The Haunched and Drawbored Mortise and Tenon by Bob Smalser

This is a 6/4 by 3” post and a 5/4 by 2” rail, and I’ll do a ¾ by 1 ¼” mortise a 16th of an inch over deep to house a 1 ½” long tenon. Mortises should always be slightly over deep to allow room for glue squeeze out. A 7/8” wide mortise would also be acceptable here. The “haunch” is the 45-degree tenon stub I’ve drawn on the upper face profiles of the stock that increases the gluing surface and aids in the joint resisting twisting stress.

You can also see in the photo above that if the rail is to be flush with the post top, then I’ve crosscut the post too long. You are correct, I have. The post’s short grain on the topside of the mortise would be far too fragile to chop a mortise and haunch without pre-drilling …and pre-drilling is unnecessarily slow, so I’ll chop my mortises vigorously and trim the tops of the posts later.

The first two chops are plumb to the work piece and just a bit inboard of the mortise ends. Inboard because that lead-weighted hard maple mallet weighs over 2 pounds, the bevel on this striking chisel is a steep 35 degrees, and hard blows downward tend to push the chisel backwards just a tad. Although it is the cheeks of the mortise that provide the majority of gluing strength, avoiding unnecessary stress or damage at the ends is simply better craftsmanship.

I’ve also marked my required mortise depth on the chisel using masking tape.

The third blow is taken bevel up about a third of the way along the mortise’s length at an angle downward toward the end…

…and the waste levered out, splitting along the grain of the wood. The deep scribe marks from the mortise gage prevent any chip out.

The fourth blow is identical from the opposite direction and that waste levered out. Subsequent blows continue with two plumb blows at each end followed by two angled blows and levering out waste…

…as the mortise gets deeper, the obstruction of the mortise ends force the angled blows increasingly steeper, eventually preventing them from reaching within clean splitting distance from the end blows…the chisel is then flipped and the angled blows struck bevel down to keep the cutting angle sufficiently acute for clean, 4-chop split outs.

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Tools and Wood with Bob Smalser