Bicycle frame downtube replacement

  1. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    Hi,
    I just made a series of pictures from a typical job I do recently.
    The steel touring frame had a bad dent in the downtube and filling that with silversolder (Thats what I do when it´s not as bad) wouldn´t work.
    So I had to replace the tube......
     
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  2. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    Some more...
     
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  3. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    .....
     
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    123hotchef, Dcal, lchris21 and 9 others like this.
  4. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    .....
     
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  5. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    Now it´s in the watertank to get rid of the flux.
    Then alignmentcheck and it´s finished.
     
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    Morrisman, 8ob, Dcal and 10 others like this.
  6. stuvy

    stuvy Member

    Looking great

    Do you do them often
     
  7. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    I have my workshop integrated into a bigger bike company. I build prototypes for them, modify or fix production frames and build frames for my own customers.
    This was a job which I have to do a few times a year.
     
  8. Shox Dr

    Shox Dr Chief Engineer to Carlos Fandango

    Messages:
    13,646
    Location:
    East Yorkshire
    Lovely work. That toob looks very thin. Whats the specs?
     
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  9. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    It´s a Columbus Zona downtube.
    38mm od, 0,7 at the end, 0,5 in the middle.
    uncutted weight is about 340g when 670mm long
     
    stuvy, Scruffywelder and Shox Dr like this.
  10. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    To keep the BB shell and headtube (which is allready reamed) round is a little challenging.
    Therefore I put dummies into the tubes.
    But that leads to very big difference in thickness of the parts, which makes welding not so easy.
    The bb shell itself is 2,5mm thick and has that heavy rings inside. And the 0,7mm downtube is the cutted part. Easy to burn holes into it ;-)
     
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  11. grim_d

    grim_d Forum Supporter

    Messages:
    1,875
    Location:
    Scotland - Ayrshire
    Less bikes, more Colchester.
     
  12. Scruffywelder

    Scruffywelder Forum Supporter

    Messages:
    393
    Location:
    Dumfries & Galloway
    What's the frame?

    Looks kinda like a Firefly?
     
    stuvy likes this.
  13. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    Yes, I like my Student 1800, had a Harrison before.
    My dream would be a Schaublin, but these are very expensive and to be honest I don´t need the precision and rigity for the stuff I make.

    The frame is no firefly. It´s from a smaller german brand specialiced in touring bikes.

    Maybe I have to fix a little problem on a ally frame next time.
    If I don´t forget it I will take some pics again.
     
  14. Ped

    Ped Member

    Messages:
    147
    Stamford, uk
    Do you have any pics of your mitre set up on the Colchester? i'd be interested to see it. It looks like you've mounted a vice where the toolpost goes?
     
    stuvy likes this.
  15. citizen kane Member

    Messages:
    152
    UK Hampshire
    Very nice work, what do you make the heatsink inserts from? Does the frame often need cold setting after a repair like this?
     
    stuvy likes this.
  16. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    Hi,
    I do the miters on a horizontal mill (old Steinel SH4). The tube in a turnable vice.
    It would work on the lathe, but the mill is there....
     
    Ped likes this.
  17. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    I have a heatsink for the bb made out of brass, but the contact area is titanium. Bronce is often used for them too.
    And if I make bearing dummies I use steel.

    To be honest, I take what´s allready there ;-)
     
  18. brockenhammer Member

    Messages:
    213
    Location:
    Freiburg, Germany
    Hi,
    I did another tube replacement today. This time on an Cannondale Ally frame.
    I know that the cannondale was 6061 ally, so usually it has to be heat treated after the welding.
    Therefore I left some material of the old weld and melted it up with 5356 filler and the new tube.
    I don´t know if it works, I don´t weld ally a lot.
    Just a try, and I will ride that frame in the city myself.

    I used a Columbus Airplane tube which was less then 1mm in the middle and less then 1,5mm at the ends.
     
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  19. citizen kane Member

    Messages:
    152
    UK Hampshire
    Didn't Cannondale use to double pass their welds to get that smooth finish.
     
    Tangledfeet likes this.
  20. stuvy

    stuvy Member

    That would make sense I had a Silk Road and the welds looked like they were fused
     
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