46 FOREST UTILIZATION 



2. Interdependence between size of cylin- 

 der and horsepower actually devel- 

 oped is approximately : 



, 



Length, inches 

 Horfepower 



18191011211212114116 

 15 15 15 15 2O 24 24 3o 

 12J15 2o|25|30 35l5(>|S5 



These figures hold good for single cylin- 

 der engines and are much lower than 

 the usual catalogue figures. A new 

 engine develops more power than aji 

 old one. 



3. The flywheel should weigh 600 pounds 



for every inch of cylinder diameter. 



4. Double cylinders -are more effective than 



single cylinders, especially if not 

 hitched tandem fashion, which ar- 

 rangement, however, allows of using 

 one piston rod. 



5. Center crank engines are preferable for 



small portable saw-mills, since they 

 allow of exchange of flywheel and 

 main driving pulley. 



6. Machines cannot get along any better, 



without care, than horses. Repair 

 and watch the smallest defects. Have 

 the firmest possible foundations. 

 Saw-mill engines are put to the sever- 

 est possible tests owing to frequent 

 and rapid change of strain. 



XIV. TRANSMISSION OF POWER. 



Belts. 



Belts "in woodworking establishments are always dry and dusty 

 and are kept at a high and often irregular rate of speed. Dust 

 materially decreases the transmitting power of belts. 



The heavier the 'belt the more powerful ; use light belt on small 

 pulleys, however, for high speeds. 

 I. Pointers about belts. 



(a) Belt tighteners are required where a belt itself is 



not heavy and not long enough to cause suffi- 

 cient sag. 



(b) The sag should always be on top and not on 



the bottom. 



(c) The angle of belt against the horizon should not 



exceed 45. 



(d) Placing one pulley above another requires tight 



belt, which causes heating in the bearings and 

 destruction to the belt. 



