Bending aluminium bar or tube.

Hello
I have been lurking arround for over a year and have learnt a lot from this group. Now, I find I have to surface and ask a rather basic question!!!!
I know this sounds really silly, but how can I bend 6mm diameter aluminium bar or tube, with out it breaking or colapsing? Can I heat it like steel?
Any advice welcome.
Cheers AC
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I was so pi**ed with the results of tube bending (whatever "tricks" or trade secrets I used) that I have built me a mandrel tube bender. I get the most incredible bends with it. Have been on shows with my Ellwe*) and nearly everyone admired my tube bends. Other HSEs came by and asked how I did that and asked me to bend their tubes (willing to pay money).
Bending a 6mm brass tube, bending radius being 6mm (relative to center line), the diameter collapses just for 0.2..0.3mm. Only minute scratches or dents left. Didn't try it with aluminium, but should work the same (adjusting bending radius).
How does a mandrel tube bender work? (I hope it is called that way): You need a roll that forms the inner half of the tube. To prevent the tube from collapsing a mandrel (stick) is in the tube right at the place where the bend takes place. While bending, the tube gets pulled from the mandrel (it if fixed) and thus supports the outer half of the bend. The end of the mandrel that supports the tube's outer wall has a somehow tricky form. It is a intersection of a torus and a cylinder. Adjusting is a bit complicated, but once it is done, I get repeatable results and a bend is just something of less than a minute.
I could make photos, but you wouldn't understand from them how it works. ;-)
*) <http://www.motor-manufaktur.de/ellwe/modellbilder.html> Only in German, sorry.
Nick
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She's quite cute, did you have any problems with the springs in the pistons fatiguing ? :-) :-)

Why do people persist with these old-fashioned languages instead of standardising on American like the English have ?
<runs away>
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Not when I made them out of titanium. :-)

I want to translate that since a year or so...
Nick
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Seriously though, is there a castings kit available for this moel anywhere ?
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Emidio Gattafoni has (or had?) them. His web-page is here (links page on my site): <http://digilander.libero.it/liguori/ . The castings costed around 250 EUR (really don't remember). Plans were included. But the plans were a nightmare. Nice drawn but _lots_ of errors. I showed him my corrected set a year later and he nearly fell unconcious. :-) He told me that he corrected them (a bit?).
Emidio only talks italian, but you can mail him in english. He has a translation program (he told me in italian, never had email-contact with him) that will help him understand what you want.
Nick
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Thanks !
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Nick Mller wrote:

Nice work, Nick!
FWIW we have a quite expensive mandrel bender at work for bending Titanium tubing. Out limits are that we cannot have more than a 5 percent change in the cross section shape of the tube after bending. Our particular machine uses an internal mandrel that appears as a series of beads on the end of a rod. As the tube is srawn around the curved form, the "beads" provide the support to keep the tube from collapsing.
If strength is not a major factor, you can soot the aluminum tube with a candle flame(a Sharpie or similar marking pen can be used , too), and heat it until the soot is burned off using a propane or Mapp gas torch. This will effectivly anneal the aluminum tao a state that is about as soft as you can get it. If it is a hardening variety, it will naturally age harden to about a -T3 or -T4 state in a few weeks. Soft aluminum is much easier to bend.
Model Engineer had a pretty decent mandrel bender a few years back. A look through one of the online indexes should find the issues involved, and copies of older articles can be bought from the publishers. IIRC the ME mandrel bender was demonstrated bending 1/2 inch inside radius bends in 1/2 copper pipe (a very tight U shape) without collapsing the pipe.
There are also some low melting temperature alloys that can be poured into tubing to keep it from collapsing when bent. Google for Cerro-bend (or Cerrobend). It is one of several alloys that melts in boiling water.
Cheers Trevor Jones
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Tweeking with my setup, the cross sections area could even be increased. But then it will be oval.

I know this principle, but at that size it would be to complicated to make. Making mine took me a week to develop. Having thrown away 2 prototypes in that time and learning what is important and trying to figure out what was the cause for a pile of badly bent tubes.

