86 



LEATHER BELTING 



pulleys are of the same diameter. If they are unequal, 

 the shafts of the mule pulleys will lie at different angles and 

 the pulleys must, perforce, be mounted on separate shafts. 

 The location of the shafts is determined by the same method 

 as described above, however, the only difference being that 

 the axis of the upper mule pulley is determined by the per- 

 pendicular to the tangent TT', Fig. 28, while that of the lower 

 one is determined by the perpendicular to the tangent SS'. 

 These tangents in this case will not be parallel. Otherwise the 



FIG. 30. BELT SHIFTER. 



construction is the same as for drives with main pulleys of 

 equal diameter. 



Belt Shifters. The fault of the ordinary belt shifter con- 

 sisting of a fork pushed to one side or the other, is that fre- 

 quently the weight of the pole operating the shifter will, 

 when it is at one side or the other of the vertical, tend to cause 

 it to resume its vertical position and so position the belt that 

 it is partly on and partly off the loose pulley. This can be 

 obviated ly the arrangement shown in Fig. 30. The pins 

 on the fork bar A are spaced apart a distance twice that 

 through which the belt is shifted. Whatever the position 



