Comparison of log segregation methods for structural lumber yield improvement

This study, based on 84 commercial logs of radiata pine grown in New Zealan d, compares branch size, Pilodyn penetration, and longitudinal stress-wave velocity as methods for structural log selection. Four case studies were pe rformed, each differing in the criterion used to define an acceptable struc tural log, i.e., different yields of machine-stress-graded F5 and better (A S/NZS 4063: 1992) or MGP8 and better (provisional grade assigned under Aust ralian Machine Graded Pine system). It is clearly shown that for plantation -grown logs, where branches can be large (often exceeding 2 in. diameter), the best results are obtained by combining branch size and sonic grading. T his method provided up to 14 percent fewer misclassified logs compared to u sing branch size or stress-wave velocity alone, and up to 12 percent improv ement in structural lumber grade recovery compared to processing unsorted l ogs. The best results using the Pilodyn were obtained when logs were sorted for structural lumber production from the outerwood only, i.e., where the juvenile core, containing approximately the first 10 growth rings, was inte ntionally cut into alternative products.