Router plane

Also called: old woman's tooth, hag's tooth

A router plane trues the bottom of a shallow recess, cut into or across a board, to a precise and consistent depth. It does not shape an edge or a whole surface; instead it levels the floor of a cut that has already been started with a saw and chisel.

Marking and truing the depth

Cutting a hand-cut half-lap joint, where two pieces cross and each has half its thickness removed so they lie flush, begins with two lines drawn to show where the pieces cross. For this marking step the plane is set to a depth equal to half the board's thickness, and running its blade down each side of a saw kerf scores a line on the surface marking the target depth. Once the bulk of the waste has been chiselled out, the plane is run over the surface to true the cut to its final depth. The same tool suits truing a groove to a precise, consistent depth, and any waste left behind after chiselling can be cleared with a chisel or with the router plane itself, working its fence over in tiny steps on each pass.

Fitting a joint

An overthick tenon is corrected most accurately with a router plane whose sole has had an offcut of rail material screwed to it. Hand work on a single-shoulder joint, a joint with a shoulder cut on one face only, calls for a dovetail plane, a small plane shaped to trim the angled sides of a dovetail joint, together with its matching saw and a router plane. An older, simpler version of the tool, known as the Old Woman's Tooth, is nothing more than a chisel jammed into a shopmade wooden block; it is occasionally pressed into service as a substitute for the plane itself.