How to bend half-round?

[Floont]

I'm making a 9" dia. ring out of brass half-round. After torturing a 36" brass h-rnd bar for about a day it now has a roughly circular shape, but I wasn't able to control the degree of axial twist, so it won't lie flat on a plane surface. If this is correctable at this point, how do I do it? Or, if I have to start over, how can I control the twist? Would it help to heat up the bar?

Thanks for any suggestions
Floont (new member, glad to have found this forum)

 

[CalgaryPT]

A pic would help. But if you are referring to what I think you are referring to, I did something similar with steel tubing once for a rolling ball sculpture. I solved the twist issue (once the tubing was bifurcated) by tack welding one half of the cut tube to another (solid) tube, and then rolled it. Ideally, you want a tubing (not ring) roller to prevent twist. But before I got a tubing roller I did run it through a regular ring roller and gerry rigged some guides to minimize twisting. Running a longitudinal Sharpie mark on the tubing helps track any twist.

Great results, but you need to do some clean up on the roller marks afterwards as the combined wall thickness will be slightly oversize for standard dies. I'm sure there are other methods, but this is how I did it with steel tubing. I think it was 1 inch, and about 1/16 wall. For brass you could just solder obviously.

BTW welcome aboard the forum.

 

[CalgaryPT]

Just noticed that PA has their min roller on clearance sale for $37. Not sure if it will work for your project's thickness of bar, but the capacity s/b higher than stated as theirs is rated for steel. I do have one of these mini ones as well as my big boy rollers, and it is great for the diameter you need.

https://www.princessauto.com/en/gear-driven-planetary-metal-ring-roller/product/PA0008536799

 

[Floont]

I take your point re a picture. I'll get one up. It'll show the real cause of the difficulty, which is that the circular bend needs to be edge-on rather than flat-on. I think the roller in your link would only be good for a flat-on curve.

 

[Floont]

For better or worse, this is a one-off project. But if I had to do it over, I think I might try "rounding out" the half-round brass with a dummy half-round of vinyl or pvc, and then use a tubing bender.

 

[CalgaryPT]

Ahh...now I understand. Yes, that is an interesting challenge. Having said that your effort here looks pretty good from the pic.

Almost tempting to just roll the circle from solid round stock, make a mold to hold a section at a time, and mill away half of it bit by bit. But I'm not sure results would be much better than what you have achieved here.

What is it for BTW?

 

[Floont]

Thanks for your ideas. Brainstorming is my favorite pass-time. Another idea would be to somehow reduce a large pulley to half its thickness (i.e. its width across the plane of its circle) and rivet it to a flat plate, so the brass stock would lie in it on edge, with its flat face to the plate; then this half-pulley could become the die for an extra-large radius tubing bender, if combined with appropriately long handles.

But actually, things are looking up, here. The twist is proving to be correctable without re-doing the radial bend, using a long handle of aluminum stock with a hole in it to match the cross-section of the brass piece. So the existing ring is salvageable.

It's intended to be a tone ring for a banjo, to go on top of the "pot" and under the head. Whether it's worth the trouble remains to be seen.

 

[CalgaryPT]

Wow, good for you. It makes me smile knowing how terrific that brass will look when you introduce it to a buffing wheel. Please post your final results. I'm always jealous of people that can play instruments, even more so of people who can build their own. The closest I ever came was taking some saxophone lessons once...but I sounded like a sodomized moose.

Best of luck.

 

[Floont]

OK, it may be a while, but I'll post some pix when all the coercion is over.

 

[Susquatch]

The closest I ever came was taking some saxophone lessons once...but I sounded like a sodomized moose.

I have literal non-stop tears running into my beard. Now that was funny! I'll be using that line myself when the opportunity arises!

Closest I ever came to a home made musical instrument was a guitar made of a cardboard box and elastics when I was a boy. I'm not gunna even try to top your moose sound. Suffice to say that ny dad was so horrified that he went out and bought me my first real guitar.

 

[Floont]

After several days of relentless dialogue with an assortment of shade-tree persuasion devices, the half-round brass rod finally submitted to circularity. Here it is free-standing, in position on top of the banjo pot, and as seen through the translucent banjo head.

In a Ludwig banjo, shown here, head vibrations are transmitted via a wide collar down to a base where you see the tension screws going through it. The top of the pot curves up under the head, but does not touch it. My idea was to use the half-round ring to extend the pot up to contact the head directly. The good news is that as expected this makes a difference to the tone; the bad news is that it wasn't necessarily an improvement — the thing still sounds pretty ricky-tick.

I doubt that I will repeat the experiment, but just in case somebody else is trying to make a ring out of half-round, here's my thoughts in retrospect: first, brass is springy, so it has to be over-bent. My first attempt involved a 4.25 inch radius armature and only gave me a 5 inch radius curve. Second, an armature to bend the rod over should be made of metal, not wood, and it should have a flat side against which the flat of the bar can be firmly clamped as bending takes place. And you need an extension arm about 3 feet long for enough leverage: just grabbing the unbent bar worked for about 10 degrees of arc, then I had to resort to a power-pull for the rest of the circle. Might use a 1/2" id pipe with set-screws to keep the rod aligned inside it.

Thanks for the suggestions and encouragement. By the way, the anguished-moose expression is going into my permanent collection...

LFMiller (Floont)

 

[CalgaryPT]

I think you pulled that off admirably. Nice work.

 

[David]

Darn fine work there!