Okay. thanks a lot for this informations. Maybe i only braze with bronze next time. But do you thinking there is a real problem with this kind of connections? i brazed it up and the front triangle is ready with this nickel silver passes. but i can see some super thin hairline cracks at some point… maybe from cold alignment?And do you think there is a problem with the vent hole from the downtube?
A tinning pass is never going to be strong enough for cold setting. I would bronze braze over everything and call it good.
The vent hole is fine. I often slot a 12.7mm hole in the BB shell for running an internal dropper post line. Just make sure you add some fillets on the seat tube before covering it with the down tube. However, in the future I would make smaller vent holes to avoid excess BB shell distortion. It seems like a lot of builders, in this forum anyways, drill 6.35mm (1/4") vent holes and call it good.
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Just found a newer video from this same guy where he visits some North American bike frame builders…
-Jim G
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Hey everyone! A little update on my brazing adventures. I ran out of flux, bought the exact same flux (even though it didnt work for me) and somehow this “same” flux behaves completely differently. Im not saying these are the best fillets you have ever laid eyes on, but no more overheating issues.
One issue i did have with this flux is that it doesnt want to dissolve in water properly, making it difficult to stick to the metal. Any solutions (pun intended) for this problem?
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Obviously, walt was right all along
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I would swear your last fillet is done with silver… Or your camera has done something to the colors, but that doesn’t look like brass to me
I got a bunch of brazing rod together with the framejig i bought of that guy in apeldoorn… Its definitely not brass but its not silver either, i think… Probably nickel silver?
Picture of the label and a picture of the brass i normally use compared to the rod i normally use.
CuNiZn is nickel silver right?
I have huge problems with the brass. It builds up tension out of nowhere and pops away. I suspect that it’s the end of the soldering tip that’s causing the problem, as it doesn’t produce a sharp, neutral flame.
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no one here with similar experiences?
I did have similar problems, for me it was resolved with a different type of flux. I guess it is something to do with some sort of contamination…
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Still work with the same brass and flux since two years… that’s why I’m bit confused
Do your regulators creep? I had a problem like this because my flame settings would drift . The neoprene gaskets in my regulators were stretched out, and I could not maintain my initial gas settings without regular small adjustments at the torch.
Eventually, If I forgot to adjust the settings as I progressed, the flame would become too oxidizing or carburizing, I don’t remember which, and bronze would almost jump out of the puddle, sometimes putting out my torch and causing a small back-fire in the torch body.
I rebuilt my regulators with rebuild kits and the problem went away. For this reason, is a good practice to always back the adjustment screws off of the gasket inside of your regulators when you turn off your torch, so they last longer without getting stretched out.
Also my neutral flame is super constant. but the tip of it isn’t sharp anymore. sometimes there is a super weird shape. So i think i should change the insert of the torch. Hope it will solve the problem.
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Yeah you might see an improvement with a new torch tip. I really hate it when I can’t get a clean, sharp flame. It can make heat control tricky and maybe even make it difficult to identify a neutral flame? I try to keep my torch tips as clean as possible but eventually they need replacing (or I’ll drop the bloody torch).
An oxidising flame is okay but carburising is bad. So I usually dial in a very slightly oxidising flame, go to neutral and then just a tad more oxy is the way I do it.
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I’m not sure what you mean by this. If you can elaborate, more folks will chime in to offer thoughts.
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the brass basically bursts apart when heated and scatters in all directions.
Do you have relief holes drilled in your tubes to allow the air pressure to equalize as it is heated?
Additionally, is everything very dry? You may want to try preheating all metal and brazing filler.
Lastly, it could be that you are overheating the brass, and are vaporizing the zinc. Are you seeing white smoke when this happens?
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Vent holes was my first thought too. @Janosch as the air inside the tube heats, it expands and as the joint gets closed off, that air has nowhere to go so it blows the molten brass away from the joint.
As I said, I do everything as usual. So far it has worked great. I am of course familiar with vent holes and will also put them in. I have now installed a new tip for the torch and hope that this will give me peace of mind again.
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