Tig brazing vs gas brazing- Mtbr.com
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  1. #1
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    Tig brazing vs gas brazing

    Does anybody have any research or data to suggest why gas fillet brazing is ok, but tig brazing is not? Just in researching forums and what other builders are doing tig brazing is not recommended, but seems like it'd be a good process for thin walled tubing because it'd be relatively easy to build a fillet 3-4x the tube thickness.
    The only data I can find other than "just don't do it" is from Jody at Welding tips and tricks
    https://youtu.be/wf-Cq5eQmt0?t=418

  2. #2
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    https://www.bikeforums.net/framebuil...-tig-weld.html

    I Stumbled across this thread a while back with legendary builder Frank the Welder chiming in on this exact topic.

    I think he may be on this forum?

  3. #3
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    This has come up over the years. I don't remember all the details but I do remember that the considered wisdom of experienced fabrication guys was that TIG brazing isn't recommended for structures undergoing cyclic stresses. It's great for statically loaded structures (sculptures for example) when used appropriately.

    The problem is that if you run too hot with the TIG torch and end up melting the parent metal a little bit you end up with microscopic bronze inclusions in the steel. These act as stress risers and result in cracking as the number of stress cycles build up.

    If you try to avoid this you might run too cold and get poor adhesion between filler and base metal which results in low peel strength.

    There was a US builder that was using TIG brazing to attach disc caliper mounts (regular TIG or brass brazing, not sure) to forks that had a bunch of failures. They switched to another method and solved the issue.

    Anyway, TIG brazing and bikes. Braze on's maybe, but for main structural joints, I was always told no.

    Alistair Spence,
    Seattle, WA.

    Quote Originally Posted by wvucyclist View Post
    Does anybody have any research or data to suggest why gas fillet brazing is ok, but tig brazing is not? Just in researching forums and what other builders are doing tig brazing is not recommended, but seems like it'd be a good process for thin walled tubing because it'd be relatively easy to build a fillet 3-4x the tube thickness.
    The only data I can find other than "just don't do it" is from Jody at Welding tips and tricks
    https://youtu.be/wf-Cq5eQmt0?t=418

  4. #4
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    Thanks Alistair for the details. I can see how you could get those micro inclusions if a welder isn't careful. Jody did a pretty good test on his joint, but it wasn't for fatigue. I've used it so far for things that are in compression so far with good luck, but I'm a lightweight and don't generally break things anyways. I need access to a test lab...

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    Sure thing, I'd be interested to hear more about the results of your experiments with this.

    I realized that I made a mistake in what I wrote above. What I meant to write was

    "There was a US builder that was using TIG brazing to attach disc caliper mounts to forks, and they had a bunch of failures using the technique. They switched to another method (regular TIG or brass brazing, not sure) and solved the issue."

    Sorry for the confusion,
    Alistair.


    Quote Originally Posted by wvucyclist View Post
    Thanks Alistair for the details. I can see how you could get those micro inclusions if a welder isn't careful. Jody did a pretty good test on his joint, but it wasn't for fatigue. I've used it so far for things that are in compression so far with good luck, but I'm a lightweight and don't generally break things anyways. I need access to a test lab...

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    I know there's a fatigue lab where I work, just need to convince them to let me try a set up. Maybe publish an article about it, but I feel like if anybody cared it would have already been published.

  7. #7
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    Silicon bronze lacks the tensile strength required for dynamic, load bearing structures. Nickel bronze has the properties frame builders require.
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    Quote Originally Posted by life behind bars View Post
    Silicon bronze lacks the tensile strength required for dynamic, load bearing structures. Nickel bronze has the properties frame builders require.
    Data that I can find doesn't support that statement, neither are as strong as the base material, but they're around the same range. With an adequate filler they could both be stronger than the tube, at least initially. 470 MPa yield for nickle bronze, 415 for silicone bronze, reynolds 631 is around 800.
    https://elginfasteners.com/resources...nickel-bronze/
    https://elginfasteners.com/resources...on-bronze-655/

    Statements like this are why I started this thread, I'm looking for more than just "don't do that" I'm looking for research or data to support using or not using this process.

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    Quote Originally Posted by A. Spence View Post
    The problem is that if you run too hot with the TIG torch and end up melting the parent metal a little bit you end up with microscopic bronze inclusions in the steel. These act as stress risers and result in cracking as the number of stress cycles build up.
    I remember something like this from old welding books. In the early days of tubular steel airplane structures, fillet brazed joints would fail sooner, especially if they were repaired. They switched to strictly gas welding (this was before inert gas shielding). But it's been a while, it might have been just that you could always braze over a cracked weld, but not weld over a cracked braze?

    You could also conclude that the problem is equally with the welder overheating the joint, so avoiding these techniques could be equally about addressing the need for inexperienced or rushed labor (war time efforts).

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    Quote Originally Posted by wvucyclist View Post
    Data that I can find doesn't support that statement, neither are as strong as the base material, but they're around the same range. With an adequate filler they could both be stronger than the tube, at least initially. 470 MPa yield for nickle bronze, 415 for silicone bronze, reynolds 631 is around 800.
    https://elginfasteners.com/resources...nickel-bronze/
    https://elginfasteners.com/resources...on-bronze-655/

    Statements like this are why I started this thread, I'm looking for more than just "don't do that" I'm looking for research or data to support using or not using this process.
    The base material isn't in question, the join strength of the two materials is vastly different. But you could pioneer the use of silicon bronze in frame joinery. Please keep us updated.
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  11. #11
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    Just a story to add to the discussion.

