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 
pulleys 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. 
Circular 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 
filing 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-tooth saics. 
Size. 
Solid 
tooth. 
Inserted 
tooth. 
Size. 
Solid 
tooth. 
Inserted 
tooth. 
40-inch 
$23 
26 
30 
36 
41 
47 
S44 
49 
53 
57 
62 
70 
52-mch 
S52 
58 
66 
74 
83 
94 
§81 
42-inch 
91 
99 
44-inch 
46-inch 
5S-inch . 
110 
48-inch 
60-inch 
121 
50-inch 
62-inch 
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 da.y ; in small mills only one-half that amount. 
63262°— 18— BulL 718 1 
