Had a great time this weekend creating fillet joints. With some coaching, proper set-up, fluxes and rods, I'm feeling better and better with each pass. The nervous hand-shake is gone, I'm working through the points on the mitered tube better and overall, I think I'm having about 90% success. I'll post some photo's of work later on, but in the meantime, here's the down-low on my set-up and tips:
1. Use a good flux- this is key. I'm using Fred Parr's Saf-T-9 of which you apply a
very thin coat.
2. The tube miters need to be good, really good. If you've used a hole-saw to rough it, clean it up with a file and get rid of inconsistencies. At the temperature which brass flows, it will flow right through any gaps to the ID of the tube.
3. Clean the tubes well. In fact, I don't think they can be too clean. I use emery cloth, then a degreaser such as Mira-Chem, (don't use any cleaners with hydrochloric acid,) then liberal, aggressive brushing with stainless brushes on the OD and ID. I don't know what the stainless is doing, maybe some sort of passivation, but it works.
4. Get it hot but not too hot! The tinning run after tacking is very important in forming that internal fillet. I'm still too conservative when tinning, but I find you actually have to run a little hotter than you think you do. Cool off the flame by backing off the oxygen a little then proceed with your fillet run with a larger rod. Keep the puddle moving, gently filling the puddle to avoid voids and watch the shoreline for temperature indication. If the shoreline is getting too wide, you've got too much heat in the tube. Back the torch off a little and keep moving away from the hot area. Do not dwell too long trying to fix it!
5. Use a bath or pot of hot water to get the flux off the tubes onces they've cooled. Water between 140 and 160 degree will get must of the flux off within 60 seconds. Flux remaining that's heavy with oxides might take a minute or two longer.
6. One more note, if you're practicing and you know its not your best work, move on. Spending an hour filing and sanding won't make it better. In fact, the better your fillet, the less you'll spend on sanding and filling.
Hope this helps. These were some hard-learned lessons for me. Here's an
example from Dave Bohm of Bohemian Cycles of what you're shooting for.