Improved Pitch Rails for Peeling Douglas-Fir and White Spruce

Industrial veneer lathes, even when well maintained, generally peel poorer veneer at small- than at large-bolt diameters. The WFPL laboratory research lathe shows a similar pattern, although the quality is generally better than that produced industrially. The laboratory lathe is fitted with curved pitch rails. The effect of this curvature on veneer quality was investigated. A set of nonsloping straight pitch rails was installed so that the pitch angle remained constant regardless of bolt diameter. A group of 10 bolts was peeled at each of 6 pith angles (88?00′ to 91?00′ in 30′ increments). Veneer was collected at sequential 2-inch-diameter increments from 26 to 6 inches and veneer quality was judged on variability in thickness, roughness, and lathe checks. The pattern of pitch angles was determined which gave the best results at each diameter, and a pitch rail designed for the research lathe which gave this pattern. Groups of 15 bolts were peeled using: 1) the curved rails furnished with the lathe, set as instructed at 89?30′ at 12-inch block radius; 2) a replica of the foregoing; 3) the newly designed rails set at 89?30′ at a 10-inch block radius as determined from the experimental peeling; 4) the original curved rails set at 89?30′ at 10-inch block radius. The designed rails gave the minimum amount of reject veneer at the smaller diameters. Compared with previous work, they also gave better results with western white spruce. The new rails have operated satisfactorily in several industrial applications with a consistent upgrading of veneer quality at the smaller diameters.

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