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Just how fragile is the 8AE balance?

I am working on an excellent condition Squadron B with a '47 8AE movement.

I could almost say for certain that the balance wheel oscillators well before disassmbly. However, after very carefully removing the dust shield, the upper balance wheel pivot was broken.

When looking for a parts movement, I noticed many 8AE's for sale or bid without a balance wheel.

Are the 8AE's balance wheels that fragile?

Hamtramck Stan's picture
Hamtramck Stan
Posted February 26, 2018 - 9:24pm

That was oscillated, not oscillators, by the way.

Club 5000Panel Member
Posted February 26, 2018 - 10:00pm

No more than any other balance staff I would image.

It's possible that the dust cover was providing some level of pressure on the balance bridge and as such keeping the broken balance staff in place (or close to it).

Simply removing the dust cover would not apply any pressure on the balance bridge, certainly not in my experience anyway.

Reverend Rob's picture
Reverend Rob
Panel Member
Posted February 26, 2018 - 10:18pm

Often balances with broken upper pivots will appear to oscillate freely, but at rest they will show the unmistakable tilt or wobble of a broken staff. 

The pivots on balance staffs are quite thin, we had to reproduce one for the exam that was .11 mm if memory serves. The steel is blue, so they are rigid but  brittle. A good sideways shock will often shear the pivots off, and sometimes take the pallet fork with it. Shocks from dropping cause damage proportional to mass, which is why you see so many pocket watches with broken staffs, cracked jewels, etc.

Parts movts are there because there is something wrong with them. The running or decent ones are still in their cases. I am always suspicious of orphan movts, if they have been out of their cases for long periods of time, they invariably get very damaged.