60 Miscellaneous Circular 39, U. S. Dept. of Agriculture 
to the mill. Here we begin to make ment. So employ only the best me- 
our calculations on economy and to chanics for your saw fitting and ten- 
get the most for our outlay. There sioning and avoid miscuts and too 
are many types of mills, each installed much allowance for dressing lumber 
in a way calculated to best serve needs after it is sawn. 
of the owner, the place, and class and To run a thin saw, naturally the 
quality of timber. stability of the blade must be such as 
First, the small circular mill set up to insure straight lines and no mis- 
to cut isolated patches of timber cuts. Hence common practice has 
where a large operaton entails too come practically to a stop at a 12-inch 
large a capital investment to justify head saw, 14 gauge, or a 14-inch saw, 
its existence. Here perforce the saw- 18 or 14 gauge. Where 15 or 16 inch 
ing must be done with a round saw blades are used in large timber, the 
where the minimum thickness is 10 gauge is as heavy as 12 or 11 gauge 
gauge (about 14 inch). This means (one-eighth-inch). A heavy blade has 
a kerf of at least a scant 14 inch to the backbone, as it were, to stand 
every cut. Saws as thin as 4% inch up to heavy feed in a deep cut with- 
can be used, but at a very consider- out dodging when strained at 10,000 
able loss of time owing to slow feed pounds, which common practice has 
and, worst of all, danger of greater set as the limit to the strain which the 
loss by reason of miscuts. You ask, bearings of the mill will carry with- 
why use a circular saw? Because a out undue heating. New engineering 
band-mill equipment again brings the has increased this strain limit as high 
capital investment higher than can be as 20,000 pounds safely by the use of 
paid back with a profit and also adds ball and roller bearings. With 20,000 
to the cost of operation by reason of pounds strain a thinner saw will 
upkeep and labor. Experience has stand the feed better, as the lack of 
shown that such operations are self- body in the blade is supplemented by 
limited in the way of kerf economy the extra tightening, 
beyond a certain point. Not long ago a mill builder sold a 
When we reach the point where a new mill which was equipped with 
band mill can be profitably installed, antifriction main bearings to enable 
kerf economy can be reached in the the operator to put 20,000 pounds 
making of boards over the use of a strain on his saws and to enable him 
circular saw. Now, how far can this to tighten up a 17-gauge saw to the 
economy go? The thickness of a band point that it would stand the feed of 
saw is not primarily determined by a 14-gauge blade. The operator’s first 
the tensile strength of the material, saws were 17 gauge, and later he went 
as modern band saws are made of back to 14 gauge. I asked him why. 
material which at the proper temper His reply, dated November 8, 1924, 
has a factor of safety way beyond was: “We discontinued their use, as 
any possible strain that can or will our timber contains a lot of nails 
be required for sawing. With a ten- driven into the trees by turpentine 
sile strength of 150,000 pounds to the men for fastening the cups to the 
square inch of cross section at the trees, and .the 17-gauge teeth do not 
weakest point (the braze), it is stand up for cutting nails as well as 
scarcely probable that the maximum the heavier saws.” 
strain of 10,000 or even 20,000 pounds You are going to experiment more 
on the mill, with a strain of twice as as time goes on, and you are going 
much when the saw hits the log, to try thinner saws with more care- 
would cause any damage to a saw 12 fully designed tooth shapes, but your 
inches wide and 7% inch thick. It is logs must be free from nails. Twelve- 
not the development of a better ma- inch band saws as thin as 19 gauge 
terial for the blade, but a knowledge have been used successfully on mahog- 
of the reduction of friction both to any and rosewood, but those mills 
blade and bearings that will help. have reverted to heavier saws because 
Friction is the bane of a sawmill, and the Africans and other heathen left 
its elimination the answer to more too many nails, arrow heads, and 
saw problems than usually supposed. other junk concealed in the logs. 
Friction causes heat, and heat In this case in particular, where 
causes an expansion of the steel where 14-gauge saws had been the rule, a 
the heat is applied. This spotty ex- 17-gauge saw was used successfully 
pansion distorts the blade—hence mis- with no reduction in speed or feed, 
cuts. Friction is caused by lack of or a saving of one-sixteenth inch in 
tooth clearance, improper or insufi- each line. The great trouble, how- 
cient dust-carrying spaces between the ever, seems to be that thin blades 
teeth, tight guides, improper align- perforce have thin teeth. Heavy feeds