Sawlog scaling accuracy before and after barking, and the importance for sawn timber recovery – A case study

Abstract

Scaling accuracy is of utmost importance to obtain optimal sawn timber yield in primary breakdown. In this article, sawmill observations, review of available publications and supplementary tests are combined to analyse the accuracy of conifer roundwood scaling. The influence of important log parameters are considered for various scaling technology: one- and two-directional (1Dir and 2Dir) shadow scanners and three-dimensional (3Dim) reflected beam scanners. Standard error for each of the terms, ovality, bark and scanner technology, is discussed. The overall accuracy for diameter under bark can be calculated by adding the variances for each independent term. Results show that for unbarked logs, 2Dir shadow scanner remains the most accurate technology. For barked logs, 3Dim reflected laser beam scanner combines the highest accuracy and the ability of providing a wide range of important log parameters. For a case study sawmill, annual roundwood consumption are reduced by 2.0% by transferring from scaling unbarked logs in a two-dimensional shadow scanner to 3Dim scanning of barked logs, while keeping the volume yield of the sawn timber.