Warping of Wood

the change in the shape of lumber and semifinished and finished products upon drying or moistening. The types of warping are shown in Figure 1.

Figure 1. Types of warping of wood: (a), (b), and (c) transverse; (d) and (e) longitudinal; (f) twist

The main reason for transverse warping is the difference in degree of radial and tangential drying or swelling. Longitudinal warping is caused by the difference in drying along the fibers of individual areas of a board (for example, when there are knots or other defects in the wood). Twist warping occurs when there is a defect in the fibers (tangential incline). Sometimes wood will warp temporarily during uneven drying or wetting. Warping can also occur during work on lumber or semifinished products in which there is significant residual tension after drying in a chamber.