Impact of log sweep on warp in Douglas-fir structural lumber

More than 7 billion board feet of Douglas-fir lumber were used in the United States for new construction or renovation of existing buildings during 1994. Past research has shown that almost every piece of Douglas-fir lumber has measurable warp. As a result, a high proportion of pieces may be underutilized or discarded at the job site. Recent research indicates that warp within structural grades of softwood lumber may not be attributable to growth characteristics such as compression wood, grain orientation, and knot size. This study investigated the impact of sweep in logs on warp in Douglas-fir lumber. Results showed that the magnitude of crook and twist in lumber produced from straight logs and logs with sweep was significantly different. Surprisingly, lumber sawn from logs with sweep had less twist than lumber sawn from straight logs and showed no significant difference in bow. Lumber sawn from logs with sweep in two planes had more crook than lumber sawn from straight logs, but the difference was slight. Although logs with sweep yield less lumber than straight logs, curve sawing in high-tech sawmills may diminish this difference. These findings indicate that Douglas-fir logs with sweep could produce straighter lumber than straight logs.

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