Been following the news on the recent failure of a headtube on a Brompton G-Line, and that weld strikes me as looking a lot like a TIG weld, the way those beads are stacked on top of each other. That said, I’m also aware that Brompton hand brazes all of their frames.
My question for those familiar with metal fabrication, is, “is that really a brazed joint, or did Brompton opt for TIG weld due to the heavier loads that the bike might have been expected to deal with?”
I don’t recall fillet brazed joints looking like that, granted those would likely be filed down to a smoother, cleaner joint?
Pic of the headtube failure for reference, where the joint can be see on the right of the crack line.
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Don’t they do a Ti frame as well? Not fillet brazing a Ti frameset. Possibly a Ti? Fillet brazing is usually ground and filed down to create that smooth join that you usually see. They could just be skipping that step, it’s mostly aesthetic.
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Yup, for the bikes running the smaller, 16-inch wheels. The G-lines run the larger 20” wheels, specifically, the 451mm variant (as opposed to the 406mm) ones. Yeah, you’re likely right, that that’s fillet brazing right there, just not smoothened. Strikes me as a little odd, given that you’re one step away from a nicer looking joint, especially given the price of these bikes.
Thanks for the response!
Remove some paint from the joint. If the fillet is the same colour as the base metal it’s a weld.
Fillet brazing alloys are gold to bronze. If in doubt apply some pickling paste: on fillet alloys it will go green almost immediately .
Interesting idea, and thanks @Lyrebird_Cycles_Mark_Kelly! Will give that a shot.
On a related note, do fabricators not use silver for brazing like such? I thought those would end up looking less yellowish, and more silvery.
Depends, you can use either. Silver is more expensive.
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