According to the Wood Handbook, Wood as an Engineering Material, a joint is the junction of two pieces of wood or veneer. Researchers at the Forest Products Laboratory (FPL) take this a step further, and identify at least 10 different types of joints.
- Adhesive Joint — The location at which two adherends are held together with a layer of adhesive.
- Assembly Joint — Joints between variously shaped parts or sub assemblies such as in wood furniture (as opposed to joints in plywood and laminates that are all quite similar).
- Butt Joint — And end joint formed by abutting the squared ends of two pieces.
- Edge Joint — A joint made by bonding two pieces of wood together edge to edge, commonly by gluing. The joints may be made by gluing two squared edges as in a plain edge joint or by using machined joints of various kinds, such as tongued-and-grooved joints.
- End Joint — A joint made by bonding two pieces of wood together end to end, commonly by finger or scarf joint.
- Finger Joint — An end joint made up of several meshing wedges or fingers of wood bonded together with an adhesive. Fingers are sloped and may be cut parallel to either the wide or narrow face of the piece.
- Lap Joint — A joint made by placing one member partly over another and bonding the overlapped portions.
- Scarf Joint — An end joint formed by joining with adhesive the ends of two pieces that have been tapered or beveled to for sloping plane surfaces, usually to a featheredge, and with the same slope of the plane in respect to the length in both pieces. In some cases, a step or hook may be machined into the scarf to facilitate alignment of the two ends, in which case the plane is discontinuous and the joint is known as a stepped or hooked scarf joint.
- Starved Joint — A glue joint that is poorly bonded because an insufficient quantity of adhesive remained in the joint.
- Sunken Joint — Depression in wood surface at a joint (usually an edge joint) caused by surfacing material too soon after bonding. Inadequate time was allowed for moisture added with the adhesive to diffuse away from the joint.
For more information about joints, bonding wood, and adhesives, please see the Wood Handbook, Wood as an Engineering Material.