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Japan’s postwar policies with respect to forestry management have led to the aging of planted forests and a shift toward large-diameter logs that has created a challenge for how to use such logs in...

When a squared lumber such as a beam and/or a bearer is produced from a log, they often show warps. Warp of the sawn lumber is practically not serious when the pith is located at the center of the cross-section, as in the lumber-with-pith, but causes serious problems in the lumber-without-pith. In the present study, a mechanical model was introduced to explain lumber warping based on beam theory, and a numerical simulation using the introduced model examined how the magnitude and type of the residual stress distribution would affect the warps of the lumbers sawn from the four-sided cants with various sizes and shapes in their cross-sections, and how the different sawing patterns would affect the production efficiency of the straight lumber, which is manufactured from the four-sided cant by quartering and subsequent correction sawing. As a result, the following suggestions were obtained. The warp of the sawn lumber is affected by the type and the magnitude of the inherent strain distribution in the log and furthermore by the cross-sectional shape and/or size of the four-sided cant. Production efficiency of the straight lumbers differs depending on the sawing patterns. In the present study, two types of sawing patterns (a) and (b) were assumed. The sawing pattern (a) gave better production efficiency than the sawing pattern (b) in the sense that straight lumbers are produced with higher volumes as well as with less variation in dimension of the cross-section.

A tree generates a complicated stress distribution inside the stem during its formation, which is called 'residual growth stress (RGS)'. The RGS often induces warp in a sawn lumber such as bow, crook, and other deformation, which causes severe losses of materials and benefits in the sawmill industry. Generally, warp becomes more serious in the lumber 'without pith' than in the lumber 'with pith'. In Japan, 50% of conifer plantations are ready to produce large-diameter logs of which diameter is more than 30 cm. The use of those logs inevitably leads to the production of the lumber 'without the pith', so we are concerned about the problems due to lumber warp in future sawmill industry using largediameter logs. Based on those practical background, this study presents a computational procedure to predict warp of the squared lumber, such as a beam, a bearer, and so forth, when those lumbers are sawn from the log and/or the thick plank. Using the derived procedure, 2-D patterns of the RGSs in the sawn lumbers and their changes during sawing processes are simulated. Simulated results will be experimentally verified by measuring the warp of the sawn lumber, as well as by measuring the RGS distributions in a log.

The purposes of this study were to accumulate fundamental data on wood properties within large Sugi logs and to take applicable variations in wood properties into consideration for sorting logs and sawing patterns. The characteristics of basic density, moisture content, growth ring width, and microfibril angle (MFA) were measured and the relationship with log and lumber quality was examined. It was considered reasonable to estimate the lumber moisture content based on the moisture content of heartwood rather than that of whole logs, especially when producing large-sized lumber. The MFA reached a constant value before the 15th ring, and within a distance of 10 cm or less from the pith. Since the E fr of lumber correlated with that of the log affected by MFA, it would be possible to produce lumber with a higher E fr from the outer position of the log, based on selecting a log above the E fr . Since the MFA would also affect the lumber warp, a sawing pattern avoiding the area around the pith or enlarging the rough sawn size when a large warp was expected could be effective in improving the lumber quality. To improve the lumber quality, not only one but also multiple wood properties must be applied to the sawing pattern.

A survey was conducted at nine sawmills in Japan to evaluate and compare the sawing of sugi (Cryptomeria japonica D. Don) logs of 30 cm and more in diameter. The purpose was fourfold: (1) to document sawing patterns appropriate to the large-diameter logs; (2) to examine the composition of wood components (structural, nonstructural, and fixtures) produced from those patterns; (3) to investigate log and product prices; and (4) to ascertain distances to the log supplier and product markets. Impetus for the study arose from a forecasted shift in the diameter distribution of plantation trees in Japan; from small and medium-sized logs to large-diameter logs. With an overabundance of large-diameter domestic logs forecasted within the next decade, the need to understand how to best utilize and effectively process the large-diameter resource is of utmost importance.

Appropriate log sorting and optimal sawing patterns are indispensable for efficient lumber production. It is also important to clarify the relationship between the quality of logs and that of sawn lumber to determine effective sorting and optimal sawing patterns. Although some information on lumber quality has been obtained for medium sugi (Cryptomeria japonica D. Don) logs, little is known about lumber quality in large logs, the supply of which is expected to increase imminently. We investigated the influence of the sawing patterns of large sugi logs on lumber quality. Large sugi logs (30 to 40 cm in diameter) were converted into sawn lumber using different sawing patterns. Sawing yields varied for each sawing pattern. Sorting logs by Young's modulus (Efr) would be useful for the efficient production of reliable sawn lumber from large logs, especially when the dimensions of the main products are large. Conversely, it is important to note the variation of Efr in logs when several main products we...

スギ（Cryptomeria japonica D. Don）中丸太一般材の挽き材試験を行い，丸太の外観的形質と鋸断面上の節の有無の関係を検討した。丸太表面を4つの丸太材面に分割した場合，末口における樹心からの距離が大きい丸太材面ほど無節鋸断面出現率が高くなる傾向が見られた。1番玉以外の丸太では，元口における樹心からの距離が大きい丸太材面ほど無節鋸断面出現率が高くなる傾向が見られたが，1番玉ではそうした傾向は見られなかった。最大曲がりの位置から丸太材面までの距離と無節鋸断面出現率の間には比例関係は見られなかった。末口における樹心からの距離が最も大きい丸太材面を挽き材を開始する第1丸太材面とした場合，最大曲がりの位置を鉛直方向に配置する一般的な製材方法と比較して，第1丸太材面における無節鋸断面出現率が10％近く向上することが示された。これにより，丸太の外観的形質の中で末口における樹心位置は，鋸断面に節の出現しにくい丸太材面を推測する上で最も有効な指標であると考えられた。