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Thread: 31.6 ID steel tubing

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    Default 31.6 ID steel tubing

    So now that my Winter frame project is almost done I am starting to think about the next job, making a SPT. For those young ones a SPT is a stem like device that hangs off the back of a seat post and allows a handle bar bag to be mounted behind the post.

    The post diameter I need to fit is 31.6. In looking at the commonly available 4130 tubing I don't find anything without a heavy wall. The closest i've seen is 1.375"x.049". This is both a bit thicker walled then i'd like as well as slightly larger an ID then best. In an ideal world I'd like to use something like a .035" wall if I could.

    My question for you all is do you know of a steel tube with an ID of 31.6 (or a bit less) and a wall of .035 (or slightly thicker)? A second question is whether any one would turn down a aprox 6" length of tubing (like 1.375"x.065") to a .035"/.040" wall?

    My lathe is in storage so I can't do the machining work. Thanks, Andy.
    Andy Stewart
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    Default Re: 31.6 ID steel tubing

    Quote Originally Posted by Andrew R Stewart View Post
    So now that my Winter frame project is almost done I am starting to think about the next job, making a SPT. For those young ones a SPT is a stem like device that hangs off the back of a seat post and allows a handle bar bag to be mounted behind the post.

    The post diameter I need to fit is 31.6. In looking at the commonly available 4130 tubing I don't find anything without a heavy wall. The closest i've seen is 1.375"x.049". This is both a bit thicker walled then i'd like as well as slightly larger an ID then best. In an ideal world I'd like to use something like a .035" wall if I could.

    My question for you all is do you know of a steel tube with an ID of 31.6 (or a bit less) and a wall of .035 (or slightly thicker)? A second question is whether any one would turn down a aprox 6" length of tubing (like 1.375"x.065") to a .035"/.040" wall?

    My lathe is in storage so I can't do the machining work. Thanks, Andy.
    I would use the 1.375x0.65 and cut/drill windows in the sides.

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    Default Re: 31.6 ID steel tubing

    Online metals has 1.375 x 0.035 4130
    Order Alloy Steel 4130 Tube in Small Quantities at OnlineMetals.com

    but the ID is 1.305
    Shiggy's 0.065 suggestion has ID of 1.245, should just fit 31.6mm/1.24409
    Order Alloy Steel 4130 Tube in Small Quantities at OnlineMetals.com
    flex hone it to fit?
    cheers
    andy walker

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    Default Re: 31.6 ID steel tubing

    going to a smaller 1.25 tube, the ID of that with 0.065 wall thickness is 1.2"
    might work that to get to 1.24409,
    how long would that take?
    Order Alloy Steel 4130 Tube in Small Quantities at OnlineMetals.com
    cheers
    andy walker

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    Default Re: 31.6 ID steel tubing

    I think reducing the wall thickness is the wrong place to try to save weight. I have made similar weight-bearing items and had the metal tear.

    My design would be something like this, with the full thickness on the clamp tube.

    (Attachment coming)

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    Default Re: 31.6 ID steel tubing

    Quote Originally Posted by shiggy View Post
    I think reducing the wall thickness is the wrong place to try to save weight. I have made similar weight-bearing items and had the metal tear.

    My design would be something like this, with the full thickness on the clamp tube.

    (Attachment coming)
    756035d1359226588-pic-test-image.jpg
    Crude drawing but you get the idea

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    Default Re: 31.6 ID steel tubing

    IMG_0440.jpgIMG_0443.jpgShiggy- I have built this kind of device more then a few times. The wall thickness (.035") has been found to be quite sufficient. Your suggestion of adding (subtracting?) lightening holes is also something I've done before. I'll try to add a couple of photos of two different SPTs to show my approach (but not sure if photos will attach this time. Have been unable to do so for a while.) Andy.
    Andy Stewart
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