Cutting forces for tension and normal wood of maple
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Sawing and planing operations consume about 15 percent of the energy requirements for manufacture of products such as oak flooring. Tension wood, present in hardwood tree species, is more difficult to machine than normal wood. In cold climates, additional energy is required to saw frozen logs. This research measured cutting forces for frozen green wood, green and dry normal wood, and green and dry tension wood of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.); an ice block was cut to compare the magnitude of its cutting forces with those obtained from frozen wood. Wood blocks were machined to simulate sawing by using a single bandsaw tooth mounted on a three-axis piezoelectric load cell to evaluate principal, lateral, and normal forces when cutting in the 90-90 direction (sawtooth's edge oriented perpendicular to the grain). Frozen, green and dry wood was cut to produce data related to primary and secondary manufacturing processes. Three tooth designs were tested. Sawteeth with larger rake angles required less energy to cut green and dry wood. The tooth with the largest rake angle required the least energy to cut dry and frozen wood, and also performed well when cutting green wood. Specific cutting force for frozen wood is nearly as great as for dry wood; specific cutting force is least for green wood. Specific cutting force is less for tension wood than for normal wood. Cutting force measures energy to sever a single chip. Previous authors have stated that the power expended to cut tension wood is greater than the power expended to cut normal wood. This is because when tension wood is machined, friction caused by fuzzy grain rubbing against the cutting tool is responsible for the increased power consumption. Increased cutting forces for frozen wood are due to cutting frozen cell walls, because ice alone requires little force to machine. The results for tension wood are apparently due to thinner fiber cell walls and the amount and type of lignin present in tension wood fibers.