What is Mortise and Tenon?
A mortise and tenon joint consists of a rectangular projection (tenon) on one piece that fits into a matching rectangular hole (mortise) in another, forming one of the oldest and strongest wood joints.
A mortise and tenon is the backbone joint of furniture and timber framing. One piece has a rectangular tongue (the tenon), and the other has a matching rectangular hole (the mortise). The tenon slides into the mortise for a tight, strong connection.
Why it is so strong. The joint provides long-grain to long-grain glue surface on all four sides of the tenon. Combined with the mechanical interlock, a properly fitted mortise and tenon is stronger than the wood around it.
Common types: - Through mortise and tenon: the tenon passes completely through and is visible on the other side. Often wedged for extra strength. - Blind (stub) mortise and tenon: the tenon stops inside the mortise. Cleaner look, no end grain visible. - Haunched mortise and tenon: a stepped tenon that fills the groove in a frame-and-panel door. - Loose tenon (Domino): both pieces get mortises, and a separate tenon bridges them. The Festool Domino automates this approach.
Sizing rules. The tenon thickness should be 1/3 of the stock thickness. For a 3/4-inch board, that is a 1/4-inch tenon. Tenon length should be 2/3 to 3/4 of the mortise piece width for maximum strength without weakening the receiving board.
Tools. Cut mortises with a hollow chisel mortiser, plunge router, or drill press with a fence. Cut tenons on a table saw with a tenoning jig, or with a router and a flat table.
In the cut list workflow, tenon length adds to the overall part dimension. A 12-inch apron with a 1-inch tenon on each end needs a 14-inch blank. SmartCutList includes these allowances so your cutting diagram gives you correctly sized blanks.
Frequently Asked Questions
- How strong is a mortise and tenon joint?
- A properly fitted mortise and tenon is one of the strongest woodworking joints. The tenon's large glue surface area and the mortise's surrounding wood create a joint that resists racking, twisting, and pulling apart. It is the standard joint for chairs, tables, and door frames.
- What tools do you need to cut a mortise and tenon?
- Hand tools: a mortise chisel and mallet for the mortise, a backsaw and shoulder plane for the tenon. Power tools: a drill press or hollow-chisel mortiser for the mortise, and a table saw with a dado blade or tenoning jig for the tenon. A router with a straight bit also works for both cuts.
- What is the rule of thirds for mortise and tenon?
- The tenon thickness should be one-third of the stock thickness. For a 3/4-inch board, the tenon is 1/4 inch thick. The tenon width should be one-third to one-half of the board width. The tenon length (depth into the mortise) should be at least two-thirds of the mortise piece width.
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