Mortise and Tenon

The King of Traditional Joinery

The mortise and tenon joint stands as perhaps the most time-tested and reliable method of joining wood in the entire woodworking tradition. Archaeological evidence confirms this joint was used in ancient Egyptian furniture over 5,000 years ago, and its fundamental design remains virtually unchanged because it simply works. When properly executed, a mortise and tenon creates an incredibly strong mechanical connection that can last for centuries.

Anatomy of the Joint

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 the mortise. The shoulder of the tenon (the step created where the tenon meets the main body of the workpiece) provides critical bearing surface that helps distribute stress and creates a clean visual line at the joint.

Critical Dimensions

Traditional joinery wisdom suggests making the tenon thickness approximately one-third the stock thickness. For a 3/4 inch thick board, that means roughly a 1/4 inch thick tenon. The tenon width typically matches the width of the workpiece minus the shoulder allowances. Tenon length depends on application—generally 1 to 2 inches for furniture work, though timber framing uses much longer tenons.

Cutting Methods: Hand Tools vs. Power Tools

Hand Tool Approach

Cutting mortises by hand requires a mortise chisel (heavier and thicker than a bench chisel) and a mallet. Mark your mortise boundaries precisely using a marking gauge. Chop straight down to establish the ends, then work from the center outward, removing waste in small increments. For tenons, use a backsaw or tenon saw to cut the cheeks, then the shoulders. A shoulder plane helps fine-tune the fit.

Power Tool Methods

A dedicated mortiser (benchtop or floor-standing) cuts clean, square mortises quickly. Alternatively, use a plunge router with an edge guide and spiral upcut bit, squaring the corners with a chisel afterward. For tenons, the table saw with a dado stack or repeated passes works excellently. A tenoning jig provides safer, more accurate cuts for the cheeks.

Fit and Assembly

Proper fit is everything. The tenon should slide into the mortise with hand pressure—too tight risks splitting the mortise walls during glue-up; too loose compromises strength. Test-fit dry before any glue application. When you are satisfied with the fit, apply glue to both mortise walls and tenon cheeks. Clamp firmly and check for square before the glue sets.

Drawboring for Extra Strength

Traditional drawboring adds mechanical lock to the joint. Drill through the mortise walls, assemble the joint dry, and mark the tenon through those holes. Remove the tenon and drill it slightly offset (1/32 inch toward the shoulder). When you drive a tapered wooden peg through the assembled joint, it pulls everything tight permanently—no glue required, though modern woodworkers often use both.

Variations for Different Applications

The through mortise and tenon exposes the tenon end on the opposite face, often with decorative wedges. Haunched tenons include a small step that fills the groove in frame-and-panel construction. Twin tenons distribute load across a wider rail. The bridle joint (open mortise) simplifies cutting while maintaining significant strength. Each variation addresses specific structural or aesthetic requirements.