Joining wood 2: frame joints

Strong, permanent and neat-looking joints in timber are achieved using one of the many types of frame joint - so called because right-angled jointed frames are common in furniture, boxes and many other types of assembly.

Simple frame joints

The simplest frame joint is a butt joint. It is easy to make, but weak. You can strengthen a butt joint by fixing a reinforcing plate over the joint.

A butt joint can also be strengthened by gluing dowel into both parts - making a dowelled joint. Dowelled joints are good for joining man-made boards (modified timbers) which might split easily if screwed or nailed.

Corner halving joints are stronger than butt joints, as there is more contact for gluing, and the shoulder [shoulder: flat surface at right angles to the projecting part in a joint ] gives extra mechanical strength. Through housing joints are used for shelves.

More complex frame joints

Mortise and tenon joints, though more difficult to cut, are very strong, because of the shoulders. If your joint is close to the end of a piece of wood, use a haunched [haunched: with a reduced projecting part or tenon ] mortise and tenon joint.

Dovetail joints are very strong and look good - but are complex and difficult to cut. They are often used in high-quality furniture.

Comb or box joints are easier to make - especially by machine - and offer good contact for gluing. They are often used in wooden boxes.

Edging

When pieces of wood are joined along their edges, the joint may need to be supported in some way to reinforce or make it look neater. Sometimes a strip of wood is glued or pinned over the joint, called lipping. Sometimes - eg with floorboards or timber cladding - a thin strip projecting from one edge slots into a slot in the other edge. This is called a tongue and groove joint.