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  1. #1
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    Mar 2009
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    Default How To Bend a 6 m Length of 12 or 16mm dia Aluminium Tubing To a 2m Dia Circle?

    How to Bend a 6 m Length of 12 or 16mm dia Aluminium Tubing To a 2m Dia Circle

    Can I ask how I should bend a 6 metre length of 12 or 16 mm dia aluminium tubing of 1.6 mm wall thickness into a 2 metre (1.909 m with 10 cm gap) circle without having kinks?
    And also for a one metre circle?

    It is for a loop radio antenna, so it doesn't have to be visually perfect (just electrically perfect!), but I thought I may as well have it look good also.

    Thanks, mike

  2. #2
    Join Date
    Oct 2011
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    Norwood-ish, Adelaide
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    Default

    I'd be tempted to borrow/ make up (or buy) a ring roller. With a 1m radius and even pressure, I'm not sure that the tubing would kink. From a quick CAD drawing, over a 200mm span you are only deflecting 5mm.
    If you did not need perfect round I guess you could go along and bend the tube so that every 100mm it is bent 5mm...

    Michael

  3. #3
    Join Date
    Oct 2008
    Location
    blackburn vic
    Posts
    297

    Default Mag loop antenna

    All of the guys in our club have made them out of 1/2 inch or simkilar copper water pipe.

    Roger VK3BKR

  4. #4
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    May 2011
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    Murray Bridge S Aust.
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    Default

    Hi Mike,
    One way without spending big bucks is to make a former out of 18 mm MDF. Cut a semi circle with a 1 metre radius, with the offcuts, place them underneath to act as a base for the tube. Then make a roller assembly to go on the outside of the tubing, using a roller bearing inside a piece of Delrin or similar (Helps protect the tube from flattening) with a U machined to the size of the tube. You'll need to make it adjustable as you'll be using it for the smaller one also, which is made on a similar set up. Have seen this set up used for bending 1" square tube for horse floats. This measurement is for an inside diameter measurement, if it need the outside measurement of 2 m reduce the diameter of the former by the diameter of the tube.
    Hope this helps.
    Kryn
    To grow old is mandatory, growing up is optional.

  5. #5
    Join Date
    Nov 2004
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    Bungama SA
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    52
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    960

    Default

    Short of wrapping it around a small rainwater tank you need to use a proper ring roller and correct grade of ally.

    Looks like 3 series is the go?

    If it was me copper would work out cheaper and easier to work with
    ....................................................................

  6. #6
    Join Date
    Oct 2007
    Location
    Alexandra Vic
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    Default

    Slightly sparse thinking but the circumference of a 2m diameter is more than 6m, (2 x pi = 6.28 approx.) so technically you can't form the 2m dia from a 6m length.

    Personally, I would be looking at a ring roller, though the usual with them is to start with an overlength piece, form in a number of stages until you reach the required diameter, at which time the ends overlap but are fully formed, then trim of the overhang at the ends. Then a very slight twist will align the ends, so you would need around an 8m length for the 2m dia.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  7. #7
    Join Date
    Mar 2009
    Location
    Brisbane
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    Default

    Thanks to everyone. I did get some ideas.

    Malb - nominal 6m lengths of ally tubing are actually 6.5m, so I would have been OK, and I did account for 2/pi = 1.909+ in my original post.
    I will probably end up with a 1.5 m dia. loop anyway, as a compromise of MF and HF frequencies.

    Looks like I may go with a DIY ring roller using a quadrant of MDF cut from a 900x900 mm sheet.

    For the radio types, ally is far cheaper than copper, and I'm no expert, but I have read that the resistivity of materials for "small" magnetic loop antennas is of no real consequence.
    The beauty of copper admittedly is it is easier to bend, with little spring back, and electrical connection is easier and a little more permanent, with less chance of electrolysis.

    regards to all, mike

  8. #8
    Join Date
    Jan 2011
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    Far West Wimmera
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    63
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    4,049

    Default

    I just watched an interesting video on building a roller although it is a bit more involved than an MDF circle.

    https://www.youtube.com/watch?v=wRNiM2AFUjk

    Dean

  9. #9
    Join Date
    Mar 2009
    Location
    Brisbane
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    Default

    Quote Originally Posted by Oldneweng View Post
    I just watched an interesting video on building a roller although it is a bit more involved than an MDF circle.

    https://www.youtube.com/watch?v=wRNiM2AFUjk

    Dean
    That is one great video - had me captive.

    Instead of my quadrant idea, I actually made up a three roller bender using cheap plastic wheels and a piece of MDF.
    Works OK.
    I rolled up a 1m loop OK, and a 1.5m loop is to follow when I get a 6m length of ally tube.
    Photos after the next loop.

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