Mortise and tenon is the most-used structural joint in furniture and timber framing because it converts the wood’s strength along the grain into a mechanical interlock that resists pulling, twisting, and racking. Every wooden chair worth sitting in, every panel door, and every chest of drawers with frame-and-panel construction uses mortise and tenon. Unlike dovetails, the joint is hidden once assembled, which is why it gets less internet attention. Done right, it is the joint that holds up for 200 years.
The geometry
A mortise is a rectangular hole. A tenon is a matching rectangular projection that fits into the hole. The tenon has four faces called cheeks (the wide faces) and shoulders (the smaller faces that close against the outside of the mortised piece). When pulled in tension along the rail axis, the tenon resists by the long-grain glue bond on the two cheeks. When loaded laterally, the shoulders bear against the mortise face and the tenon walls jam against the mortise walls.
The strength comes from the cheek-to-wall glue surface, which is long-grain to long-grain (the best wood glue joint there is). The shoulders close any gap and make the joint look clean.
Sizing the joint
The classic rules of thumb work for nearly every situation:
- Tenon thickness: 1/3 of the rail thickness
- Tenon length: 2 to 2.5 times the tenon thickness for casework, up to 3 times for chair work
- Tenon width: full width of the rail minus 1/8 to 1/4 inch on each end (haunched tenon) for frame work, or about 75 percent of the rail width for chair work
- Mortise walls: 1/3 of the rail thickness on each side (matches the tenon thickness rule)
For 3/4 inch frame stock, a typical mortise is 1/4 inch wide, 5/8 inch deep, and either full-width or with shoulder reductions. For 1 inch chair stock, the mortise is 3/8 inch wide, 1-1/4 inch deep, and 75 percent of rail width.
The haunch is a small lip at the top of the tenon that fits into a haunch cut at the top of the mortise. It keeps the rail from twisting in the frame without weakening the show face. Standard on panel doors.
Cutting the mortise: three reliable methods
Method 1: Chisel and mallet
Mark the mortise outline with a sharp marking gauge and a knife. Drill out the bulk of the waste with a brad-point bit slightly smaller than the mortise width, then pare the walls clean with a chisel that matches the mortise width. A 1/4 inch chisel for a 1/4 inch mortise, used vertically with a wooden mallet.
Total time for one mortise: 6 to 10 minutes in soft wood, 10 to 15 in hardwood. Tooling cost: 0 dollars beyond the chisel kit you already own.
Method 2: Drill press with a Forstner bit or mortising attachment
Set the drill press fence to position the bit on the mortise centerline. Drill overlapping holes the full length of the mortise at full depth. Square the corners and clean the walls with a chisel.
Total time per mortise: 3 to 5 minutes. The Powermatic and Grizzly hollow-chisel mortisers ranging 350 to 900 dollars cut a perfectly square mortise in one operation but most home shops use a drill press plus chisel.
Method 3: Router with edge guide or plunge fixture
A plunge router with a 1/4 or 3/8 inch straight bit and an edge guide cuts mortises in 90 seconds each. The Pat Warner plunge fixture and the Mortise Pal jig are reference tools. Result is a round-ended mortise, so the tenon also gets round ends (sawn square then radiused with a chisel or rasp) or the mortise corners are squared with a chisel.
Total time per mortise: 90 seconds to 3 minutes. Tooling cost: 200 to 500 dollars for plunge router and edge guide.
Cutting the tenon: three reliable methods
Method 1: Tenon saw and shoulder plane
Mark the tenon with a gauge. Saw the cheeks first (with the rail vertical in the vise), then the shoulders (rail horizontal). Use a shoulder plane to bring the cheeks to final fit.
Time per tenon: 4 to 7 minutes. Tooling: tenon saw (60 to 180 dollars), shoulder plane (160 to 250 dollars).
Method 2: Table saw with a tenoning jig
Stand the rail vertically in a tenoning jig that rides the rip fence. Cut the cheeks in two passes (one per side). Lay the rail flat on the miter gauge for the shoulders.
Time per tenon: 60 to 90 seconds. Tooling: tenoning jig (90 to 230 dollars), assuming you already own the table saw. Most consistent method for batches.
Method 3: Router table with a sled
Stand the rail vertically against a backer board. Push it across a large straight bit set to leave the desired tenon thickness. Flip for the other cheek.
