The other day I was working at some parts for some joined stools; and was able to get a few photos of some of the drawboring process. I still haven’t assembled this particular stool, but cut most of the joinery. The stool is for a demonstration I am doing down at Colonial Williamsburg on Feb 2; so it’s one of those Julia Child scenes; where I make most of the parts up here, then chop two mortise-and-tenon joints down there & presto! joined stool.
The essentials of drawboring a mortise and tenon are simple. The holes for the pegs which secure the joint are intentionally offset in such a way that a tapered peg, when driven through the holes, will pull the tenoned rail up tight against the mortised member. No glue, no clamps. Simplicity itself.
Here I am testing the thickness of the tenon in its mortise. I pare the tenon with a wide framing chisel; then I will saw & split off the upper 3/8″ of the tenon.
Once I’m satisfied with the fit, I insert the tenon and mark with an awl the location of the mortise’s holes on the face of the ten0n.
Here is a detail of the piercer style bit used to bore these holes. This bit is about 1/4″ to 5/16″. I eyeball the amount to offset the holes, towards the shoulder of the tenon – “about the thickness of a Shilling” says Joseph Moxon. This view shows a drawbored joint, unpegged, so we can sight through the offset holes. This much offset is perhaps a tad overdone, but it will work.
I make the pegs from split, straight-grained oak. I shave them with a chisel to a tapered octagon. I eyeball the size. Here is a cross-section of the peg’s path through the intentionally mis-aligned holes. This view is of a sample joint I made about 15 years ago. It has many of the hallmarks of seventeenth-century New England joinery: an undercut front shoulder, a tenon that is shorter than the mortise is deep, and in this case, no rear shoulder to speak of at all. This joint is only fastened with 1 peg, plus this 2nd one that is cut through. It has been handled by thousands and thousands of people over 15 years, and is as tight a joint as one would ever need.