Bending copper tube?

[Bo’sunParticipant @bosun58570]

Good afternoon,

I want to put a couple of small radius bends into 5/32″ (4mm) copper tube.  I have a small tubing bender but the internal radius is too large at 12 mm.  Something a little smaller would be useful.

I’ve tried an external bending spring, but the annealed tube didn’t fare too well.

My next attempt will be to make a simple bending die with a smaller radius.  Just need to grind the form tool.

Any other suggestions appreciated.

[DiogenesParticipant @diogenes]

If you can ‘rough’ a groove for a die, 5/32″ dia. is a common size for round chainsaw files.

[Martin KyteParticipant @martinkyte99762]

You don’t need to grind a form tool just turn up a button harden and fix to a shank.

[noel shelleyParticipant @noelshelley55608]

Machine a groove in a lump of metal 5/32″ wide, no need to radius the bottom and to the radius you want. Anneal the tube first.  Ali will do. Noel.

[old martParticipant @oldmart]

Fill the tube with fine dry sand and block both ends, that will reduce the kinking. If a second bend is to be made, repack the sand before doing it.

[Michael GilliganParticipant @michaelgilligan61133]

Cerrobend [Wood’s Metal] is an ideal filler … if you can find any these days

MichaelG.

.

Ref. http://www.csalloys.com/products-cerrobend-alloy.html

[MacolmParticipant @macolm]

As you might expect, success bending copper tube improves with greater wall thickness, a larger bend radius, well annealed tube, and a former with close width constraint. I personally have had little success with sand filling (it always eventually still kinks for a tight bend radius). Cerrobend works the first time, but not so good with reuse, though I seem to remember there is guidance somewhere of what to do about that.

You can contrive an adequate former with a circle of ply etc. of the right radius and thickness clamped in a wood vise. Bending springs work well for plumbing pipe, but annealing is essential except for very gradual bends for adjustment of alignment, and there is a very definite limit for these thin wall tubes. Small diameter bending springs tend to be a pain.

One thing to appreciate is that with a proper commercial tube bender, the inner diameter of the former has to be the neutral axis, and the outside of the bend is progressively stretched using tension and an internal nose piece to avoid flattening. That is why tight bends are a challenge with amateur methods, and there is limited potential to replicate commercial results.

 

[noel shelley]

On noel shelley Said:

Machine a groove in a lump of metal 5/32″ wide, no need to radius the bottom and to the radius you want. Anneal the tube first.  Ali will do. Noel.

Thanks Noel, that’ll save me having to grind a form tool.

[Anthony KendallParticipant @anthonykendall53479]

You may enjoy reading this article which tries various methods and endorses Noel’s method I think. No need for the luxury of the washer on the side – just stick it horizontally in a smooth-jawed vice.
Theory being pipes flatten when bending by squeezing out sideways  – so stick it in a groove so it can’t do it.
Make up one for each pipe size you might use?

Have loaded to my webspace – not sure of copyright issues – will leave it for a few days. Enjoy!
https://www.tonykendall.co.uk/SimplePipeBenderB.pdf

[Michael GilliganParticipant @michaelgilligan61133]

Excellent article !

MichaelG,

[Andy StopfordParticipant @andystopford50521]

Definitely the easiest method I’ve seen – I’ll adopt it in future.

I did make a bender like this one –

https://modelengineeringwebsite.com/artisans_pipe_bender.html

It works well, but it’s a bit of a pain making all the different wheels (so I haven’t), worth having though for bending flat stuff for little brackets and things.

[noel shelleyParticipant @noelshelley55608]

An interesting article. I made one back in the 70s for bending 3/16″ brake pipe, it seemed a good idea and worked well. With the groove a little deeper than the pipe dia it could be clamped in the end of the vice jaws, pipe slid in and bent. Noel.

[DalboyParticipant @dalboy]

This guy uses lead look about 1:30 minutes.

https://youtu.be/K5CPuJwH1x0?si=wXuIONJ8mIEYTb50

[PeteParticipant @pete41194]

If the pipe length isn’t too long. Temporarily cap one end, even a plug of wood will work. Fill with water, cap that end and freeze it. Obviously you have to have everything ready and make any bends before it melts.

[old foolParticipant @old-fool]

The profesional folk do it by filling the pipe with “gum tree resin” no idea where you’d get any of that though. Ice seems a good alternative. I wonder if you could freeze it with that freezer spray they sell in the DIY stores for stopping water coming out of a pipe while you dismantle a system and re-make it. Just a thought

Bob

[cogdobblerParticipant @cogdobbler]

<p style=”text-align: left;”>Why? When the deep-groove bender linked to above by Anthony Kendall does a flawless job without need to fill the tube with anything? Simple but effective, as the author’s photos of a host of finished jobs shows, and several posters have found from experience.</p>

[vintagengineerParticipant @vintagengineer]

Table salt works very well and you can wash it out afterwards.

[not done it yetParticipant @notdoneityet]

I have a CZ Universal metal bender that I acquired, quite cheaply, umpteen years ago.  That does all I have needed within its spec (and a fair bit bit beyond, at times).  It was covered in ME, over a couple of issues, several years ago.

Chronos are again offering their modern iteration, but at over £100.

The original, if one comes up on epay cheap enough, is well worth the investment.

[Bo’sunParticipant @bosun58570]

Thanks for the suggestions.  Noel’s idea worked just fine.  I made said former to suit several internal radii.

[bernard towersParticipant @bernardtowers37738]

I have used woods metal in the past for anything over 3/16” tube and you only need a kettle to melt it out again.

[Tim StevensParticipant @timstevens64731]

If anyone does have similar problems and suffers flats (or near-flats) where the tube has bent too much – there is a possible solution: Fill the tube from the shorter end with ball-bearings of the inner diameter of the (straight) tube. When you can get no more in, tap repeatedly on the last ball, and it should move down a bit, pushing the too-flat bit back to round.. As soon as there is room for another ball, add one, and carry on. Eventually the balls will work their way through the damaged section, and it should be almost as round as a new bit.

Further work on the pipe should be delayed until you can soften the whole length – simply heat over a blow-lamp (eg) until just visibly red in a dark room, and leave to cool. The result will be more softness that you might need, so be gentle, but it will be the same all the way along, so safe to carry on.

And good luck. It works for me.

Tim Stevens

[Nigel Graham 2Participant @nigelgraham2]

“… leave to cool”, or

Unlike high-carbon steel, copper can be quenched from dull red heat in cold water or left to cool naturally, when annealing it. I normally quench it, if only to save time.

There is a reason pipe-benders use what seem generous radii at 3 X Diameter (hence the 12mm radius for 4mm pipe).

It is generally the tightest safe radius.

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