Once the saw cools down from cutting all of those tenons out on our legs, it’s time to create a plane for them to go. Cutting out all of the mortices in an accurate manner will be important when we put stretchers on, so BE CERTAIN about your layout. Superimpose individual legs over where they need to go and mark from them, rather than trying to measure. It’s less precise, but more accurate.
I started by knifing in all of my layout lines to prevent any splintering, then hogged out most of the waste with an auger. I will admit to a certain amount of cheating in this regard, using electrons as allies. When it’s your arms, feel free to be a purist. But as my Drill Instructor once said, “If you ain’t cheatin’, you ain’t tryin'”. Be sure to bore from both sides so that any inaccuracies will meet in the middle and leave your outer, show surfaces precise. It’s all too easy to wander off a little, and with 3½” of mortice depth, it will go rather far afield.
Once the bulk of the waste has been bored out, I clean up with a chisel, trying to keep everything as well-fitted as possible.
Then it’s time to work on the outer mortice, which is actually rather similar to a crossing joint. Either way, it’s got to go. The knife lines should already be there from where you laid out your mortices. I go ahead and use a large tenon saw to cut down to my knife lines.
I stop a little bit shy of full depth. This lets me sneak up on a good fit. After splitting off most of the waste with a chisel and mallet, I ease it the final bit with my router.
Then starts a trial and error process. You want it to fit easily, but not loosely. Snugly, but not tightly. These are big joints with lots of bearing surface and friction. If they’re too tight, it will be a real struggle to get everything together during glue-up. So try to put it together, but if it needs more than a few taps with a mallet, refine your fit. Remember to start working from the middle out (including the possibility that your tenon might be a little fat yet) so that your show edges are touched last.
Eventually, the tenons will go all the way through the slab top. When seated fully (check your shoulders!), they should be a smidge proud. We’ll trim them flush later. Only three more legs to go–guess I should switch batteries in the drill…