30 



LEATHER BELTING 



tions, such as countershaft and jackshaft belts, and therefore 

 can be run at high tensions. This explains the reasons for 

 presenting two sets of figures in the horsepower tables for 

 machine and countershaft belts respectively. 8. An initial 

 unit tension of 200 Ib. per square inch is about the maximum 

 that should be put upon a belt if it is to be used under the 

 most economical conditions. 



Before taking up the theory enunciated by Mr. Earth 

 we will examine the general theory of transmitting power by 

 means of belting. 



General Theory of Power Transmission by Belting. A 

 belt one inch wide is stretched on a pulley as in Fig. 4, by 



FIG. 4. DIAGRAM ILLUSTRATING THEORY OF BELTING. 



two equal forces T\ and Ti. The pull on the shaft is T\-\-Tz 

 = W. If R is the radius of the pulley in inches, the radial 

 or normal pressure P brought on the pulley at each inch of 



T 



length of contact is ~, assuming that the belt is elastic 

 R 



and free to move around the pulley without friction. Now 

 assume that there is friction between the pulley and the 



