28 BULLETJlsr 118, U. S, DEPARTMENT OF AGEICULTURE. 



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 saw3'ers 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 

 awa}^ 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 sraa'S., 

 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 all the power in speed without doing any \york. 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 

 giAe 30 tec(h to a 48-inch saAV. With larger power the teeth should 

 be closer together until they reach the limit of 3 inches apart. As 



