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I was having trouble bending ebony for 1/16" rosette purflings. I was determined to use ebony not dyed maple or black fiber doubled up. I could bend them ok but they had flat spots. I wasn't getting a fair curve. I was trying to inlay them into a sound board and those flat spots and inconsistent curve was making it quite hard with the real possibility of damaging the edge of the grove in the spruce. I could do it but not all my tests came out well and didn't want to risk it on the real thing. So this is what I came up with:

I took plate aluminum scrap. 1/2" thick is fine. Ripped it on the table saw (regular carbide blade with some bar soap on the blade works fine) Then cut it into a square on the chop saw. Made a small dimple in the center and with a compass drew a circle the size I wanted. Then I used a hole saw to cut out the center. ( I did this to use the inside gripping jaws of a metal lathe) Then back to the chop saw to cut the corners off of the square at 45°. (Now I had a octagon ) Then at 22 1/2° cut the corners again. (It is close to round at this point and if you don't have access to a metal lathe any machinist could take it from here and finish one in literally 2 minutes or less. A couple of bucks, beer, some trade, done. )


You need to pre-bend the wood on the hot pipe. Just enough so you can clamp it up with out it breaking. I use a thin piece of popluar, ash , maple or other non staining wood for a caul between the wood you are bending and the hose clamp. This is reusable and should be quite thin, 1/16". Clamp up the wood you want to bend and regester the clamp, caul and wood to one edge of the aluminum ring. (This will keep the wood away from the heat source.) Put the clamped up stuff on a head source. Wood stove or electric burner works best. You can use the oven or a gas store but on a gas stove watch out for the flames going around the edge of the doughnut and scorching the wood. I heat it until water sizzles off of it like you would look for on a bending pipe. Then take it off and let cool. As soon as it's cool you have a perfect ring. I have done up to 1/8", I am sure one could do thicker. On thicker you may need to tighten the clamp after things got hot.
The neat thing is that it is so easy to make the doughnuts any size you want. For sound hole binding you should make the doughnut bigger than the opening for 3 reasons. 1. is that you need extra length to fit your joint especially if you are doing a scarf joint. 2. If it is bigger than the opening it is almost self clamping as you compress the ring to get it in the opening. 3. You get a fairer curve by making the circle tighter than by trying to open it up.
Pictures should tell story even if they are not the best.
Link

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Cut to size.....Beat to fit.....Paint to match.

A couple more pics.

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Cut to size.....Beat to fit.....Paint to match.

Pretty nifty Link!

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Bill Hodge


One does not simply, own enough guitars!

Not a bad little trick there. I would have to make it out of wood, but its only holding the form to keep flat spots out, so a wood one would work fine I imagine. Necessity is the mother of all invention. Well done.

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http://www.sixgunguitars.com

Brian,
A wood one wouldn't work because you couldn't get it hot enough. On second though it might work if you heated it in the oven and perhaps had some wet kraft paper between the wood you were bending and the wood doughnut. Wood would work fine to laminate some veneer with glue but that is a different animal. The aluminum conducts heat really well and this gets as hot as a bending pipe.
One of these could be made with a router and I designed a jig to do it for folks who don't have a lathe but it is fairly easy to find someone who has a metal lathe.
Aluminum scrap is pretty easy to source as well. Aluminum works really well with standard woodworking tooling such as circular saws, table saws, chop saws, and routers.
Link

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Cut to size.....Beat to fit.....Paint to match.

That's a great tool. I've always had some stubborn flat spots to sand out on my sound hole binding and now I won't have to. I disagree that wood would make a good ring. Much harder to heat and probably wouldn't last so long.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com