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  1. #1
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    brazing or soldering non-structural components

    hi all,

    i've recently picked up a basic aluminum frame for cheap. it's a no-name taiwanese frame that i'm planning on stripping the paint from and adding my own 'custom' touches before repainting with my chosen paint scheme. it currently is set up for the screw-on downtube cable stops, but i'm thinking of opening and profiling those holes a bit and running the cables internally. whether that's a good idea or not is beside the point, i just want to try it. the tinkering engineer in me wants to play around and braze up nice looking inlet/outlets for the cable. i also have a few other ideas that would require brazing or soldering.

    Any additions or modifications i've got in mind are basically non-structural. Should I braze on the bits and pieces or would a clean solder job do just as well?

    Any tips or info would be appreciated.

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    aaron
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  2. #2
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    In theory you can't braze aluminum, since the 800 degree temp that constitutes the threshold of soldering and brazing is at the lower end of melting point of aluminum. In practice they used to braze aluminum all the time, because the alloys extend the range, and it was considered a reasonable practice. That said, I don't know where you get the materials to do it, as even the tinman seems to be holding that info close to his chest, you might try his site.

    There are some zinc products that work on aluminum. I found an old fashioned recipee on one of those country projects type sites that harve old articles on making your own tractor or skidoo. There are also some commercial products on ebay etc...

  3. #3
    Healthy and active twobikes's Avatar
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    Quote Originally Posted by Peterpan1 View Post
    In theory you can't braze aluminum, since the 800 degree temp that constitutes the threshold of soldering and brazing is at the lower end of melting point of aluminum. In practice they used to braze aluminum all the time, because the alloys extend the range, and it was considered a reasonable practice. That said, I don't know where you get the materials to do it, as even the tinman seems to be holding that info close to his chest, you might try his site.

    There are some zinc products that work on aluminum. I found an old fashioned recipee on one of those country projects type sites that harve old articles on making your own tractor or skidoo. There are also some commercial products on ebay etc...
    Home Depot sells some rods made by Bernz-O-Matic that attach aluminum pieces together and are supposed to have good tensile strength. It can be applied with a MAPP gas torch. I think it is nearly identical to what you would buy on e-Bay.
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  4. #4
    THE Materials Oracle Falanx's Avatar
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    It's possible to braze aluminium alloys - it's just that the alloys used are far, far removed from what you wuld consider to be a brazifn alloy. They are a modified high silicon aluminium alloy. Theyr'e used in some aerospace fixtures for dip-brazing of some assemblies.

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  5. #5
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    "Any more is classified"

    That would explain the cloak of mystery. On the tape, they show examples of fuel tanks made in large quantities for WWII aircraft, and the tanks are welded together, and I believe that mounting tabs, are also welded on. The spouts, though, are mounted though a surface drilled hole and brazed to the surounding material. I was just a little surprised they wouldn't talk about the brazing material. The modern fabricator might TIG weld that kind of part, or machine an interface. Doesn't mean that would work better than the lower temp braze.

  6. #6
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    One problem you might encounter with this project is that if you heat the aluminum to approximately 500 deg F or above . . . any heat treatment in the frame will be gone. In other words . . . any aluminum in the heat affected zone will be soft. I have tested 6061-T6 @ 500 deg. Other alloys might react differently.

    I was involved years ago in the manufacture of an aluminum-framed bike formed with .065 sheet aluminum. The aluminum alloy used was 6061-T0 [zero]. Once it was formed and welded . . . it was sent to a heat-treat plant and was brought up to T6 condition to make it strong enough. Any welding done later would have ruined the frame.

    YMMV.

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