A little trial and error showed it could be done with a simple jig. Like the flush-cut saw, the ryoba has no set to its teeth, so it won't damage the jig (not too much, those teeth are wicked) and leaves a smooth surface.
The jig took all of 10 minutes to make. The only requirements are a flat base board and guide pieces of equal thickness. You can see where I let the saw flex too much and the sides of the teeth chewed on the jig. It uses my favorite all-purpose precision shims, children's flash cards. The ones here are notched to slip over the parallel guide on my leg vise.
A test piece of cherry ready to cut, with enough shims to leave the desired tenon thickness.
Cutting the first corner. Use the rip side of the ryoba.
The next corner. The teeth of the ryoba actually work quite well against the grain like this.
Taking it flat down to the mark.
After flipping the piece over in the jig and cutting the other cheek, resulting in a perfectly centered tenon. Notice how uniform and parallel the cuts are.
Setup for the flush-cut shoulder cut.
Cutting the shoulder.
The photo just doesn't capture how clean this cheek is. Notice the small reddish streak lower right on the bench: the back edge of the flush cut saw is sharp, so don't flatten your fingers against it while sawing!
The other shoulder. I did a lousy marking job on this test piece, so my shoulder lines don't match on both sides.
The finished tenon straight from the two saws. Provided the mortise is an accurate match, this will be a nice fit.
My personal goal is to develop the skill to saw tenons like this free-hand with a backsaw. I'm not there yet, so it's nice to know this technique is available.
Stupid Sawyer Tricks: the precision of this cut got me to wondering just how thin a slice I could take. I added 6 flash cards to shim it up a bit higher.
Ridiculously thin resawing.
The slice isn't much thicker than the saw kerf.
Finally Monsieur, a waffer-thin mint!
There are some practical applications for such thin stuff:
- Slice off small veneers of really expensive stuff like zebrawood for book-matching on a small box lid.
- Make matching veneers for shimming up a loose joint or dutchman patches.
- Do a series of slices for a small bent-wood lamination.
- Make various small craft items, like bookmarks, wooden cards, or Christmas ornaments.
- Use the jig to cut key slots in the mitered corners of a frame (make two cuts, leaving thin waste that you can clean out with an extra-thin mortise chisel), then cut contrasting key stock this way.