Influence of Certain Variables on Veneer-Cutting Behavior

Laboratory-scale apparatus was used in extensive veneer-cutting studies to determine the effects on equilibrium cutting properties of variables of tool geometry, cutting conditions, species characteristics, and grain orientation. Cutting behavior was analyzed for energy consumption, strain recovery in the workpiece, and veneer quality–green thickness, depth of knife checks, and tensile strength perpendicular to the grain. Within a species, increased nosebar pressure resulted in increased energy consumption and block strain recovery, while reducing depth of knife checks and thus reducing surface roughness and veneer thickness. Though increased nosebar pressure initially increased the strength of the veneer in tension perpendicular to the grain, an optimum level of compression was reached, beyond which further increases caused a decline in tensile strength retention and a reduction in thickness, due to excessive compressive set. Knife angle had the greatest effect on energy consumption and strain recovery, which were maximum at 89?, the minimum knife angle tested. Increasing the knife angle generally reduced both energy consumption and strain recovery, though minimum energy consumption may be reached at knife angles near 91? to 92?. In all species, cutting at higher temperatures generally consumed less energy. Cutting temperature had little effect on strain recovery at lower levels of nosebar pressure; however, at nosebar pressures above 10 to 15 percent, strain recovery with higher temperatures rose sharply. Higher temperatures generally also reduced the depth of knife checks and thus improved veneer quality and tensile strength. At higher temperatures, the optimum level of nosebar pressure with respect to tensile strength retention was reduced. Cutting of fully saturated wood involved greater energy consumption and strain recovery, and produced thinner veneer of lower tensile strength, than cutting wood at a moisture content slightly above the fiber saturation point. These effects were due to the hydrostatic bursting of cells during the cutting process. To attain equilibrium, a greater number of cuts from wood saturated with water than from wood at the fiber saturation point is generally required. Though specific gravity is significant in determining the amount of energy required in high temperature cutting with moderate nosebar pressure, block strain recovery and veneer thickness are apparently not correlated with species density. The influence of growth-ring orientation with respect to the cutting plane is due mainly to planes of relative strength or weakness as determined by characteristics of ray structure and earlywood-latewood contrast. Planes of weakness have an important effect on cutting action when they occur either in the plane of cutting or in the plane of potential check formation.

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