Moisture Content of Southern Pine as Related to Thrust, Torque, and Chip Formation in Boring

Holes 3-1/2 inches deep were bored with a 1-inch spur machine bit in southern pine having specific gravity of 0.53 (ovendry weight and volume at 10.4 percent, moisture). The bit was rotated at 2,400 rpm and removed chips 0.020 inch thick. For wood moisture contents ranging from ovendry to saturation, thrust was lower when boring along the grain (average 98 pounds) than across the grain (average 138 pounds), while torque was higher when boring along the grain (average 42 inch-pounds) than across the grain (average 33 inch-pounds). For both boring directions, torque and thrust increased with increasing moisture content to a maximum at about 5 to 10 percent, then decreased to a constant value at about the fiber-saturation point. For the type of bit tested, net power at the spindle required to cut 0.020-inch-thick chips at speeds of 2,400 rpm or less should not exceed 2 hp regardless of boring direction or moisture content; thrust should not exceed 200 pounds. Chip types resembled those obtained in orthogonal cutting.

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