Investigating the Resistance Expression Method of Wood Resistance Drill Instruments

Wood density is an important attribute that is positively correlated with many wood quality parameters. How to express wood density with drill resistance is a challenge. In this study, we determined the optimal resistance expression using the current, voltage, and power of the DC (Direct-Current) motor. Nine wood blocks crossing over the pith, with widths and heights of 2 cm and 5 cm, respectively, were obtained from three larch (Larix spp.) trees. The microdensity of each wood block at every 0.1-mm length was measured, and the average current, voltage, and power of the DC motor was recorded when the drill fed forward at every 0.1 mm by a self-manufactured resistance drill. The drill path was parallel to the lengthwise direction of the block. The linear models between the current, voltage, and power of the DC motor and wood microdensity were subsequently established, and the model with the highest R2adj was selected to express the resistance. The adjusted R2adj of the forward stepwise regression models between the current, voltage, and power of the DC motor and wood microdensity were determined as 0.2943. This suggests that the drilling needle resistance expressed with the current, voltage, and power or other combination may be optimal.