FOREST UTILIZATION 73 



clamps together for several minutes and 'allow- 

 ing them to cool, the braze is dressed down with 

 a file to the proper thickness. 

 The filer arrests cracks by punching a small pin 

 hole or dot at extremity of crack. 



(d) The wheels. 



The band saw runs, belt like, over two wheels 

 weighing from 1,500 to 3,000 pounds (the lower 

 heavier than the upper) ; the lower wheel driving 

 the upper by the band saw. 



The strain on the saw, which should not exceed 

 5,000 pounds and by which slipping off is pre- 

 vented, is obtained by raising the upper wheel. 



The diameters of the wheels are 8 to 10 feet, the 

 face about n inches, the teeth overlapping the 

 wheel. 



The crown of the tire is up to 1-64 inch. 



The entire length of the log band saw varies from 

 30 feet to 70 feet. 



The saw guides, lined with wood or babbit metal, 

 prevent the cutting part of the blade from bend- 

 ing toward the carriage or toward the wheels, 

 while the guard rolls, standing about 2 inches 

 back of the saw, prevent it from slipping back- 

 ward at the approach of the log. 



The maximum diameter of logs that can be handled 

 by band saws is about 90 inches. 



The weight of a band saw mill complete is 20,000 

 to 40,000 pounds. 



(e) The "Allis" double cutting telescopic band saw. 

 The saw blade has teeth on both edges, so that a 



board is obtained at each trip of the carriage. 



The entire mill is raised or lowered by hydraulic 

 pressure with a view to bringing the top of the 

 logs immediately underneath the upper wheel. 

 IV. Conclusions. 



(a) The superiority of the band over the circular saw 

 lies in a saving of 1,000 board feet in every 16,- 

 ooo feet of 4/4 inch boards obtained. In heavier 

 planks the saving is less, in lighter boards more. 

 The boards obtained have a better width. Logs 

 over four feet through cannot be handled by 

 circular saws. Further, the band saw allows of 

 a more rapid feed. Hence it is used preeminently 

 for valuable logs, for big logs and for high out- 

 put. 



Frequently mills of large output employ simul- 

 taneously band, circular and gang saws, allotting 

 the logs according to their quality, the best to 



