Saturday, June 21, 2008
Accurate layout is essential for a tight-fitting tusk tenon. Start by drawing a line on all four sides of the tenon where it exits the legs. Next, trace the wedge's angle onto the tenon and transfer this line the entire way around the tenon. In so doing, you have a reference line with which line up the angle of your chisel as you chop the mortise.
I used a mortising gauge to mark the long walls of the mortise, defined the shape with an exacto knife and chisel, removed some waste at the drill press, and cleaned up the mortise with chisels.
In the second to last photo, you may notice that the wall of the mortise that is closest to the leg assembly is actually stepped back a bit. I did this for two reasons: I still have final planing to do on the legs (which will reduce their thickness slightly); and to ensure a tight fit. With the mortise embedded inside the legs, the wedge pushes against the part of the leg that is above and below the mortise. I don't know if this is normally how it's done since I've never seen a tusk tenon disassembled, but it worked, and that's good enough for me. One down, one to go!