Tube Bending Help

[Andrew R Stewart]

So I have a possible project which would be best done with a tube bent that I can't produce myself. Tube diameter around 1.25" + or -. Wall .035 - .049. About a 90* curve at approximately a 5-6" radius. I can make a stem like two piece part, brazing two tubes together, but if a single piece could be crafted it would be nicer.

Any one care to offer assistance? Andy

[thollandpe]

So I have a possible project which would be best done with a tube bent that I can't produce myself. Tube diameter around 1.25" + or -. Wall .035 - .049. About a 90* curve at approximately a 5-6" radius. I can make a stem like two piece part, brazing two tubes together, but if a single piece could be crafted it would be nicer.

Any one care to offer assistance? Andy

Andy, you can find some rules of thumb here: Bending Formulas | Bend Tooling

That sounds like a really aggressive bend for thin-wall tubing. Your outer radius is 15% longer than the inner, that's a lot of elongation.

If you follow the rules of thumb above, your bend difficulty rating is 6.3 to 10.1.

Todd H.

[Andrew R Stewart]

My gut said as much but without the math:) Andy

[Clockwork]

Would one of these help?
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[halekai]

If you figure that bend out you come on back and tell us how you did it!

Ive done a lot of bending with a JD-2 model 32 and a Diacro #2 . I can tell you that a conventional bender will not even come close to what you are shooting for even packed with sand and welded shut.

There might be a way to do it but you would need to sand pack and use a roller bender from harbor freight and some custom dies from Swag Offroad.
You would need to modify the centers of the rollers and bring them closer together. Still not sure you would get it that tight.

The other way to do it is with an internal mandrel, essentially a round ball that is pulled through the tube as it is being bent. This setup is very expensive.

The third way to do it is Yoshimura style. He is a Japanese motorcycle builder who makes sick exhaust pipes. You pack with sand (or not) and use a torch to heat up the tube at just the right places and slowly add pressure to get your bend. There are some videos of this on youtube. I have tried and failed. It is way hard. As soon as you think things are going wrong...its already too late.

One way that Ive been thinking about is to set it up on a JD2 with very gentle pressure being added to the system slowly over a period of days. My experience with bending thin walled tubes is that any slip or relaxation provides an opportunity for a deformity.

You can try giving the people at Diacro a call. Family business. The son does a lot of the R and D and he would be happy to 1. Answer any questions and 2. If you sent him a few samples he may agree to do some test bends to see what is possible with state of the art benders and follow bars. Maybe pack one with sand and let him have a go.

Good luck to you.