FOREST UTILIZATION 11 



(usually) vertically to back of saw. Sometimes, however, 

 they are in the direction of the radius of the saw. 



Large "bow" saws allow of a very thin blade and have a bow 



instead of handles. They are not used in America. 

 VIII. The effect of a saw is equal to the number of square inches 

 cut by one man per minute. The effect is small in pole- 

 woods, increasing gradually up to- a diameter of i^ ft. and 

 decreasing thereafter owing to increasing friction. 



In cutting longleaf pine, the saw is continuously sprinkled 

 with turpentine. 



The effect of curved saws is from 40 % to 50 % higher than 

 the effect of straight saws. 



The saw overcomes 



(a) The resistance of the fibre by the sharp points acting 



as knives and planes ; 



(b). The friction at both cheeks of the blade by smooth 

 cheeks and by a gauge narrowing toward the back ; 

 (c) The friction of sawdust by deep teeth, curved line of 

 teeth, perforation, large dust chambers and possi- 

 bly by "cleaning teeth." 

 IX. Dressing of cross-cut saws. 



' (a) ''Jointing" means filing all cutting teeth down to 



exactly the same circumference. 

 The tool used is called a jointer. A file is placed 

 in the joints and by a screw pressed into the proper 

 curvature. 



(b) "Fixing the rakers" means filing them down with the 



help of a raker gauge. The rakers act as brakes 

 if they project into the cutting line. Outside and 

 forks of rakers are slightly filed to remove case 

 hardening, and the point is sharpened to a planer 

 edge. 



A raker swage is being introduced to spread the 

 points of the rakers and to give them a hook-like 

 point, which is said to tear but long slivers instead 

 of tearing out dust. 



(c) "Setting the cutter teeth" is done under the control 



of a "set gauge" with the help of a "set block and 

 hammer," giving 3 to 4 taps (the best method when 

 clone by experienced men) or with the help of a 

 "saw set." "Saw sets" are constructed either 

 wrench-like or after the hammer and "block prin- 

 ciple. 

 Rules of setting are : 



1. Setting should never go lower than half the 



length of the tooth. 



2. It should never exceed twice the gauge of the 



teeth. 



