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  1. #1
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    Surface flaws on aircraft tubing?

    So I made this seat sleeve for my next frame and after reaming out some of the brass drips I noticed what looks like a crack running perpendicular to the length of the tubing.

    The tubing is your standard ASTM aircraft tubing and it's 1.8mm thick. I reamed it with an 8" crescent wrench on my adjustable reamer so I can't see that I was getting enough force to pop a crack in the tubing. But it sure looks like a crack. I don't see anything on the inside, though.

    I'm going to slot the binder next and hope tightening it down on a post might reveal if it's a crack. I obviously don't want to finish the whole frame and have the seat tube split on the first ride, so I'm hoping it's just a surface flaw. Anybody ever seen anything like this?

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  2. #2
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    Magnaflux? You can fabricate an electromagnet quick and dirty, and filings usually live under the vise on your workbench.

  3. #3
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    You could get some welding crack penetrating dye. Local welding store should have some and the associated developer for under $20. Will work well on applications like this where you have a smooth surface easily accessed.

  4. #4
    WIGGLER
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    One of the legs on my Amp fork has a similar flaw. It doesnt seem like a crack just ugly.
    PAYASO 36er.....Live the Circus

  5. #5
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    If this was my result, I would go back to the donor tube that I cut the sleeve from and cut another piece off it. The common dominator for me would be heat, so I would torch it up to the brazing temp. and let it cool down and inspect. If I replicated that line, I would crush it in the jaws of a vise with the line in the open area, not against the jaws. If it split real easy on the line, I would be going back to the supplier of the tubing....

    Eric
    If I don't make an attempt, how will I know if it will work?

  6. #6
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    Quote Originally Posted by Eric Malcolm View Post
    If this was my result, I would go back to the donor tube that I cut the sleeve from and cut another piece off it. The common dominator for me would be heat, so I would torch it up to the brazing temp. and let it cool down and inspect. If I replicated that line, I would crush it in the jaws of a vise with the line in the open area, not against the jaws. If it split real easy on the line, I would be going back to the supplier of the tubing....
    Oh yeah, that would be the smart thing to do, wouldn't it? (smacks head)

  7. #7
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    Hey, I contemplated that answer for some time, I knew I had to be careful....

    Eric
    If I don't make an attempt, how will I know if it will work?

  8. #8
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    A test piece of tubing passed the heat 'n squash test, so I guess the tubing is ok. Looking closely at the rest of the stock in better light I can see the surface flaw continue through the whole length.

  9. #9
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    Without going to the use of dye, if you were to polish the blemish, how would it look?
    I mean, if it polishes clean and in good light you cannot see a hairline, it would be good?
    If when you polish and there is a slight depression leaving a darkened line it would be a flaw as it should be fully round. But it may not be a crack (glass half-full thinking) a light filing to even up the thickness might see off any concerns though the picture seems to show an even surface. I have had tapered fork blades have a look like that and when I polished up with emery cloth found it to be mandrel marks, but I would not expect a seamless 4130 round tube to show those sort of marks. Otherwise...?

    Eric
    If I don't make an attempt, how will I know if it will work?

  10. #10
    Randomhead
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    probably a piece of cruft in the die that then got rolled out in the drawing process. There has been some really crummy 4130 floating around for the last couple of years

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