Things going any better yet Greg? I Hope so, I have seen that you are doing nice work and I am sure this is aggravating the $#*! out of you. This is not always easy to do, some things that may help -building a fire for the purpose at hand makes a big difference, even more so when brazing with copper due to the higher heat required. You want a good amount of coke in the center of the fire with no voids and surround it by fuel (coal) banked against the sides and layer over the top. It's like building a fire for welding, you want a fire that eats up oxygen, insulates itself and reflects heat back into itself. Also a good coke bed will help support the part to be brazed. If it is not supported, parts can bend and riveted joints can slip under heat. The key is a even burning, clean fire, no hot or cold spots.
When your coal on top of the fire has burned a little bit, pull it to the sides some. Make sure your air supply is well covered with coke and you have a good layer between it and your part to be brazed - again, no voids. Set your fluxed guard in the fire and rake coke around it so it is both supported and surrounded. When welding you should wait until the metal has some color in before fluxing , but I have had fine results brazing by wetting the joint with alcohol and sprinkling with borax before any heating of the part.
Pull the fire partially back over the top, but leave a gap so you can watch your braze joint. If you knock any green coal down into the joint, best to pick it out. From there let the part to soak a while, give a little air if needed to bring the heat back up, but the idea is to allow the part to come up to the heat of the fire rather than force it. Another way to describe it - you want to bring the FIRE up to a brazing heat then hold it there while the metal catches up. Cranking a lot of air into the fire to speed the process will just blast your part with oxygen, scale it up and increase the likelihood of burning something. Until you get the hang of it just take your time and sneak up on the brazing point.
After your braze melts, cut off the air and resist the urge to pull the guard out, best to carefully pull the top of the fire back and then leave it sit, allow everything to cool a little and let the braze solidify. You can safely remove it when it is red.
Something related - if you punch a hole in a plate and set it over your fire it will shoot a flame that I have soldered small parts with a couple times (socket worms, rod tips etc) I am not sure if this would work for brazing, one of those things I always want to try and never get around to it. Anybody done that before?
