Wood on the Move

 

Wood Shrinkage I

What shrinkage does to wood Woodworkers call the change in shape of a piece of wood warp. And it takes several common forms, all of which distort the wood.A board has cup when it is no longer flat from edge to edge. Cup always occurs in the opposite direction of a flatsawn board's annual growth rings.

Bow, as its name implies, describes the lengthwise curvature of a board -- end to end along its face.

When a board has crook, all the curvature runs from end to end along its edge.

Twist means that all of a board's corners won't lie equally flat.

Although not a distortion like any form of warp, checking refers to small splits along the grain. You'll most often see checks in the ends of boards, but they can occur on surfaces, too. That's because as wood dries, it loses moisture along its length about 10 times faster than across its width. So end grain dries more rapidly and shrinks faster, causing these small ruptures.