Sawteeth in Action

Waste in sawing is caused both by inaccurate sawing, with the excess being planed off, and by excess kerf. Research to reduce waste cannot be initiated on commercial machinery, but must be done in the laboratory. Research equipment built at the Forest Products Laboratory to study sawing consisted of two thin-wall tubular pendulums, one holding a specimen, the other a cutting tool. An insert-type sawtooth, lapped and polished to a mirror finish, was used to cut dry sugar maple across the end grain with a metered feed increasing from 2.5 mils to 100 mils. It was noted that chip breakage became increasingly severe as feed rate increased; this led to an analysis of the four simultaneous actions within the kerf which form chips, or sawdust. Work is exerted to sever the fibers along the bottom of the chip; the severed chip is pried loose; the loosened chip is broken into pieces; and the chip is removed from the kerf. Chip loosening, break-up, and removal require a uniform amount of energy per inch of sawline, but fiber severance raises the total energy required to high values at slow feeds, because more cuts per inch are made. Sharper teeth reduce the total energy required, but the faster feeds still require the greater energy. A heavy cut per tooth is desirable to do the most sawing with the power available Sharpness is of little importance in heavy cuts, but it is crucial when feed rates are light. What happens to the force exerted on the chip by the face of the tooth, and the wear pattern on the tooth, are analyzed. The fundamental knowledge of the mechanics of a single sawtooth led to the development of an improved saw. To permit. free movement of the chip after release and to provide a zone into which sloping grain can run without extending into uncut fibers, it is necessary to widen the initial kerf as soon as possible after it is started. This is done, without waste, by making the original kerf very thin. The Duo-kerf circular saw alternates narrow “chipper” teeth with wider and lower “side-dresser” teeth, preferably having parallel sides and concave faces. If this system is developed, it should have wide applications and should lower costs.

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