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  1. #1
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    question on tig welded frames

    I am thinking about painting my lemond frame. How is it that some of these builders get the joint "SO" smooth? Do they spend hours on the joint with a file, or do they use a filler like bondo to get that ultra smooth joints. weld marks can be seen where the pieces of tubes joint together. If I decide to file it, will that weaken the joint?

    I will be painting the frame myself with my company name on the down tube. Any suggestions? I do not know where to start with the decals. I like the look of the mid 80s (my cycling era as a kid) simple plain look with just letters and no graphic on the frame. Will the vinyl decal do the trick you see at the mall where some kid cuts it on that little cutting machine? I am even thinking about painting the name with the vinyl decal as a guild or stencil and spray painting it then clear coat.

  2. #2
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    It is possible to weld the joints so they are utterly smooth, but it is unlikely you have run across that kind of skill often. Some smooth joints you see may be fillet brazed. Another approved technique in fabrication, is to tig weld the joint, then "bondo" it with brass. This is common in general, but since at the loads we are talking about one can use brass to braze the joint in the first place, it would not be useful on bikes. In a situation where you need full penetration weld on 1/8" material and a smooth look, it's the done thing.

    Bondoing a tig joint, is totally OK, but we don't tend to see it with bikes, because: a) There is a prejudice against non-metal finish on joints; b) On quality TIG, particularly custom, guys like to flaunt the quality of their work; c) On cheap stuff they don't care. I have used 5 minute epoxy and micro balloons with success on non-bikes, I like the adhesion epoxy gives, needs to be the good epoxy though, like WEST, DEVCON, etc... The epoxy approach is ok for joints, for larger areas you need a specialty product that allows blocking out the finish. Also, with any of these products the coat needs to be thin, so the underlying welds need to be clean. too lumpy and the coat required to hide the mess will probably pop off. Powder coat won't stick to bondo and may melt it, though there are special fillers for that. On a one off it would be cheaper to brass it.

    Filing is bad for 2 reasons, one, cuts through the grain structure are bad for the weld. These are essentially porous free form castings, and interrupting the grain structure is to weaken it. Or something. The welds might still be strong enough, but you are undermining them, and since additive processes are cheaper, why do it. Second reason is you may end up cutting into the adjacent tube.

    Other part of your post might get more attention on the vintage forum.

  3. #3
    Randomhead
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    On steel and titanium, typical paint systems are thick enough to cover up evidence of the welds. Cannondale is famous for having a second weld on their aluminum frames that is mainly cosmetic. They shape the cosmetic weld to look like a fillet.

  4. #4
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    This is what I am talking about. I am not sure how they do that? With brass after a weld?http://www.cxmagazine.com/wp-content...0/photo_41.jpg
    [Click to Close]

  5. #5
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    Thanks guys. I am not a welder and have no clue what to do beside a welding class in High school back 20 years ago. Do you think epoxy can achive that look or do you think it will fall off after beating on the frame for a couple of years? The joint or fillet is no way near the thickness of that blue frame on my Lemond Zurich.

  6. #6
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    Epoxy should hold up, The key is to mold it, but do no more than a thin coat. And you can sand it, with care since the sandpaper won't cut into the tubes if you are careful. I add some filler to the epoxy, normally some micro baloons, or 410. This helps stabilize the epoxy so it won't run. But if one uses too much it will not adhere. So it needs to be wet but not runny, like peanut butter of the sugary kind. Do not run the epoxy down the tube, just in the radius of the corners.

    The way one gets smooth welds in the raw, without brass (don't know any bike people who do that) is by running the wire in such a way that it is constant, sorta a push welding. The simplest example is simply placing it at a tangent and running over it. That won't work on tubing, because it is not constant in form or geometry. But it does work in seams. Another way to look at it is to ask how you get the dimes. Pulse in the weld set up, or pulsing the wire feed, or a pulse with the pedal. A case of heat, cool, heat, cool. On my welding gloves I have the knuckles on the right hand marked HEAT, and on the left COOL. So smooth is the opposite of all that stuff. And then it can look like this (Don of Anvil fame):
    Attached Images Attached Images

  7. #7
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    That exactely what my lemond looks like. I want to do away with the weld marks similar to the baby blue bike I posted above. Epoxy is the way to go for my application? What do you think about JB Weld in the joints as fill?

  8. #8
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    I've never used JB weld, I come from the boat side of the equation. A lot of people swear by it, and I have heard some people say they successfully powder coat over it, though I would use the stuff intended for that purpose that Eastwood sells, or make sure my powdercoated was onside first. But obviously if they do that with JB they were fairing with it.

  9. #9
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    Peterpan,

    do you suggest that I apply epoxy in layers of no more then 1/16" to fill the joint until smooth then sand to finish? It has to go on bare metal, right and not over primer or paint?

  10. #10
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    I mean you should do a thin layer and leave it at that. You can build a fat layer, and there is some chance it will be fine, but the thicker it is the worse it. Also, getting rid of the texture is one thing, and that should be possible with a thin coat. If you want to fake a thick fillet, as from a fat brass job, then it's a different story.

  11. #11
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    Yeah, I really just want to get rid of the weld texture and get it as smooth but as little (not thick fillet) as possible. Thanks for all your help. Do you build much bicycle frames for others?

    Jeff

  12. #12
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    No, the insurance thing doesn't work for me. But I'm all set-up.

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