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Open Source Spaceframe recumbent bike build

  1. Dec 18, 2014 #1
    Okay, so I'm new to this forum, but I'm hoping I can get some help. I live in the United States, and I'm having trouble converting from metric to standard with the build plans given. I want to build the open source Spaceframe recumbent bike which the build plans can be found here http://www.n55.dk/manuals/spaceframevehicles/DIY.pdf The problem, the entire build plan is in metric, and I'm not sure about the best method to go about converting metric build plans to standard.

    Specifically, the build plans ask for 25mm square aluminium tubing with 2mm material thickness. Can someone maybe point me in the right direction as to how I should go about this build? Can I buy these materials at say Home Depot that would be the same size?

    Thanks for any help I receive. I have no degree in any kind of mechanical engineering, and I've only taken a beginners level physics course in college. I'm building this bike, because recumbent bikes are out of my price range to buy outright. This open source design is supposed to be strong, cheap, and effective.
  2. jcsd
  3. Dec 18, 2014 #2


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    Staff: Mentor

    Welcome to the PF.

    I would think you should be able to get metal stock in metric sizes at most metal supply houses. Have you tried searching in your area for Metal Supply House or similar?
  4. Dec 18, 2014 #3


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    Gold Member

    Keep in mind also that for a bike the tolerances aren't critical. If you just use a standard conversion chart and happen to be out by .01", nobody will notice. Anything where clearances are important such as hubs will be prebuilt to spec anyhow.
  5. Dec 18, 2014 #4


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    Science Advisor

    You can use inch dimensioned material. As a guide, use the following translations.

    For M6 use 1/4”
    For M8 use 5/16”

    2mm is 0.08”
    3mm is 1/8” (= 3.175mm)
    3.5mm use 1/8” or 5/32”
    4.0mm is 5/32”
    22 mm is 7/8”
    25 mm is 1”
    30 mm is 1.25”
    60 mm is 2.5”
  6. Dec 18, 2014 #5
    This is helpful, thanks. I managed to find a fairly cheap Aluminum square tubing on the Home Depot website which had similar dimensions. I'll keep this thread updated on the progress, and hopefully receive more help that will most likely be needed.
  7. Dec 18, 2014 #6


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    Gold Member

    Looking forward to it. I might not be of any assistance, but that's never stopped me from chirping up before and it won't now.
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