Sawing Hardwoods for Grade with Short-Log Bolters

The investigations were conducted along two general lines: studies carried out at commercial operations and a short-log bolter research installation. Part of these latter studies were of a comparative nature, that is similar material was sawn on a conventional circular headsaw and on the short-log bolter. A table bolter was employed because of its wide commercial use. Bolt diameter sharply influenced lumber recovery. Lumber recovery ranged from between 38 and 48 percent for 5-inch bolts to between 50 and 58 percent for 15-inch bolts. In general, recovery was higher in bolter mills than in the sawmills. Up to 12 inches diameter a higher grade recovery was obtained by bolter methods. However, above 13 inches, the sawmill produced lumber of better grade. The explanation may be attributed almost entirely to the usual sawmill practice of removing large slabs during the first cuts. Sawing time required to produce equal volumes of lumber tended to be longer for bolter conversion. However, sawing accuracy was considerably better during bolter conversion. The effect of log size on yields is not as pronounced for bolter production as for conventional production. Capital investment is usually smaller in a bolter mill, but this type of mill is at a considerable disadvantage in terms of productivity. However, the better quality and higher price for bolter mill products compensates part of the disadvantage. In conclusion, the bolter is not competitive with the sawmill for sawing normal commercial hardwood logs. The increased productivity of the sawmill materially outweighs the several advantages of the bolter when sawing this type of material. It appears that bolters could be advantageously used to produce furniture stock from types and sizes of trees or logs that could not be satisfactorily used in a conventional sawmill. Perhaps the ideal employment of a bolter mill is as a complementary unit to a sawmill with both producing stock for furniture plants.

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