FOREST UTILIZATION 67 



fro), that high speed may be appHed and that 

 a thin gauge can be used. 

 The best make is Kirschner's, Leipzig, Germany. 

 II. Circular saws. 



(a) Power. 



Ten horsepower sliould manufacture S,ooo b. feet 

 per day; 20 horsepower should manufacture 

 10,000 b. feet per day; 30 horsepower should 

 manufacture 30,000 b. feet per day, and each ad- 

 ditional horsepower should add 1,000 b. feet to 

 amount cut. This amount depends on size of 

 logs. 



Five horsepower is required for a 20-inch to 30- 

 inch saw ; 12 horsepower for a 30-inch to 40- 

 inch saw ; IS horsepower for a 48-inch to So- 

 inch saw ; 25 horsepower for a 50-inch to 62- 

 inch saw. 



(b) Right hand and left hand mills. 



If the carriage is to the left of the observer while 

 the saw runs towards him, the mill is a left 

 hand mill, and vice versa. A right hand saw is 

 screwed to the arbor by a left hand nut and is 

 usually driven by a left hand steam engine. 



Center crank engines can be used for either right 

 or left hand mills. 



(c) Speed. 



The proper speed at the rim of any circular saw 

 is 9,000 feet per minute. 



There should be a speed indicator to control the 

 saw's speed. It costs 75c. 



If the power is too light to run| the mill at stand- 

 ard speed, portable mill men usually increase 

 the speed of the engine, putting a larger receiv- 

 ing pulley on the saw mandrel. 



(d) Proper qualities of a saw. 



1. The usual thickness is 7, 8 or 9 gauge. 



Frequently the center is one gauge heav- 

 ier than the rim. 



2. There ■ should be a sufficient number of 



teeth for the amount of feed. 



Each tooth should cut as much as is of- 

 fered to it at a revolution. 



To cut one inch of lumber one may use 

 either : 



Eight teeth, cutting Ys inch each at a 

 revolution, or 



Sixteen teeth, cutting 1-16 inch each at a 

 revolution, or 



