Before I attached the uprights to the feet, I needed to cut the through mortises for the lower stretcher. As in most things, accurate layout is the beginning of a good joint. I wanted the top edge of the stretcher to be the same height as my sawbench, so I measured accordingly, and subtracted 3″ for the height of the foot. This gave me the distance from the shoulder of the tenon to the top of the stretcher. Since I was going to be working on the mortise from both sides, I carried this measurement all the way around the upright. For this kind of job, a saddle square like this large model from Veritas can’t be beat.
Following the first mark, I made another mark to show the bottom edge of the stretcher. This mark isn’t absolutely necessary, but it helps me visualize things. I then marked in 1/4″ for the tenon shoulders.
Next, I laid out the mortise width. I wanted the tenons to be as wide as possible, so I allowed for 1/8″ tenon shoulders. Since I was working with 7/8″ stock, this gave me a final mortise width of 5/8″. I set up my marking gauge accordingly, and marked the mortises as close to centered as possible. Since I was going to attack the mortise from both sides of the board, I marked the other side to match. When you do this, it’s important to flip the board end-for-end so that you register the marking gauge on the same edge of the board. This ensures that, even if the mortise is slightly off-center (as is usually the case), the marks on the two faces line up and all is well.
To remove the bulk of the waste, I prefer a brace and bit. No other technique gives me the same level of control and ability to adjust to variables. My sawbench and posterior give an excellent clamping arrangement for this technique. Of course, if I were boring into the edge, I would have to use a couple of holdfasts instead.
Since this is a 5/8″ mortise, I used a 1/2″ bit. This allowed me some leeway for final trimming. I bore from one side until the point of the auger breaks through the far side, stopping before the spurs break through. I repeat this for a series of overlapping holes, the result of which you can see above.
Now, with the board flipped over, I bore in the opposite direction, using the pilot holes to register the bit. The result is a scalloped opening. Note the wood border between the holes and the marked lines. Note also how some of the scallop points have broken off with the grain. More on this in a moment.
The rest is simply a matter of cleaning up with a chisel. Since the sides are parallel to the grain, this doesn’t require a great deal of force. On the contrary, the wood is often too willing to break away, as was seen in the previous photo. Go slowly and gently with this operation, or you may find yourself staring at a chunk of wood that you didn’t intend to remove. As with dovetails, work towards the center from both faces to avoid surface tearout.
Unfortunately, I didn’t get a photo of a completed mortise. However, really, there’s not much to see – a rectangular hole in a board, not very exciting. Of course, if I had messed one up, THAT would have been blog-worthy. Fortunately, I managed to avoid that. Next time, I’ll make the matching tenons. Stay tuned!