34 



ARMATURE CONSTRUCTION 



inside parts left after cutting these stampings are subsequently 

 used up for the making of core discs of smaller diameter. 



Figs. 19 and 20 show typical stampings for large armatures, the 

 minimum waste being obtained by progressing down the sheet as 

 shown. 



Sometimes a series of external and internal diameters is so 

 standardised for a set of designs as to greatly minimise the waste 

 in punching. In Fig. 21 is given an instance where, by means of 

 a double series of diameters, A, C, E, and B, D, F, etc., the sheets 

 are almost entirely used up. Diameter B is chosen about midway 

 between A and C, and so on with the other diameters. From these 

 two sets of diameters may be obtained thirteen different combina- 

 tions, half of this number being of narrow depth radially and half 

 of wide radial depth. These possibilities are shown in Table VIII. 



TABLE VIII. 



SIZES OF STAMPINGS OBTAINABLE FROM TWO SETS OF DIAMETERS 



IN FIG. 21. 



Frucht alludes to the difficulty of obtaining a smooth, clean 

 surface on the sheets, and at the same time retaining good 

 magnoLic quality ; for the smooth surface is only obtained by a 

 greater number of passages of the sheets through the rolls, ;ind 

 with each passage the sheets become harder and magnetically 

 inferior. Nevertheless, unless the plates are rolled fairly smooth, 