    A friend of mine who is involved with very niche cars showed me a pedal box where each foot face had this beautiful bronze 'tack' symmetrically laid on a surface. Described process as above.
    I was able to speak to the welder who knowing my interests in frame building said that the method was not suited to cycling structures.

    Great for artistic designs, but not the same as a full fillet would appear to be the best approach. I would like to be proven wrong though.

    Eric
    If I don't make an attempt, how will I know if it will work?

  12. #12
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    The joint is as good as the prep and the welder and the process used.

    Any little thing could go wrong, and the joint is compromised.

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    Jodi is admitly a much better welded than I am. But Tig brazing is incredibly difficult. Like even on heavy stuff the difference between too cold and melting the base metal in my experience is only a couple amps. The Tig just pinpoints the heat too much. I've done it before to link a steel shaft with mystery metal X that looked like steel but would just blow up when you started to melt it (I'm guessing its iron/bronze) and it held up fine. I've tried doing it on other stuff without much success. For any purpose other than sticking dissimilar metals together, I've got the tig welder I'm just going to tig it. If you're doing stainless you're gonna sugar it trying to tig braze it anyways so you might as well bond it with the base metal, just grab a small container of solar flux, it'll last you a lifetime.

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    Dude i think the whole tig brazing thing was set off when some clown put up a picture of a motorcycle frame and suggested it was tig brazing (it wasn't it was meant as a tongue in cheek post but gained an entire life of its own) Dave bohm even had an entire Meme mocking it...however time moved on a lot of new guys joined in in framebuilding land and didn't get the joke.

    But to answer your question yes tons of information is out there

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    Do you have any sources to share? Like I said, I can only find "what I've heard" or "so and so says", I've been looking and I can't find anything beyond that. Homebuilt aircraft builders say it's for non-structural, but they also say the same about fillet brazing. So the bottom line is what's so different about tig brazing vs fillet brazing?
    If anything the people on this forum have reinforced that it's all hearsay and not based on research and data. I'm not saying it is adequate, I'm saying we don't have enough information, unless I'm missing something.

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    Quote Originally Posted by wvucyclist View Post
    Do you have any sources to share? Like I said, I can only find "what I've heard" or "so and so says", I've been looking and I can't find anything beyond that. Homebuilt aircraft builders say it's for non-structural, but they also say the same about fillet brazing. So the bottom line is what's so different about tig brazing vs fillet brazing?
    If anything the people on this forum have reinforced that it's all hearsay and not based on research and data. I'm not saying it is adequate, I'm saying we don't have enough information, unless I'm missing something.
    Why not go to a welding forum, there are hundreds out there.

    Bicycle forum not that big on welding techniques of seasoned and experienced welders.

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    Quote Originally Posted by compositepro View Post
    Dude i think the whole tig brazing thing was set off when some clown put up a picture of a motorcycle frame and suggested it was tig brazing (it wasn't it was meant as a tongue in cheek post but gained an entire life of its own) Dave bohm even had an entire Meme mocking it...however time moved on a lot of new guys joined in in framebuilding land and didn't get the joke.

    But to answer your question yes tons of information is out there

    http://eprints.whiterose.ac.uk/14763...azing%20fi.pdf

    http://shura.shu.ac.uk/20091/1/10697398.pdf

    https://books.google.com.au/books?id...0joint&f=false is a good book google can find you a free pdf

    theres more but

    now all that sciencey stuff is great it will give you a foundation in theory you will need to have a go yourself though good on you for looking further than a guy said so on the internet

  18. #18
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    Quote Originally Posted by wvucyclist View Post
    Do you have any sources to share? Like I said, I can only find "what I've heard" or "so and so says", I've been looking and I can't find anything beyond that. Homebuilt aircraft builders say it's for non-structural, but they also say the same about fillet brazing. So the bottom line is what's so different about tig brazing vs fillet brazing?
    If anything the people on this forum have reinforced that it's all hearsay and not based on research and data. I'm not saying it is adequate, I'm saying we don't have enough information, unless I'm missing something.
    But why? It's super difficult to do adequately it looks like shit (compared to novice gas brazes) even once you've figure out your technique and you need to have a tig welder to do it. If you have a tig welder, just tig weld

  19. #19
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    Quote Originally Posted by A. Spence View Post
    The problem is that if you run too hot with the TIG torch and end up melting the parent metal a little bit you end up with microscopic bronze inclusions in the steel. These act as stress risers and result in cracking as the number of stress cycles build up.

    If you try to avoid this you might run too cold and get poor adhesion between filler and base metal which results in low peel strength.
    I've actually done quite a bit of tig brazing, and while I haven't researched the method other than to learn how folks do it, I wouldn't use it for really anything under any kind of repeated stress. Based on my experience (not he said she said) the above statements are the main reason tig brazing is really difficult to get perfect. For as many hours as I've done it, I don't feel like I could do a single bike tubing joint without melting the parent metal at least somewhere. It's astonishingly tricky. Flame brazing is completely different and quite a bit easier.

    I think you should go try it out for yourself and report back with your experience. Maybe you'll figure out a great way to do it.
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