Friction in Wood Cutting

This paper discusses a recent investigation in which friction coefficients were measured using special apparatus on the effects of variables, such as pressure, contact area, sliding speed, surface roughness of the tool, wood species, grain direction, and moisture content. The investigation was not concerned with rolling friction but with friction between wood and steel. The study indicated that most species had approximately the same friction coefficient. Another variable was the effect of moisture content. At slow speeds, the friction coefficient is slightly higher for wet than for dry wood. However, at normal cutting speeds, the friction coefficient will be lower for wet than dry wood. The effect of grain direction showed no significant variation in friction coefficient with grain direction. The variable of tool roughness showed that the effect of steel roughness is important at slow speed but at speeds higher than 55 millimeters per seconds there is practically no effect of either wet or dry wood. The cutting speed is not important. The effect of bluntness was also considered. A constant friction coefficient implies only that the forces are borne by the tool face and does not indicate a particular relationship between the forces and other factors. Results from the study suggest that the plane bisecting the angle between the tool face and the cutting plane may be important in determining average tool forces in repeated cuts.

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