# Tig brazing vs gas brazing



## wvucyclist (Nov 8, 2007)

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


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## thedudeman (Nov 10, 2006)

https://www.bikeforums.net/framebuilders/855328-bronze-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?


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## A. Spence (Sep 25, 2009)

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.



wvucyclist said:


> 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


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## wvucyclist (Nov 8, 2007)

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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## A. Spence (Sep 25, 2009)

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.



wvucyclist said:


> 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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## wvucyclist (Nov 8, 2007)

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.


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## life behind bars (May 24, 2014)

Silicon bronze lacks the tensile strength required for dynamic, load bearing structures. Nickel bronze has the properties frame builders require.


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## wvucyclist (Nov 8, 2007)

life behind bars said:


> 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/materials/material-specifications/aluminum-nickel-bronze/
https://elginfasteners.com/resources/materials/material-specifications/silicon-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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## dr.welby (Jan 6, 2004)

A. Spence said:


> 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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## life behind bars (May 24, 2014)

wvucyclist said:


> 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/materials/material-specifications/aluminum-nickel-bronze/
> https://elginfasteners.com/resources/materials/material-specifications/silicon-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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## Eric Malcolm (Dec 18, 2011)

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


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## matt4x4 (Dec 21, 2013)

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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## Leafy1 (Feb 17, 2019)

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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## compositepro (Jun 21, 2007)

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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## wvucyclist (Nov 8, 2007)

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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## matt4x4 (Dec 21, 2013)

wvucyclist said:


> 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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## compositepro (Jun 21, 2007)

compositepro said:


> 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/147639/1/25_06_2019_Brazing fi.pdf

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

https://books.google.com.au/books?i...age&q=plastic constraint brazed joint&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


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## Leafy1 (Feb 17, 2019)

wvucyclist said:


> 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 **** (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


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## Erichimedes (Jul 30, 2010)

A. Spence said:


> 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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## AdamR83 (Jan 21, 2021)

A bit of a bump here but I just had a go at this and wondered if it would be strong enough for a frame... I need to do the same joint again with regular TIG, and the same test, but my gut feel is yes.

I'm an average welder, but found this very easy, I felt like a had a lot of time and the stuff flowed nicely. Ran at 20-22 amps for the brazing as opposed to 32-34 for proper welding. 0.8mm 4130 tubing with a nice tight join, would normally be using 1.0mm filler rod for TIG, this bronze stuff is 1.6mm.

First test... got a bit hot at one point - that little volcano - and melted some steel into the mix. It cracked as stated earlier in the thread.











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Sensitive content, not recommended for those under 18
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2nd attempt, went for a multi pass. Really like how this looks!










Tested the first one for strength...




























Can still see a HAZ, but the tube broke before the filler...

And it ended up at quite a funky angle, lots of ductility!










Video here

So I need to go another test, but definitely considering TIG brazing a whole frame...


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## Little_twin (Feb 23, 2016)

I tig braze my cable guides on because I hate cleaning flux. I wouldn't trust it for anything structural.










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## JackOfDiamonds (Apr 17, 2020)

I don't see why it wouldn't work just fine. The question for me is just why. Why do something with a $2k tig welder that you could do with a $200 torch that is proven. And is it any faster or cheaper than just TIG welding the joint? But I definitely think it would hold up just fine, like the testing shows. I'm not one of those people who think you need a degree in metallurgy to make a bike, then they go and do things that would get you fired in any normal welding shop anyway and tell the world it's ok because bikes are different for some reason.


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## compositepro (Jun 21, 2007)

Little_twin said:


> I tig braze my cable guides on because I hate cleaning flux. I wouldn't trust it for anything structural.
> 
> View attachment 1918453
> 
> ...


you should be elevated to god like status , WELL DONE you actually had a go did a thing and proved something rather than it just being conjecture or opinion , but most of all you actually did something


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## compositepro (Jun 21, 2007)

AdamR83 said:


> A bit of a bump here but I just had a go at this and wondered if it would be strong enough for a frame... I need to do the same joint again with regular TIG, and the same test, but my gut feel is yes.
> 
> I'm an average welder, but found this very easy, I felt like a had a lot of time and the stuff flowed nicely. Ran at 20-22 amps for the brazing as opposed to 32-34 for proper welding. 0.8mm 4130 tubing with a nice tight join, would normally be using 1.0mm filler rod for TIG, this bronze stuff is 1.6mm.
> 
> ...


Another well done to you you get a grammy for post content too


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## Little_twin (Feb 23, 2016)

compositepro said:


> you should be elevated to god like status , WELL DONE you actually had a go did a thing and proved something rather than it just being conjecture or opinion , but most of all you actually did something


Doing things is the only way to learn. 

Sent from my iPhone using Tapatalk


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## Ben.land101 (Dec 25, 2012)

Not sure if this was mentioned earlier or not, but another thing to keep in mind between TIG and Gas brazing is the fillet size and shape.
Gas brazing makes HUGE fillets, with nice soft edges that are tied into the base metal well. Stresses like big soft fillets.

Also overall heat input. When you braze something with a gas torch, you're basically annealing the entire area around the joint. Not so much with TIG.



JackOfDiamonds said:


> I don't see why it wouldn't work just fine. The question for me is just why. Why do something with a $2k tig welder that you could do with a $200 torch that is proven. And is it any faster or cheaper than just TIG welding the joint? But I definitely think it would hold up just fine, like the testing shows. I'm not one of those people who think you need a degree in metallurgy to make a bike, then they go and do things that would get you fired in any normal welding shop anyway and tell the world it's ok because bikes are different for some reason.


