Tube bending theory
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  1. #1
    Rods 'n' Sods Junkie
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    jonal is offline

    Tube bending theory

    Can any one tell me the theory etc for bending tube. I want to bend a piece of 22mm tube by 11 degrees and want to know if the pipe will stretch when I do this. I know there is an equation when you bend flat sheet/bar metal so am hoping someone will be able to advise me. The reason being I want to make some ladder bars and want to thread the straight bar on a lathe before I bend it and still have it come out the length I want..

    Cheers Jon..

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    You need to start with a longer piece as any bend will eat up some length.
    Draw a template and measure it.

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    605 heavy is offline
    You could run the the thread cutter deep into the tube , say 2" , this will give you something to play with if the tube end is too long when you bend it , or bend the tube first , cut the pipe to length & use a manual thread cutter , if you're just putting a kick in the tube (11*) then you should'nt have any issues , if you're familiar with a pipe bender all the better.

    When tube is bent it will stretch on the back (arse) & retract on the inside (throat)
    Last edited by 605 heavy; 16-03-2010 at 01:20.

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    Nowheresville JackGriffin's Avatar
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    We used to reckon on two thirds stretch, one third shrink, so the length would be calculated on the radius 1/3 from the inside of the bend, although that is only a rough guide.

    But on that small a tube and shallow a bend there will be little variation - just do as 605 heavy said.

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    Official RnS Addict old pizz yella's Avatar
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    the easiest way is trip downto bq buy a bit of 22mm copper tube and do some test bits as every tube bender gives a different length of bend due to the formers wearing from use ,custom car a million years ago did an artical about fitting roll cages and gave all the spec for bending if i remember corectly

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    Cheers all for that, that pretty much answers my question. Next stop is to go an have a look at the formers on the bender I will use..Cheers J

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    It all depends on the material, copper will stretch a bit more than mild steel. As a rule of thumb, if you were bending a 90 deg bend in mild steel, you would take off 1/2 id from where the bend needs to be, then bend it, but I would imagine for an 11 deg bend the material wouldn't move about too much. As said before leave the tube longer then cut off to length afterwards. Hope this helps. I have the pipefitters and plumbers handbook here somewhere, not sure where it is but I can have a look and see what it says in there, when I find it.

    Cheers,

    Stu.

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