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Tig brazing over Tig welds for for a little razzle dazzle.

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Tig brazing over Tig welds for for a little razzle dazzle.

Old 05-09-20, 11:43 PM
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Tig brazing over Tig welds for for a little razzle dazzle.

So, a little bit of background is that I'm a welder,went to school for it, certified in carbon steel,stainless steel and aluminum. Been working and Tig welding 6000 series aluminum for the past few years. I have a frame that isn't a big deal(KHS Urban X), I got a powder coater I helped out when he needed to get some jobs done quick and I can get it done for cost of powder.

What I was thinking was I would Tig braze over the welds and polish the frame and powder a candy color over it so that the braze being a different color than the steel would shine through Are there any problems I might encounter?

This is purely for looks.
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Old 05-10-20, 02:06 AM
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I'm TIG brazing with silicon bronze over TIG welds on steel for a project I'm working on now where he wants a "raw" finish. I'm going for the look of a fillet brazed frame, but I only have/know how to use the TIG. Silicon bronze on its own might be strong enough but I don't want to chance it.

The process works well. The hard part, that needs a lot of practice and patience, is filing down the fillets. A "dynafile" or "finger sander" can be used where you can reach things without gouging the actual tubes. In tighter spots you need to use hand-files, which actually aren't much slower at removing material, just harder work. So as with anything I'd try it all out on a couple of bits of scrap first.

The brazing does put a bit of heat into the tubes. It melts at a lower temperature than steel but it's still a big chunk of red-hot copper you're wrapping around those joints, so watch out for distortion. Bolt a bit of threaded rod securely between the dropouts to hold them at the correct spacing and leave it there throughout the process. Space your work out-- do a bit on each joint at a time before moving to somewhere else on the frame while it cools down, and recheck the alignment when you're done.
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Old 05-10-20, 02:18 AM
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Originally Posted by guy153 View Post
I'm TIG brazing with silicon bronze over TIG welds on steel for a project I'm working on now where he wants a "raw" finish. I'm going for the look of a fillet brazed frame, but I only have/know how to use the TIG. Silicon bronze on its own might be strong enough but I don't want to chance it.

The process works well. The hard part, that needs a lot of practice and patience, is filing down the fillets. A "dynafile" or "finger sander" can be used where you can reach things without gouging the actual tubes. In tighter spots you need to use hand-files, which actually aren't much slower at removing material, just harder work. So as with anything I'd try it all out on a couple of bits of scrap first.

The brazing does put a bit of heat into the tubes. It melts at a lower temperature than steel but it's still a big chunk of red-hot copper you're wrapping around those joints, so watch out for distortion. Bolt a bit of threaded rod securely between the dropouts to hold them at the correct spacing and leave it there throughout the process. Space your work out-- do a bit on each joint at a time before moving to somewhere else on the frame while it cools down, and recheck the alignment when you're done.
Thats a lot of good info,thank you. I didn't consider distortion.

As far as finishing the braze,I thought that maybe since it's softer metal I could make it look just like a weld,stack of dimes like.
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Old 05-10-20, 10:29 AM
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As mentioned the trick is in the results. Meaning practice until it's easy to finish with the look you want. Industry has filleted over welded tacks for decades. In this case the tack is REALLY big Of course that the tubes have now gone through two major heat cycles... might be a concern for more temp sensitive tubing.

A note about primerless finishes. It's well known that power paint is porous at the microscopic level and water can and will attack the steel. Wet clear coats also are well known for rusting, often at the cable stops, drop outs and the BB and headset faces. No issue for a show piece but a no go (IMP) for a working bike. Andy
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Old 05-10-20, 01:29 PM
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Originally Posted by BoozyMcliverRot View Post
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As far as finishing the braze,I thought that maybe since it's softer metal I could make it look just like a weld,stack of dimes like.
If you get that Instagram-worthy stack then yes otherwise you always have the option of filing

Although actually if you are intending to file it's better to shove a bit of extra rod in and build it up a little too high.

It's not too hard to get a decent-looking stack in the actual fillets, it's down the sides that are harder because the braze is pretty much lying on top of the metal instead of having a corner to go into.
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Old 05-10-20, 01:35 PM
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Originally Posted by Andrew R Stewart View Post
A note about primerless finishes. It's well known that power paint is porous at the microscopic level and water can and will attack the steel. Wet clear coats also are well known for rusting, often at the cable stops, drop outs and the BB and headset faces. No issue for a show piece but a no go (IMP) for a working bike. Andy
I know, I'm not a big fan of of them. But the friend it's for is doing me the favour of letting me build him a bike so I can't argue too much.

​​​​It is a good challenge in that you really have to try and get a good finish. Paint kind of smooths things out a bit.

I'm hoping the two heat cycles isn't much of a problem but certainly I don't feel that the bronze is adding anything structurally. I've never been able to break a TIG weld in a destructive test.
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Old 05-10-20, 02:04 PM
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Originally Posted by guy153 View Post
I know, I'm not a big fan of of them. But the friend it's for is doing me the favour of letting me build him a bike so I can't argue too much.

​​​​It is a good challenge in that you really have to try and get a good finish. Paint kind of smooths things out a bit.

