If you are really bad at cutting mortise and tenon joints, making frame saws is a great way to put your lack of skill to use. There are only two things to worry about when cutting the tenons – the ends. As long as the distance between shoulders remains long enough match the span between the braces, you’re golden. It’s actually beneficial to the operation of this tool if the tenons are too short, and a little loose. As tension is applied by turning the cordage along the back, the bracing arms will flex, using the tenons at the stretcher as a fulcrum to make the saw-plate taut. If the joints allow the braces to rotate just a bit (by not bottoming out on the tenon ends) the whole part can teeter at the tenon before strain is put on the wood, though the tension does make it to the saw-plate. As long as everything is mostly centered, the joints match, and there’s a little bit of play, this part of the construction is pretty easy. As said, if you are bad a mortise and tenons, this is a chance for you to excel.
Just keep the stretcher long enough.
For me, it was a matter of setting the saw-plate into the respective brace ends and making sure they were square. Oh, yes, and I cut some 1/4″ round barstock to length and drove it through the holes in the kerfed ends and saw-plate to hold everything together. I’d prefer to use brass than steel, but I’m also working out of a scrap metals bin as well as scrap wood pile. Regardless, I tapped the steel rod through the brace ends and saw-plates with only the most minute vulgarity when things didn’t quite want to line up. A bit of wax or oil inside the pilot holes might have helped. After all, if it’s a pain in the backside, use lubricant.
Squared braces with the blade mounted I marked the span between the braces onto the stretcher material. Doing this twice with a thumbs-width more on each end set me up to have sufficient material for tenons on both stretchers. Once crosscut to length both of these were set up in the brace where the shoulders were marked and the sawdust making continued. Or more accurately, the chips flew as most of this work was hacked out with a chisel.
The next part was equally tricky: Figuring out how far up to cut the mortises. Trick question, really. I knew where the saw plates ended, and I could grip the wood above it, so the solution was a little bit more than the width of my hand above the back of the saw plate. I marked this on one brace, then disassembled everything to have all four brace parts ready to work. I used the mark to base where the shoulder of the tenons should go, then marked each mortise off the tenons that were already cut.
One good mortise chisel and about ten minutes and I had four well cut mortises that were a little deeper than the tenons which would mate with them. A little paring cleaned up the cheeks and everything went together smoothly, and a little sloppy, just like I wanted.
The final bit was then shaving a little material below the notches of each brace where the cord would be looped. Took just a couple minutes paring, though I did get a little overzealous at one point and ended up cracking off a corner. No big deal really, if it split during construction, it would have split in use soon enough… and this is a service tool, not a wall hanger.
Ready for final assembly… Locked, Cocked, Ready to Rock.
The paddles were the last part before final assembly. I happened to have a short piece of walnut that had once been intended to be the wedge for a wooden rabbet plane. For the other I took a bit of off-cut from the stretcher material and planed it thinner. Both got a little tapering and paring on the end which rests on the stretcher. Since I have little interest in wearing out the hemp cord either, a quick rounding with a block plane broke all those pesky sharp arrisses.