Tenoning

Also called: cutting tenons

A tenon is a tongue cut on the end of a piece of wood, shaped to fit snugly into a matching mortise, a slot cut into another piece, so the two lock together. Tenoning is the work of cutting that tongue, and the term sometimes covers the whole job of making the joint, mortise included, as Audels (1923) put it: "The operation of making mortise and tenon joints sometimes is termed tenoning which implies mortising also."

Cutting a tenon by hand

Cutting tenons by hand takes real time and skill, especially on wide rails, where a circular saw in good working order does the job far faster. As Ellis (1908) advised, "it is advisable to cut out the haunching between and beyond the tenons before ripping them down": the haunching is the short extra stub left at the top of a tenon to fill the matching groove in its mortise, and it is easier to remove before the long cheeks are sawn. Those cheeks are then sawn down to the shoulder line with a half-rip saw, run just outside the gauge marks rather than on them. On chair rungs cut by hand, the tenon's faces are aligned with the long grain at the rung's ends. On a rail joint carrying an ovolo, a rounded, convex moulding profile, the wood is pared square down to the tenon before the ovolo is scribed onto it. One traditional saw pattern, suited to cutting both with and across the grain, is prized particularly for tenon work.

Tenoning jigs on the table saw

A tenon is first marked out from its mating board before a tenoning jig, a sliding carriage that holds the work upright and square to the blade, makes its first pass. A plain jig sees more actual use in the shop than an elaborate one, and a table saw fitted with one ranks among the easiest and most accurate ways to cut a tenon; besides tenons, the same jig can cut bridle joints and spline slots, the narrow grooves that take a loose spline between two boards. The jig is set to cut half the stock's thickness, keeping the saw kerf on the waste side of the line, and it must be adjusted accurately and travel precisely within its gauge slot, the same slot on the saw table normally used by the mitre gauge. It must never be allowed to tip toward the blade while the work is fed past it. One method kerfs the shoulders to width first, then pares each tenon cheek away from the outside with a jig riding in the mitre slot.

Router-table and other machine methods

A router table offers further ways to cut a tenon: a sliding sled with a fence that positions the stock much as a mitre gauge does on an ordinary saw table, or a horizontal router table fitted with sliding tables that move the work in two directions. A tenon cut on a router-table sled should be checked for fit against its mortise afterwards. Cutting small stock on a radial-arm saw is riskier than either method, since it puts the hand close to the blade.

Machine tenoning and its history

Riley (1905) explained why tenoning machines were once so common in a shop: "As most framing is held together with mortise and tenon joints, both tenoning and mortising macliines are largely used." On a dedicated tenoning machine, a tenon's shoulders can be scribed either fully across or only part way, and the cutter-blocks that shape the tenon itself carry separate shouldering cutters, extra blades set to trim the shoulders clean and smooth as the same pass is made. One class of tenoning machine, worked by a reciprocating plane action, was represented by the hand-operated Barnes model. On another type of machine, a single arbor could swap between a saw and various cutter blocks: for thicknessing, for moulding, or for a block that cut just one face of a tenon, with a roller feed carrying the work through the same rig for whichever job was set up.

Where mortise-and-tenon fits, and where it does not

Among the joinery choices for door frames, cabinet carcasses and chair construction, mortise-and-tenon is reckoned to hold up strongest; in general building framing, though, one particular method is rated stronger again than either nailing or a mortise-and-tenon joint. In balloon-frame construction, a light timber-framing method built up from continuous wall studs, stair-well openings rarely call for mortise-and-tenon joints, though care is needed on the occasions they do. Fixing floor joists into a partition's sill by tusk tenoning, a tenon cut with an extra tapered tongue driven through and wedged from the far side, was once the usual method, even though it cuts into the sill's own strength to do it.