Fixed Knife-Pressure Bar System for Surfacing Dry Wood

Conventional planing methods can cause surface defects and subsurface damage such as torn grain. A fixed-knife method may avoid many of the defects commonly associated with planing, but cleavage failure ahead of the knife frequently occurs and results in torn grain when surfacing wood, especially with high rake angles. To minimize this failure, 5/8-inch roller and single-face pressure bars were placed ahead of the knife. The horizontal and vertical gaps were decreased until surface quality deteriorated. Compressions of 0, 10, 20, and 40 percent of the two depths of cut (0.010 and 0.020 in.) were applied by decreasing the vertical gap a fraction of the depth of cut. Yellow-poplar, hard maple, and red oak were dried to 8 percent moisture content and then surfaced with 45- and 52-1/2-degree rake angles in combinations with the pressure bars. The specimens were fed parallel and across the grain and at 10 and 20 degrees from parallel and across the grain at 30 inches per minute. The pressure bars reduced or prevented the cleavage failure ahead of the knife. The best results were from specimens fed at 20 degrees from parallel and across the grain.

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