Graduate Thesis Or Dissertation
 

Predicting the machinability of finger-joints in ponderosa pine cutting stock

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3f462761r

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  • Cutting forces and the occurrence of chip-out were investigated in finger-joints machined into ponderosa pine (Pinus ponderosa) cutting stock. Finger-joints were orthogonally cut in sample blocks at four depths of cut (chip thicknesses) from 0.005 to 0.020 inch, twelve fiber angles from -30 to +40 degrees, and at specific gravities from 0.35 to 0.50. Cutting force measurements were made with reference to the machined surface in all three axes. The results showed that cutting forces are directly related to specific gravity and chip thickness. Fiber angle was found to effect only the cutting forces perpendicular to the cut surface, but it was found to determine the occurrence of wood failure (chip-out) at a block's trailing edge. It was further established that there was no measurable interaction of forces between the finger-joint cutting bits. Observation also showed that a joint's surface quality was inversely related to chip thicknesses but directly related to fiber angle. A cutting force model for the peripheral milling process used in production line finger-jointers was developed from the orthogonal cutting tests. It predicted that the cutting forces reach a maximum at the beginning of the cut when the full length of the finger-joint bits' sides are cutting wood. A peripheral milling model for predicting the probability of chip-out for a given chip thickness and fiber angle was also developed. A theory to explain the relationship between fiber orientation and the occurrence of chip-out was developed. It postulates that chip-out is determined by how the cutting force is oriented with respect to the fibers and not by the magnitude of the cutting force. Chip-out occurs when the cutting force is approximately perpendicular to the fibers. This theory suggests that chip-out can be eliminated by orienting blocks so the cutting edge loads the fibers in tension parallel to the fiber direction. Preliminary studies of growth ring patterns, knot parameters (including knot-wood density distribution), and fiber-flow models were conducted to determine the feasibility of using them for predicting the machinability of wood surrounding knots. Results indicate that a comprehensive model using these factors is possible following further verification studies. Portions of the preliminary study may also prove useful in defining sawing boundaries close to knots.
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