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  1. #1
    Randomhead
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    building a fillet brazed frame

    My daughter helped me at NAHBS, so I told her I would build her a bike. Here are some pictures
    First, I'm brazing the seat tube to the bb because the down tube covers part of the seat tube.



    Checking the alignment after tacking




  2. #2
    Randomhead
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    I should have spent some time cleaning up my work area, but brazing is more fun.

    The seat tube is in a 1 1/4" piece of tubing held in a Park stand. That way I can rotate it -- with a gloved hand of course. I added some flux after this.



    My goal is to have the brazing filler as smooth as possible, particularly where it hits the tubes. It's really easy to leave a small lip right at the edge of the filler. The trick is to get rid of that discontinuity while brazing instead of having to file and sand it off and risk cutting into the tube. I thought this looked good, but it will have to wait until I get a chance to soak the flux off.


  3. #3
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    Will be following this build... am enjoying my new work as an apprentice frame builder and have been working on some very nice frames and should be starting my first complete build very soon.

    Most of the work we do at the shop is filet brazing...

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    Randomhead
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    You can tell where the area I put flux on ends in that picture, there is a layer of carbon on the steel. What you want to avoid is a lot of carbon where the flux was applied, that means the flux was overcome by heat. This is pretty good.

    Quote Originally Posted by Sixty Fiver View Post
    Will be following this build... am enjoying my new work as an apprentice frame builder and have been working on some very nice frames and should be starting my first complete build very soon.

    Most of the work we do at the shop is filet brazing...
    I really like fillet brazed frames because there is so much freedom in what you can do. This bike is going to have a curved top tube. That's the problem in taking the kids to NAHBS, they get ideas.
    Last edited by unterhausen; 07-31-10 at 12:16 AM.

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    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    It looks very good.

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    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    I have a short list of bike I want to build and besides one of my own (a touring bike) am looking to build a bicycle for my youngest daughter.

    Next week I will be doing repair work to existing frames and doing some modifications to my folder.

  7. #7
    Senior Member mudboy's Avatar
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    Can I help you at NAHBS next year so you'll build me a frame?

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  8. #8
    tuz
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    Great thread!

    I don't know if this is too technical for the interwebs, but what sort of flame you're using for fillet brazing? I've had relative success with a soft flame and the sequence melt brass puddle, back away and let solidify, add on top, repeat going around... But my fillets are kinda small. Too strong a flame and the fillets melt away on the side, but even with the soft flame I can't stay long enough to build a large fillet...
    homebuilt commuter, mixte, road and track (+ Ryffranck road)
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    legalize bikes
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    Quote Originally Posted by tuz View Post
    Great thread!

    I don't know if this is too technical for the interwebs, but what sort of flame you're using for fillet brazing? I've had relative success with a soft flame and the sequence melt brass puddle, back away and let solidify, add on top, repeat going around... But my fillets are kinda small. Too strong a flame and the fillets melt away on the side, but even with the soft flame I can't stay long enough to build a large fillet...
    when starting out learing to fillet a softer slower flame is easier to work with, it slows down everything to give you a chance to pull back before your puddle gets away from you.
    as you get better a faster more neutral flame lets you get it done fast, which is important to maintain the strength of the tubes. also the neutral flame allows you to to have a bigger puddle which goes to the root of the joint, and will give you a fillet that requires less finishing.

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    legalize bikes
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    Quote Originally Posted by unterhausen View Post

    My goal is to have the brazing filler as smooth as possible, particularly where it hits the tubes. It's really easy to leave a small lip right at the edge of the filler. The trick is to get rid of that discontinuity while brazing instead of having to file and sand it off and risk cutting into the tube. I thought this looked good, but it will have to wait until I get a chance to soak the flux off.
    unter-
    when im doing fillets to avoid the lip i like to check buy wiping away excess flux with my rod, then if i need to feather out the edges i hit em with the torch real quick just enough to wash it out a little.

    taking off those shoulders with a file, shop cloth, or bearing scraper is definitely to be avoided!

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    Randomhead
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    Quote Originally Posted by tuz View Post
    I don't know if this is too technical for the interwebs, but what sort of flame you're using for fillet brazing? I've had relative success with a soft flame and the sequence melt brass puddle, back away and let solidify, add on top, repeat going around... But my fillets are kinda small. Too strong a flame and the fillets melt away on the side, but even with the soft flame I can't stay long enough to build a large fillet...
    Interestingly enough, I was experimenting with my flame on this joint. Started out with a smaller flame than I usually use and then got tired of it and went to a hotter neutral flame. The key is flicking the torch away at the right rate that the heat doesn't get away from you. It is a lot easier to manipulate the brass with a small flame, but the brass doesn't melt fast enough for me. But it should be possible to build as big a fillet as you want with a small flame; the problem I would have is getting it to melt smoothly. I didn't mention I am using 3/32" rod, so a little more heat is needed.

    Quote Originally Posted by legalize_it View Post
    unter-
    when im doing fillets to avoid the lip i like to check buy wiping away excess flux with my rod, then if i need to feather out the edges i hit em with the torch real quick just enough to wash it out a little.
    That's what I do. I try to feather the edges as I'm going, but then when I'm done before I turn off the torch I go around the joint and look for problem areas. That's when it pays to have a fairly energetic flame. My goal is no sanding/polishing, but that hasn't happened yet.
    Last edited by unterhausen; 07-31-10 at 09:50 AM.

  12. #12
    Senior Member Cassave's Avatar
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    This is gonna be fun to watch. Thanks!

  13. #13
    Bicycle Repair Man !!! Sixty Fiver's Avatar
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    Quote Originally Posted by unterhausen View Post
    That's what I do. I try to feather the edges as I'm going, but then when I'm done before I turn off the torch I go around the joint and look for problem areas. That's when it pays to have a fairly energetic flame. My goal is no sanding/polishing, but that hasn't happened yet.
    The fellow I am learning from has been doing this for 30 years... a few ex frame builders used to call him "OK" Arvon which stood for "overkill"...

    A few more minutes of post build work and it should look like these brake posts are flowing out of the frame...



    Still have a little touching up work to do here but am quite pleased... was looking for a smooth line / flow on my brake mounts and got the brass flowing very nicely with a fairly hot flame and am blessed with quick hands and apparently... not a bad set of eyes for this.

    Will be cleaning up the frame and adding more in the way of cable stops and guides, a spoke holder, and will be smoothing out the original work, especially in the bb area as that looks like crap.

    But that is really another thread.

  14. #14
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    I thought when I got into frame building it would be great to build my girls some nice bikes. So far they aren't interested, and regular bikes seem to just fall into our laps. They were quite a bit smaller even 2 years ago, and I thought maybe a nice 20 inch bike with and IGH would allow me to just keep rolling top of the line components onto different frames until they left the home with a folder that would last them a lifetime. Best laid plans!

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