48 FORHSl UTILIZATION 



B. Pulleys. 



Pulleys are made either of iron or of wood. 



The adhesion of leather to wood is much greater than to iron, 



hence greater transmitting power of wooden pulleys. 

 Split wood pulleys are preferable. The best make is the Dodge 



split wood pulley, costing for 24-inch diameter and lo-inch 



face $11.20. 

 The so called clutch pulleys consist of two wheels wedged one into 



the other, the inner one loose, the outer one fastened onto the 



shaft. 

 Iron pulleys must be absolutely symmetrical. 

 Pulleys for stationary belts are slightly crowning, while those for 



shifting belts are straight faced. 

 Pulleys for heavy work should be placed close to bearings of 



shaft. The main driving pulley must stand between bearings not 



over four or five feet apart. 

 The ratio between the speed of driving and driven pulley is inverse 



to the ratio of the diameter. 

 Remarks relative to starting and stopping machinery : 



I. Machinery is started by belt tighteners, the belt running 

 over flanged pulleys, by clutch pulley, by tight and loose 

 pulley with shifting belt, by eccentric boxes and by fric- 

 tion pulleys. 



II. A rotation is reversed by crossed belts (belt turning 180°) 

 or by papfer friction pulleys or by forcing the belt 

 against a driven pulley remaining outside the belt cir- 

 cuit. 



III. A rotation is turned at right angles by giving the belt a 

 . quarter-twist (90°), or by gear and pinion or by beveled 

 friction. 



C. Shafting. 



Cold rolled shafting is said to have a torsional strength 30 % 



greater than that of hot rolled shafting. 

 The usual diameters of shafting in saw mills are from i^/^ inch to 



3J4 inch. The proper speed for shafting is 300 to 400 revolutions 



J V , v.- ■ • D' X R 

 and Its transmittmg power is given as = horsepower. 



80 

 Herein stands: D for diameter of shafting; 



R for revolutions of shafting per minute ; 

 80 for a constant factor. 

 Couplings by which the sections of shafting are joined should be 

 close to a, hanger or a support. They should be easily detachable 

 without driving keys. 



Shafting comes in sections usually 12, 14, 16 or 18 feet long. 

 The section closest to the main driven pulky is often stronger than 

 the other sections. 



