Aluminum Frame repair

Discussion in 'Cycling Equipment' started by Shandit66, Sep 1, 2011.

  1. Shandit66

    Shandit66 New Member

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    Hi,

    [SIZE=10.0pt]I have an old (circ 1990) Klein Quantum with a broken rear derailleur hanger. From that era the hanger arn't replaceable, so I'm guessing I need to re-weld it. Can anyone recommend a competent person who does this? Preferably in Canada.[/SIZE]

    [SIZE=10.0pt]I know its an old bike, but it fits me like a glove and otherwise still rides extremely well (just heavy by today's standards).[/SIZE]
    [SIZE=10.0pt]I could turn it into a single speed, but due to vertical dropouts the spacing adjustment is extremely limited.[/SIZE]

    [SIZE=10.0pt]T[/SIZE][SIZE= 10pt]hanks[/SIZE]
    [SIZE= 10pt]Olaf[/SIZE]
    [SIZE=10.0pt][/SIZE]
     
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  2. dabac

    dabac Well-Known Member

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    Welding repairs on aluminum frames is a frequently debated subject. The alloys used for bike frames often require extensive heat treatments(called annealing) to reach full strength after having been welded. And that's still ignoring the changes brought on by the actual weld itself.

    Ideally, to get an as-good-as-possible repair, the welder need to know what alloy you have, what welding rod to use, and how/if to heat treat it afterwards. If required he need to have an oven big enough for a frame. And you need to be ready to cough up the dough for all that.

    Now for a derailer hanger, some might say that the weld itself isn't critical, but odds are that it'll still heat up the dropout all the way to where the stays attach. And if your fram is made from one of those finicky alloys, this CAN be bad news. Having the derailer coming off(maybe do the 1st hundred miles with a spoke protector) is probably a manageable event, but a simultaneous failure of both stays on the same side would be scary.

    Packing the dropout in ice, working with a TIG, doing the job in small increments, it might be possible not to disturb anything else. But you'd need a welder who knows what he's doing. "Aeroplane Repair" is often held to be what to look for.

    In your case, whu not consider an Adaptor claw. Not as elegant but about a thousand times easier, and quite probably just as functional.
     
  3. tafi

    tafi Member

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    Agreed, Aluminium welding is quite different to your standard metal-working skills (usually done with steel - and quite thick steel at that). Since most aluminium structures are lightweight and have very thin walls (and therefore little margin for error). You need to find someone who has appropriate qualifications, equipment and, most importantly, experience in this sort of repair.
     
  4. Shandit66

    Shandit66 New Member

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    I'll try the idea of adding a derailleur hanger. At worst, I might have to drill some holes in the dropout to get it really solid. The drop out is about 1/4" think so I'm not worried about strength.

    Thanks for the ideas guys!

    Olaf
     
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