Question: Looking over the current and past issues of Woodworking Magazine, I see how drawboring or wedging a mortise and tenon joint will improve the strength and fit of the joint. But is there a reason to pick either drawboring or wedging over the other technique in terms of the strength or durability of the joint?
The only advantage I can think of so far is that it might be easier to disassemble a drawbored joint.
– Wilbur Pan
Answer: I’m not aware of any studies that compare the relative strengths of these two joints. For me, they both fit into the category of “stronger than typically required.”
And that is probably why both joints show up frequently in chairs, which are the most-abused category of furniture.
I think that choosing one joint over the other depends on your materials, your tools at hand, the fit of the components and your desire for being able to disassemble the joint.
Materials: I would choose drawboring if my wood was a little wet and hadn’t reached equilibrium with my shop. Drawboring will keep things tighter as the wood dries and shrinks. I would choose wedging if my material was less stout than oak (say, cherry or walnut). Drawboring is more likely to result in a split during assembly.
A drawbore joint, split open for your inspection.
Tools: I would choose drawboring if I had a set of drawbore pins. I don’t like drawboring without them in typical frame construction — though you can do it with small hole offsets. I would choose wedging if I had a band saw. Nothing makes wedges faster than a band saw and the wedge sled we showed in the magazine. Also, I would choose wedging if I had lots of clamps; I would choose drawboring if I didn’t.
The Fit of Your Components: Drawboring is more accommodating to a joint that isn’t as perfect. It will draw up tenon shoulders tightly more than wedging will. Wedging a through-tenon requires particular attention to the way the tenon and mortise fit.
A wedged through-tenon. Note that this is but one way to wedge this joint.
Reversibility: I actually think that a wedged joint (with hide glue) is more reversible than a drawbored joint. If you drill out a drawbore pin, you are generally going to make it so that the joint cannot be reassembled in the same way without some serious fussing. I know some people have assembled their drawbored joints without glue and then knocked out their pins later. I haven’t had much luck with this, but I’ve only tried it a couple times. Early accounts of wedging recommended that the craftsman glue only the wedges when assembling the joint — no other glue in the mortise. So with a little steam and heat, the wedges could be worked loose to repair the joint.