The King of Traditional Joinery
The mortise and tenon joint has been around for over 5,000 years — archaeologists have found it in ancient Egyptian furniture — and its basic design hasn’t changed because there’s nothing to improve. A rectangular peg fits into a rectangular hole, and when properly executed, the result is a connection that can last centuries. That’s what makes the mortise and tenon endearing to us traditional woodworkers — it’s simple in concept, demanding in execution, and absolutely bulletproof when you get it right.
Anatomy of the Joint
Two components, both of which you need to understand completely before cutting anything. The mortise is the receiving cavity — a rectangular pocket cut into one piece of wood. The tenon is the projecting tongue machined on the mating piece, sized to fit snugly into that mortise. Then there’s the shoulder — the step where the tenon meets the main body of the workpiece. That shoulder isn’t decorative filler; it provides critical bearing surface that distributes stress and creates the clean visual line you see at the finished joint.
Critical Dimensions
Traditional joinery wisdom says make the tenon thickness approximately one-third the stock thickness. Working with 3/4 inch boards? That’s roughly a 1/4 inch thick tenon. The math is straightforward but the execution needs precision. Tenon width typically matches the width of the workpiece minus your shoulder allowances on each side. Tenon length depends on what you’re building — furniture work generally calls for 1 to 2 inches, while timber framing uses much longer tenons because the forces involved are entirely different.
Cutting Methods: Hand Tools vs. Power Tools
Hand Tool Approach
Cutting mortises by hand is meditative work once you develop the rhythm, and frustrating work before that. You need a mortise chisel — heavier and thicker than a bench chisel, designed to handle the levering forces involved — and a good mallet. Mark your mortise boundaries precisely with a marking gauge. Chop straight down to establish the ends first, then work from the center outward, removing waste in small increments. Rushing this produces ragged walls that weaken the joint.
For tenons, grab a backsaw or tenon saw and cut the cheeks first, then the shoulders. A shoulder plane lets you fine-tune the fit by shaving off tissue-thin amounts until the tenon slides home perfectly. This is where hand tool joinery becomes genuinely satisfying — that moment when a hand-cut tenon drops into a hand-cut mortise with just the right amount of resistance.
Power Tool Methods
A dedicated mortiser — either benchtop or floor-standing — cuts clean, square mortises faster than hand tools by a wide margin. If you don’t want a single-purpose tool, a plunge router with an edge guide and spiral upcut bit works well, though you’ll need to square the rounded corners with a chisel afterward. For tenons, the table saw is hard to beat. A dado stack removes waste quickly, or you can make repeated passes with a standard blade. A tenoning jig that holds the workpiece vertically provides safer, more accurate cheek cuts than freehanding against the fence.
Fit and Assembly
Fit determines everything. The tenon should slide into the mortise with firm hand pressure — not so tight that you need to force it (that risks splitting the mortise walls during glue-up) and not so loose that it rattles around (that compromises the entire point of the joint). Always test-fit dry before any glue touches the wood. When the fit is right, apply glue to both the mortise walls and the tenon cheeks, clamp firmly, and check for square before the glue grabs. You get one shot at this — repositioning a glued mortise and tenon is not a thing.
Drawboring for Extra Strength
Drawboring is old technology that adds a mechanical lock to the joint, and it’s worth knowing even if you don’t use it on every project. Drill through the mortise walls, assemble the joint dry, and mark the tenon through those holes. Pull the tenon back out and drill it — but offset slightly, about 1/32 inch toward the shoulder. When you drive a tapered wooden peg through the assembled joint, that offset forces the tenon tight against the shoulder permanently. No glue required, though modern woodworkers often use both for belt-and-suspenders security.
Variations for Different Applications
The basic mortise and tenon adapts to a surprising range of situations. The through mortise and tenon exposes the tenon end on the opposite face — often with decorative wedges that look striking and add mechanical strength. Haunched tenons include a small step that fills the groove in frame-and-panel construction, preventing the panel groove from showing as a gap. Twin tenons split the load across a wider rail for better resistance to twisting. The bridle joint, which is basically an open mortise, simplifies cutting while still providing significant strength for lighter-duty applications. Each variation exists because someone encountered a specific structural or aesthetic problem and adapted the basic joint to solve it.