Meh, I think all framebuilders like to ignore the why every now and then. We don't question it, or do reasonable things, we just do what makes us happy. 
I've been doing a little testing and such on adding Aluminum-Bronze TIG-braze _over_ the welds on my next bike. 
The reason why? It'll look cool. It's totally stupid in all other aspects. But it'll make me happy.


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## compositepro (Jun 21, 2007)

Ben.land101 said:


> it'll make me happy.


 And if you are building bikes for yourself is ALL that matters, **** the peanut gallery


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## AdamR83 (Jan 21, 2021)

Ben.land101 said:


> The reason why? It'll look cool. It's totally stupid in all other aspects. But it'll make me happy.


This is a totally valid reason IMO! Especially for a DIY-er.

I've been some more digging into this these last few days... and I'm gonna go for it.

A15 (ER70S2 for those the 'wrong' side of the pond) has a yield at about 440MPa (again, sorry for the 'wrong side of the pond' units!). 4130 after TIG welding without heat treating comes in around 680MPa. So, the filler rod we would normally use is of technically lower strength than the tubing. However, these numbers are all 'strength per unit area'. To make up for this, we just use a bit more area, building up a fillet.

Same deal with TIG brazing - something like a SIF Phosphor Bronze No8 is a lower yield yet again of more like 200MPa, but those fillets are big and chunky compared to a diddy little TIG weld with a 0.8 or 1.0mm filler (remember going up a rod size drastically increases the amount of actual material being deposited for the same 'dab' - 1.6mm rod is 250% more volume than 1.0mm rod!).

So running those numbers again (I know - this is all theory, the dude under the helmet could make a right mess of any of this at any time):

TIG weld with 1.0mm rod at 440MPa vs TIG braze with 1.6mm rod at 200MPa, you could technically have a stronger weld with the TIG braze.

Benefit: We are only having to heat the frame tubing enough to melt the filler (which melts at ~1800-1900'F), rather than all the way to ~2800 to melt the tubing itself. Less heat is good.

Benefit: The bronze doesn't shrink anywhere near as much as steel when cooling, so things don't pull out of line.

Downsides? Well cost is one, obviously. Approx 3x more expensive. Weight - using more volume of filler rod at a higher density than steel means a heavier frame. And why would a customer, buying a factory built frame, shell out money for something that's heavier and more expensive? For a DIY-er who wants to build something unique I think it's feasible.

Why does nobody use it? Well it's a similar effect to normal brazing I guess, just normal brazing is said to be easier (I haven't tried it personally) and you can work with whatever's left to make it all smooth and yummy if you want. If you want fast, TIG it; if you want pretty, braze it. This is a bit of a no man's land.

Some practical experience... well obviously there's the video from Jody at weldingtipsandtricks, showing a butted 4130 tube breaking before his TIG brazed joint. The guy I buy my welding supplies from also tells me there's a lot of motorbikes out there (mainly classic stuff) built the same way - including a few he knows race with up to 700cc engine sizes. Frank The Welder stuck V brake bosses onto Yeti frames for years with no issues. And I did some more testing today on my 2nd and 3rd attempts with this process and they passed easily.

Some info that goes with the pics:

- The bits where there is penetration right through the tube is from the tacks, which were done with no filler.

- The bent pole / lever is 7/8" x 14g ERW mild steel.

- The 'plug' I turned up is a bit of old steerer tube so I could clamp the test pieces in the vice better.

- One of these test joints was done with 1.6mm filler, the other with 2.4mm filler. Both I would say passed.

I feel like I just need some more practice now to get settings dialled and things neatened up - however, I will do the same tests with a 'normally' welded sample of the same tubing to make sure I'm not being an idiot and led on by the lovely coppery-bronzey-ness!


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## AdamR83 (Jan 21, 2021)

Little_twin said:


> I tig braze my cable guides on because I hate cleaning flux. I wouldn't trust it for anything structural.


May I ask why not? Have you had an issue with the cable guides failing or something like that?


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## Little_twin (Feb 23, 2016)

The fillet size I can achieve while keeping heat input low does not seem sufficient to creat a structurally superior joint vs standard tig welding. The time needed to create a large enough fillet negates the benefit of lower temp brazing because it takes more time. Time is the enemy when it comes to a part being heat soaked. I'd rather just run a single hot and fast bead and move on. This is of course all just my opinion, knowing what my strengths and capabilities are and the equipment that I have.

One of these took much longer than the other and at a much higher amperage, yet total heat input is very similar.



















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## AdamR83 (Jan 21, 2021)

Fair play! Everyone has their own limitations and to know those and respect them is an excellent quality to have IMO.

I did some more testing today, and found that a really really sharp point to the tungsten helped a lot to soften the arc and reduce the chance of melting the tubing. The tip needed needed tidying up more often than 'normal', but this allowed the puddle to flow better and I could move pretty fast with the torch. Full details here: Luddite 26AD (DIY Frame Build)


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## JackOfDiamonds (Apr 17, 2020)

No surprises about the testing. I've never got a torch-braze joint to fail in testing (or in the real world for that matter). I've even butted test joints together with absolutely no mitering, just leaving giant 1/8" gaps, and brazed it up, and tested it and it still didn't fail. I've made test joints where I brazed through the mill scale, those didn't fail either. I made test joints with almost no fillet, just sweating them together solder-style, and those didn't break either. It's really quite a reliable process. The FUD'ers always say the tests aren't valid because joints fail in fatigue. But I think it's close to the truth that if the joint is stronger than the tubes, then the only way that joints can fail at all is through fatigue, so the only joint failures we ever see are from fatigue, and that doesn't necessarily mean it was a bad joint but a marginal engineering of the frame itself. 

The smiley face is a cool idea. I always struggle for how to put serial numbers on my frames because I don't like the idea of scribing them with a dremel all ugly. I might try drawing a number on the BB with a bead of braze or something.


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