Originally Posted by nome.king
my plan is to wrap very fine brazing wire tightly around the ends of the tubing, then to insert the tubes into the lugs, which would need to be heated enough that they would expand to accomidate the increased diameter. Perhaps bisque moulds could be used to hold additional braze-ons in place.
Sounds somewhat similar in principle to what Masi did with the 3V, but they put a spring of silver wire in the joint before brazing, they didn't wind it around the tube. I imagine that getting the proper interference fit between tube and lug would be impossible, given the 1/16" thickness of typical silver rod. How small can you go with silver? Probably not something in the 1 or 2 thousands of an inch you're thinking of.
Fred Parr described something similar; the Schmidt (spelling??) technique for making internal fillets. He would wind Allstate 11 rod into a spring, saddle-form it to mate up against the intersecting (head?) tube and then lightly tack it with silver into the other (down) tube. When you heat the tubes to create the external fillet, it makes the internal fillet too.
He also said to make use of gravity. And there's your next problem. How would you use gravity to your advantage to draw the filler through the lugs?