Twist (Lumber Defect)
Twist is a warp defect where the four corners of a board do not lie in the same plane, creating a propeller-like distortion. It is measured by holding three corners flat and measuring how far the fourth corner rises. Twist is often caused by spiral grain in the tree or improper drying.
In-Depth Explanation
Twist is generally considered the most difficult warp defect to correct because it involves a complex three-dimensional distortion. Unlike bow or crook, which can sometimes be jointed or planed out, twist requires removing material from diagonal corners, which dramatically reduces the board's thickness. Spiral grain — where the wood fibers wind around the trunk rather than running straight — is the primary natural cause. Some species, like elm and certain tropical hardwoods, are inherently prone to spiral grain and therefore to twist. During kiln or air drying, proper stacking with closely spaced stickers and adequate top weight helps restrain twist. In grading, twist is evaluated per foot of board length, and severe twist can downgrade an otherwise clear board significantly.
Usage Example
The woodworker used winding sticks to check for twist in the walnut board before milling it for a tabletop, finding a noticeable wind across the 6-foot length.