Impact of curve sawing on kiln-drying and MSR grading

This research evaluated how Curve sawing affects drying degrade and machine stress rating (MSR) of lumber. The study was based on comparative mill tests involving a sample of 204 black spruce 16-foot logs. From this sample, a first lot was processed by conventional straight sawing, the second lot by optimized curve sawing (arc sawing), and the third according to the natural curve sawing. The results demonstrated that, as expected, the two curve sawing techniques allowed for improved volume recovery and a higher proportion of 16-foot lumber than straight line sawing. Yield was increased by 2.4 percent with optimized curve sawing, and 2.2 percent with natural curve sawing. From the drying process, the sawing technique was found to have little effect on warp. Curve sawing was observed to cause a slight increase in face warp (bow), but this did not affect grade recovery under National Lumber Grade Authority (NLGA) rules. For the three sawing techniques under study, overall drying degrade was mostly due to twist. Drying degrade was slightly lower in lumber produced by natural curve sawing. Curve sawing led to enhanced mechanical properties. The average MOE for curve-sawn lumber was approximately 4 percent higher than for straight sawing, and the premium achieved through improved MSR yield was about $4 per thousand board feet (MBF) to $5/MBF. Finally, an economic analysis comparing net finished product values from 1 m(3) of logs showed that optimized curve sawing could increase value recovery by 3.5 percent over straight sawing, and by 5.7 percent over natural curve sawing.