Static Poising

Would you put greater trust in something made by hand or by a machine? You're free to have you own opinion, but watchmakers err on the side of handcraft. Poising is one great example.

In a previous post, I talked about truing a balance wheel to make sure it spins flat. Today, we're learning to compensate for manufacturing errors, and helping them to spin evenly.

Manufacturing errors happen. It is an unavoidable part of life. In balance wheels, they can cause one side to be slightly (emphasis on slightly) heavier than the other, which can play tricks with the oscillator's rate. Poising fixes this error.

To poise a balance wheel, it's placed into a poising tool, consisting of ruby jaws and a level. The wheel is spun, and if it falls to a certain point repeatedly, that's identified as a low spot. Low spots are heavier, so we have to make them lighter with drilling.

The drill is incredibly small and delicate—and unusual. It's actually a carbide drill tip on a screwdriver blade, and it's only about 0.25 mm across. Carbide is delightfully sharp, but it shatters easily... Especially at this scale. Great care is required when handling this tool, even when just picking it up and setting it down.


Removing metal with the drill is easy, but you have to be careful. Very little drilling is required to properly poise a balance wheel, and the more you remove, the more you affect the rate.

I'll pause to note here that the balance wheel in the header image was previously poised by another student, and that I only put two holes in this one after re-staffing it. Three holes is about the maximum you'd want to put in a wheel, but this ended up with at least six, thanks to its past life.

Next up is hairsprings and timing. Soon, we'll be able to service a time-only watch from top to bottom, and it's only been two months.


Watchmaking student at the Lititz Watch Technicum, formerly a radio and TV newswriter in Chicago.