This shrinking and swelling may result in warping, checking, splitting, or performance problems that detract from its usefulness. It is therefore important that these phenomena be understood and considered when they may affect a product in which wood is used. Wood is an anisotropic material with respect to shrinkage characteristics. The combined effects of radial and tangential shrinkage can distort the shape of wood pieces because of the difference in shrinkage and the curvature of annual rings. The major types of distortion due to these effects are illustrated in Figure 3-2.
Tangential shrinkage is about twice as great as radial.
These shrinkage values, expressed as a percentage of the green dimension are summarized in Table 3-5. Shrinkage values collected from the world literature for selected imported species are summarized in Table 3-6. The shrinkage of wood is affected by a number of variables. In general, greater shrinkage is associated with greater density. The size and shape of a piece of wood may also affect shrinkage, as may the temperature and rate of drying for some species.