Servicing old movements and amplitude

I was fortunate enough recently to get my hands on some New Old Stock (NOS)  ‘A Schild’ automatic movements that I can use to build some watches.

These movements were produced between 1960 and 1969 which makes them 50 years old – there is a good chance that the oils and greased may be a bit stale.

Before servicing I decided to see how they were running, always a good indicator. The movements ran well, timing very close to perfect after a bit of regulation, but the amplitude was a little bit low.

So what does this mean, and what it’s all about?

Amplitude is the swing of the balance wheel past the rest point. A healthy amplitude is in the 270-300 degrees range. It gives a flavour of the power behind the swing. A powerful swing denotes a clean well oiled train of motion.

The first thing to do was to strip the movement, polish the jewels with peg wood, clean everything thoroughly. (A few random shots)

Once cleaning had taken place I decided to put the original mainspring back in just to test the amplitude and see how the service had changed things (makes for a more interesting post) I was also waiting for a new spring to be delivered.

As expected the amplitude had improved almost to very acceptable levels, but since the spring is 50 years old, certainly worth changing to alleviate any future issues.

With the spring changed – testing time again. 

276 degrees or there abouts either way up when flat – perfectly acceptable. Ready to put the movement into a watch.

I will post that when ready.

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