FOREST UTILIZATION 47 



(e) Belts should run off a shaft in opposite directions 



to relieve one sided friction of shaft in bearings. 



(f) The pulley must be wider than the belt. 



(g) The larger the pulley the greater the tractive 



power of the belt, 

 (h) Be sure that the belt does not rub against any 



beam or other solid object, 

 (i) Long belts have greater adhesion than short belts 



because they have more weight, 

 (j) Belt dressing, to prevent slipping off of belt, is 



objectionable, because it gathers dust and dirt, 



except perhaps linseed oil used on rubber belts, 

 (k) Belts will slip if: 



1. The pulleys do not. run in one and the same 



plane. 



2. The shaftings are not parallel. 



3. The pulley is not as wide as the belt. 



4. The belt ends are improperly joined. 



S- The speed is too high for the weight of the 

 belt. 



11. Kinds of belts: 



(a) Leather belts. 



Leather belts are either single or double. They 

 come in rolls of from 200 feet to 300 feet, are 

 run with the grain side in and are preferably 

 joined with studs — not by leather laces requiring 

 hQles; belt cement is now largely used, laps 

 being joined to a fine edge. 



Leather belts must be very well protected from 

 moisture, grease, lubricating oil etc. 



Transmitting power of a single belt is only 70% 

 of that of a double belt. 



The price of a 7-inch single belt per running 

 foot is $1. For double belt $2. 



(b) Rubber belts. 



Rubber belts withstand moisture better than 

 leather belts. They are cut from ^ inch to J4 

 inch shorter per foot than the circuit on which 

 they run and are run with seam side out. 



They are sold as 2, 4, 6 or 8 ply rubber belt, the 

 4 ply being equivalent to single leather belting 

 and the 6-ply to double leather belting. 



The price of 4-ply 7-inch rubber belting is 70c 

 per running foot ; of 6-ply, $1. 



The ends are joined either by belt cement or by 

 lace leather. The laps are strengthened by a 

 strip of leather on the outside. 



Never use metal studs in rubber belts. 



