28 BULLETIN 718, U. S. DEPARTMENT OF AGRICULTURE. 
tension, the plate must be hammered lightly all over on both sides 
to within 6 or 8 inches of the center and to within 2 inches of the 
bottom of the sockets. The hammering must be distributed evenly 
with a round-faced hammer. When adjusting the tension, leave the 
shanks in the plate. 
When hammering a saw it is necessary to know the speed at which 
it is to run. No saw will run properly unless hammered for the 
correct speed. A saw when running must be perfectly flat on the 
log side, although some sawyers prefer to have the edge lean slightly 
towards the log when the saw is standing still. This means that it is 
dished a very little on the log side. If, however, any such dish is 
allowed, it would, of course, be so slight that it could not be distin- 
guished by the naked eye and could hardly be found with a straight 
edge. 
A saw often becomes full on the log side. By this is meant that 
the rim has been forced away from the log so as to cause the dish 
on the board side. If there are no uneven spots in the plate other 
than this dish, the saw can easily be brought back by lightly ham- 
mering on the log side. 
Always make sure before any hammering is done that the part 
of the saw which is to receive the blow is well bedded or flat on the 
anvil. In a perfect saw the apex or point of the V of the socket is 
central with the plate. If it is not central, the bit, when inserted, 
will lean to one side. This causes the saw to lead into, or be forced 
away from the log, as the case may be, and besides dishing the saw, 
divides the strain on the bit and shank unevenly, causing them to 
break. 
SAW SPEED. 
There is a wide difference of opinion as to proper speed of saws. 
The manufacturers give the maximum speed at which their saws may 
be operated with safety on the basis of the highest power the saws 
are calculated to withstand. These speeds can not be used for portable 
mills because of insufficient power. They are given by saw makers 
to show what the saw will stand and not what it is supposed to ac- 
complish in practical work every day. While speed is power, it is 
easy to consume ail the power in speed without doing any work. A 
48-inch saw run by a 10-horsepower engine should have a speed of 
300 revolutions per minute, or to give the best results, 350 revolutions 
per minute, and should have 24 teeth. The proper saw speed for 
portable mills running with 20 horsepower and under may be ob- 
tained by multiplying the horsepower by 360 and dividing the prod- 
uct by the circumference of the saw. 
For 20 horsepower the teeth should be 5 inches apart, which will 
give 30 teeth to a 48-inch saw. With larger power the teeth should 
be closer together until they reach the. limit of 3 inches apart. As 
