Hello all,

This is my first post. Apologies in advance if I'm asking questions that have been asked before. I've been a machinist for 25 years, and have lots of experience silver soldering all sorts of decorative and architectural assemblies. However, I've never built a lugged bicycle frame, and I'd like to give it a go, with the idea of making a few of them to zero in on a combination of size and geometry that suits my riding taste. I'm usually brazing bronze castings, or brass/steel assemblies. I tig weld when working exclusively in steel, so I'm a bit out of my depth here, and have a really basic question about jig and brazing strategy in constructing a lugged steel frame.

The methods I've read about involve sequential brazing steps, such as brazing the DT/HT combo, then the ST/BB, then the DT/BB. That's sensible enough, but would one ever want to braze all the BB locations at the same time, in order to only have one heat cycle and cleaning step? Is maintaining alignment too difficult? By extension, is it just not practical to design a jig that locates everything on the main triangle so one could braze all the joints in one operation? Is there too much expansion between lugs for that to work out? The brazing setups I've made have to allow for movement and distortion, but due to using different metals, in different sizes and masses and therefore different heat saturation, I'm just not sure if these experiences are a good reference. In a production environment, I'd think manufacturers would have jigs that were really comprehensive, so they could reduce setup time and cleanup time.

Back to the bottom bracket, I have a question about heat control. When doing each next brazing operation, do you ever have problems with silver starting to run in the previously set joints? If I'm working with a bronze casting, it has much greater mass than a steel bottom bracket, and I need to get a lot of heat into the part overall. I'm guessing it is easier to keep the heat localized in a steel lug. I'll soon be experimenting with all this, but it's always good to get some expert advice beforehand. Thanks for reading.