How to assemble a mortise-and-tenon chair leg and apron setup
A mortise-and-tenon chair earns its strength from accurate shoulders and clean glue joints rather than heavy fasteners. In a traditional leg-and-apron design, each horizontal rail has a tenon that fits into a matching mortise in the legs. The rails below the seat are commonly called aprons, and their joints must stay square for the chair to stand evenly.
The method here suits a four-legged indoor chair with aprons between the legs and shoulders bearing against the leg faces. It also works for a heavier hall chair if timber dimensions, glue and clamping pressure are adjusted. Build a full-size drawing before cutting, showing finished widths, tenon lengths and the distance between each pair of legs.
Australian timber merchants commonly offer radiata pine for concealed parts alongside harder local species such as spotted gum, jarrah and blackbutt. Select straight-grained, dry stock, label every component, and let it acclimatise indoors before machining. Measure in millimetres with a steel rule, since nominal timber sizes and workshop equipment are metric here.
Prepare the components and workshop
Inspect each leg and apron before assembly. The tenon shoulders must be square, the end grain should be free of tear-out, and every tenon should pass through its own mortise without forcing. A tenon that bottoms out early needs shortening; a gap at the shoulder means the shoulder or mortise face still needs correction.
Set up a broad, flat bench with padded clamps and simple cauls to spread pressure without bruising the legs. Before switching on dust extraction or a router, use a workshop safety checklist to isolate household appliances and inspect power leads, plugs and guards. Keep the floor clear so a clamped chair frame cannot slide into a bench edge.
Mark and test the dry fit
Push each tenon into its mortise by hand and check that it reaches the shoulder without a lever action. If it is tight, pare it with a sharp chisel rather than sanding; if it is loose, the tenon may need to be narrowed or the mortise adjusted. Dry-fit every joint, because one proud shoulder can twist the whole apron frame.
Mark each leg and apron with matching clock-face registration lines, and mark the shoulder positions in pencil. Assemble the frame without glue on the bench, checking that all shoulders close at the same time. A shoulder-to-shoulder spacer or two fixed bench stops can preserve the intended width while the joints are brought together.
Assemble the legs in pairs
Glue one apron between two legs as the first rigid assembly. Brush a thin, even coat of PVA glue onto the tenon and into the mortise, then seat the tenon fully against its shoulder. Draw the legs together with a padded clamp across their outer faces, using light, steady pressure and wiping squeeze-out before it skins over.
Repeat on the opposite leg pair. Check that each pair is flat and that the apron sits square to the leg, then leave both units undisturbed for at least an hour. Keeping the work flat prevents the fresh joints from creeping before they gain strength, especially when using soft radiata pine.
Connect the apron frame
Bring the two leg pairs together with the side aprons, working on the flat bench and keeping the seat opening at its designed size. Glue one side apron at a time, starting the tenon by hand and closing the shoulder before applying clamp pressure. Alternate the opposite side so the frame is not pulled permanently out of square.
Use a second clamp or a temporary stop to hold the already joined corners while the remaining tenons seat. Do not squeeze the completed frame to correct a diagonal measurement; if the shoulders resist, release the clamp and identify the joint that is out of position. Let the side joints reach their initial set before making any fine adjustment.
Square the frame and let it cure
Measure both diagonals across the leg openings and compare the readings. Equal diagonals within about 1–2 mm indicate a square frame on a typical chair. Also check each shoulder-to-shoulder width against the drawing, then place the frame on a flat floor without tightening anything further.
Leave the frame clamped or lightly braced for at least 24 hours, longer in cool or humid conditions. Melbourne's variable humidity and humid days in Sydney or Brisbane can slow PVA cure and move the timber, so keep the chair away from direct sun and heating vents. For a verandah or garden version, compare joinery and finish options in the site's outdoor woodworking projects, because exposed seats need regular inspection.
Sand the joints and choose a finish
After the glue has cured, remove the braces and sand only where the squeeze-out or tool marks remain. Use progressively finer abrasives, working with the grain and preserving the square shoulder edges. For shaped edges and rounded transitions, the advice on sanding curves and contours can help avoid flat spots around the tenon shoulders.
Break sharp external edges with fine sandpaper or a small radius so clothing and skin do not catch. Seal the end grain, then choose a finish suited to the location: quality hardwax oil for an indoor dry area, or a durable water-based coating for a busy household. Australian hardware shops generally stock metric M6 and M8 fittings if the seat needs separate fixings. If selling the chair, the Australian Consumer Law still requires it to be fit for its disclosed purpose and free from hidden defects; relevant Australian Standards may also apply to commercial seating.