Chas.,
Actually the melting temp of the silver alloy I use is 1150 degrees; which is a significant difference. Also the remelt temp is not much higher. With brass the remelt temps are quite a bit higher than the original brazing temp.
Brian Baylis
La Mesa, CA
OK, lunch break over. Back to making frames.
Brian,
To add to what you said, the original melting temperature of the brass or bronze brazing material is 1600°F to 1800°F. The tubes and lugs need to be heated slightly higher to insure good flow of the molten brazing filler.
When disassembling a brazed joint the lugs can be easily overheated and at that point they're extremely fragile. Features like long points can stick to the tube and just break away from the rest of the lug.
I agree about silver brazing alloy. The initial melting temperature is from around 1400°F to 1600°F.
Chas. Colerich Oakland, CA USA
brianbaylis@juno.com wrote:
> Garth,
>
> I didn't watch the video yet, but absolutely without a doubt the remelt temp is higher than the original brazing temp. Furthermore, in order to get the tube out the old braze material must be liquidous all at the same time, which is no small chore. Care must be taken in the cooling stage of the repair because that's when the potential damage can occur to the tubes. Lugs are not effected in the same way, but care should be taken to not break them as you disassemble the frame. The old tubes are no matter; but the tubes that remain are the concern. Ideally, once the un brazing is accomplished (using lots of flux as a heat sink and to prevent oxidizing of the tubes), the new tubes should be silver brazed back together, Unlikely this was done in this case; but that's what I'm comfortable with. Bikes are repaired like this all the time and survive fine, apparently. When one uses the proper low temp silver braze material in the beginning; removing and replacing tubes can be don
e with virtually no negative effects to the tubes at all. That's one of the primary reasons I prefer silver brazing frames. These sorts of situations are avoided if a repair ever becomes necessary. There are LOTS of ins and outs to doing first class frames repairs. Top quality frame repairs are more difficult and require more knowledge and skill than building frames from scratch.
>
> Brian Baylis
> La Mesa, CA
>
> ---------- Original Message ----------
> From: Bianca Pratorius
>
> In this video, it sure takes a lot of heat to get the old headtube out.
> Does that amount of heat exceed the amount that was needed to braze the
> original? The top tube was totally glowing red hot when he was done,
> Did the frame get damaged in the process?
>
> http://www.youtube.com/
>
> Garth Libre in Miami Fl USA