Jack Dover
the issue here is that the original form of a blade before bending is not a band (i.e. a long rectangle). You can easily see that a rectangular blank isn't going to work by doing some paper folding: just cut a piece of paper and try creasing it so that two lower edges are at a right angle to each other and that they stay like this while being stretched. https://www.holzwerken.de/werkzeug/saegen3.jpg -- doesn't show that the first few inches don't have enough steel to file a tooth.

The actual blade has a shape as if two bands were connected sidewise for a couple of inches at ends, kinda like a stretched out Teris Z-piece. Not sure whether it was stamped out and then folded, or maybe an L-corner was ground to shape. Then a horizontal part is ground to a taper for a few inches and doesn't have teeth on that tapered part.

No doubts you can figure how to fold a blade in your garage. However I don't think it's going to be something that produces a result comparable even to crudest coping saws. Let's consider how it works.

So we made a vertical and about to enter it with a horizontal part. You would have to force about an inch of a ~1/8" wide tapered steel plate that doesn't have any teeth in a vertical kerf horizontally before the first tooth on a horizontal section will get engaged. It's possible on some really soft woods, but I can't imagine doing it even in poplar. And even on softwoods it breaks a good chunk of wood out, so big that a knife line doesn't really stop it and a blowout goes well below a base line. Blowouts are actually visible on that video everyone is so amazed with, Frank just puts it on the inside face, but it's still visible even at 360p. If I would need something faster than a regular coping saw for a finer piece I'd use a sharp turning saw just for its long blade.

That being said I'm having troubles finding good joinery blades for my frame saws: thin plate, wide, 15ppi or higher, minimal set, both in cross and rip patterns. Ideally it'd fit a Highland Woodworking's classic frame (their universal blade is too thick, overset and too coarse), but I would even make yet another frame or two just for such a blade. I have an old Jorgensen miter box blade that lost its teeth, but I'm not really good at re-toothing, also it was impulse hardened, so the rest of the blade is probably be too soft. I was about to try what you did for that resaw frame, but if you or anyone else knows a US-based source for such blades I'd really appreciate a link or contact info.