Steer tube bend?
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  1. #1
    Vintage bike and rider
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    Steer tube bend?

    Got a mild steel fork with a steer tube bent about 2 degrees. Anyone had one straightened? How did it work out?

  2. #2
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    How far above the crown is the bend?

    You should be able to straighten a 2 bend in a steel steerer tube by cold setting.

    Secure the bottom of the steerer in a bench vise using 1" split clamping blocks (assuming it's a 25.4mm steerer) and insert a length of pipe with roughly the same O.D. as the I.D. of the steerer into the top of the steerer and apply enough force to the pipe to straighten the steerer.
    -Stan
    my bikes

  3. #3
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    WTH is "mild steel"?

  4. #4
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    Scooper, the bend is (well, really was, my LBS just did a procedure just like what you described -- $5.00!!) about 3 inches above the fork crown, and about 3 inches from the threads. The fork is a old Peugeot from a 1972 UO-8, and it has an internal sleeve to reinforce the fork crown rather than a butted or splined section. The bend was above the sleeve.

    LBS got it pretty good, there are some witness marks from clamping the low section, but no new bending, and the internal view is clear.

    I used the term "mild steel" to refer to the lower-carbon, non CrMo, non MnMo steels that are really the most common ones. Mainly it has a fairly low carbon content, and probably "low carbon" is a better term. I don't really know what these Peug's were made of. The seat tube says "Tube Special Allege Peugeot," which for all I know means "Special Volume Steel Discount For Peugeot, content unspecified."

    So that's at least what I meant.

  5. #5
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    Actually I just looked at Wikipedia, which says ("Bicycle Frames") that lower cost bike frames were made of mild steel. It has a higher carbon content than low-carbon steel, around 0.16% versus 0.05%. Neither types have any minimums specified for alloying materials, like chromium, manganese, molybdenum, or vanadium. Mild steel should be more ductile than high strength alloyed steel, bending more easily.

    For context, Reynolds 531 is a manganese molybdenum alloy, Columbus SL and SP are Cyclex a chromium molybdenum alloy, and 4130 is a CrMo allow meeting an SAE specification. All of these will be stronger and harder to bend (distinguished from flex) than mild steel and low carbon steel.

    Notice the bikey term "high ten" or "high tensile" does not fit in here and is not defined in the more techinical Wiki articles. It's pure marketing fluff, with no technical meaning. I think it's used to to fluff up a product for which they can't say "extra-strong CrMo (or MnMo)!" Just advertising filler.
    Last edited by KensBikes; 11-13-2009 at 06:11 AM.

  6. #6
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    Quote Originally Posted by Kristatos
    WTH is "mild steel"?
    "Mild steel" is just 10xx plain carbon steel, typically AISI 1010, 1020, or 1030.

    http://www.materialsengineer.com/E-Alloying-Steels.htm

    OP, I'm glad your LBS was able to straighten it.
    -Stan
    my bikes

  7. #7
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    Yes, it looks straight, but the threaded section is now ovalled due to the pressure of the bending bar. I'll see if I can squeeze it back near round with a big channel pliers and some wood buffers. Right now the stem won't slide in and the headset threaded race will not thread. We'll see what's the next step.

  8. #8
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    Quote Originally Posted by KensBikes
    Yes, it looks straight, but the threaded section is now ovalled due to the pressure of the bending bar. I'll see if I can squeeze it back near round with a big channel pliers and some wood buffers. Right now the stem won't slide in and the headset threaded race will not thread. We'll see what's the next step.
    Ahhh..

    He probably used a bending bar that was too small in diameter. Also, it wouldn't have hurt to have the headset top nut threaded onto the steerer while he was bending it straight.
    -Stan
    my bikes

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