CUTTING PERFORMANCES OF LIMBING KNIVES OF LOG HARVESTERS .1. EFFECT OF WEDGE ANGLES ON CUTTING RESISTANCE OF SINGLE-TAPERED KNIVES

Cutting resistance of limbing knives of log harvesters is known to be affected by the wedge angles of their blades. For softwood logs, the c utting resistance of limbing knives has not been a critical problem in harvesting. However, it has become an important subject these days wi th the increase in practical interest in the machine harvesting of low grade hardwoods. In this study, preliminary to the practical investig ation to determine the proper blade shapes of limbing knives, the effe ct of wedge angles of single-tapered knives on their single sides, on the cutting resistance of air-dried hardwood rods under static loading was investigated experimentally. Wedge angles of seven sizes, 22, 24, 26, 28, 30, 45, and 55 degrees, were adopted in cutting tests, and Ac er mono grown in Hokkaido was selected as the test material. The resis tance measured by the static cuttings of hardwood rods was increased a s the wedge angles became larger through variation of wedge angle test ed in this study. The cutting process was speculated considering some components of cutting resistance in which the cutting resistance was c onsidered to consist of compression normal to the blade surface, frict ion between the blade and the wood caused by this compression force, a nd disconnection of element bundles of wood fibers. The last component seemed to show the repetitive process of static bearing and bending o f the layered bundles of wood fibers and the sudden disconnection of s ome element bundles together with the stick-slip behavior on the frict ion surface. This component was nearly constant regardless of the wedg e angle. The cutting resistance due to this component was far less tha n the compressive resistance except in the initial stage of the cuttin g process, so that the difference in cutting resistance was considered to depend on the difference in compressive resistance due to the wedg e angle.