The problem that you can run into trying to remove braze-ons with a torch is that the remelting temperature of the brazing material is usually much higher than it's original melting temperature.
The melting temperature for most copper/zinc brazing materials is between 870°C to 980°C or 1600°F to 1800°F. The Critical Temperature of Steel is around 724°C or 1335°F. So it's easy to overheat thin wall steel tubing trying to remove braze-ons.
I've watched frame builders do it but they have a lot of experience working with thin walled tubing.
You could grind away most of the braze-on and then quickly remove the rest with a torch.
I remember playing around trying to remove some braze-ons from some old wrecked gas pipe frames to reuse them. It was a bear to get them off as the remelting point of the braze material was so high.
Chas. Colerich Oakland, CA USA
Ken Foster wrote:
> A couple of weeks ago (BFC) I recall someone asking the best way to
> remove later braze ons (dare I say, including a derrailleur hanger). I
> have a similar dilemma and was surprised there were no replies on the
> group and wondered what the consensus was grind them or burn 'em or will
> it cause irreparable weakening
> btw when finished it will have one brake. as in the original 1952
> catalogue...
>
> Thanks
>
> Ken Foster
> Eastbourne
> England