SMALL SAWMILLS, THEIR EQUIPMENT, ETC. 



25 



both belt and machinery. Regardless of the width of belt or diam- 

 eter of pulley, the adhesion of the belt to the pulley is the same in 

 all cases, provided the arc of contact and aggregate tension or weight 

 are the same. Thus, other things being equal, a belt will slip just 

 as readily on a pulley 4 feet in diameter as it will on a pulley 2 feet 

 in diameter. To obtain the greatest amount of power from belts the 

 puUej^s must be covered with leather. This will allow the belts to run 

 slack and will increase their durability by 25 per cent. 



CIRCULAR SAWS. 



KINDS AND COSTS. 



Cifcular saws are either of the solid-tooth or inserted-tooth type. 

 The advantages of inserted-tooth saws over solid-tooth saws are : The 

 bits are cheap and can be readily set in position with the special 

 wrench ; less experience is required in dressing the saw ; there is less 

 jRling and gumming ; there are fewer saw repairs, which is important 

 in a backwoods locality; and the diameter of the saw remains un- 

 changed during its use. The disadvantages are: The saw kerf is 

 heavy; the teeth are larger and fewer than in a solid-tooth saw; 

 feed is comparatively slow ; and the cost is higher. 



For big logs and high speed a double circular saw must be used. 

 The two saws are hung to revolve in opposite directions, so that the 

 sawdust from the top saw will not be thrown into the lower one. 

 The advantages of a top saw (double mill) are: It will saw bigger 

 logs than a single mill; it will make a truer cut and saw lumber 

 more evenly; it takes faster feed, saws more lumber, and entails less 

 expense for saws and less repairs. The top saw may remain inactive 

 when small logs are being cut, to avoid using up power. Inserted 

 teeth are not used in a top-saw rig. 



The approximate prices of solid-tooth and inserted-tooth saws 

 f . o. b. Seattle, in 1916, were : 



Approximate price of solid-tooth and inserted-tootli saivs. 



Size. 



Solid 

 tooth. 



Inserted 

 tooth. 



Size. 



Solid 

 tooth. 



Inserted 

 tooth. 



40-inch 



,123 

 26 

 30 

 36 

 41 

 47 



S44 

 49 

 53 

 57 

 62 

 70 



52-inch 



$52 

 58 

 66 

 74 

 83 

 94 



S81 



42-inch 



54-inch 



91 





56-inch 



99 



46-inch 



58-inch 



110 



4S-inch 



60-inch 



121 



50-inch 



62-ineh 



134 









\ 



The amount of horsepower required for a circular saw is equal to 

 approximately one-third of the saw's diameter in inches. In large 

 mills each horsepower is supposed to manufacture 1,000 feet of lum- 

 ber per day ; in small mills only one-half that amount. 

 '63262°— IS— BuIL 718 4 



