A mortise and tenon joint is a classic timber connection where a protruding part (the tenon) is inserted into a rectangular hole (the mortise) in another workpiece. It is one of the oldest and strongest timber joints, used for centuries in furniture, window frames, doors, and structural frameworks.
How does it work?
The principle is simple:
- On one workpiece, a tenon (tap) is cut: a rectangular protrusion
- In the other workpiece, a mortise is chiselled or routed: a rectangular recess
- The tenon fits precisely into the mortise
The joint is secured with:
- Wood glue — The most modern and common method
- Wooden dowels — A wooden pin driven through the joint
- Wedges — The tenon passes through the mortise and is wedged from the other side
Types of mortise and tenon joints
| Type | Application |
|---|---|
| Through tenon | The tenon goes all the way through the workpiece. Strongest variant, visible on both sides. |
| Blind tenon (stub tenon) | The tenon is shorter than the mortise depth. Not visible on the outside. |
| Double tenon | Two tenons side by side for extra strength on wide workpieces. |
| Chamfered tenon | The tenon is chamfered at the end for easier insertion. |
When do you use a mortise and tenon?
- Window and door frames — The stiles and rails of a timber frame are traditionally joined with mortise and tenon
- Table and chair legs — Legs are attached to the top or frame with mortise and tenon
- Timber frame structures — Traditional timber construction with heavy beams
- Garden gates and fencing — A strong joint that withstands outdoor conditions
Making a mortise and tenon joint yourself
Tools
- Firmer chisel (for the mortise)
- Saw (for the tenon)
- Try square (for square lines)
- Wood glue
- Optional: router with mortise and tenon bits (faster and more precise)
Steps
1. Mark out — Mark the tenon and mortise accurately. Both must be exactly the same size.
2. Cut the mortise — First drill out most of the material, then clean up with a chisel
3. Cut the tenon — Cut the tenon to size. Better slightly too thick (plane down) than too thin (loose fit)
4. Test fit — The tenon should fit snugly into the mortise without forcing
5. Glue up — Apply glue to both the tenon and the mortise, clamp and leave to cure
Rules of thumb
- Tenon thickness = 1/3 of the timber thickness (for a 30 mm board, the tenon is 10 mm thick)
- Tenon width = 2/3 of the timber width
- Mortise depth = 2/3 of the timber the mortise is in (for a blind tenon)
Mortise and tenon vs. other joints
| Joint | Strength | Difficulty | Visible |
|---|---|---|---|
| Mortise and tenon | Very strong | Medium-high | Optional |
| Dowel joint | Strong | Low | No |
| Half-lap | Moderate-strong | Low | Yes |
| Screw joint | Moderate | Low | Yes (screw head) |
| Dovetail | Very strong | High | Yes |
Related terms
- Dowel
- Dovetail joint
- Half-lap joint
- Half-lap splice