Effect of Scan Spacing on Trimming Efficiency

A theoretical method was developed to determine the effect of scan spacing on trimming efficiency. Besides scan spacing, the method considered the movability of the fence of a multiple-saw trimmer, and the percentage of total production that requires trimming at the lumber-line end (near the fence). Using this method, trimming efficiency was shown to increase linearly with declining scan spacing. With 2-foot scan spacing and a fixed fence, the theoretical trimming efficiency was found to be 98 percent of optimum for a sawmill with 20 percent of its total production requiring trimming at the lumber-line end. The theoretical efficiency can be increased to 99.9 percent with 1-inch spacing, a moveable fence with 1-inch increments, and a 23-inch maximum shifting distance. For a given scan spacing, trimming efficiency was found to decrease linearly with the percent of total production that required trimming at the lumber-line end. Thus, trimming efficiency can be improved by feeding logs through a mill oriented so that most of the lumber ends that require trimming are away from the fence.

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