スギ大径材からの心去り平角の製材: 作業特性と製材コスト

摘要

送材車付き帯鋸盤を用いてスギ大径材から心去り平角を生産する製材作業を対象とした作業時間分析の結果に基づき，スギ大径材の効率的製材方法の構築に向けた諸検討を行った。スギ大径材の製材においては芯出しに要する作業時間が非常に大きくなっていた。また，挽き幅が大きい場合には挽き幅が小さい場合と比較して送り速度を20%以上遅くして製材が行われていた。これらのことから，スギ大径材製材の効率化を図るための方策として，プリセット装置の導入や木口面における樹心位置の自動認識技術の開発などによる芯出しの作業時間の短縮や，挽き幅が大きい場合の高速製材を可能にする鋸の開発などの大径材に対応した製材技術開発を行うことが必要と考えられた。一方，モデル工場における心去り平角の製材コストは仕上げ寸法換算で43,600円/m~3と試算され，スギ心去り平角の価格競争力を高めるためには，製材生産の効率化や製材歩止りの向上による製材コスト低減を図る必要があることが示された。%Accompanying with maturity of planted sugi (Cryptomeria japonica D.Don) forests, the supply of large-diameter log is increasing. Most of these forests has not been managed to produce high-age and high-quality logs, so that many large-diameter sugi logs supplied henceforth are classified as medium-quality. Conventionally, large-diameter sugi logs of nigh-quality have been converted into high-quality sawn lumber, but those of medium-quality are unable to convert into such sawn lumber. Therefore, the development of effective sawing system of medium-quality large-diameter sugi logs is requested. In this study, we conducted a time study on producing flat square lumber without pith from large-diameter sugi logs using a band mill with an auto-feed carriage. In order to obtain fundamental data to establish an effective sawing system for large-diameter sugi logs, the characteristics of sawing work and the work efficiency are clarified and the lumbering cost is calculated in this report. The sawyer spent considerable time for sawing work "Centering" and longer time for sawing work "Sawing with an increase in sawing width. It was thought that work efficiency would be improved by shortening the working time taken for these two sawing works. Lumbering cost of the flat square lumber without pith was calculated as 43,600 JPY/m~3 by the condition not including the drying cost. It was thought that the reduction of lumbering cost by improving the work efficiency was necessary to compete with flat square lumber of imported species and glue-lam.