36 



ARMATURE CONSTRUCTION 



disadvantage of greater expenditure for time and labour on the 

 other hand. It thus usually resolves itself into a question of 

 whether enough plates will be required (as would be the case with 

 standard designs built for stock) to justify the outlay for the com- 

 pound die. The compound die has up to recently been considered 

 indispensable for the highest class of work. With the most 

 modern machinery, however, equally good results may be obtained 

 by means of index die-work. Even for discs of quite small 

 diameter, the cost of a compound die is a very appreciable item ; 



FIG. 22. Power Shears for cutting Sheet Steel prior to punching 

 Armature Core Plates. 



and for large discs or segments, it runs into hundreds of pounds. 

 Another consideration affecting the decision, is that of practicable 

 sizes of presses. A press with a capacity for providing a pressure 

 of over 200 tons may be required in stamping out slotted discs 

 with a diameter of one metre, by means of a compound die. 



Brunswick and Aliamet 1 give the following rule for obtaining 

 the total pressure for which the press must be capable, in order to 

 punch a disc or segment of given dimensions : If t = thickness 



1 Construction des Induits a Courant Continu (Gauthier Vi liars ; Maison 

 et Cie.), p. 69. 



