SMALL SAWMILLS, THEIR EQUIPMENT, ETC. 



29 



the power be increased the speed of the saw is increased correspond- 

 ingly. 



Saws for cutting hard wood or frozen timber are run at a higher 

 speed than those cutting soft timber, but have more teeth. 



If a saAV is run at a faster or slower rate than it is hammered for, 

 it is sure to work improperly and give trouble. A saw hammered to 

 run at 500 r. p. m., if run at 350 to 400 r. p. m. in the cut, will be loose 

 in the center and tight around the rim. This will cause it to run 

 snalry or crooked in the log, heat rapidl}^ in the center, and consume 

 a great deal of power. On the other hand, if a saw that is ham- 

 mered for slow speed, say 300 or 400 r. p. m., is run at 500 r. p. m., 

 it will stretch too much and be tight in the center and loose and 

 wobbly in the rim. This will cause it to heat on the rim, " flutter," 

 run crooked in the log, and consume power uselessly. Improper 

 speed and giving the saw too much lead into the log are the causes of 

 nearly all the trouble experienced with saws in portable mills. 



The following table, based on a saw 48 inches in diameter, may be 

 of use in determining proper saw speed. 





Horsepower. 





6 



8 



10 



12 



15 



20 



Distance between teeth irom point to point inches. . 



Teeth in saw number. . 



Speed of saw revolutions per minute. . 



7 



22 



300 



7 



22 

 300 



6 



24 

 300 



6 



24 



350 



5 

 30 



400 



5 



30 



450 



To find the proper speed of larger or smaller saws, multiply the 

 speed given for a 48-inch saw by 48 and divide the product by the size 

 of the saw selected. A larger saw should have a greater number of 

 teeth and a smaller saw a lesser number, the distance apart remaining 

 the same. In the case of a double mill, both saws should have the 

 same rim speed. 



FILING. 



Solid-tooth saios. — Do not file all the teeth from the same side, 

 especially if each alternate tooth is bent for the set. File the teeth 

 that are bent from you on one side and leave them on a slight bevel, 

 with the outer corners a little the longest, and then reverse the saw 

 and treat the other side in the same manner. Never file any saw 

 to sharp or acute angles at the throat or roots of the teeth, but on 

 circular lines. Any saw is likely to crack from sharp corners. The 

 filing of angles or square corners will cancel the warranty of the saw. 



Saw teeth wear narrow at the extreme points; consequently they 

 must be kept spread (s wedged) so that they will be widest at 

 the very points. The teeth should be kept as near a uniform shape 

 and distance apart as possible. The back or top of the tooth leads or 



