Quality of Squared Lumber without Pith Sawn from Large-Diameter Sugi (Cryptomeria japonica) Logs

Abstract

The quality of squared lumber without pith and sawing yields were investigated on large diameter sugi logs with a top end diameter of 30 cm or more, the supply of which is expected to increase imminently. A strong positive correlation was observed between the moisture content of heartwood and that of squared lumber, and between the Young's modulus of logs and that of lumber. It was found to be reasonable to sort logs based on the moisture content of the heartwood and Young's modulus of logs to improve the production efficiency for reliable lumber. The size of the rough sawn lumber had to be increased for finishing accuracy; taking into account shrinkage and warp after kiln-drying. Current rough sawn size is often determined uniformly with target size. However, since warp and shrinkage due to drying vary depending on sawing pattern, there is the possibility of high sawing yield by setting the adaptable rough sawn size depending on the sawing pattern. There is potential to produce squared lumber with the required quality and with a high sawing yield by sorting logs suitably and setting the adaptable rough sawn size depending on the sawing pattern.