Expert: Martin Meyer - 1/9/2009

Question
how is the end cap on the barrel(which has the teeth) which holds the spring held in place..noticed it came off some way..can't tell how it was held in place.

Answer
Hi Julie,

If I understand you correctly, you are referring to the large geared plate which forms the base of the mainspring barrel, not the cap, which simply snaps into place.

The mainspring barrel gear plate is soft-soldered to the barrel. As this connection is under quite a lot of strain due to the force of the mainspring, the solder connection must be quite carefully done. Clockmakers use special low-temperature, high-strength solder, such as Stay Brite or Tix for this purpose. This solder is quite different from ordinary electrical or plumbing solder. The solder joint must be continuous all around the barrel, with no gaps or impurities.

As a footnote, the other type of soldering used in clockmaking, hard soldering (also called silver soldering or silver brazing), can not be used in this application, even though it forms an extremely strong bond. This is because hard soldering requires the brass to be heated to the red-hot stage, which anneals (softens) the brass, making it too weak for the purpose.  http://www.clockmasteronline.com