What is Drawboring?
Drawboring is done in a mortise and tenon joint and is similar to a pegged mortise and tenon joint, but instead of simply drilling a hole through the mortise and tenon, and inserting a peg, the hole drilled in the tenon is offset by about a 1/16 of an inch. This is done so that, when the peg is hammered through the joint, it draws the joint together very firm and creates a very strong mechanical joint. In fact, some people don't even use glue with a drawbore joint because it is so strong, but I think glue is still a great idea, you know, just in case.
What do I need?
In order to create a drawbore joint, you don't necessarily need anything special, but I will recommend getting getting a set of drawbore pins. I ordered a 3/8" pin from Lee Valley to match the size of the drawbore pegs, or dowels, I am going to use. A drawbore pin is a tapered piece of smooth steel that, once you have the joint prepared, you push the drawbore pin into the joint to "loosen" the joint a bit so the peg or dowel will be able to make its way into the joint without completely breaking the peg.
So, how do you make a drawbore joint? Christopher Schwarz has a really good article on drawbores that I suggest you check out for some great details. If you are, like me, more of a visual person, Paul Sellers has a good YouTube video on his channel. There are several others that have examples of how to make a drawbore joint as well.
The basic premise of the drawbore is actually pretty simple. First, make a standard mortise and tenon join, nice clean joint, firm fit, etc. Next, disassemble the joint and drill a 1/4" or 3/8" hole through the side of your mortise joint. I suggest clamping a scrap piece to the back of the mortise so you don't have a blowout on the back side; always start drilling on the show side so it stays nice and clean.
Next, put the joint back together and insert a brad point drill bit the same size as the hole you drilled. I prefer a brad point because it has a nice sharp tip on it that will give you a crisp center mark. Insert the bit into the hole that was drilled in the mortise and give it a light tap to make a mark on the tenon. Do this for all joints.
Once you have done that, take the joint back apart and locate that tick mark you just made. Now, make another tick mark about 1/16" towards the shoulder of the tenon; that is key. If you go the wrong way, you will actually loosen your joint. Next, drill a hole through the tenon on that mark closest to the tenon shoulder. Once all those are drilled, reassemble the joint and use your drawbore pin and carefully push it into the joint to make way for the peg, then remove the pin.
The last thing to do is to take your peg or dowel and taper one end of it so that it can get into the joint without getting hung up. Put glue on your mortise and tenon joint, put some glue on the tapered end of your peg, and carefully drive the peg into the hole until it comes out the backside of the joint. You now have both a mechanical and a chemical bond in your joint with virtually no way to get it apart and should last a lifetime.
So, that is the quick and dirty of the drawbore joint, I will provide a little more visual elements when I get to make the joints for this table. In the meantime, check out the resources above or just do a Google search for "drawbore joint" and you will get a lot of material. I suggest giving the joint a try; it is a very strong joint and also adds a nice design element to your piece. You can use all different types of shapes, sizes and colors of pegs that help your joint standout. Experiment and have fun with it!