Mortise and tenon

A mortise (occasionally mortice) and tenon joint connects two pieces of wood or of material. Woodworkers around the world have used it for thousands of years to join pieces of wood, mainly when the adjoining pieces connect at right angles.

Diagram of a mortise (on left) and tenon joint
Tusked through tenons used on a French granary.
1) Through tenon and 2) mortise as a shouldered joint

Mortise and tenon joints are strong and stable joints that can be used in many projects. The mortise and tenon joint is considered to be one of the strongest joints next to the common dovetail joint. They furnish a strong outcome and connect by either gluing or locking into place. The mortise and tenon joint also gives an attractive lookout. One drawback to this joint is the difficulty in making it due to the precise and tight cutting required. In its most basic form, a mortise and tenon joint is both simple and strong. There are many variations of this type of joint, but the basic mortise and tenon has two components:

  1. the mortise hole, and
  2. the tenon tongue.

The tenon, formed on the end of a member generally referred to as a rail, fits into a square or rectangular hole cut into the other, corresponding member. The tenon is cut to fit the mortise hole exactly. It usually has shoulders that seat when the joint fully enters the mortise hole. The joint may be glued, pinned, or wedged to lock it in place.

This joint is also used with other materials. For example, it is traditionally used by both stonemasons and blacksmiths.

Etymology

The noun mortise, "a hole or groove in which something is fitted to form a joint," comes from c. 1400 from Old French mortaise (13th c.), possibly from Arabic murtazz, "fastened," past participle of razza, "cut a mortise in."[1]

The word tenon, a noun in English since the late 14th century, developed its sense of "a projection inserted to make a joint" from the Old French tenir "to hold."[2]

History and ancient examples
Experimental archaeology; cutting a mortise with a cannonbone chisel

This is an ancient joint dating back 7,000 years. The first examples, tusked joints, were found in a well near Leipzig - the world's oldest intact wooden architecture.[3] It has also been found joining the wooden planks of the "Khufu ship",[4] a 43.6 m long vessel sealed into a pit in the Giza pyramid complex of the Fourth Dynasty around 2500 BC. The oldest known use dates from the Early Neolithic Linear Pottery culture, where it was used in the construction of the wooden lining of water wells.[5]

It has also been found in ancient furniture from archaeological sites in the Middle East, Europe and Asia. Many instances are found, for example, in ruins of houses in the Silk Road kingdom of Cadota, dating from the first to the fourth century BC.[6] 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.[7] Archaeological evidence from Chinese sites shows that, by the end of the Neolithic, mortise-and-tenon joinery was employed in Chinese construction.[8]

The thirty sarsen stones of Stonehenge were dressed and fashioned with mortise-and-tenon joints before they were erected between 2600 and 2400 BC.[9]


Types

Mortises
A through mortise is used in this wooden hinge
Brick mold from ancient Egypt held together with mortise joints

A mortise is a cavity cut into a timber to receive a tenon. There are several kinds of mortise:[10]

Open mortise
a mortise that has only three sides. (See bridle joint).
Stub mortise
a shallow mortise, the depth of which 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 in which the back is wider, or taller, than the front, or opening. The space for the wedge initially leaves room to insert the tenon. The wedge, after the tenon is engaged, prevents its withdrawal.
Through-wedged half-dovetail
a wedged half-dovetail mortise that passes entirely through the piece.

Tenons

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 tenon:

Stub tenon
short, the depth of which 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").
Through tenon
a tenon that passes entirely through the piece of wood it is inserted into, being clearly visible on the back side.
Loose tenon
a tenon that is a separate part of the joint, as opposed to a fixed tenon that is an integral part of one of the pieces to be joined.
Biscuit tenon
a thin oval piece of wood, shaped like a biscuit[11]
Pegged (or pinned) tenon
the joint is strengthened by driving a peg or dowel pin (treenail) through one or more holes drilled through mortise side wall and tenon;[12] this is common in timber framing joints
Two tusked through tenons are used to hold the trestles of this trestle table together
Tusk tenon
a kind of mortise and tenon joint that uses a wedge-shaped key to hold the joint together.
Teasel (or teazle) 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.
Hammer-headed tenon
a method of forming a tenon joint when the shoulders cannot be tightened with a clamp.
Half shoulder tenon
An asymmetric tenon with a shoulder on one side only. A common use is in framed, ledged, and braced doors.

Further details about the completed joint

Generally, the size of the mortise and tenon is related to the thickness of the timbers. It is good practice to proportion the tenon as one third 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. The remaining two-thirds of the rail, the tenon shoulders, help to counteract lateral forces that might tweak the tenon from the mortise, contributing to its strength. These also serve to hide imperfections in the opening of the mortise.

  • A traditional through, wedged, mortise and tenon joint
  • A stub tenon corner joint
  • A haunched stub tenon corner joint
  • A foxtail wedged tenon joint
  • A pinned corner tenon joint
  • A modern feather tenon joint (primarily called a loose tenon)

See also

References
  1. Harper, Douglas. "mortise". Online Etymology Dictionary. Retrieved 2019-02-19.
  2. Harper, Douglas. "tenon". Online Etymology Dictionary. Retrieved 2019-02-19.
  3. "The Neolithic Toolkit". Archaeology.org. Retrieved 7 January 2015.
  4. Ward, Cheryl. "World's Oldest Planked Boats," in Archaeology (Volume 54, Number 3, May/June 2001). Archaeological Institute of America.
  5. Early Neolithic Water Wells Reveal the World's Oldest Wood Architecture Tegel W, Elburg R, Hakelberg D, Stäuble H, Büntgen U (2012) Early Neolithic Water Wells Reveal the World's Oldest Wood Architecture. PLoS ONE 7(12): e51374. doi:10.1371/journal.pone.0051374
  6. Roberts, Rachel (2012). "House-building in Ancient Niya". IDP News. 39. Retrieved 26 October 2012.
  7. Steinhardt, Nancy W. (2002). Chinese Architecture (English ed.). Yale University Press. pp. 1. ISBN 978-0-300-09559-3.
  8. Xujie, Liu (2002). Chinese Architecture - The Origins of Chinese Architecture (English ed.). Yale University Press. pp. 11. ISBN 978-0-300-09559-3.
  9. "Building Stonehenge". English Heritage. Retrieved 2020-10-27.
  10. Dekker, Michael. "Mortise-and-Tenon". Woodwork Details. Retrieved 2015-02-18.
  11. "Our Reviews, Your Decision". Man Of Family. Retrieved 2017-07-28.
  12. Teague, Matthew (May 2007). "The Pegged Joint, Exposed". Fine Woodworking. Taunton Press. Retrieved 2015-02-18.
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