Definitions

mortise-and-tenon joint

Mortise and tenon

Simple and strong, the mortise and tenon joint has been used for millennia by woodworkers around the world to join pieces of wood, usually when the pieces are at an angle close to 90°. Although there are many variations on the theme, the basic idea is that the end of one of the members is inserted into a hole cut in the other member. The end of the first member is called the tenon, and it is usually narrowed with respect to the rest of the piece. The hole in the second member is called the mortise. The joint may be glued, pinned, or wedged to lock it in place.

Types of mortise and tenon

A mortise is a cavity cut into a timber to receive a tenon. There are several kinds of mortises:

  • Open mortise - a mortise that has only three sides. (See Bridle joint).
  • Stub mortise - a shallow mortise, depth depends on the size of the timber; also a mortise that does not go through the workpiece (as opposed to a "through mortise").
  • Through mortise - a mortise that passes entirely through a piece.
  • Wedged half-dovetail - a mortise where the back is wider, or taller, than the front, or opening. The space for the wedge initially allows room for the tenon to be inserted, the presence of the wedge, after the tenon has been engaged, prevents its withdrawal. Sometimes called a "suicide" joint - since it is strictly a "one way trip".
  • Through wedged half-dovetail - a wedged half-dovetail mortise that passes entirely through the piece.

A tenon is a projection on the end of a timber for insertion into a mortise. Usually the tenon is taller than it is wide.

There are several kinds of tenons:

  • Stub tenon - a short tenon; depth depends on the size of the timber; also a tenon that is shorter than the width of the mortised piece so the tenon does not show (as opposed to a "through tenon").
  • Tusk tenon - a kind of mortise and tenon joint that uses a wedge-shaped key to hold the joint together
  • Through tenon - a tenon that passes entirely through the piece of wood it is inserted into, being clearly visible on the back side
  • Teasel tenon - a term used for the tenon on top of a jowled or gunstock post, which is typically received by the mortise in the underside of a tie beam. A common element of the English tying joint
  • Top tenon - the tenon that occurs on top of a post.
  • Feather tenon - a round-shouldered machined fillet or feather which is glued into a machine (router) made slot or mortise on each side of the joint.

Generally the size of the mortise and tenon is related to the thickness of the timbers. It is considered good practice to proportion the tenon as 1/3rd the thickness of the rail, or as close to this as is practical. The haunch, the cut away part of a sash corner joint that prevents the tenon coming loose, is one third the length of the tenon and one sixth of the width of the tenon in its depth.

Gallery

History

This is an ancient joint and has been found joining the wooden planks of the "Khufu ship", a 43.6 m long vessel sealed into a pit in the Giza pyramid complex of the Fourth Dynasty around 2,500 BC.

It has also been found in archeological sites in the Middle East, Europe and Asia. In traditional Chinese architecture, wood components such as beams, brackets, roof frames and struts were made to interlock with perfect fit, without using fasteners or glues, enabling the wood to expand and contract according to humidity. Archaeological evidence from Chinese sites show that by the end of the Neolithic, mortise and tenon joinery was employed in Chinese construction.

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