Kirby uses mortise and tenon joinery to construct the base. This is a traditional method that is strong and durable, but it takes a little practice and is a bit time consuming to do well. Niall Barrett modified Kirby's bench by throwing out the mortise and tenon work and creating a joint that uses draw-bolts and biscuits. (Biscuits are thin wafers of wood that fit into slots you cut.)
I liked the idea of draw bolts for a couple of reasons. First, there's a lot of movement of wood owing to seasonal variations in humidity, and I can only imagine that this is amplified in my unheated, un-air-conditioned shop. Many woodworkers even put draw bolts on the fancy cabinetmaker's benches to allow them to tighten up the bench as needed, but they hide them. Niall Barrett doesn't bother with this, and though I don't have a photo to show you (owing to respect for copyright), you'll have to take my word for it that the result is classy, in an industrial materials sort of way. As my friend and neighbor, architect Upe Fluekiger would say, it celebrates the bolt.
Upe is originally from Switzerland, though, so it comes out sounding more posh in his Swiss accent than it does in my West Texas one. More like, "It cey'-lee-brates de bolt."
Well, after seeing Barrett's bench, I decided I needed to celebrate de bolt for sure. I wasn't really all that keen on celebrating the biscuits, however, thinking that mortise and tenon joinery would be stronger, and though hidden, more elegant. Besides, I needed the practice cutting and fitting mortises and tenons, and with twelve such joints, I'd get plenty of it.
There's one other, very important reason I decided to use draw bolts, though, and that is that it eliminates the need for glue. This bench will be very heavy and large, and should we ever move, it will be much easier to transport it if I can break it down.
So the base of my bench is a hybrid of Kirby's and Barrett's, taking the features of both that I like. After I milled all the wood so that everything was square, I cut the mortises by first drilling out most of the waste with a Forstner bit, and then cleaning it up with chisels to make it square:
Then I cut stub tenons, using dado blades on a radial arm saw, and fit them to the mortises using chisels and a shoulder plane:
As you can see from the photo above, after I trimmed each mortise and tenon to mate, I labeled them so that when I take the bench apart, I can put it back together again with the best fit possible.
These joints aren't perfect, but their messiness is hidden and the shoulders are square, so they sit very well when they are fit together. After I had the mortises and tenons fitted, I drilled the nut and bolt holes in the stretchers. In order to align the bolt holes in the center of the mortises, I'd previously drilled them as I'd hogged out the waste. So to line the stretcher hole up perfectly, I drilled a hole in a scrap of wood on the drill press so that it was square, then used it and the bolt hole in the leg as guides to steady my bit:
You can see from some of the photos that I cover the work pieces with various "witness marks" and notes to myself to keep from messing up. I also dry fit everything eleventy-million times throughout the process. It might seem to slow things down a bit as I go along, but it is faster than having to re-do something because I've mis-aligned a hole, or have leg "A" mismatched to stretcher "C"...
Square and true:
The result turned out pretty well, I think. In fact, I'm celebratin' all to heck about it.