THE JACOT TOOL
Is the weapon of choice for fine sizing, burnishing, and polishing pivots. It's hand-powered via the small bow, and invites imagery and sensation of watchmakers from generations past using a similar tool. It's crude yet elegant in design.
Using a 'dog' and lantern a collet
You mount your gear with a pivot in need of burnishing, or in the example here; some raw cut pivots. We made small brass carriers for the 'ears' of the dog to lock onto. You can see the bow twisted around it. As you operate the bow, it spins the dog, which the ears engage the spokes of the gear or in our case, the long screw of the carrier.
In motions opposite of your bow, you place your burnisher atop the pivot which rests in a lantern collet slightly smaller than the target you plan to size your pivot to. For example, you want to cut your pivot to .25mm, you'd use a groove in the collet sized to .22mm or .20mm. That way the burnisher doesn't bottom out and some material of the pivot sticks up, able to be cut.
A DELICATE TOUCH
Is needed to not break, deform, or taper (and any other number of things) your pivot. You must be focused, relaxed, and patient when cutting and burnishing pivots. Rough cutting is done on the watchmakers lathe, expect a couple pivots to break, so make extras. Frustration will only impair your ability to do good work, stay centered and remember that breaking pivots is normal.
It is here that numbers need to be exact. A piece of dust or oil on the pivot or your measuring device can obscure an accurate reading. If your pivot isn't sized perfectly it wont function. Generally pivots are .25mm and under, even handling them takes a bit of learning.
WHY IS A BURNISHED PIVOT GOOD?
A properly burnished and polished pivot not only has less friction but it wears less over time. The act of burnishing actually compresses the metal, making it denser and harder to corrode. Many brands and movement manufacturers have acid washed and tumbled pivots, this technique is cheaper and creates a hard outer surface, but once that hardened surface wears through, the softer insides degrade quickly. This is where burnishing shines, it's a rare practice, a good repair technique and an extreme challenge to master.