I’m not a scientist, but I’ve destroyed a lot of stuff. I get the sense that bronze is less ductile than tig filler metals.
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TIG welds crack all the time right at the edge of the weld. From my understanding it’s a fatigue life problem stemming from a stress riser. Of course it could other issues too. Good TIG welds have a pretty smooth transition between tubes, which reduces the possibility of fatigue stress right at the joint.
Look, I’m not stopping anyone from making bikes with raw fillets. Have at it. However, there are a lot of beginners on here whose fillet brazing trends to the very lumpy. It’s my opinion that if those lumpy edges aren’t filed smoothly there’s an increased risk of tube failure.
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Manganese bronze is 25% elongation. More ductile than TIG welds.
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All good. I just felt finishing fillets smooth was more a traditional process for aesthetics more than anything. Myself, I always strive to get as even and consistent a fillet when I’m doing brass fillet brazing so I don’t have to spend forever sanding my fillets smooth afterwards.
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I can sometimes cause an unfinished brazed joint to fail in a way that bronze shears off of the tube leaving bare steel with almost no bronze remaining on it. I’ve attributed this to less elongation than steel, but maybe ductility is the wrong word, plasticity? I might just misunderstand what’s happening.
It’s usually very thick to thin scrap pieces, like a tube belly to a steerer.
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Agree to disagree. I don’t buy that for a hot second, not without hard evidence.
I’d honestly be more worried about beginners (anybody really) accidentally filing into the steel tubes!
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The great file/no file fillet debate is here 
it’s a big one here in France,I can name only a couple “pros” doing no file here.
There is a big assumption about filed filet being stronger, and you guys stated some obvious reasons above(stress riser), not just " it has to be file because it’s how it is and you’re going to hell if you leave a raw filet". Aesthetic is another big one, and as much I like to see baby skin smooth filet, I hate the process myself.
I tend to agree that you could accidenty file into steel tubes, or remove too much bronze to a point the filet is too small and not strong enough ( I’ve seen that…)
FWIW I have a couple bmx frame with raw filet out there and they have been going strong for close than 2 years now ( it’s a long lifespan for a bmx that is ridden hard)
that’s what I aim for when filet brazing
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Generally I reckon filed fillets look better but I wouldn’t touch those either. Nice work ay!
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