Impact of curve sawing on southern pine dimension lumber manufacturing. I. Lumber volume and value yields

This paper, which is based on an actual mill study conducted in Alabama in 2003, discusses the impact of curve sawing on southern pine dimension lumber manufacturing with emphasis on potential improvements in lumber volume and value yields associated with various input log distributions in terms of size and severity of sweep or crookedness. It was determined that with curve sawing, southern pine dimension mills like the study mill could improve their conversion efficiency or lumber recovery factor (LRF) to 7.5 board feet (BF) per cubic foot (ft3); i.e., about 8.7 percent more than what could be attained with conventional sawing, given the input log distributions and operating conditions at the time of the study. The corresponding improvement in lumber value yield was about $0.31/ft3 of log input or approximately 9.2 percent, based on December 2003 prices. Evidently, such yield improvements increase inversely with input log diameter and directly with sweep severity or crookedness. However, it was determined that the lumber yield of curve-sawn logs with a sweep severity of 2 inches or less was not significantly different statistically (with a 95 percent level of confidence) from that of conventionally sawn straight logs of the same size. In other words, significant advantages of curve sawing over conventional sawing accrue only when the input log sweep severity is over 2 inches. Regression analysis revealed that for every unit increase in the percentage of input logs with 3-inch sweep, 4-inch sweep, or a combination of the two, the LRF could increase by an average rate of about 0.0169, 0.0255, or 0.0183 BF/ft3 of log input, respectively; i.e., about 0.2265, 0.3410, or 0.2447 percent, respectively. The corresponding expected average increase in lumber value yield could be about $0.0081, $0.0113, or $0.0086 per ft3 of log input per unit percent increase in the volume of tree-length logs with 3-inch sweep, 4-inch sweep, or a combination of the two, respectively; i.e., about 0.2364,0.3312, or 0.2514 percent, respectively.