How to create basic mortise and tenon joints

A simple mortise and tenon joint consists of a protrusion (the tenon {male}) that is inserted into a hole of corresponding size (the mortise {female}), which has been cut or drilled in the mating piece of wood. The secret to a well formed joint is the snugness of the fit. The tenon must be a neat fit into the mortise for the joint to be strong.  A rule of thumb says that the tenon width should be one third the width of the timber into which it is to be fitted.

In building structures, old world mortise and tenon joinery is called timberframing or "post and beam" construction that is very popular today.  There are different types of mortise and tenon cuts, but they serve the same purpose Some designs are stronger than others, and different cuts are used to conceal joint construction.

Basic tenon

A straightforward mortise and tenon employs a tenon cut into a rail (A) and a mortise cut all the way through the corresponding rail (B).  This type of joint can be strengthened by fitting dowels or wedges in the end of the tenon (C).  To strengthen with wedges, the end of the tenon will be expanded to tighten the two pieces snugly.

Blind tenon

A blind or "stub" tenon (A) does not extend through the mortised member (B), so that the tenon is hidden. This joint can be strengthened using dowels (C) or wedges.

If you decide to strengthen your joint with dowels, assemble your joint and make certain the shoulders of the tenon fit snugly against the mortised piece before you drill the holes for the locking dowels.

If using wedges, you will need to cut the mortise (A) making the bottom of the hole slightly larger than the top because the wedges will expand the tenon (B).  You will make two tapered saw cuts in the tenon to accept the wedges as illustrated at right.

Note: This is a permanent joint with or without glue as the wedged action creates an extremely tight fit.

Double tenon

This is typically used when joining wide boards. Multiple tenons create larger surface areas providing more strength than a single tenon joint. Multiple tenons can be cut, but make certain that the width and gaps between the tenons are the same. You can increase the joint's strength by utilizing dowels or wedges as explained above.

Loose-tenon joint

Where the tenon is not attached to a rail but floats inside two opposing mortised holes.  This is a variation of a "biscuit joint" where a biscuit (wooden shim) fits into slots when joining two flush boards together. 

In some sophisticated timberframe applications, more exotic and specific mortise and tenon joints are utilized. However, most are just variations on these basic joints.  "Haunched" tenons and "twin" tenons are used in door construction and other specialized projects.

See how to cut a round tenon