Seat Tube Out of Round- Mtbr.com
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  1. #1
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    Seat Tube Out of Round

    I am nearly finished with my frame. I have built it up and I am now cleaning up the joints. Playing around, I went to put the seat post in the seat tube. Yep, the seat tube has gone out of round. Any ideas on how to round it out? I could ream it, if I had one but that doesn't seem like the best idea as I will have some slop on the "longer" side of the oval.

    I'm really bummed and exasperated, but I will persist. Any help would be much appreciated.

    Thanks a bunch.
    Cycle tracks will abound in Utopia. ~H.G. Wells

  2. #2
    pvd
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    Ream.

  3. #3
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    You could mill the seatpost to match the gimp seat tube. Just need a 4-axis mill and some 3D contouring CAD/CAM software.

    Or, if you can find a bearing ball that matches the seat tube ID, weld a bar to the ball and hammer it in. You'll need the welded bar to remove the ball.

    Then ream.

  4. #4
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    Quote Originally Posted by EricTheDood View Post

    Or, if you can find a bearing ball that matches the seat tube ID, weld a bar to the ball and hammer it in. You'll need the welded bar to remove the ball.
    Now that's a novel idea. Have you done this before?

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

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    Quote Originally Posted by Eric Malcolm View Post
    Now that's a novel idea. Have you done this before?

    Eric
    On tubing, no. In solid machined parts, yes.

    It's not uncommon to "burnish" a precision bore with relatively cheap bearing ball, especially in a thru-hole.

    Bal-tec - Report On Ball Sizing

  6. #6
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    Thanks for all the ideas. I have an old seat post that is the same size. I may try to reround the tube by gentling hammering that into the tube then see if I can ream it after. I will be using a dropper post so if its not super smooth going in and out its not a deal breaker.
    Cycle tracks will abound in Utopia. ~H.G. Wells

  7. #7
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    Quote Originally Posted by GhisalloWheels View Post
    Thanks for all the ideas. I have an old seat post that is the same size. I may try to reround the tube by gentling hammering that into the tube then see if I can ream it after. I will be using a dropper post so if its not super smooth going in and out its not a deal breaker.



    Save yourself seizing a seatpost in the frame and ream it out.
    "These things are very fancy commuter bikes or really bad dirt bikes, but they are not mountain bikes." - J. Mac

  8. #8
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    I'd think about slugging it like a rifle barrel (small spherical steel slug on a rod). Grease it and drive it in and out to round the tube. Alternately you could make an oval slug and twist it around the tube pushing it lower with each turn.

  9. #9
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    Ream it.
    Myth Cycles handbuilt bike frames
    Durango, CO
    http://www.mythcycles.com

  10. #10
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    What on earth is this hammering advice? Seat tubes are *always* ovalized after you weld them or braze them. Always. You ream them back to round. Period.

    -Walt

  11. #11
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    All the above is true, but if you totally pood the screwch and have a wacky seat tube you're better off putting in a shim. Although reaming the seat tube is part of building a frame, if it's totally fuct up cuz it's your first frame and your metalworking sucks... it's easy to ream so much the seat tube ends up so thin it cracks in short order.
    "Things that are complex are not useful, Things that are useful are simple."
    Mikhail Kalashnikov

  12. #12
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    My local bike shop has a "burnishing tool". I will try that first. I went back and did some additional investigation and it doesn't seem as bad as I originally thought. Crossing my fingers that will be enough.

    Thank you all for your input. It's much appreciated.

    Hopefully pictures of finished frame will be posted within the month. (Kitchen renovation must take priority if I want to stay married.)
    Cycle tracks will abound in Utopia. ~H.G. Wells

  13. #13
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    Adjustable reamers work reasonably well and are pretty cheap. In this case, you don't need to spend hundreds on a specialty tool.

    I would think you could find one for closer to $30, but here's a link to one on ye olde amazon

    I guessed you wanted this size based on using a dropper post. It should work for 30.9 or 31.6 posts. Get the next size down if you are using a 27.2.

  14. #14
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    Quote Originally Posted by Feldybikes View Post
    Adjustable reamers work reasonably well and are pretty cheap. In this case, you don't need to spend hundreds on a specialty tool.

    I would think you could find one for closer to $30, but here's a link to one on ye olde amazon

    I guessed you wanted this size based on using a dropper post. It should work for 30.9 or 31.6 posts. Get the next size down if you are using a 27.2.
    Thanks. Thats perfect.
    Cycle tracks will abound in Utopia. ~H.G. Wells

  15. #15
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    Quote Originally Posted by Walt View Post
    What on earth is this hammering advice? Seat tubes are *always* ovalized after you weld them or braze them. Always. You ream them back to round. Period.

    -Walt
    Why remove material when you can reform it and maintain wall thickness?

  16. #16
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    Quote Originally Posted by EricTheDood View Post
    Why remove material when you can reform it and maintain wall thickness?
    Have you ever forcibly reshaped a welded joint made from thin tubing? It's a great way to cause it to fail either immediately or a bit later when you're riding the bike. Hammering a big steel ball through the seat tube... the mind boggles. You are almost certain to wreck your frame.

    I've reamed something like 750 seat tubes at this point - the same way pretty much every other builder reams seat tubes, since forever. It works great. The tools are cheap and easy to use, and it's fast. Assuming you did an even halfway decent job of selecting tubes and joining them, the material you remove poses no danger to the integrity of the frame. Hammering something through the joint, on the other hand...

    Look, I know you were trying to be helpful here. But you don't know what you're talking about. There's a simple, proven, safe process to accomplish what the OP wants to accomplish.

    -Walt

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