I'm hoping the two heat cycles isn't much of a problem but certainly I don't feel that the bronze is adding anything structurally. I've never been able to break a TIG weld in a destructive test.
And I would be surprised if you did break a weld. But most all the cracks I've seen are from fatigue, not poor welds. Of course choosing too thin tubing and then welding with a root undercutting might be called a poor weld Still this generally needs many cycles of below max strength to fail. Andy
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Old 05-11-20, 02:55 AM
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Originally Posted by Andrew R Stewart View Post
And I would be surprised if you did break a weld. But most all the cracks I've seen are from fatigue, not poor welds. Of course choosing too thin tubing and then welding with a root undercutting might be called a poor weld Still this generally needs many cycles of below max strength to fail. Andy
Yes I can't be sure how good the fatigue life is going to be without just riding the bikes and keeping an eye on them and trying to stick to the textbook for how to do a decent weld. Frame #00001 now has about 5000km on it with no issues so that's looking all right so far.
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Old 05-11-20, 12:30 PM
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I think a first frame should have as little razzle-dazzle as possible. Leave that for the 20th frame
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Old 05-12-20, 07:27 AM
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Originally Posted by unterhausen View Post
I think a first frame should have as little razzle-dazzle as possible. Leave that for the 20th frame
I do have an old Schwinn Moab with a dented top tube I was going to practice on before moving to prime time.
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Old 05-12-20, 11:36 AM
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Tig fillet brazing has long been an interest of mine. I used to paint John Cherry frames and he gave me some filler rod to try many years ago. I don't know what rod he gave me. We went to the very 1st titanium tig welding class together UBI offered in the early 90's. Anyway I got awesome results with a very consistent and even fillet pattern. The fillet was a bit smaller than what I usually do with a brazing torch although I liked that look just fine. The problem was that the joint had no strength. I could break the tubes apart without having to use super strength. I've never been ambitious enough to study what other kinds of filler rod could be tig brazed. However what rod I used would work just fine as a cosmetic filler over a joint already welded. Whatever I had was a low temperature melting rod.
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Old 05-12-20, 03:00 PM
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Originally Posted by Doug Fattic View Post
Tig fillet brazing has long been an interest of mine. I used to paint John Cherry frames and he gave me some filler rod to try many years ago. I don't know what rod he gave me. We went to the very 1st titanium tig welding class together UBI offered in the early 90's. Anyway I got awesome results with a very consistent and even fillet pattern. The fillet was a bit smaller than what I usually do with a brazing torch although I liked that look just fine. The problem was that the joint had no strength. I could break the tubes apart without having to use super strength. I've never been ambitious enough to study what other kinds of filler rod could be tig brazed. However what rod I used would work just fine as a cosmetic filler over a joint already welded. Whatever I had was a low temperature melting rod.
The rod I use is called Sifsilcopper 968. Its quoted UTS is 350MPa, not far off the 500MPa of a regular mild steel rod that you would normally use for welding. I think the torch brazing rods like Sifbronze No 2 are 500MPa plus however.

I've tried break tests on it and it is very strong. By which I mean you whale on a cromo offcut attached to something with it with a BFH and it will break eventually at about the point where the tube is fairly well buckled. But a weld cannot be broken at all. The very first test I tried was a bevelled butt joint on some 3mm flat bar. I almost bent it right back on itself before the braze material broke.
​​
I use it on its own for bridges and bosses (although I did weld the cantilever posts) to reduce heat input and it's plenty strong enough for those. I think it would actually be fine to make a whole frame with it but it's better to weld. And I have no idea about its fatigue life.
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Old 05-12-20, 04:32 PM
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testing with a hammer really means nothing in bicycle frame construction. I mean, it will tell you if you are so incompetent that you really need to take up knitting instead, but not much more. Bicycle frames fail in fatigue, that can't be tested with a hammer. Unless you are really, really patient.

It will be interesting to see your results.
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Old 05-12-20, 09:17 PM
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Lots of good info here guys. Thank you. I've watched a couple videos of Jodi over at welding tips and tricks and he used silicone bronze. Is there a specific rod I should use? 1/16 tungsten or 3/32? What type of tungsten do you recommend?

I have experience brazing heat exchangers that I did for about a year but that was with flame and not electrode.
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Old 05-13-20, 02:53 AM
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Originally Posted by BoozyMcliverRot View Post
Lots of good info here guys. Thank you. I've watched a couple videos of Jodi over at welding tips and tricks and he used silicone bronze. Is there a specific rod I should use? 1/16 tungsten or 3/32? What type of tungsten do you recommend?

I have experience brazing heat exchangers that I did for about a year but that was with flame and not electrode.
Silicon bronze is the stuff you want. Make sure it's a TIG rod and not one meant for a gas torch. If it's the latter it will fry and spit and try to poison you with fumes.

I use 1/16 tungsten but it's not critical. Get the 1/16 bronze rod (but for welding use a 1mm rod on most joints). I use 2% lanthanated for everything as per Jody's advice (I have an inverter machine).
​​​
Start heating the joint but don't wait for it to puddle like you would for welding, or only just. Just enough heat is when the puddle is making a nice profile at the edges rather than being convex on top. But if it is convex it's easy to just run the torch over it again to zap it in.

​​​The idea is not to mix too much steel in with the braze. You shouldn't be melting the steel.

You can turn the gas up a bit if you like but it will always look a bit grimy when you're done. A very little wire brushing and/or scotchbrite will quickly bring back the bling.

The bits that will kick your ass are behind the seat stays and between where the chainstays join the BB shell. You will need to wrap things in foil and be creative to keep the gas where you need it. The other spot to be aware of is where the DT meets the ST. Both tubes are thin at that point so take care. Everything else on the bike is thin to thick. The top of the ST and the HT usually are thicker than the main tubes and the BB shell is really thick. So direct the heat accordingly, although this applies more to welding.

Have fun and post pictures!
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