The effect of curve sawing two-sided cants from small-diameter hardwood sawlogs on lumber and pallet part yields

Curve sawing is a primary log breakdown process that incorporates gang-saw technology to allow two-sided cants from logs with sweep to be cut parallel to the log surface or log axis. Since curve-sawn logs with sweep are cut along the grain, the potential for producing high quality straight-grain lumber and cants increases, and strength, stiffness, and dimensional stability are maximized. Presently, curve sawing methods are widely incorporated in high production softwood lumber manufacturing facilities. However, with a few exceptions, the practice of curve sawing is virtually nonexistent in hardwood sawmills. A previous study indicated that approximately one-third of hardwood sawlogs contain measurable sweep. The purpose of this study was to investigate the impact of sawing pattern (straight vs. curve sawing) on lumber, cant, and pallet part yield from small-diameter hardwood logs with varying degrees of sweep. The results of this study indicate that cant and pallet part yields are not affected by sweep since cants are cut from the center of a log. Although curve-sawn pallet cants did not straighten out completely when stacked, they did not cause handling problems during the pallet part manufacturing process. The yield of lumber from the outside of curved logs increases significantly when curve sawn. The results indicate that lumber yield can be as much as 10 to 12 percent higher when curve sawing hardwood logs with an average sweep of 3.3 inches and greater (12-ft basis). Since approximately one-third of hardwood logs are not considered straight, significant lumber yield improvements can occur when curve sawing lumber and cants from these logs. Of the total solid wood used to manufacture wood pallets, approximately 67 percent (4.41 billion board feet [BF]) is mixed hardwood species in the form of lumber, cants, and small-diameter logs. Approximately 40 percent of all hardwood material processed in the United States is channeled into the pallet manufacturing industry (Bejune et al. 2002). Integrated pallet mills will purchase small logs and saw them into pallet cants or lumber using small-log processing systems. Pallet manufacturers without log sawing capability will purchase cants from hardwood grade sawmills or sawmills sawing small lower grade logs. Pallet cants sawn from small-diameter logs will often contain higher quality material than cants sawn from the center of the larger diameter grade logs. While it is important that pallet manufacturers strive to maximize yield and quality of cants and lumber, the occurrence of a log defect known as sweep limits traditional saw milling efficiency. Sweep is traditionally characterized as uniform curvature along the entire log length. The measure for sweep is the maximum deviation of the curved surface of a log. Hardwood sawmills traditionally straight saw their logs, allowing for taper only when the sawlines are parallel to the log central axis and/or straight surface. When straight sawing lumber, yield decreases as the level of sweep increases in a log (Ronnqvist et al. 2000). Furthermore, processing curved logs The authors are, respectively, Research Associate and Professor, Thomas M. Brooks Forest Prod. Center, Virginia Tech, Blacksburg, VA ([email protected], [email protected]); and Research Project Leader ([email protected]), USDA Forest Serv., Southern Research Sta., Blacksburg, VA. The authors wish to acknowledge the following contributors to this study: The USDA Forest Serv., Wood Education and Research Center (WERC) for funding this study; Amelia Lumber Company, Amelia, VA, for straight and curve sawing the study logs; and Scott Pallets Inc., Amelia, VA, for sawing pallet cants into pallet parts. This paper was received for publication in September 2005. Article No. 10113. ✳Forest Products Society Member. ©Forest Products Society 2006. Forest Prod. J. 56(10):80-85.