Bending square sect tube

[Osprey]

Time for another project ... need to put a 90 degree bend in some

1.25" square section tube. Not bought the section yet but guessing something like 16 gauge (0.064") or maybe I will need 14 gauge (0.08") Obviously the bend radius will mean a reasonably gentle bend.

I have 2 questions if anybody has experience of such things.

# What is the minimum bend radius, I'll make sure I keep above this.

# Is this a practical bend to do at home ... or should I go to a fabricator and buy it 'bent'

If you are interested the project is:

[Baz]

Baz

[Cicero]

fairly specialised (and expensive) mandrel and a heavy duty bender. If a curved bend isn't actually necessary it would be far easier to cut the tube and weld it up. There are different ways to do this but the easiest method would be to cut out a 90 degree triangle and bend the tube to close the resulting gap before welding it up. This method would probably be stronger than the bend shown in your pictures, if that is an issue.

A radiused bend can be achieved by a similar method to that described above by making several cuts in the tube before bending and welding, but the result can look a bit clumsy.

Cic.

[Dave Plowman (News)]

Fill it with fine sand and plug the ends - one first, obviously. Heat to red and bend. In theory. But probably easier to find a place that has a bender for this.

[The Natural Philosopher]

yes..something like that, or bend round a pretty large radius using a few tons..like run it over with an articulated lorry on a gravel bed to start it off...:-)

[Cicero]

==========================================

These methods might be worth a try but be prepared for failure. A mandrel for bending square tube has a projecting rib on the face of the curved mandrel to push the centre of the tube face inwards. This relieves the squashing effect on the two sides and helps to make a clean bend. You might be able to replicate this effect with a cold chisel before trying the 'heat and sandfill' method, but it seems a lot of effort if a radiused bend isn't essential.

Cic.

[Andy Dingley]

Not a hope, even if you fill it beforehand. It will crimp (it has to - can't do it with pure stretch). So either indent it, notch it, or join it.

Indenting is pretty strong and simple on a production line (look at a lot of office furniture) but hard to do neatly as a one-off. You crumple the inner surface deliberately, thus providing somewhere for the excess steel to fold up fairly neatly. The outer circumference remains pretty constant, i.e. no stretching required, so you don't need tooling that has enough grip to exert a longitudinal tension.

Notching (Wikipedia describes) is how I'd generally do it in my workshop, but then I'd MIG weld it back together afterwards.

Joining it is simple cut & shut, perhaps even with a plastic plug joiner in there afterwards. Dead simple, only tool is a hacksaw (or for Doctor Drivel, a pipe cutter) but the result's not so strong.

[Rick Hughes]

I thought of this ... have bent many a copper pipe that way.

It's looking like I need to find a shop that will do it.

[Rick Hughes]

I would prefer to end up with a proper radiused bend for appearance sake.

Maybe I should start looking for something that already has square section with a bend in it, and help it to become a scrap item :-)

10 brownie points if anybody can think of something in 1.25" steel square section that has a 90 degree bend ...

[Andy Dingley]

Cut, shut, grind a radius onto the outer face, weld a strip over it.

[Rick Hughes]

ribbed mandrel.

Does anyone know of any 'on line' sources for engineering firms that will do such small orders ? only need 2 pieces...... or I'll have to trawl around local companies.

[Baz]

Try these.

I have used them in the past. Baz

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Osprey saying something like:

An utter bastard to do at home - when made, that would have had a jig and plenty heat. I would weld a braced joint.