Case joinery is used to assemble structures whose parts are deeper than they are wide. Examples are boxes, crates, drawers, chests, armoires and most enclosed furniture--that is to say, cases. It is distinguished from frame joinery in that the properties of wood call for different techniques when joining panels than when joining sticks..
Because the task is joining one long, narrow strip of end grain to another, a single slot or open mortise-and-tenon joint wouldn't do. But a series of slots and pins, spaced out along the length of the joint, would have enough cellective strength to hold the two ends, while also giving enough side-grain to side-grain surface area between the pins to produce a good glue bond.
These slots are milled directly into the end of each board, accurately spaced so that the two halves fit tightly together. The box joint shown here is very simple to cut, and though it can easily be pulled apart while dry, the large amount of side-grain surface makes it very strong when glued together.
Tapering the tenons on one of the mating pieces greatly enhances the mechanical strength of the joint, especially in the direction of the tapers. Shaped like tiny dove's tails, these little wings of wood act to wedge themselves into their slots. When it is accurately cut, this joint is nearly impossible to pull apart, even without glue.
Once it has been glued together, the many points of side-grain surface contact in the dovetail joint make it nearly indestructible.
Dowel joints are another option, and when used in case construction they are even stronger than in frame construction, probably because cases allow a greater number of dowels be used. A series of holes is drilled along the end of one board, and a matching series drilled into the face of the mating board. Wooden dowels are inserted into the holes, and the case is glued and clamped together. A doweled joint is a strong alternative to box or dovetail joints, especially when one piece (side or top) needs to overhang the other.
If the case is built of veneer, or plywood, these techniques usually will not work, since plywood has no single grain orientation; notches or holes cut into the edge of a piece of plywood will have no strength. Instead, plate or "biscuit" joinery (described in the About Building: Frame section) is especially effective in joining plywood panels, and represents one of the handful of worthwhile recent innovations in woodworking.