ORTHOGONAL CUTTING STUDY OF WOOD AND KNOTS OF WHITE SPRUCE

Wood defects can cause important loss of raw material and tooling during wood machining. White spruce (Picea glauca [Moench] Voss) is a wood species widely used in Canada, which presents an important occurrence of knots. These knots provoke several problems during machining affecting the final surface quality. The main objective of this research was to evaluate the orthogonal cutting forces and surface quality of white spruce wood with and without the presence of knots. Wood pieces of 12% MC were machined at four rake angles (10°, 20°, 30°, and 40°). Cutting forces and roughness were measured on clear wood (90°-0° cutting direction), knot (90°-90° cutting direction), and surrounding knot areas (before and after knot). Wood density in matched pieces were analyzed by X-ray densitometry. The results showed that the density of knots was in average 2.4 times higher than the density of clear wood. However, cutting forces of knots were up to eight times higher than those of clear wood. For all cutting areas, the parallel force increased as rake angle decreased. However, the sensitivity of cutting forces to changes in rake angle was higher for knots than for clear wood. Furthermore, surface roughness was positively correlated with the cutting forces. The rake angle of 40° produced the smaller cutting forces and lower surface roughness for clear wood, knots, and surrounding knot areas