Cutting Characteristics of Chain Saw Teeth

A machine capable of measuring forces on and energy requirements of a single chain saw tooth was constructed. A study was also conducted on the effects of several parameters on cutting forces, energy requirements, and chip formation. The machine developed was a variable-velocity whirling-arm wood-transport machine combined with the power, feed table of a milling machine. Cutting forces and energy were measured for speeds of 500 to 3,640 feet per minute at depths of cut from 0.010 to 0.060 inch. Green red oak (Quercus rubra) was cut radially with an Oregon chipper 7/16-inch pitch saw tooth. Three directions relative to a chain saw tooth were defined as longitudinal, transverse, and normal; tooth shearing and planing components were identified. In the longitudinal, direction (direction of wood motion) the cutting force and energy requirements are dependent upon depth of cut and relatively independent of cutting speed. There was an exact correlation between force peaks and the number of annual rings; magnitudes of from 5 to 75 percent of the mean cutting force occurred. There was a rapid decrease in cutting force above a cutting speed of 3,000 feet per minute where the tendency to crush cell walls ceases and failure occurs by severance of the fibers by the planing edge. In the transverse direction (parallel to cells, per- pendicular to direction of wood motion) no grain structure was cut, but the tooth vibrated perpendicular to the cutter bar at a frequency correlated with the grain structure because the tooth planing surface was dragging across the grain. The cutting force was dependent upon speed and depth, with speed the least prominent. No cutting edge cut across the grain structure in a normal direction (tangent to growth ring, perpendicular to direction of wood motion), but the saw tooth vibrated normal to and in the plane of the cutter bar, due to tooth shearing surface dragging across the grain structure. At a cutting depth of 0.011 inch, the normal force on the tooth was directed away from the wood, while at depths of 0.025 inch or greater, the normal force was directed toward the specimen, indicating that the tooth was pulling itself into the wood. A major portion of total energy consumption was taken by the planing component and increased with depth of cut, while the shearing component remained low and was independent of depth of cut. The energy consumed by cutting in the longitudinal direction was relatively independent of the cutting angle of the tooth within the limits investigated. A cutting angle between 10 and 15 degrees is optimum with respect to energy consumption operator effort and fiber separation. The basic chip type formed was independent of speed but was greatly affected by depth of cut. At depths less than approximately 0.030 inch, “plastic” chips peeling off in a curve 1/2 to 2 inches long were formed. At greater depths chips which fracture into short segments from 1/8- to 3/8-inch long were formed.

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