserted in the square openings in the 

 die block. 



After the filing operation, the die block is heat treated and the 

 upper and lower surfaces are then ground parallel. Although proper 

 heat treatment is an important factor in the production of fine tools, 

 it is too broad and extensive a subject to be considered in this paper, 

 as the art has been developed to the point where it is now done on 

 practically a scientific basis through the use of the most improved 

 equipment and automatic temperature recording and control, with 

 many different heating methods, etc., being employed for the various 

 grades of steels and the different purposes for which they are used. 



The next operation after heat treatment is the grinding of the die 

 block openings, which is done on the bench lathe by means of the 

 grinding attachment shown in Fig. 19. By this means the surfaces are 

 brought to within .0003 in. to .0004 in., the most important dimensions 

 as previously mentioned being those which affect the distance between 

 corresponding surfaces of the blanking and forming die openings. The 

 surfaces are then stoned or lapped by hand with about .0002 in. or less 

 being removed as required, to give the final finish and accuracy, and 

 the insert and forming dies, which are made with a similar degree of 

 accuracy, fitted in place. 



As can be seen from the foregoing, the highest precision work 

 requiring the most expert workmanship comes in the final grinding, 

 lapping, and fitting. The degree to which this must be carried, of 

 course, depends on the requirements of the particular tool being made. 

 In the case of the multiple bank strip and the rack tools previously 

 described, the punch and die sections are ground to within .00005 in. 

 of the required size and then lapped to the final dimensions, using a 

 flat cast iron block or some other soft metal charged with an abrasive 

 dust, such as emery, carborundum, or diamond. 



