FOREST UTILIZATION 69 



Mandrels run hot owing to excessive fric- 

 tion in bearings, to excessive tightness 

 of belts, insufficient lubrication or heat- 

 ing 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 sufficiently 

 to keep the saw in the cut. The proper lead is 

 J/6 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 l /$ 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 ; 

 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 % 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 3-32 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 round- 

 ness of the gullet. 



Gumming as well as sharpening are usually done 

 with emery wheels. 



Emery wheel rules are as follows : 



i. 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). 



