The mortise and tenon is the oldest and strongest structural wood joint. A rectangular projection (the tenon) fits into a matching rectangular hole (the mortise). This joint connects table legs to aprons, chair legs to rails, door frames to stiles, and timber frames to posts. It resists racking, supports heavy loads, and with glue holds for centuries. Every serious woodworker needs to know how to cut mortises and tenons — by machine or by hand.

Mortise and Tenon Basics

Anatomy of the Joint

Mortise: A rectangular pocket cut into one piece (typically the leg or stile). Defined by its width, depth, and height.

Tenon: A rectangular tongue left on the end of the mating piece (typically the rail or apron) after cutting away the surrounding wood. The tenon fits snugly into the mortise.

Tenon cheeks: The broad flat surfaces on the top and bottom of the tenon where material was removed.

Tenon shoulders: The flat faces where the tenon meets the main body of the rail. Shoulders hide the mortise opening and provide the joint’s visual crispness.

The rule of thirds: For a standard mortise and tenon, the tenon thickness should be approximately one-third the thickness of the stock. In 3/4-inch stock, the tenon is 1/4 inch thick. In 1.5-inch stock, the tenon is 1/2 inch thick. This leaves enough material on each side of the mortise for strength.

Mortise and Tenon Variations

Through mortise and tenon: The mortise goes all the way through the piece, and the tenon end is visible on the opposite face. Structural, decorative, and the easiest to fit because you can see both ends. Often wedged for a mechanical lock.

Blind (stopped) mortise and tenon: The mortise does not go all the way through. The tenon is hidden inside the joint. Cleaner appearance on the outside face. Standard for table and chair construction.

Haunched tenon: The tenon has a shallow step cut on one edge. The haunch fills a groove in the mortise piece (common in frame-and-panel doors where the panel groove would be exposed at the end of the stile without the haunch).

Twin tenons: Two narrower tenons separated by a gap, used on wide rails to prevent cupping and provide more glue surface.

Loose tenon (Domino joint): Both pieces receive mortises, and a separate loose tenon (a rectangular dowel) bridges them. This is the principle behind the Festool Domino ($1,100+), which cuts mortises with a machine and uses factory-made loose tenons. Fast, strong, and precise.

Cutting Mortises

By Drill Press and Chisel

The most common home workshop method:

Mark the mortise outline on the workpiece using a marking gauge for the width lines and a square for the end lines.
Select a drill bit matching the mortise width (a 1/4-inch mortise gets a 1/4-inch Forstner bit).
Set the drill press depth stop to the mortise depth.
Drill overlapping holes along the mortise length, staying slightly inside the end lines. The overlapping holes remove the bulk of the waste.
Clean up the sides and ends with a sharp chisel matching the mortise width. Pare the walls flat and the ends square.

This method is accurate and accessible with tools most workshops already have.

By Router

A plunge router with an up-spiral bit and an edge guide cuts clean mortises quickly:

Set the edge guide to center the bit on the mortise location.
Set the depth stop to the mortise depth.
Plunge the bit, move the router along the mortise length to the end marks, and retract. Take multiple passes of 1/4-inch depth increments.
The mortise will have rounded ends. Either square them with a chisel or round the tenon edges to match.

The router method is fast and consistent for multiple identical mortises (batch work for table or chair builds).

By Hand

Cut a mortise entirely with chisels and a mallet:

Scribe the mortise outline deeply with a marking gauge and knife
Start in the center of the mortise. Drive a chisel (slightly narrower than the mortise width) into the waste at a 60-degree angle to the grain, then lever out the chip.
Work from the center toward each end, deepening the mortise incrementally.
Pare the walls and ends to the scribed lines.
Check the depth with a depth gauge or combination square.

Hand-chopping mortises is slow but requires no power tools. It is meditative, quiet work that some woodworkers genuinely prefer.

Cutting Tenons

By Table Saw

The table saw cuts tenons accurately with either a dado blade or repeated passes with a standard blade:

Dado blade method:

Set the dado blade width to remove the waste from one cheek in a single pass
Set the blade height to the shoulder depth (the amount removed from each cheek)
Use the miter gauge to push the workpiece across the blade, nibbling away the cheek from the shoulder line to the end
Flip the workpiece and cut the opposite cheek
Re-set and cut the edge shoulders if needed

Standard blade method:

Set the blade height to the shoulder depth
Make the shoulder cut first — a single crosscut at the shoulder line, indexed off the miter gauge
Make multiple passes to nibble away the remaining cheek waste, or use a tenoning jig that holds the workpiece vertically against the fence

By Hand

Mark the tenon layout with a marking gauge: shoulder lines around all four faces, cheek lines on both edges and the end
Cut the shoulders first with a backsaw (dozuki or tenon saw), cutting down to the cheek line on all four faces
Clamp the workpiece vertically. Cut the cheeks with the backsaw, following the cheek lines down to the shoulder cuts
The waste falls away, leaving the tenon

Hand-cut tenons paired with hand-cut mortises is the traditional approach and produces excellent results with practice.

Fitting the Joint

A mortise and tenon should assemble with firm hand pressure or a few light mallet taps. It should not require hammering, and it should not fall apart under its own weight.

Too tight: Pare the tenon cheeks with a sharp chisel, removing thin shavings. Check the fit frequently — removing too much creates a loose joint.

Too loose: If the tenon is slightly undersized, glue a veneer shim to one cheek. If significantly loose, cut a new tenon on a fresh piece.

Checking for square: Assemble the joint dry and check with a square. The tenon shoulders should seat flat against the mortise face with no gaps. A gap at the shoulder means the tenon is too long or the mortise is too shallow. Trim as needed.

Gluing Up

Dry-fit the entire assembly first to verify all joints fit and the project is square
Disassemble and apply wood glue to both the mortise walls and the tenon cheeks
Assemble quickly — glue starts setting in 5 to 10 minutes
Clamp across the joint, pulling the shoulders tight against the mortise face
Check for square immediately while the clamps are on
Wipe excess glue with a damp rag before it sets

For through tenons, add wedges after the tenon protrudes through the mortise. Cut kerfs in the tenon end, apply glue, and drive small hardwood wedges into the kerfs. The tenon expands inside the mortise, creating a mechanical lock in addition to the glue bond.

Bottom Line

The mortise and tenon is the strongest joint in woodworking and the foundation of furniture construction. Start with the drill press and chisel method for mortises and the table saw for tenons. Get the proportions right (rule of thirds), fit the joint so it assembles with hand pressure, and glue it up square. Once you can cut this joint confidently, you can build tables, chairs, beds, and frames that last generations.