TRANSMISSION OF POWER 285 



journal; the other that the line-shaft and counter-shafting 

 should be in line with each other. Unless these precautions 

 are taken much difficulty will be experienced in the trailing of 

 the belts. One of the best methods of making sure that two 

 shafts are in line with each other is to place two slender reach 

 poles or rods of exactly the same length from one shaft to 

 the other at their opposite ends. The shaft may then be 

 adjusted until the distance is the same at each end. 



324. Flange Couplings. Line-shafting which is to en- 

 counter much shock and sudden variations of load must be 

 coupled with what are known as flange couplings. The dis- 

 tance between the hangers must be regulated by the number 

 of pulleys on the shaft. If the number is large the hangers 

 must be closer together. 



325. Bending and Twisting of Shafting. Shafts are 

 subject to bending and twisting. The bending is due to the 

 load strain of the pulley, while the twisting is caused by the 

 rotation of the shaft. Because it is liable to be rendered use- 

 less in this way, it is important that the shaft selected be of 

 a size suitable for withstanding the expected load. 



326. Leather Belting. Most belts used in machine shops 

 are made of oak-tanned leather (Fig. 141), but canvas is 

 sometimes substituted for leather belting. Single belts are 

 made from one thickness of leather or canvas, and are TQ of 

 an inch thick. Double belts are made from two thicknesses 

 cemented together, triple belts from three thicknesses, and 

 quadruple belts from four thicknesses. As a rule it is not ad- 

 visable to use anything but single belts on pulleys smaller 

 than 12 in. in diameter. Double belts, however, transmit 



