Two joints account for a disproportionate share of the structural integrity in solid-wood furniture: the mortise and tenon, which handles the connection of rails to legs and stiles to rails; and the dovetail, which locks drawer sides to fronts and carcase corners together. Both predate power tools by centuries; both remain the standard for furniture intended to last longer than its maker.
The mortise and tenon: how it works
A mortise is a rectangular recess cut into one piece of timber. A tenon is a rectangular projection cut on the end of another piece that fits into the mortise. The mechanical principle is simple: the tenon fills the mortise, glue bonds the long-grain surfaces of the tenon walls to the short-grain surfaces of the mortise walls, and the result is a joint that resists racking (twisting) as well as tension and compression.
The sizing convention that has evolved over centuries of practice is to make the tenon thickness one-third of the rail thickness. For a 45 mm thick rail, the tenon would be 15 mm thick. The width of the tenon is typically the full width of the rail minus a short shoulder at top and bottom — around 5–8 mm per side — to prevent the long grain of the tenon from splitting out under lateral stress.
Through tenon versus stopped tenon
A through tenon passes completely through the mortised component and is visible on the opposite face. A stopped (or blind) tenon ends inside the mortise and is invisible from the outside. Through tenons can be wedged for a mechanical lock that does not depend on glue alone — a technique used in timber framing and in some furniture forms where glue-free construction is desirable for later disassembly.
The depth of a stopped mortise is typically the width of the tenon plus 3–5 mm of clearance. This clearance prevents the end of the tenon from bottoming out in the mortise before the shoulders make full contact with the face of the mortised component — a common cause of poorly fitting joints in student work.
Haunched tenons
Where a rail sits at the top of a frame — for example, a top rail connecting two table legs — the groove for a panel or the full width of the stile would be exposed at the end of the frame if a plain tenon were used. A haunch — a short extension of the tenon's upper edge — fills this exposed groove section and prevents the joint from twisting. Haunched tenons are the standard form for frame-and-panel cabinet doors.
Cutting a mortise and tenon by hand
Lay out the mortise with a mortise gauge set to the chisel width that will be used. A 12 mm mortise chisel in a 45 mm rail is a common combination. Score the end lines with a marking knife registered against a square. Begin chopping slightly away from the end line, removing small amounts of material in repeated downward strokes with a mallet, working toward the centre from both ends. Clear waste periodically. As the mortise approaches full depth, undercut the ends slightly so that when the tenon is pushed home, its shoulders make contact with the face before the tenon bottoms out.
The tenon is cut with a rip saw (tenon saw) on the waste side of the marked line. Sawing the cheeks first and then the shoulders — rather than shoulders first — keeps the reference face visible during cutting. A shooting board and shoulder plane clean any inaccuracy from the cheeks and shoulders once the initial cuts are made.
The dovetail joint: how it works
The dovetail is an interlocking wedge-shaped joint. The tails — fan-shaped projections on one piece — slot between the pins on the mating piece. The geometry means that once the joint is assembled, the tails cannot be withdrawn in the direction they were inserted. This mechanical resistance to tension, combined with glue on the long-grain surfaces, makes the dovetail the standard joint for drawer construction and carcase corners where racking forces are present.
Tail-to-pin ratio and angle
The slope of the dovetail affects both appearance and strength. A 1:8 ratio (one unit rise to eight units run) is standard for hardwoods; a shallower 1:6 ratio is used for softwoods, where the steeper angle would cause the grain to break along the narrow pin section. The number of tails varies by taste and the width of the board; a typical 150 mm wide drawer side might carry three full tails and two half-pins at the edges.
The half-pins at each edge are not decorative — they are structural. The outermost pin is the component most exposed to racking stress; a full tail at the edge, which would have unsupported grain running to the corner, would be weaker than a half-pin of the same material.
Through dovetail versus half-blind dovetail
A through dovetail is visible on both faces of the assembled joint. It is used at the back of drawers where the joint is not seen in normal use, and in carcase constructions where exposed joinery is part of the aesthetic. A half-blind dovetail — the standard for traditional drawer fronts — has a thin layer of timber left in front of the tails that hides them when the drawer is closed. The front piece is left thicker than the side to accommodate this remaining layer, typically 5–8 mm.
Cutting dovetails by hand
The conventional sequence is to cut the tails first and then use them as a template to mark the pins. Lay out the tail slope with a sliding bevel set to the chosen ratio. Saw the tails on the waste side with a dovetail saw (a fine-toothed cross-cut saw with a reinforced back). Remove the waste between the tails with a coping saw, finishing with a chisel pared to the baseline.
Register the tails over the end of the pin board and scribe around them with a marking knife. Saw the pins slightly fat and pare to the line. The test fit should be firm enough that light hand pressure is needed — not so tight that a mallet is required, which risks splitting the pins. A joint that assembles freely by hand will be loose once the glue swells the timber.
Common errors and how to avoid them
- Mortise walls that are not vertical — causes the rail to sit at an angle in the finished frame. Remedy: chop the mortise in two stages, checking alignment with a small square after each stage.
- Tenon shoulders that are not square to the face — the most common cause of twisted frames. Remedy: use a shooting board and shoulder plane to correct before assembly.
- Dovetail pins that split during assembly — caused by pins cut too narrow relative to the timber's grain. Remedy: observe the 1:6 rule for softwoods; avoid very narrow pins in straight-grained, short-fibred timber.
- Gaps at dovetail baselines — caused by waste not fully cleared before the shoulders are pared. Remedy: undercut the baseline by 0.5° so that the front face makes contact before the back.
Machine-cut versus hand-cut joints
Router jigs and dedicated dovetail machines produce joints that are geometrically consistent. Hand-cut joints are not more durable, but they allow more flexibility in tail spacing and proportions, and they do not require specific tooling for each timber thickness. For production work, machine-cut joints are rational. For one-off or custom furniture, hand methods allow the maker to adjust the visual weight of the joint to the piece — more tails for a lighter appearance, fewer for a bolder statement.
Last updated: 1 April 2026