Help needed...

[allegro]

Does anyone know what kind of minimal radius you can achieve bending a 15mm, 1mm wall steel tube to around 75 degrees before you get excessive distortion or breakage.

Secondly can anyone suggest a way of achieving said radius as conventional pipe bending gear have a larger radius than i am looking for. Could i make up my own jig with the correct size, round internal profile, pulley?

Thanks guys... and girls

[sparkythecat]

Why not use flexible copper pipe like this?

[allegro]

Its got to be steel and unjointed

[sparkythecat]

allegro said:

Its got to be steel and unjointed

What are you making ?

Is it some sort of thermonuclear device for use in orbit ?

Or maybe a vent pipe for a superheated urine container ?

Edited by sparkythecat on Tuesday 16th August 19:22

[Marty63]

if you heat bar up to bend it, it could be as sharp a bend as you want it.

[Sam_68]

Minimum recommended bend radius is a centreline radius of 2.5 times the tube diameter, I think (so about 38mm centreline radius or 31mm internal radius for 15mm tube).

The old way of bending steel tube (before the Safety Elf got involved) was to fill the tube with fine sand (to stop it buckling/collapsing), plug the ends (to stop the sand escaping, obviously), heat with a blow torch until fking hot, then bend by hand around a suitable mandrel.

If you want to try this;

• Use CDS tube, not seamed, if you can;
• Bear in mind that the tube can sometimes burst, showering you with white hot sand (which is why the safety elf doesn't like it, of course) and;
• I've only ever seen it done, not done it myself, so I deny all responsibility if you manage weld yourself to the scenery.

[Sam_68]

Marty63 said:

if you heat bar up to bend it, it could be as sharp a bend as you want it.

The OP specified tube, but even bar will 'neck' down to an inconsistent diameter if you try to bend it too tight.

[Condi]

Sam_68 said:

The OP specified tube, but even bar will 'neck' down to an inconsistent diameter if you try to bend it too tight.

If it necks over then heat it up again and put the offending part in the vice. It might come out somewhat square, but stuff will flow though.

[Sam_68]

Condi said:

If it necks over then heat it up again and put the offending part in the vice. It might come out somewhat square, but stuff will flow though.

This will work if it has ovalised, but not if it has necked out (ie. stretched and become thinner), which is what usually happens. But I was talking about bending rod, not tube as the OP specified - if you try heat bending tube around a tight radius without packing it with sand, it will usually simply buckle in my experience... perhaps I'm just ham-fisted, though!

[allegro]

Sam_68 said:

Minimum recommended bend radius is a centreline radius of 2.5 times the tube diameter, I think (so about 38mm centreline radius or 31mm internal radius for 15mm tube).

The old way of bending steel tube (before the Safety Elf got involved) was to fill the tube with fine sand (to stop it buckling/collapsing), plug the ends (to stop the sand escaping, obviously), heat with a blow torch until fking hot, then bend by hand around a suitable mandrel.

If you want to try this;

• Use CDS tube, not seamed, if you can;
• Bear in mind that the tube can sometimes burst, showering you with white hot sand (which is why the safety elf doesn't like it, of course) and;
• I've only ever seen it done, not done it myself, so I deny all responsibility if you manage weld yourself to the scenery.

Cheers Sam68, i did think a radius of around 30mm would be the limit although i would like it tighter, 18-20mm ideally. Heat and an internal pipe spring were my first thought but the bend needs to be quite accurate and controlled in both its angle and its position along the pipe.