Brian B wrote:
> > The "old school" which is Mario and friends where the
> > torch is oxy/propane
and Dave Tesch replied
>
> I would have loved to have tried that, when I did my stint at
> Trek we used a synthetic gas called "Flame-X" which was designed
> to duplicate Acetylene. Propane would have been interesting.
I've probably brazed more frames with Propane/Oxygen than with acetylene. I think it's better for lugs because the bigger, lower temperature flame heats lugs up more evenly by its nature. A skilled brazer with acetylene gets the same effect by keeping the torch moving and paying attention, but propane makes it easier, and I believe faster. The propane flame is softer, seems like the gas is coming out at a lower velocity, so it wraps around the joint rather than caroming off like acetylene. Acetylene is so much better for braze-ons, dropouts and fillet brazing, that you have to have both if you want propane for lugs. The torches, regulators and all are different for propane so there's a lot of duplicated expense. Since acetylene can do it all and propane can't, acetylene is the obvious choice if you don't want to get into all that extra expense.
The cool setup is two torches, one in each hand, for the warm-up part of the job. One is your regular torch, the other is a rosebud that puts out an astonishingly large amount of heat, gets the joint to brazing temperature quickly. The brazer then hangs the rosebud up on a "gas miser", a big ol' hook you can hit without taking your eyes off the lug. The hook is connected to a switch that shuts off the gas to the rosebud, so it shuts down while leaving it's knobs adjusted for the right flame. And next to the hook is a pilot light, so when you pick up the torch it's instantly ready to use - very clever!
I never tried the firebrick technique as described by Brian. It's the old world standard, and I think it is designed to minimize the cost of the fuel gas by keeping all the heat in near the joint instead of wasting so much out into the room. It also would allow fuel gasses with less heat capacity to be used, or fuel/air torches instead of fuel/oxygen that requires bottled oxygen; I believe I've heard of coal gas or some such where you need the hearth to get the joint hot enough for brass brazing. Minimizing fuel usage is admirable, but on a multi-kilodollar frame it doesn't make economic sense if it slows you down at all.
That hearth technique always seemed so limiting to me - with the frame in a
Park stand or the like, you can get at all sides of the joint, and rotate it
so that gravity is helping, keeping the flux where you want it and assisting
the capillary action that gets the brass where you want it.
> both at Trek, and at my place, there was an in line
> Gasfluxer that made a huge difference, no matter what,
> but was a Godsend for fillet brazing.
Yes, the Gasfluxer is a big plus, I'd recommend it even for hobbyist
builders if they can afford it, quality does go up.
> I stopped buying premade flux, and went to buying bulk
> powdered Boric acid. this was mixed with water, and applied
> in powder form like the stuff Ted had left over from Masi.
> I came to realize that a 50# bucket of flux was 40# water.
Davidson was getting this powder flux from Japan that was noticeably better than any US flux we could find. Probably brought in hundreds of kilos over the years. You definitely don't want to pay to ship that much water from Japan. Later when we were running out of the good Japanese flux, we extended it by mixing it with US flux, and this cocktail was the best of all, can't say how exactly but it had all the best of both worlds. Sure wish I could get some now.
Mark Bulgier
Seattle, Wa
USA