Wedging
Also called: fox wedging
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Wedging is driving a tapered piece of wood into a joint to lock its parts together. Pinning, plain wedging, and keyed or tusk wedging, where a tapered key is driven through the joint from outside, are the standard ways of stopping a joint pulling apart, and wedging in general cuts down movement in a joint and adds to its strength.
How a wedge locks a joint
A splayed mortise, one cut wider at its far end than at its mouth, or a through-tenon, a tenon that passes right through the mortised piece and shows on the far side, wedged with a key, resists being pulled apart until the wood itself gives way. In a dovetail joint, Hoadley (1980) held that wedging by the tails against the pins helps, but that gluing their side-grain faces is what mainly holds the joint together; he also noted that a wedged joint loses its locking grip if its angle is cut too shallow. An overly broad tenon can work against itself: it can distort under the pressure of wedging, straining the mortise around it and sometimes splitting it.
Blind and foxtail wedging
Blind wedging is used from time to time on a mortise that does not run through the piece. Foxtail wedging is a form of this, driving its wedges from inside such a blind mortise as the joint is closed up. An inserted tenon can be secured the same way, by fox-wedging, or it can instead be let into the wide rail from the edge rather than wedged blind. A tenon need not be wedged from within a blind mortise at all; it can equally be wedged from outside the joint.
Wedging up in practice
A haunched tenon, one with a short stub left to fill part of its mortise, should not be given more than half its housing's width, or the end of the stile risks being driven outward as the joint is wedged up. Knocking the core loose from the show-face side, rather than the back, leaves more room for the wedges and guards against the edges breaking out. Wedging up a staircase takes two workers, one driving the wedges and one watching to confirm the treads and risers have gone fully home. Laying out a window transom includes marking space on its head for the wedging room the mortices will need. Once a joint is wedged fully home, as Hasluck (1907) described the finish of the job: "take off the cramp, oil the tenon saw with olive oil (not linseed), and cut off the projecting ends of the tenons and wedges." In floor-joist strutting, whichever method is used, the gaps left between the end joists and the walls are closed with packing and wedging.
Wedging outside the joint
The same principle appears elsewhere in the shop: a holdfast sits loose in its hole in the benchtop, yet grips the work firmly through a wedging action once it is tapped down. The word also has a separate, mechanical sense in sawing. A ripsaw's leading tooth strikes the wood close to a right angle to the grain and severs the fibres at that one point only, the throat of the tooth wedging the waste free rather than shearing it away.