Filling the tube will not work. If it is bent, the inner part of the tube is not (or just a tad) compressed, but the outer part is stretched. This increases the volume of the bent section. The volume of the alloy in the tube stays constant, so it can't support the tube that much.
Nick
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Also try Wood's metal; that is either the same as Cerrobend, or very similar. IIRC, they used to sell teaspoons made of it in joke shops. Not a great idea as some of the constituents are not altogether human-friendly.
Various recipes in Henley's Formulas:
Wood's Metal: Tin 2 lead 4 bismuth 5 to 8 parts, MP 66-72C Other similar alloys: Bismuth 7 lead 6 cadmium 1 parts, MP 82C Bismuth 7-8 lead 4 tin 2 cadmium 1-2 parts, MP 65-71C
Several other recipes involving the same 4 metals in different proportions giving different melting points.
Probably best avoid the ones containing cadmium if you can.
David
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wrote:

Cheers for all the replies.
I am making an engine cage for a 1/10th scale car. As it is cosmetic, strength is not at all important. So I think I will be sooting , heating and carefully bending!!!. Would love to have mandrel bender, looks like th eperfect solution, but I think its slightly out of my reach.
I notice that the replies are all about bending tubes, and not bar (6mm ish dia). Can I bend the bar in the same way, or is there a problem trying to do that?
Cheers AC
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AC wrote:

Bar is easier to bend than tube, and mandrel benders are for tube specifically. The mandrel is a bar that slides inside the tube and supports it at the point where the bending is taking place. There is little or no opportunity to redo a bend in mandrell bending.
There are a bunch of different bending machines out there ranging from the sublime (DiAcro bender) to the ridiculous.
DiAcro Bender pics
http://www.machineco.com/Bender_man_Diacro_No2_Turcot_1_stk2352.jpg
http://www.machineco.com/Bender_man_Diacro_No2_dies_TX_2_stk2352.jpg
The Diacro's have been around for years. Calling them the sublime may be pushing things, but they are a flexible shop tool. Note the variuos dies that are used for specific sized pipes or bars, each for a different radius.
The other end of the spectrum is something like this. http://www2.northerntool.com/product/200012574_200012574.htm
Not a lot that could not be made at home, given the ambition.
There are a pile of usefull tools out there, between and beyond both ends of the spectrum if you go looking.
Cheers Trevor Jones
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I was taught to anneal aluminium by coating it with a thin layer of soap and heating it until the soap blackened.
Is that better or worse than the soot method ?
-adrian
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Adrian Godwin wrote:

I've read of the use of soap to prevent surface oxidation on steel when heat treating, but have not seen soap used for aluminum.<shrug>
Did it work OK? Was it easy to clean off after?
I used soot from the oxy-acet torch when I had one handy, and used the torch to anneal with, and used a sharpie when I only had a propane torch.
Cleanup is non-existant for both of those methods.
Cheers Trevor Jones
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It was fairly easy to see the change, and the aluminium could be beaten into shape afterwards, so I guess it worked OK. Difficult to know if something else would have worked better (hence my question). I don't remember it being difficult to clean up.
-adrian
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I have learned to check the temperature of aluminium (for welding), by pulling a thin wooden stick over it. If it sparkles, the ali has the right temperature.
Nick
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wrote:

I was also taught to use soap when annealing aluminium and I still do it this way; it would seem to be more accurate as it depends only on temperature to blacken, I would imagine soot would only burn off if the flame was played directly onto it. Martin
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Martin Whybrow wrote:

It should so seem, but the soot will not burn away until the underlying metal reaches an appropriate temperature. I have used both soot and marker pens on thicker(1/4") as well as thin sheet stock. Takes much longer to burn off the thicker stock.
The only thing to watch with the acet torch is that you do not start a molten puddle by leaving the torch in one place for a period of time.
Cheers Trevor Jones
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Some extremely fine models there, Nick. I only wish I had not let my German get so rusty (I had to learn some technical German at university and pass an exam, but a long time ago!) as I would have liked to read the descriptions.
David
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Nick Mller wrote:

http://vansantent.com/definitions.htm
BugBear
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