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Final report: what worked for me
I can't leave this thread without sharing how I set my secondary bevel and got a decent shaving edge on the Takamitou wedge razor. The key for me was to change the conventional taping method, which doesn't work with this razor. The reason is the razor's irregular geometry.
On a hollow ground razor the spine is machined to a consistent distance from the edge. Also, the fat part of the spine creates a consistent height and length for the angle of the secondary bevel. That makes it simple to tape: you don't have to center it exactly, as long as both sides extend into the hollow.
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On the Takamitou wedge, you do have to be exact about taping, because the edge of the tape, which touches the hone, determines the height and length of the honing angle. What's more, the Takamitou's spine is not machined, and it's curved a bit from one end to the other. So if you wrap your tape around the spine in the usual way, it's unlikely to be the same distance from the edge of the blade at every point. As a result, the angle of your secondary bevel will be inconsistent, making it impossible to get a well-honed edge. I suspect this is why people haven't been able to sharpen this razor.
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Enough theory, here's the method I used:
1. Cut a piece of electrical tape the length of the spine. (Note, I used a single piece of tape, not two, to keep the angle within recommended limits)
2. Cut the tape in half lengthwise. Note the "factory edge" of each piece (the edge you didn't cut), and put it some place where you can easily pick it up later.
3. To make the jig, cut a piece of heavy-gauge paper to the long dimension of the blade.
4. Fold the paper in half along the length, creating a sharp, straight crease. Using a straightedge, cut your jig to the width of the bevel.
5. Open the paper and carefully place the sharp edge of the blade into the crease. Hold the jig snugly against the edge and sides of the bevel, being careful not to cut the paper (or yourself!).
6. Tape the spine, one side at a time, using the jig as a guide. Be sure to apply the factory edge of the tape against the jig, not the edge you cut.
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That did the trick for me. With this taping, my honing was pretty standard: after a Norton 4k/8k pyramid sequence, I finished on my Chinese waterstone and a few strokes on the CR 0.5 balsa strop.
I'm getting good shaves with this razor. Before each shave (after the first one) I give it 30 or so strokes on the leather strop, with a little slack since this is a wedge. I've kept the paper jig so I can use it the next time the blade needs honing.