Tube Bending Questions

[Chris Kelley]

I'm designing a product that will incorporate a bent-tubing handlebar, and I'm wondering about the feasibility of producing this design as it currently stands. I'd like to use either 1/2" medium-wall steel conduit (actual OD is approx. 0.70" with a 0.042 wall thickness) or some 3/4" steel tubing that isn't much heavier.
So my questions are these:

1. Is a 1" centerline radius bend in 3/4" tubing with said wall thickness doable? A little bit of kinking isn't necessarily a show stopper as long as it doesn't collapse to the point of ruining the structural integrity of the handle.

2. Could we achieve this with something simple like custom dies in a hydraulic press, or would outsourcing to a CNC bender be the only option?

3. If outsourcing is the better option, do I need to choose a material with a more precise OD than inexpensive steel electrical conduit?

Thanks in advance for any knowledge shared.

 

[mjr6550]

I'm no expert in bending, but have expermented bit with bending. In general, the thinner the wall the more problems you will have. Packing the tubing with sand and using heat (several details and precautions are involved) would probably get the best results, but I don't think that you will get that radius. Others will more experience may correct me.

Would using solid bar for the bend and then weld, thread, or press fit tubing to that be an option?

 

[memphisjed]

That is 3/8 pipe not 3/4. Not sure what schedule it is with your wall thickness being a typo.
Only need cnc if making thousands, a few hundred and a rotary draw or even Hossfeld. If you just need a few a conduit bender would work.

 

[Chris Kelley]

@mjr6550 Thanks for weighing in. Some sort of fitting at the joint could be an option, though it'd far less ideal from a production standpoint.

@memphisjed Oops. I meant to say 1/2" conduit and 0.042" wall. Just corrected the OP.

 

[Scottl]

Before trying to bend production quantities yourself you might want to get quotes from shops that specialize in it.

 

[Garwood]

1" CLR sounds pretty severe for that size and wall thickness stainless.

If you said 2" CLR I'd say that sounds reasonable to do with a hand or bench bender and no mandrel. But 1" CLR sounds hard into mandrel territory to me.

 

[Graham Gott]

Woolf Aircraft shows 3/4" x 0.065" wall tube elbows at a 1" centerline radius. That is certainly mandrel bent, which would be a huge investment in equipment to do in house, but they do contract bending.

Hossfeld sells a 3/4" tube die that is 1-7/8" centerline radius which bends 0.065" wall mild steel tube. They typically have the smallest radius dies for a reasonably affordable machine, 2.5 diameters is about as tight as you can bend without a mandrel. For comparison, the smallest CLR that JD2 sells for their machines is 2-1/4" (3 diameters).

 

[memphisjed]

1" CLR sounds pretty severe for that size and wall thickness stainless.

If you said 2" CLR I'd say that sounds reasonable to do with a hand or bench bender and no mandrel. But 1" CLR sounds hard into mandrel territory to me.

Not stainless and can have wrinkles. That is a tight radius, wasn’t impossible with 3/8 pipe.

 

[Garwood]

Not stainless and can have wrinkles. That is a tight radius, wasn’t impossible with 3/8 pipe.

He edited the post. It said stainless tubing. Now it says steel conduit.

 

[Chris Kelley]

Thank you guys for the help. I'm currently trying a redesign with 2" CLR based off what what I'm hearing here.