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MEMBER Forest Operations; Pulp, Paper and Bioproducts;

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Summary

Douglas-fir (DF) is an important high value commercial wood species that presents some challenges for wood machining owing to its high and variable average density and therefore cannot be processed at the same feed speeds as softer species such as spruce and pine. New DF saws designed in this project for operation at BC Interior sawmill were optimized for Douglas-fir by reducing the number of teeth to maximize tooth strength and gullet area, increasing the saw plate thickness for improved lateral stiffness while maintaining the existing saw kerf by utilizing a thin rim. In laboratory testing, the new DF saws exhibited a 50% reduction in mean wedging at current mill speeds and a 65% reduction in mean wedging at a higher speed. There was a 15% reduction in top edge standard deviation at mill speeds with the DF saws and this increased to a 21% reduction at the higher speed tested. In addition, owing to the reduced number of teeth in the DF saws compared to the mill saws, cutting power was reduced by 3-5% depending on feedspeed. Mill testing of the new DF saws cutting spruce and pine showed a similar improvement in sawing accuracy as seen in the laboratory testing. Mean wedging was found to be 46% lower with the new DF specific saws, while top edge deviation was reduced by 40%. Implementation of the new DF saws for this specific mill application on a permanent basis would require minimal changes to the guide set-up and side grinder settings. Overall saw costs would be a higher as the thicker saw plate with a ground thin rim is more costly to produce however, this additional cost could easily be recovered by extended saw run-times and reduced unscheduled saw changes. Also, with the higher overall sawing accuracy, feed speeds on Douglas-fir could be maintained at levels similar to those on spruce and pine, improving overall production.

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