Friction in orthogonal cutting of Douglas fir at varying grain orientations: Measurements and consequences

Samples of dry Douglas fir were orthogonally cut at varying grain orientations. The forces were measured in the direction of cut and perpendicular to the direction of cut. These measured forces were then resolved to enable their components along the cutting blade and perpendicular to the blade to be established. The calculated coefficient of friction between the chip and the surface of the blade was found to vary with depth of cut and grain orientation. When the friction is plotted against depth of cut, a linear relationship with positive intercept is found. An interpretation of the physical meaning of the intercept is proposed, based on cutting mechanics concepts and microscopy of the "process" zone.