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 saw 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 
snaky or crooked in the log, heat rapidly 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 
Teeth, in saw 
from point to point inches. . 
number. . 
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 sates. — 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 (swedged) 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 
