FOREST UTILIZATION 75 



(d) The set works consist of: 



The set beam, a shaft running underneath the car- 

 riage from head block to head block, with a 

 pinion at each head block. This pinion corre- 

 sponds with a rack forming the tongue or basis 

 of each knee. 



The index disc and ratchet. 



The set lever, handled either by the sawyer, in 

 small saw mills, or by the setter, in larger mills. 



The set works are usually double acting, so that 

 the knees advance with the to and fro motion 

 of the set lever. 



In addition, each knee can be moved individually 

 on its rack by the so-called taper movement. 



The knees, before a new log is loaded, are receded 

 either by a spring device or, on the gig motion 

 of the carriage, by a friction device. 



The brake wheel on the setshaft acts as a buffer 

 when logs are loaded on the car. 



(e) The wheels. 



The wheels are attached either to the carriage or 

 to the floor. The near wheels are flat on the 

 tire and "the far wheels, called guide wheels, are 

 grooved on the tire. 



In band saws, an automatic off-set is required to 

 prevent the face of the log from striking the 

 saw on the gig motion. 



The steel rails are invariably placed on stringers. 

 II. Driving machinery. 



The to and fro trips of the carriage are known as feed- 

 ing and gigging. 



In small mills the motive power is derived from the saw 

 arbor by: 



(a) Rack and pinion device. 



(b) Chain, rope or cable running over one or several 



sheave drums. 



The speed is regulated either by so-called cone 

 pulleys (two, three or four on the same shaft) 

 or by a paper friction device. 



The so-called Reamy Disc Friction allows, of freely 

 varying the speed. 



The usual feed, with the cone pulley, is from y$ 

 inch to 3 inches per revolution of saw. 



In large saw mills the piston of a steam cylinder 

 pushes the carriage to and fro (so-called shot- 

 gun feed). In that case the carriage usually 

 runs on three rails (center guide rail). 



