Synopsis: David Lehman’s mortising jig uses two vertically aligned, rotating circles with protruding metal bolts to center workpieces automatically and create matching mortises for use with loose tenons. It uses a simple stop-block setup to align mating pieces so that mortises will align precisely. To ensure lasting consistency, it is made of Baltic-birch plywood. Lehman explains how to build the jig and how to use spacers to vary mortise size and location so that it is possible to accurately cut narrow mortises, thick or offset pieces, and off-center mortises.

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Recently, as I considered a set of bedroom furniture I was designing, I counted more than 50 mortise-and-tenon joints. I needed a way to make them as simply, precisely, and consistently as possible. To me, that meant using loose tenons; it’s much easier than with standard tenons. There are no shoulders to cut (and then fine-tune) for a perfect fit.…