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Thread: Silver Brazing

  1. #1
    Mitcholo CrimsonKarter21's Avatar
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    Silver Brazing

    Hi, I'm receiving a new (actually old, but new to me, and not used a lot) Erba NJS track frame. My coach got it and a U-Haul of other pro-Keirin stuff from an ex-Japanese pro now situated in Detroit. He'd giving me the frame for practically free. The only problems are:
    1.) For some reason, this racer drilled brake holes in the fork and rear stay bridge.
    2.) During shipping, an axle put a small dent into the down tube.

    My coach says that I could use silver and braze everything up with a propane otrch since I don't have access to an acetlyne torch.

    So my questions are:

    1.) Will silver and a propane torch be suitable?
    2.) Will the fork and bridge be as structurally safe as before?
    3.) When brazing the holes, should I put something behind the hole, or should I just plug it up by making the hole smaller and then filing?

  2. #2
    Senior Member Nessism's Avatar
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    I don't understand why you would want to fill the holes. Assuming the crown was drilled through a solid section the hole won't hurt anything...in fact, you could throw a brake on there if you are going to ride the bike on the street at some point. Brake bridge hole won't hurt anything either. Not sure I'd put a brake on it though since many track frame rear bridges are not strong enough to support a real brake. At any rate, you will gain nothing structurally by filling the holes.

    BTW, propane does not get hot enough for brazing. Some low budget people use MAPP gas though which is reputed to work okay in a pinch.
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    Senior Member PaPa's Avatar
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    Quote Originally Posted by Nessism
    BTW, propane does not get hot enough for brazing.
    When mixed with oxygen, propane does just fine (and is preferred by some professional frame builders) . Both oxy-propane and oxy-acetylene are well above 5000 degrees, with only about 4oo degrees separating them. Air-propane, on the other hand, (i.e. BERNZOMATIC) produces less heat and is not suitable for frame work.
    Last edited by PaPa; 07-05-07 at 11:57 AM.

  4. #4
    Mitcholo CrimsonKarter21's Avatar
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    Quote Originally Posted by Nessism
    I don't understand why you would want to fill the holes. Assuming the crown was drilled through a solid section the hole won't hurt anything...in fact, you could throw a brake on there if you are going to ride the bike on the street at some point. Brake bridge hole won't hurt anything either. Not sure I'd put a brake on it though since many track frame rear bridges are not strong enough to support a real brake. At any rate, you will gain nothing structurally by filling the holes.

    BTW, propane does not get hot enough for brazing. Some low budget people use MAPP gas though which is reputed to work okay in a pinch.
    This is a track only frame, I'm not a hipster. I also want it to be as aero as possible without interruptions in the wind. Neither of the holes were supposed to be there in the first place.
    Either way, the dent at least needs to be filled. Are there any lower cost alternative brazin techniques? I might be able to find someone with an oxy-acetlyne torch, but I've only used oxy-acetlyne to cut metal, not braze.

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    Senior Member Nessism's Avatar
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    Quote Originally Posted by CrimsonKarter21
    This is a track only frame, I'm not a hipster. I also want it to be as aero as possible without interruptions in the wind. Neither of the holes were supposed to be there in the first place.
    Either way, the dent at least needs to be filled. Are there any lower cost alternative brazin techniques? I might be able to find someone with an oxy-acetlyne torch, but I've only used oxy-acetlyne to cut metal, not braze.
    You want to fill the holes because they create wind resistance?

    Fill the holes with bondo or epoxy if you must. Brazing them closed will do nothing positive for the frame and will ruin the paint job.

    The lowest cost braze worthy torch is a MAPP gas torch - looks similar to a Propane torch but burns hotter.
    Becareful buying/selling bike parts on-line. I learned the hard way. :(

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    Healthy and active twobikes's Avatar
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    A carbon arc torch on a 230 volt arc welder works well, too. For those unfamiliar with a carbon arc torch, it is a "V" shaped device you hold by its handles and squeeze together. There are also two holders for carbon rods. Squeezing the handles brings the carbon rods into contact. They get very hot. The user allows them to spread apart slightly and a brilliant hot arc forms between them.
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  7. #7
    I pedal what I ride
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    if you're that worried about wind resistance then you should be petrified about the additional weight brazing would add to your frame. Use duct tape.

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    Senior Member Homebrew01's Avatar
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    Quote Originally Posted by CrimsonKarter21
    This is a track only frame, I'm not a hipster. I also want it to be as aero as possible without interruptions in the wind. Neither of the holes were supposed to be there in the first place.
    Either way, the dent at least needs to be filled. Are there any lower cost alternative brazin techniques? I might be able to find someone with an oxy-acetlyne torch, but I've only used oxy-acetlyne to cut metal, not braze
    .
    Why ? If it's not a restoration project, leave it alone and ride it. If it bugs you, sand the paint off and use automotive "Bondo" or some kind of filler. Then you'll need to decide what to do about repainting.

  9. #9
    Mitcholo CrimsonKarter21's Avatar
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    I think Bondo would be the best option in the end, the steel is pretty thin, and even though I know how to use everything, I can't trust myself to mess around like that.

  10. #10
    Ho-Jahm Hocam's Avatar
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    Do you really think that Keirin frame was designed with aerodynamics in mind?
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