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  1. #1
    mtbr member
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    Retrofit frame for belt drive, TIG / Silver filler?

    I'm considering upgrading an existing frame to add belt drive. I've been looking at the tube splitter from Paragon Machine Works www.paragonmachineworks.com - MS103558InchStainlessTubeSplitterStep



    The frame is chromoly, the insert is stainless steel.

    I know the traditional thing to braze the inserts in place is to use silver filler (e.g. FilletPro or similiar blend from our friends at Cycle Design Group, Link: SILVER BRAZING WIRE "BRAZAGE" ).

    On the other hand, the beautiful dropout attachment work by trailmaster on Krooser got me thinking. If I was to create a 45 degree bevel on both the chromoly seat stay tube and the edge of the step on the insert, can I TIG weld the thing in place, old skool pipe welding style? After welding is complete, carefully hand file flush? I'm assuming 309 filler rod or something similar.

    Pros / cons of doing this? What would provide the strongest most robust result, silver braze or TIG ? Your thoughts? (Dave Bohm, are you out there?)

    Additional question.. Where is the best place in the seat stay to put the insert, in the middle somewhere or towards dropout/ or seat post end of the stay?? Anybody got a feel for this?

    Photo of a Soulcraft with what appears to be TIG welded adapter, mounted near dropout, but I've also found photos of road bikes with the adapter mounted near the top of the Seat Stay. I'm sure this Soulcraft adapter is built on a new frame... a retrofit would be a slightly different story...



    Many thanks,
    zip
    Last edited by zipzit; 12-03-2012 at 11:13 PM.

  2. #2
    RCP Fabrication
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    I did this one about a year and half ago. Put the frame in the fixture, cut the stay with a pipe cutter, TIG'd the insert in with some 880T.


  3. #3
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    The place to locate the splitter is where the stay ID matches the OD of the splitter.That gives you a nice slip fit to help locate the splitter and a silver-friendly gap.This would be a good place to use a preformed piece of silver braze. Flux the joint and stuff a little loop of brazing material into the tube, then the plug. You'll want the the whole joint oriented with the plug downwards so gravity will keep the brazing material in the proper location. Heat it up and wait for the silver to appear at the bottom of the joint, and you'll know that the silver has melted at the top and flowed all the way through.

    As far as the TIG vs. brazing question goes, it's mostly a matter of which process you're more comfortable with. Blowing soot all over a joint with a carbon-rich flame can set you just as far back as hacking around with an arc. Which tool are you most experienced with?

    And don't forget to drill vent holes--you'll need at least one.

  4. #4
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    Both processes are fine

    But keep in mind that filing TIG beads flush is not a very good idea in general. If you do that, there won't be much fused material left to hold everything together.

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  5. #5
    Nemophilist
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    Quote Originally Posted by Walt View Post
    But keep in mind that filing TIG beads flush is not a very good idea in general. If you do that, there won't be much fused material left to hold everything together.
    In VERY general;

    Yes. The golden rule is that a weld should never be altered for surface quality. If you can't weld well enough not to have to touch up those welds to suit your esthetic desires, then practice welding, not grinding/filing. The possibility of ugly welds being strong and beauties being weak is another topic altogether.

    IF you have good solid penetration of the welds through the material, truly fusing the parts together, AND you have a healthy amount of weld surface area for the load the joint will see, AND you are VERY careful to only remove weld material above the surface of the parent pieces - without altering the properties of the tubes, in other words - then it can be done successfully because the extra weld material is redundant.

    How do you know and prove all of these IFs & ANDs? That is where the general rule gets its traction, because it is hard to determine and easier to just not have to. Playing the percentages, if you will.

    I'd say build it the way you envision, as best as you are able. Then go beat the tar out of it. If it breaks, there's your answer. If it doesn't, keep testing!

    -
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  6. #6
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    Let me rephrase that:

    If you need to ask questions about how to join tubes and splitters on the forum, you probably should not be grinding your welds flush unless you have a ton of experience with TIG in some very similar application (in which case why are you asking us?)

    If you want a really clean look, I'd do silver (as long as you have some experience brazing stainless). Seatstays are pretty much always in compression so the danger from a so-so joint is minimal. Like TM said, you're your own best test monkey!

    -Walt
    Waltworks Custom Bicycles
    Park City, UT USA
    www.waltworks.com
    waltworks.blogspot.com

  7. #7
    Nemophilist
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    Just for the Record;

    I was agreeing with you, Walt. In general.
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

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