So, I'm building my first frame with the help of a local builder, and last night we brazed the main triangle. The builder told me that he normally uses 45% silver brazing material with cadmium, because it flows better. Of course, it's also toxic. He said that since it's expensive stuff, he wanted me to provide my own brazing material (he's only charging me $15/hr for lessons), so I went to Airgas and all they had was Harris 45% safety silver without cadmium, so I bought a 3 oz spool of 1/16" wire.
He hadn't used safety silver, so we used it on the first braze when we were tacking the frame in the jig. He had the torch, and was having a very difficult time to get it to flow....to the point where we reverted to silver with cadmium to get the rest of the main triangle brazed. He theorized that perhaps cadmium needed lower tolerances between the tube and lug in order to flow.
Anyway, is there some sort of trick with safety-silver that you need to do in order to get it to flow? Do I need more space between lug and tube in order to get a proper joint? I'd rather not use the toxic stuff, but the silver with cadmium really was pretty easy to work with...