Time per tenon: 2 minutes. Works well, requires a tall backer and a careful setup.
The Domino question
The Festool Domino DF 500 (1100 dollars) and DF 700 (1400 dollars) cut a precise rounded mortise into both pieces being joined, then a proprietary tenon (the Domino) glues into both sides. Functionally it is a floating tenon joint. Tested in side-by-side break testing by Fine Woodworking and others, the Domino joint comes within 90 to 95 percent of the strength of a traditional integral tenon of the same size, which is far above the strength needed for any real-world furniture.
The Domino wins on speed (10 seconds per joint), repeatability, and the ability to make multiple tenons per joint for wide rails. It loses on cost, on the dependency on Festool tenon stock (or shop-made copies), and on the look of the joint if you ever expose it.
For workbench builders and chair makers, traditional integral tenons with through-pegs are still the reference. For casework, doors, and aprons, the Domino is nearly universal in production shops.
Fit tolerance
A correctly fitted mortise and tenon should slide together with steady hand pressure and stop just before bottoming out. Two specific tests:
- The dry-fit should hold the rail in the mortise upside-down without slipping out.
- The fully seated joint should leave a 1/32 to 1/16 inch gap at the bottom of the mortise so glue squeeze-out has somewhere to go.
Too tight and the joint splits the mortise leg when you tap the rail in. Too loose and the glue is the only thing holding the joint, which is exactly the wrong way to use the joint.
Wedging and pegging
Two reinforcements add durability:
- Wedged through-tenon: a sawkerf cut into the end of the tenon, with a hardwood wedge driven in after the tenon is through the mortise. Spreads the tenon end inside the mortise and locks it mechanically. Classic on Shaker chairs and timber-frame joinery.
- Draw-bore peg: a tapered peg driven through aligned holes in the leg and tenon, with the tenon hole offset 1/32 inch toward the shoulder. The peg pulls the joint tight as it drives in.
Both reinforcements add 10 to 15 minutes per joint and are well worth the time on any joint that will see real stress (chair stretchers, workbench legs, post-and-beam framing).
For sharpening the chisels you will use, see our methodology page for the workshop test routines. A clean mortise and a snug tenon are 80 percent of the joint. The rest is glue and patience.
Frequently asked questions
How thick should the tenon be?+
One third of the rail thickness is the classic rule. For a 3/4 inch rail, the tenon is 1/4 inch thick, leaving 1/4 inch of wood on each cheek. For 1 inch stock, the tenon is 3/8 inch. Going thinner sacrifices strength. Going thicker leaves the mortise walls too weak. Floating tenons (Domino, Beadlock) follow the same one-third rule using the proprietary tenon stock thickness.
How long should the tenon be?+
About 2 to 2.5 times the tenon thickness for stub tenons in casework, and up to 3/4 of the mortise leg width for through-tenons or heavily loaded joints (chair stretchers, table aprons). A 1/4 inch tenon should be 1/2 to 5/8 inch long for casework, and up to 1-1/2 inch for chair work. Longer is generally stronger up to the point where it intersects another mortise.
Domino vs. traditional mortise and tenon for furniture?+
For aprons, frames, and faceframes in casework, the Festool Domino at 1100 to 1400 dollars produces a joint that is structurally equivalent to a traditional integral tenon for any reasonable load. For chairs taking lateral stress, traditional joints with longer tenons and (optional) draw-bore pegs are stronger. The Domino wins on speed. Tradition wins on chair stretchers and frame doors that will see decades of stress.
What is a draw-bore peg and when do I use one?+
A draw-bore peg is a tapered wooden pin (typically 1/4 or 3/8 inch oak or hickory) driven through a hole that passes through the mortise leg and the tenon, with the tenon's hole offset 1/32 inch toward the shoulder. As the peg drives in, it pulls the tenon shoulder tight against the mortise face. Used in timber framing, chair making, and Roubo-style workbenches. Lets the joint stay tight without glue.
Should I cut tenons first or mortises first?+
Mortises first, then size the tenons to fit each individual mortise. Mortises are harder to widen or narrow after the fact, while tenons can be pared down with a shoulder plane or rabbet plane in 30 seconds. If you cut tenons first to a target size and the mortise comes in even 1/64 inch off, you have to remake one of the two parts.
