Groove Joint

A groove is a channel cut into a board running with the grain, cut into the middle of a face rather than along an edge -- the distinction that separates it from a dado (cut across the grain) and a rabbet (cut into an edge, open on one side). A groove joint captures a panel -- a cabinet back, a drawer bottom, a frame-and-panel door's floating center panel -- inside two or more grooved frame pieces.

Sizing for movement

Because a groove joint often has to hold a solid-wood panel that expands and contracts across its width with the seasons (see the Wood Movement Estimator), the panel is deliberately cut slightly narrower than the frame opening and left unglued in the groove -- floating -- so it can move without splitting the frame or blowing out the joint. A plywood panel, which doesn't move appreciably, can be sized to fit snugly and even glued in without that concern.