The purpose of this study is to investigate and record the principal problems associated with chipped surface quality at canter lines and evaluate degrade and value losses due to these problems.
Mill measurements were conducted in five member sawmills in British Columbia to evaluate the value losses and lumber degrades due to chipped surface defects. The test lumber was sampled from the planing mills to identify the chipping losses and main problems. The five types of chipped surface defects influencing lumber grade are: knot tear-out; failure to remove chipped spline channel; torn grain without knots; scalloping; and chipped thin end.
Average value losses for all mills were $11.4/MBF and $12.6/MBF in freezing and non-freezing conditions respectively. Removing the non-freezing data from one mill changed this to $11.4/MBF and $9.0/MBF respectively. Knot tear out caused 60% of lumber to be degraded. On average, over 55% of knots had tear-out. 42.3% of trim length was caused by failure to remove chipped spline channel.
The primary objective of the study is to measure the effect on cutting accuracy of side grinding swaged tooth bandsaws. The effect of side grinding on surface finish is included for comparison with previous work.
Swaged tooth bandsaws tend to leave quite a rough sawn surface. Cutting with large bites or uneven teeth aggravates this problem. Previous studies have shown that side grinding could improve surface finish but it was not shown to have any effect on cutting accuracy. However, sawmills and saw manufacturers have indicated that side grinding can improve cutting accuracy. Therefore, this contradiction needs to be resolved in order to quantify any benefits from side grinding.
The results indicate significant improvements in cutting accuracy and surface finish are possible. Side grinding 17-gauge and 16-gauge bandsaws respectively improved sawing accuracy up to 22% and 44%, reduced sawblade lateral displacement up to 36% and 68% and improved the sawn surface finish up to 24% and 11%.
Extremely careful bandsaw fitting and tooth alignment was necessary in the preparation of side ground saws. This cost-time-effectiveness has to be considered when adding side grinding to swaged saw preparation.
The potential usefulness of X-ray CT scanning as a means of grading aspen logs is investigated. This work is important because logs that can be selected for lumber or veneer production have much higher value than those for OSB chips. X-ray data from an industrial-style scanner using only three measurement directions is shown to give realistic and stable CT reconstructions of the interior features of aspen logs. Two CT reconstruction schemes are described, specifically tailored to the cylindrical geometry of logs. These have annular and sector-shaped geometries, and they effectively reduce the dimensionality of the measurement task from three dimensions to two. This is the key feature that enables credible CT reconstructions to be created from very modest amounts of data, less than 1% of those used by typical medical-style scanners. Although they give much less resolution of fine detail, the two CT reconstructions are still able to identify the main physical freatures that control log grading, such as knots, rot and heartwood/sapwood regions. The much smaller amount of data to be measured and processed enables an industrial-style scannner to operate in real time, which is an essential feature for practical use.