Thread: How to bend 40mm copper pipe 180° ?

So I have a project on the go..... I need to bend some 40mm copper pipe into a tight 'u' to make a wet back for a 'rocket stove' I have built.
It needs to be a tight bend, as the rocket stove is made from two D size oxygen bottles welded together.

I have acouple of copper 90° elbows to use, but thought it might be better to bend it... am I being paranoid about the brazing in the hot box?


Any of you clever shooters happen to be a plumber?

You can fill it with sand and heat and bend, or use a plumbers spring if yo can find one of that diameter

Copper tig welds really well, but welding with silfoss will be fine. If you get it hot enough in use to melt silfoss you’ll have other problems to worry about.

Originally Posted by 2post

Copper tig welds really well, but welding with silfoss will be fine. If you get it hot enough in use to melt silfoss you’ll have other problems to worry about.

Ok, I thought as much.
Will run with the elbows, as I reckon a 180° bend will be a mission.

Thanks guys.

+1 for the silfoss, just make sure the copper gets to cherry red in colour when you're heating it with the torch.

All wetback units I have seen have been bits of straight pipe with the corners done using two 90degree elbows, all silfos'd together. As long as the copper pipe is always full of water the silfos should not be able to get hot enough to melt.

....Let the water boil dry though, and all bets are off!

P.S. if you need a stick or two of 15% sending up give me shout.

Originally Posted by 40mm

Ok, I thought as much.
Will run with the elbows, as I reckon a 180° bend will be a mission.

Thanks guys.

Make sure the sand is DRY

Originally Posted by 40mm

Ok, I thought as much.
Will run with the elbows, as I reckon a 180° bend will be a mission.

Thanks guys.

My dad made a 1/2” copper coil about 4 foot long to fit in an 8” flue to heat water using the sand. He was one clever bugger. Fitted to a small chip heater, fired with waste oil. Emery thing glowed orange, down to the feet, when it was fired up

I bent some 25mm steel tube for a motorbike into a tight U bend a number of years back. I flattened and folded over one end, packed the tube as full as possible with sand (like compress it in there as much as possible as you add it) then flattened and folded over the other end until I could not fold it any more and the whole thing was tight. I then made a former for the shape I wanted from MDF scraps, clamped one end of the tube down and bent it around by hand. It held its shape perfectly and I could tweak it to exactly the bend I wanted. I then cut the ends off, got the sand out and trimmed it to final length. Great way to do one or two bends in a pinch, prob easier to pay a fella for more than that.

The sand or plumbers spring method is the classic one. I can remember dad doing this I got to hold the blowlamp to heat the section, the colour changes on the pipe when the flame was on it fascinated me.

Just use the pre bent piece. most plumbing pipe is hard drawn and requires annealing by getting cherry red and then cooling. Otherwise bending is nigh impossible.

unless you have a hard round surface it is difficult to bend 40mm pipe.

use plumbers silphos as it is cheaper than fridgie stuff.

Originally Posted by 2post

P.S. if you need a stick or two of 15% sending up give me shout.

@2post what would you recommend I use to clean up the 40mm pipe? It is old stuff, so pretty tarnished etc.
I was thinking of a wire wheel and sand paper before some kind of acid flux etc? Am I on the right track?

Cheers

@40mm Normal household vinegar will do the trick after a quick buff with a wire brush.

Originally Posted by 2post

@40mm Normal household vinegar will do the trick after a quick buff with a wire brush.

@2post, so with the vinegar flux, do I need to rinse it off with water before welding?
I do have some 'spirits of salts' on the shelf if that is better? Also, I suppose it will need to be rinsed off prior to welding??

Cheers, 40mm