Sawing Wood with Circular Headsaws

A research sawmill, typical of the circular headrigs in Canada, was equipped with instruments needed to investigate the many variables inherent to the sawing of wood. Instruments made it possible to measure and record simultaneously for any position of the saw during the cut and for the saw as a whole, saw speed, carriage speed, torque on the headrig saw shaft, and the horizontal and vertical forces exerted on the saw. Instruments used to measure these forces were two brush oscillographs, a Baldwin SR-4 torquemeter, and two strain gages mounted on the head saw shaft. The basic tests conducted were as follows: l) Affect of specific gravity of wood on headsaw power requirements. This was determined under actual operating conditions for saw cuts in white pine (Pinus strobus), birch (Betula spp.) and sugar maple (Acer saccharum). Power required increased as specific gravity increased. 2) Effect of depth of cut on head saw power requirements. For a given species a linear relationship between depth of cut and horsepower was established. 3) Effect of bite on head saw power requirements. Doubling the bite does not double the power required, so if sufficient horsepower is available power efficiencies can be obtained through increasing the bite. 4) Effects of tooth width on power requirements of 7/, 8/, 9/, and 10/32nds of an inch were tried, and the 7/32nd resulted in excessive saw overheating. 8/32nd was found to be the most efficient tooth width since it required less horsepower than wider teeth and also resulted in less waste. The cost of more frequent replacement of teeth because of their shorter life will be more than offset by gains in lumber volume. 5) Effect of tooth sharpness on sawing. More power is required as teeth become dull. A combination of these studies led to the following conclusions: The amount of power required to saw various commercial Canadian species depended on the depth of cut and the specific gravity of the wood. Based upon the four sample species, a table showing the average power requirements for the head saw for Canadian species according to depth of cut shows that a 75 horsepower saw is adequate for depth of cut less than 8 inches for all Canadian species, and for depth up to 14 inches for the lowest specific gravity species. A 14-inch cut in white oak (Quercus alba), however, would require 137 horsepower. The efficient use of power depends upon the right combination of saw speed and carriage speed to obtain the largest possible saw bite while maintaining the quality of sawing. Of course, bite cannot be increased if sufficient power is not available. The horsepower requirements for inserted teeth of various designs varied, the most efficient being hollow-ground 1/2-inch radius, and the least efficient being the chip breaker type. Surface quality of hardwood lumber sawing with hollow-ground teeth appeared to be improved.

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