Sawmillers want to have predictable and homogeneous timber outcome from their industry. This paper analyses and discusses how well timber quality of boards from the same log, and in particular pairs of sister boards, correspond to each other, i.e. the limit for quality homogeneity. Observations from three different sawn timber outcome experiments were analysed. Varying quality traits were observed: appearance and machine strength grading, knot size and number, and board value. The results showed that 80% and 53% respectively, for two different samples, of the boards had different quality grade from their sister boards, and less homogeneity when more boards are sawn from the same log. The correlation between observations made in sister boards were modestly 0.42 for biggest green knot diameter, and almost absent for dry knots and other traits. Board value and machine strength are better correlated, 0.76 and 0.69, respectively. Relative pairwise difference for these parameters was found to follow the exponential distribution with mean 0.169 and 0.068, respectively. The results clearly indicate that there is no easy way achieving a consistent and pre-requested quality, at the same time avoiding an inherent portion of diverted quality boards.
Keywords: Main yield, machine grading, pair-wise quality agreement, quality distribution, visual grading
Authors
Gjerdrum P.
Section Wood Technology, Norwegian Forest and Landscape Institute, Aas, Norway
Login to download the PDF