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Elgin Grade 97

This Elgin is a grade 97, 18 size, 7 jewels, made about 1891

The movement needs a replacement balance staff. Staffs come with different pivot sizes, and often have to be reduced. Naturally, one the pivots can not be made larger, but they came be cut down and refinished, smaller.

We're looking for a 5-7% angle, leaning, on the staff just resting in the jewel.

This replacement needed the pivot reduced a little. It is often the case that factory replacement parts are not exactly correct.  The upper pivot will just get a quick polish.
The old staff is removed by cutting away the hub, or seat, to almost, but not quite, nothing in the lathe. The remaining bit is then broken off with the staking set.

What's left is a cut up staff, and a tiny washer. Here we have that washer of steel that is all that remains of the hub, the old staff, and the replacement.
The replacement staff is riveted to the balance wheel, then the roller table and hairspring are installed, completing the balance assembly.

Balance staff pivots almost always break when a watch is dropped, or otherwise receives a hard, solid, blow. This is an extremely common repair.

This is a key-set movement, meaning that the time is set using a key that fits over the square hub in the middle of the hands. The hands are then turned directly.

Such watches have a minute hand with a square hole at the end (the "boss") to fit on the hub. In this case it looks to me like a normal round-holed hand, for a stem-set movement, has had the hole filed roughly square. It didn't really fit though, and would not go on far enough to allow the use of the key.
In order to preserve as much "as found" as possible, I expanded and squared to hole a bit rather than stick a new hand, or the expected type, on there.

This is a case where this past repair does no harm, and is just part of the history of the individual piece.

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