THE SAWMILL 115 



5. The teeth must have the proper pitch. A shallow tooth cuts the smoothest lumber, but forbids 

 of rapid feeding. 



The modern shape of teeth is such as will facilitate filing and as will preserve the 

 original pitch. 



A tooth gets dull over as much of an inch as it cuts. 



The gullet of the tooth must be larger for softwood than for hardwood. Large gullets 

 weaken the saw, small ones increase the friction very badly. 



A tooth should be filed two to four times a day. The backs of the teeth must never 

 protrude beyond the point. 



Gullets must be kept circular carefully. Any sharp edge in a gullet is sure to cause a crack. 



6. The mandrel must not heat in the journals. The boxes require frequent rebabbitting. The 

 stem of the mandrel must be exactly level and perfectly straight. 



Mandrels run hot owing to excessive friction in bearings, to excessive tightness of belts, 

 to insufficient lubrication or to heating of the saw in the center. 



A hot mandrel expands the saw in the center, causing crooked sawing. 



(e) Lining of the saw with the carriage into the log. The saw must "lead into the cut" just suf- 

 ficiently to keep the saw in the cut. The proper lead is Vs inch in 20 feet. Too much lead into the cut 

 causes the saw to heat at the rim. A lead out of the cut causes the saw to heat at the center. 



The \'-,-inch lead in 20 feet is obtained by sighting over the saw and fixing the saw plane for a radius 

 of 10 feet. This may be done by putting two staffs vertically into the ground 10 feet from the saw center 

 behind and in front of the saw within the plane of the saw; that done, a horizontal stick is fastened to a 

 head block so as to just touch the forward staff. Then the carriage is gigged backward to the other 

 vertical staff where the horizontal stick must lack exactly Vs inch from touching. 



(f) Filing room. Automatic sharpeners and gummers are required for mills having over 15,000 feet 

 daily capacity. 



Setting instruments for spring set are similar to those used with cross cut saws, constructed either 

 after the wrench principle or after the block and hammer principle. 



The spring set is gradually discarded for the swage set. 



In swaging use oil on the point of the tooth, after filing to a sharp point. Swaging should draw 

 the tooth out and should not shove it back. 



The set or swage of teeth should increase the gauge at the rim by at least V,, of an inch. 



The pitch of the tooth might be controlled by a so-called trammel. 



Gumming is required to preserve the original hook or rake of the tooth as well as the original 

 roundness of the gullet. 



Gumming as well as sharpening are usually done with emery wheels. 



Emery wheel rules are as follows:- 



1. Do not put too much pressure on emery wheel so as not to change the temper of the tooth 

 (bluing and casehardening and consequently crumbling of the tooth). 



2. Do not try to fix a tooth fully at one time. Treat it gradually at five or six revolutions of 

 the saw. 



3. Proper speed for emery wheels at the rim is 4,500 feet per minute. 



4. After gumming remove the irregularities at the edges with a side file, since cracks in saw are 

 apt to start from them. 



5. Hammering becomes necessary when the use of emery wheels has caused the saw to expand 

 ("let down") at the rim. 



For small mills gumming with a file or a butt gummer is preferable to the use of 

 emery wheel. 



Softwoods require more set or spread and less pitch than hardwoods. 

 Swaging is also called upsetting or spread setting. 



