This is an excerpt from “The Intelligent Hand” by David Binnington Savage.
Joinery – that’s what this is about. Joints that hold components together. In this case, versions of one joint, the mortice and tenon. There are on this bench frame three different versions: stub mortices and tenons; through-wedged mortices and tenons; and through dry-tusk-wedged mortices and tenons. So that you can take this structure apart to move it, the tusk wedges are just friction fit, but the bench is solid as a rock when assembled.
To gain strength, we use wedges in two of the three joints. In the knockdown joint, the top of the mortice is angled – a wedge is driven in above it to hold the structure. But this is getting too complex too soon – let’s look at the simple through-wedged mortice-and-tenon joint.
Basically, a mortice is a hole. With hand tools, you can chop it out with mortice chisels or drill out the waste and pare to the lines. But we use a morticing machine, which saves lots of work. This is basically a drill bit that cuts slightly ahead of a square cutter that chops out the corners.
First let’s get into marking-out mode. This diagram gives you the idea. Mark distinctly both the component position and the mortice position. Mark the mortice with a mortice gauge, with the knives set 30mm apart. As always, mark from the face side of each component.
This is the type of drawing that I like to see every student make before making a joint – it helps one to think about what is being done, and to think about the mechanics of this joint. This is not just a peg in a hole with glue; it’s a mechanically effective joint that would hold up without any glue. The two small wedges turn the tenon into a dovetail, splayed wider at the outside than the inside. It’s as tough as old boots.
First make the hole (the mortice) then the plug (the tenon) to fill it. Our morticer cuts pretty cleanly; I like and use machines that save me time and do a better job than I could. Chopping out a mortice by hand is nice and sweaty work – and some of you will be happy doing it.
The tenon gets marked out with the same mortice gauge setup (30mm, marked from the face edge). We use a setup on the band saw to cut those tenon cheeks to exactly the right size. Because this joint gets cut a lot, a dedicated setup for it makes good sense.
Have a careful look at the drawing above right, noting the stop and spacer at the bottom of the page. This stop is simply a block of wood cramped to the band saw table. Next to it is 31.5mm-wide spacer against the fence. The fence has a stop at the end to prevent you from going too deep past the shoulders. The idea is this: After the first cut, you need to move the fence 31.5mm to make the second cut and get a 30mm tenon. Try it out with some scrap. Cut one tenon cheek, take the spacer out, move the fence then cut the second shoulder. Does this give you the tenon you want? If not, cut a new spacer, thicker or thinner, as needed.
Make sure your blade is good and sharp and that you run slowly into the blade. Chunka, chunka, chunka….
We cut the tenon shoulders at the table saw. The blade height will be the same for all; the shoulder position will be measured for all and a stop set up probably off the end length. Tenon lengths will be different for the different kinds of joints.
— Meghan Bates