Shakes

Also called: ring shake, star shake, heart shake, cup shake

A shake is a crack that opens up inside a piece of timber along the grain, usually following the curve of the growth rings, most often as the wood dries and shrinks.

Why shakes form

Drying an unsplit, whole log brings on shakes and wind cracking, splits that open from the outside inward, as the wood shrinks unevenly across its section. Converting a log into planks or quarters before drying can avoid the problem, because once it is cut up the position of the growth rings governs how each piece shrinks, rather than the whole trunk shrinking against itself. Thunder shakes are a different kind of defect: irregular breaks running across the grain rather than along it, found mostly in Honduras mahogany.

Which timbers are prone to shaking

Some timbers are more troubled by shakes than others. Holly, a hard, horny, difficult-to-saw evergreen native to the Mediterranean, is so liable to shaking that planks cannot reliably be cut from it at all. In bent veneer work, where a thin sheet of decorative wood is glued over a curved backing, a backing that runs cross-grain to the veneer shrinks unevenly against it, and that mismatch can start shakes or bulging in the veneer itself.

Choosing timber free of shakes

Because shakes weaken and disfigure wood, selecting stock free of them matters across the trade. A joiner's chosen stock, called stuff in old usage, must be well seasoned and dried and carry none of several flaws: sap, dead knots, meaning knots from a branch that had already died before the tree was felled, cracks, or shakes. The same standard applies to backing wood, or groundwork, chosen for veneer work, which must be well seasoned, free of knots and shakes, and free of turpentine content; to panel stock for everyday work, expected to be sound yellow pine with no knots or shakes; and to the thin, dry pine used for templates, patterns used to mark out curved or wreathed work, which likewise needs to be free of knots and shakes. Even where shakes cannot be avoided altogether, as with pallet and container timber, minimum grading limits for shakes are set according to how the timber will be used. Aircraft timber is judged to a similarly strict standard: a typical specification calls for clean, straight grain and excludes only those shakes judged harmful, along with knots, resin pockets, pockets of trapped resin, and dote, a form of early decay.