Characteristics of sugar maple wood surfaces machined with the fixed-oblique knife pressure-bar cutting system

Oblique cutting differs from orthogonal cutting by an inclination given to the knife edge, which induces several changes on tool geometry, cutting forces, as well as on the quality of machined surfaces. In this work, a pressure bar was used during oblique cutting to reduce the occurrence of torn grain. The effects of cutting depth, rake angle, and oblique angle on cutting forces and surface quality were studied. Surface topography, cell damage and wetting properties were used to assess surface quality. All force components were increased by increasing cutting depth and decreasing rake and oblique angles. The lateral force, however, increased as the oblique angle increased. The surface roughness increased with increasing the lateral cutting force. Higher cutting depths and oblique angles tended to provide higher surface roughness, while higher rake angles tended to reduce surface roughness. The pressure bar was not always able to completely prevent the occurrence of defects when cutting against the grain. The occurrence of machining defects increased at higher cutting depths and oblique angles. As the rake angle decreased, the type of machining defect tended to change from torn grain to slight fuzzy grain. Moreover, the best wetting properties were obtained at lower rake angles, as they induced higher surface roughness. A 25° rake angle, a 30° oblique angle, and thinner cutting depths should be preferred to reduce dependence on ulterior sanding.