Mortise and Tenon by Hand

The mortise-and-tenon is the backbone of furniture joinery — tables, chairs, doors, and workbenches all rely on it. Cut by hand, it’s mostly about layout discipline and working to your lines. Here’s a reliable approach for a standard blind (stopped) mortise and tenon.

Proportions to start from

These are common rules of thumb, not hard laws:

• Tenon thickness: about one-third of the thickness of the rail. For 3/4” stock, a 1/4” tenon is common. Practically, match the tenon to the width of your mortise chisel.
• Tenon length: as long as the leg allows, often about 1”–1 1/4” in table legs, leaving enough wood at the back of the mortise. Where two mortises meet at a corner, miter the tenon ends so they don’t collide.
• Shoulders: a small shoulder (often about 1/4”–1/2”) on the top edge of a rail hides the mortise and keeps it from running out the top of the leg.

1. Lay out the mortise

• Mark the mortise length on the leg with a square and knife or pencil.
• Set a mortise gauge (it has two pins) to the width of your chisel, and set the fence so the mortise is positioned where you want it. Scribe between the length marks.
• Use the same gauge setting for the tenon. That shared setting is what makes the parts match.

2. Chop the mortise

• Clamp the leg over a solid part of the bench, not over a vise jaw or gap.
• Start near the middle of the mortise, chisel held vertical and its bevel facing the direction you’re going to travel. Chop straight down, move the chisel about 1/8” along, and chop again, working toward one end and stopping about 1/16” short of the end line. Lever the loosened waste out against the area you’ve already chopped, never against the finished end walls.
• Turn the chisel around and work toward the other end the same way. Repeat in layers until you reach depth, clearing waste as you go.
• When you’re at depth, pare the end walls back to the lines last, with the flat of the chisel facing the end wall and held vertical.
• Methods vary — some woodworkers start at one end and chop toward the other, and mortise-chisel and bevel-edge-chisel techniques differ a little. Whatever the method, keep the chisel vertical and do your heavy levering away from the walls that will show.
• Mark the depth on your chisel with tape so you can tell when you’ve reached it.

Some woodworkers drill out most of the waste first with a brace or drill press and then pare the walls. Either way, keep the walls parallel to the leg’s faces — sight along the chisel, or stand a small square nearby as a visual guide.

3. Saw the tenon

• Using the same gauge setting, scribe the tenon cheeks around the end and edges of the rail, registered from the same face as the mortise.
• Knife the shoulder lines all the way around with a square.
• Saw the cheeks on the waste side of the line. A good method: saw diagonally from one corner, flip and saw from the other corner, then saw straight down to the shoulder line.
• Saw the shoulders. A small knife-wall chiseled into the waste side of the shoulder line gives the saw a clean start.

4. Fit the tenon

• Aim for a fit you can push together with firm hand pressure — not loose, not needing a mallet.
• Trim fat tenons with a shoulder plane, router plane, or careful paring. Take a little off both cheeks evenly to keep the tenon centered.
• Check that the shoulders seat fully on both faces; if one side gaps, pare the shoulder that’s holding it off.

5. Drawboring (optional, very strong)

Drawboring pulls a joint tight with a wooden peg and adds mechanical strength even if the glue fails:

1. Bore a hole through the mortise cheeks (with the tenon removed).
2. Insert the tenon, mark the hole’s center on it, then remove the tenon.
3. Bore the hole through the tenon, offset slightly toward the shoulder — on the order of 1/16”–3/32” is common for furniture-scale joints in hardwoods; heavier work sometimes uses a little more, and the right amount depends on the wood and peg size.
4. On assembly, drive a tapered, straight-grained peg through. The offset pulls the shoulders tight.

Practice on scrap first: too much offset can split the tenon or bend and break the peg.

Common problems

• Mortise walls not parallel: pare carefully with a wide chisel, using the gauge lines as a guide.
• Tenon twisted: usually from sawing out of square; check your cheek cuts before cutting the shoulders.
• Gappy shoulders: knife the shoulder lines deeply and pare to them.

Put these skills to work on the Roubo-style workbench — a big, forgiving project full of mortises and tenons.

Sources & further reading

• Popular Woodworking — Drawboring resurrected
• Paul Sellers — Chopping mortises with bevel-edged or mortise chisels