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  1. #1
    mtbr member
    Reputation: frankzetank's Avatar
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    Feb 2013

    My first brazed joint

    So you guys inspired me to finally get my frame building project going. As I learned a lot lurking in this forum, I'll try to give back by sharing my experience. I'm no expert, but hopefully, my mistakes will help others!! For those interested, I posted in the "roll call" thread

    So first things first, learning to braze! I've bough my torch set up this winter and have been through the "melting brass on a thick plate" to practice control heat and movements coordination. Yesterday, I completed my 1st thin walled tube on tube fillet braze. Nothing fancy, a short chromoly 25.4x1.2mm tube file mitered at 90 to a 38.1x2mm base tube. It was my first weld with paste flux and LFB rods. Products where bought from Cycle Design USA with which I had impeccable service and great advices (I'm in no way affiliated to him, just had a great customer experience).

    All in all, the braze went pretty smoothly. I felt the flux paste got a little bit in the way to see the color of the steel being heated (compared to flux covered rod) but I guess I probably put too much flux in the first place. Tacked and thinned the joint 3/32" rod and completed the fillet with 1/8".

    Pictures below are "as is" right after hot water soak. I did some destructive tests to check out the strength. I hammered as hard as my vise and bench set up could take and it held! Did some cross sectioning and I'm happy with the brass distribution albeit I might like a little bit more fillet for a structural bike frame joint. My fillet was about 3x the thickness of the thinnest tube.

    Feel free to comment!

    My first brazed joint-p3260083.jpg

    My first brazed joint-p3260082.jpg

    My first brazed joint-p3260085.jpg

    My first brazed joint-p3260086.jpg

    My first brazed joint-p3260087.jpg

    My first brazed joint-p3260092.jpg

    edit: spelling!
    Last edited by frankzetank; 03-28-2013 at 05:17 AM.

  2. #2
    Reputation: TrailMaker's Avatar
    Join Date
    Sep 2007

    I haven't brazed in decades. Doubtless could not do that good. Those are far from the worst fillets I've ever seen on here. I think you're off to a good start. Let the build begin!
    Most people ply the Well Trodden Path. A few seek a different way, and leave a Trail behind.
    - John Hajny, a.k.a. TrailMaker

  3. #3
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    Apr 2012
    Looks better than my first braze attempt. I'd say you did a pretty good job with the heat and laying the metal down. It's only going to get better
    andy walker

  4. #4
    mtbr member
    Reputation: Feldybikes's Avatar
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    Feb 2004
    Your fillet on the outside looks not bad. It's bigger than it needs to be, but that's the directional in which you want to err anyway. Plus some/most people like the look. I'm looking at this on my phone but it looks like you could stand to get a bit more penetration on the inside. Try pulling the brass around more from your tacks before adding more filler.

    Also, I've read it's not terribly hard to make a joint that will easily pass the vise test but would fail in fatigue. I tend to believe this based on having a couple of early frames with tiny fillets develop cracks.

  5. #5
    mtbr member
    Reputation: adarn's Avatar
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    Aug 2009
    Yeah that looks pretty good. I don't know what I'm talking about really, but I've found that doing things just a tad hotter will get you a bigger internal fillet. Mess around with some practice joints at different temps and see what you come up with.

  6. #6
    mtbr member
    Reputation: frankzetank's Avatar
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    Feb 2013
    Thanks for the comments! The true test will definitively be the test of time. Agreed on trying to build a bigger fillet inside. I was able to achieve that where I initially tacked the joint but failed to do it all around. More practice during the week end!

    My first brazed joint-p3280009.jpg

  7. #7
    mtbr member
    Reputation: frankzetank's Avatar
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    Feb 2013
    Been doing some more brazing practice. Overall things are going good (I think!?). On top of many tube on tube joints, I brazed a "mini front triangle". With this, I got the chance to practice the whole process including proper brazing sequence, access, etc. Definitively a positive learning experience.

    I did some destructive cross sectionning to see how I did on my braze joints. Overall all, I'm happy with the filet shape and penetration inside the joint. I did notice that where my mitter is really tight, I don't get as much brass inside the joint as where the fit is loose(r). Ultimatly I want some brass inside but not at the price of sloppy fits. What's the "happy medium"? How tight is "tight enough"?

    Any comments, feel free. FNG wants to learn!

    For scale, the tubes are 1" and the background is 8.5x11" white paper sheet
    My first brazed joint-p5010013.jpg

    Not the smoothest...
    My first brazed joint-p5010015.jpg

    Taking alook inside
    My first brazed joint-p5010017.jpg

    My first brazed joint-p5010018.jpg

    My first brazed joint-p5010019.jpg

    My first brazed joint-p5010020.jpg

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