The practice of applying flux (borax) on the joint is in addition to applying the paste form of flux on the tubes and inside the lugs before assembly of the frame. I can't imagine a builder assembling a frame without putting flux on the tubes and lugs before putting everything together. At Masi in Carlsbad the frames were fluxed internally prior to assembling in the fixture and then tack brazed. Once removed from the fixture the frames were heated at the joints and covered with flaked borax which acts as both a heat sink and an anti oxident while brazing. Mario would describe this as brazing "through" the flux. I use the silverbrazing equilevent, although not as neccessary because of the vastly lower brazing temps.; but it never hurts to protect the tubes from oxidizing while brazing regardless of which method. You can never have too much flux, but one should never have too little. I just fixed a frame yesterday that the builder must have negelected this principal, resulting in a "cold joint" like situation. Hope that clarifies the flux issue.
Also, I doubt that silver brazing is done using the hearth brazing method. Silver flux has a rather narrow range of working temperature as compared to brass flux.
La Mesa, CA
> In a message dated 5/21/01 9:56:56 AM Eastern Daylight Time,
> email@example.com writes:
> << if you look at the confente brochure, he's brazing up the bb shell with
> firebricks as a backdrop. this could be a 'modern' version of the hearth
> method. >>
> Oh yes, I remember that now, Richie...
> I have seen a number of builder's using a fire brick surround as an
> "environment" to hand braze joints as a means of retaining heat... To my
> mind, this is still a far cry from classic hearth brazing though as it
> doesn't involve inserting the joint into a constant blast of flame. Rather
> than increasing or reducing heat by manipulating the flame, it seems to me
> that hearth brazing is liking diving into the deep end of the pool!
> For those with a little knowledge of the craft world (art world?) the open
> hearth methods reminds me a bit of Raku pottery making. A little bit fire
> and brimstone!
> Also interesting in Bob's scanned article was the mention of paddles being
> used to apply Borax (flux) after the joint was assembled. (Was I just reading
> that into it?) In any case, I would think that odd and maybe an error as most
> often the flux is painted on the tubes before assembly.. But maybe some
> workshops/factories applied the flux after assembly? Would that ensure a good
> Dale Brown
> Greensboro, North Carolina