This is a plea to our fellow clock repair and clockmaker friends. Please stop soldering mechanical horological parts!
We have seen our share of disastrous and unsightly solder globs, burnt and warped parts, corrosion and rust related to the flux used in soldering. And what’s worse: most solder joints performed on clocks don’t hold worth a darn! Why bother, folks?
Unless two parts to be joined are fully disassembled, the space between them thoroughly cleaned of tarnish, oxidation, oil and cleaning solutions, the solder will not flow into the joint anyhow. What good does it do to have solder globbed onto the surface? It does no good. And if you are going to go through the trouble to disassemble the parts to properly prepare them for solder, there is almost ALWAYS a better way to carry out the repair.
Recently we disassembled a clock in which someone decided to solder the hub to the wheel. The proper repair of the problem would have taken no more than 5 minutes done correctly (stake the hub). Instead, someone soldered the wheel with the mainspring still adjacent to it, assembled in the barrel! The heat from (presumably) the blow torch destroyed the temper of the spring, defaced the part, ruined the arbor (due to acid corrosion), and didn’t solve the original problem anyhow.
Removing solder is one of the most difficult challenges we face. You cannot simply heat it and remove it; there is always a residue left. This residue is resistant to brushing, abrading, even sanding. It is difficult and expensive to remove. Often, underneath the solder we find a randomly scratched and scraped surface (this isn’t how you clean two surfaces in preparation for solder!).
Just say no to soldering horological parts. There is always a better way!