The Effect of Boring Speed and Feed Rate on the Strength of Glued Dowel Joints in Tension

Extensive tests were made to determine the effect of boring speed and feed speed on the strength of glued dowel joints. The experimental work was performed on specimen holes bored at 1620, 2880, and 4430 rpm. Feed speeds were controlled to produce chip thicknesses of 1/128, 1/64, 1/32, and 1/16 inch. Species of wood tested were sugar maple (Acer saccharum), red oak (Quercus borealis), and northern white pine (Pinus strobes). All dowels were yellow birch (Betula lutea) with nominal diameter of 3/8 inch. A polyvinyl acetate adhesive was used in making the dowel joints. The glued dowel joints were tested in tension in three species of wood using one dowel size, two dowel types, one adhesive, and one boring tool. The independent variables were the boring conditions. Ten specimens were prepared for each species at each of the conditions, making a total of 720 specimens. The test results showed that hole wall surface quality is effected both by thickness of the chips removed and rotational speed of the boring tool. Chip thickness on hole wall smoothness is an important factor, contributing to the strength of dowel joints in northern white pine, the effect is less important in the boring of sugar maple; red oak showed somewhat lower joint strength with boring speeds that produced large chip thickness. Joint strength, for constant chip thickness, showed a reduced value at the highest boring speed in sugar maple. For red oak and northern white pine, joint strength for holes bored at 1620 and 4430 rpm were below the value obtained at 3880 rpm. This significant observation is attributed to temperature effects due to the balance between heat generated in cutting and heat dissipated into the tool bit and the wood. Spindle speed has a greater influence on joint strength than chip thickness. No significant difference was found when using either spiral grooved or plain dowels.

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