Shake (Wood Defect)
A shake is a separation between growth rings in wood, creating a gap or crack that follows the ring boundary. Unlike checks, which radiate outward from the pith, shakes run parallel to the growth rings. Shakes can occur in the standing tree from wind stress or frost, or they can develop during drying.
In-Depth Explanation
Shakes are a significant defect because they compromise the structural integrity of the wood along the weakest plane — between the growth rings. Ring shake occurs as a separation that follows the circular path of a single growth ring, while heart shake radiates outward from the pith along the rings. Wind shake, caused by repeated bending of the tree during storms, can affect large sections of the trunk. Frost shake occurs when water in the wood freezes and expands, splitting the rings apart. In grading, shakes are a more serious defect than surface checks because they penetrate deeper and are harder to detect without close inspection. Shakes are particularly problematic in timber framing and structural applications where the wood must resist shear forces parallel to the grain.
Usage Example
The timber grader rejected the Douglas fir beam after discovering ring shake that ran several feet along the length, which would compromise its shear strength.