Young-Growth Douglas-Fir: Is It Predisposed to Warp?

Approximately one hundred 8-foot, rough, green studs were randomly selected from 2-by 4-inch young-growth Douglas-fir (Pseudotsuga taxifolia Britt.) lumber at each of 20 western Oregon sawmills. One sample of 99 sticks was selected from green, surfaced material. The green studs were inspected for straightness and rough-graded during the piling operation. From the wafers cut from the end of each stud, ring count and specific gravity were determined. The wafers were also used to classify this material with respect to the position in the cross sections of the logs from which they came. During seasoning the piles of studs were broken down and the moisture content and magnitude of warping were determined. The bulk of each sample of rough, dried studs received no further observation, but 10 to 15 pieces from each mill were brought successively to 16.4, 11.5, and 6.5 percent moisture contents in a dry kiln for the study of the relationship of warping to moisture loss under controlled conditions. The degrade potential from predisposition to warp of virtually unrestrained studs is relatively small. Seasoning restrained studs according to the normal practice should result in much less warping than that encountered this study. Young-growth Douglas-fir lumber products consisting of heart-center material have a predilection to twist. It is thought that in numerous cases the twist would depreciate the grade, appearance, usefulness, and marketability of these products. Seasoning under restraint would correct or reduce much of the twist, but it is also likely to cause stress relief of twistable material in the form of splits and seasoning checks. Therefore, potential twist of young-growth Douglas-fir lumber products should be examined critically with a veiw toward developing practical corrective measures which can be applied by the ever-expanding young- growth fir log-conversion industries.

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