The Future of Quality Control for Wood & Wood Products

Abstract The basis for the derivation of settings for a grading machine is a comparison between destructive test data and data recorded by the machine. If the knots are part of the strength predicting model, the model covers the length effect in timber as it predicts the relatively lower strength for longer boards. This paper discusses the influence of the location of the maximum knot value on the performance of the machine. The maximum knot value between the inner load points is used for model derivation in approval bending tests. In practise, these machines do not only consider knots in the centre part of the board, but over the full length. Therefore, the indicating properties during deriving settings and during grading in practise differ from each other. The grading machine detects the largest knot value independent of the position along the length of the board; by means of this value the strength class is predicted. The influence of these differences is discussed. Finally, the effect on yield is shown