Random bending q

[Dammit]

I need to get a nice tight radius in some thin wall 4130 tube.

Now this will fit in my (plumbing) pipe bender, but I don't want to crush the inner face of the tube.

If I fill the tube with dry sand before bending, will this support the profile of the tube sufficiently to stop the crushing normally observed (on copper tubes)?

[jas xjr]

You could try heating the tube too.I reckon the sand would help retain some heat too

[Dammit]

My concern there would be that if the sand was anything other than kiln dry it might expand in a rather excited fashion when I apply the torch.

Sealed tube full of damp sand+heat=pipe-bomb

[226bhp]

It depends on what you mean by tight, but from my experience your chances of success range from slim to fk all....

[Dammit]

Hmm. Inner diameter would be ~10cm.

[stevieturbo]

Dammit said:

I need to get a nice tight radius in some thin wall 4130 tube.

Now this will fit in my (plumbing) pipe bender, but I don't want to crush the inner face of the tube.

If I fill the tube with dry sand before bending, will this support the profile of the tube sufficiently to stop the crushing normally observed (on copper tubes)?

Diameter ? How tight ? for what application ?

[andyiley]

I think I would be looking for a mandrel bent tube on the 'bay for a handfull of quid to be safe.

[Dammit]

Stevie - 15mm tube (OD), for part of a frame that runs around a tyre.

It's structural, but doesn't have to be too strong as it's tying things together rather than resisting load.

[43655]

4130 is a stiffer and harder than copper!
you might be okay on a plumber's bender if it's a proper drawing bender and the dies fit properly, but it probably won't be easy.
if so you shouldn't need to pack it. although you'll probably lose some shape on the tube but hardly noticable if done right
my roll cage tubes show a little flattening on the outside of the radius

[Dammit]

I was going to clamp one of these in my big vice:



Once the tube turns up (next few days hopefully).

[Dammit]

It's for the seat-stays on this, btw (apols for the post in the engine/drivetrain thread, didn't know where else to put it):

[stevieturbo]

Dammit said:

Stevie - 15mm tube (OD), for part of a frame that runs around a tyre.

It's structural, but doesn't have to be too strong as it's tying things together rather than resisting load.

So are there any pre-formed bends you could buy and just weld to straights ?

If it isnt structural, filling with sand and heating/bending should work just fine ?

[Dammit]

Not to my knowledge.

My plan was to bend the tube, then trim the ends and then turn some male/male plugs out of stock to join onto some straight lengths of tube, then braze the whole lot together.

[Mr2Mike]

I've managed to bend 1mm wall mild steel tube in a plumbing pipe bender, but it was bit hit and miss; sometimes it worked and sometimes it put some creases on the inside radius.

Filling with sand and making sure it's tightly compressed will certainly give you a better chance. Weld/braze one end of the tube closed, and weld/braze a suitable sized nut on the other. After you fill it with sand, use a bolt to compress the sand as much as possible before bending.

[jas xjr]

Used to be able to get springs that you placed inside the pipe. I was a little confused with the diameter you require

[PhillipM]

I would think you're going to have issues given the strength of that steel, even if you pack it with sand.

If you can cope with a bit larger diameter I can bend you 1" on a 3" radius.

Edited by PhillipM on Thursday 8th January 00:17