A New Approach to Calculating Target Sizes

Conventional target size calculations contain inherent inaccuracies which may result in a loss in lumber recovery. Improper setting of the fixed head planing depth, which traditionally is done by trial and error, can also result in a loss in lumber recovery. This study was conducted to develop more accurate equations for calculating target sizes and for estimating the fixed head planing depth. The equations were developed for two models which describe the planing process. One model assumes that the board is rigid along the length while being planed. The other model assumes that the board is flexible along the length while being planed. The adequacy of the equations was confirmed in a lumber size study. Analysis of skip area and number of skip pieces indicated that the target size and fixed head planing depth could be accurately determined. The equations require the use of rough dry sawing variations, rather than the conventionally used rough green sawing variations. For effective lumber size control, a method is provided for estimating rough dry sawing variations from rough green sawing variations and shrinkage variations.

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