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  1. #1
    Senior Member Briareos's Avatar
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    Smooth Aluminum Welds: How Do They Do It?

    I had an earlier thread (old) where I asked about cutting my GT Strike's horrible welds to smooth them out. I have filed a bit of them, and it seems to work, but it is definitely tiresome and very tedious.

    Just how does Cannondale or any other manufacturer make their welds so smooth? Someone in my thread mentioned Bondo, and I had no idea what they meant. I know now Bondo is some sort of goo that eventually hardens, does Cannondale just slop the goo on and mold it around the welds to make it appear smooth?

    Thanks!

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    Most like Klien, Cannondale use a handheld belt sander to do this and will use different grade of belt to clean them up. However they use a form of welding where they will build up multiple layer of weld before they smooth them out. If you do this to your GT you severely weaken the welds and this is not recommended.

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    Senior Member Iowegian's Avatar
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    How 'bout steel? I have an old Schwinn High Sierra mtb made of 4130 that has some ugly TIG welds. I need to move the brake bosses so I was planning on re-finishing the frame anyway and was wondering if I could touch up the welds while I had it stripped.

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    Senior Member Briareos's Avatar
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    Quote Originally Posted by Iowegian View Post
    How 'bout steel? I have an old Schwinn High Sierra mtb made of 4130 that has some ugly TIG welds. I need to move the brake bosses so I was planning on re-finishing the frame anyway and was wondering if I could touch up the welds while I had it stripped.
    WE'VE BEEN HIJACKED!

    LEAVE ALL YOUR BELONGINGS ONBOARD, THAT INCLUDES THE BAG THAT HAS THE ANSWERS TO ALL THE WORLDS PROBLEMS! GRAB A PARACUTE, PUT IT ON AND JUMP! I'LL CYA ON THE EARTHSIDE!

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    Making smooth welds is all a mater of heat control. There was a TIG thread on the other frame forum a while back, and Don showed some of his welds for steel that come off the torch absolutely perfect. These are not a pretty string of pearls, they looked like a finished (post sanding) fillet braze though less built up, they looked as though they could go directly to paint.

    In general it is a bad thing to sand/file welds. I don't really know why, but it is one of those injunctions one comes across in welding texts. Do nice work from the torch, or use bondo to fair in your mess. That said, bike welding is really not conventional welding. There are a number of ways in which it is quite atypical, and the usual rules about dressing the weld may not apply. Bike welding often uses a massive fillet build up over a thin wall tube junction. So it may be possible to remove some of this "excess" material. I hang out in the motorsports column, and notice that sometimes people quote back "correct" processes, and when one checks the source in some online manual, as often as not the basis is structural plate steel welding, where the material baseline is often a 1/2" plate.

    A factory welded frame is not a piece of art welding. I personally just take the welds as is, though they have to be be safe. Beyond that I accept them as I would a "messy" sky with different shaped clouds.

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    Senior Member Iowegian's Avatar
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    Quote Originally Posted by Briareos View Post
    WE'VE BEEN HIJACKED!

    LEAVE ALL YOUR BELONGINGS ONBOARD, THAT INCLUDES THE BAG THAT HAS THE ANSWERS TO ALL THE WORLDS PROBLEMS! GRAB A PARACUTE, PUT IT ON AND JUMP! I'LL CYA ON THE EARTHSIDE!
    Yeah, sorry about that! Just seemed like a logical diversion at the moment.

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    Senior Member Iowegian's Avatar
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    Quote Originally Posted by Peterpan1 View Post
    In general it is a bad thing to sand/file welds.
    I thought that would be the case but this frame almost looks like it has welding splatter near the joints, thought I might clean it up a bit since it would be getting new paint anyhow.

    But to get back on topic...my son's Klein has normal looking TIG joints, nothing real smooth. This is just a Pulse Comp rigid mtb, though, so maybe they do something different on their high end bikes.

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    Senior Member Nessism's Avatar
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    Quote Originally Posted by Iowegian View Post
    How 'bout steel? I have an old Schwinn High Sierra mtb made of 4130 that has some ugly TIG welds. I need to move the brake bosses so I was planning on re-finishing the frame anyway and was wondering if I could touch up the welds while I had it stripped.
    You can file on steel TIG welds. Just focus on skimming off the high spots and spatter and don't dig into the main body of the weld very much. I've done it and the frame looked great with no loss of structural integrity.
    Becareful buying/selling bike parts on-line. I learned the hard way. :(

    Good/Bad Trader Listing

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    does anyone know of filler that can go through a powdercoat process and not get destroyed?

  10. #10
    Works BrooklynMachine's Avatar
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    Quote Originally Posted by nitropowered View Post
    does anyone know of filler that can go through a powdercoat process and not get destroyed?
    Labmetal supposedly does.

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    "with no loss of structural integrity."

    I agree with you, as I said bikes are over-welded in the sense of having masses of filler. Still hard to know whether the strutural integrity has been affected or not without a more rigorous process. I draw the collective attention to that Nash Touring bike with the crappy welds we had pictures of a month or two ago, who know what one is messing with. What we do know is the welding didn't succeed in looking good and there may be other things about it no more successful.

    I think the concern is that filing creates stress risers. You have this flow of metal that is joining the frame, like an oxbow in the river, and while there is a weld that could look like the filed down version that would be strong, one may be cutting across the grain in filing the metal. I don't know and would love to have some weld-tec guidance. I can try and post this on Miller site.

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    This question seems like it would be pretty easy for any reasonably trained welder. I don't include myself in that category but I have some basic instruction. From what I have been taught I would intuit that this is about right:

    Quote Originally Posted by Nessism View Post
    Just focus on skimming off the high spots and spatter and don't dig into the main body of the weld very much.
    There are high-spots and low spots. High spots could be removed but it probably wouldn't give you that clean smooth look without removing critical material. I'm not sure if this is what they do with bike frames, but you would usually add excess material and skim it off with a file or rotary grinding tool, modeling it into the desired shape. This would add some more weight wouldn't it? Makes me think that some kind of bondo'esque compound would used to save weight or they just wouldn't do it at all. Bondo is the stuff used for quickly adding martial to auto body's for modeling purposes...

  13. #13
    Sub
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    I read on another forum recently that someone stripped the paint off a high end bike and there was bondo all around the welds. I'm having an issue with my De Rosa Merak right now that I just posted in another thread..I have a crack in one of the welds from tightening a seat post clamp in the wrong position. I'm gonna strip down the paint tomorrow to get a look at it and possibly get the weld fixed. The welds are perfectly smooth, can't even tell it was welded so I have a feeling there is some type of bondo under there.

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