Lumber strength grading using X-ray scanning

A multi-channel X-ray scanner is described that can be used to estimate lumber strength. The scanner measures lumber density at about 1-inch intervals along the full length and width ofeach board. The locations and approximate sizes of knots are identified by the presence of areas of high wood density. This detailed information is used to get an improved estimate of the strength of the lumber. Correlations of the destructively measured strength with the density-based estimated strength give r 2 values around 0.70. This compares well with r2 values of around 0.55 for traditional bending-based lumber strength grading machines. The density-based data also indicate that destructive measurements of bending and compression strengths are also subject to uncertainty because less than the entire volume of each test board is fully loaded. Thus, observed differences between estimated and destructively measured strengths are due to uncertainties in both strength quantities, not just in the estimated strengths. A lumber strength grading machine based on the principles described here has been commercialized, and several machines are now operating successfully in sawmills.