For the most part, accuracy in different positions is a matter of poise—the even distribution of weight around the balance wheel. We thus look for ways to add weight to a light spot or remove weight from a heavy spot.
Aftermarket timing screws can help us do both. You don’t see these around often, but you should snatch some should you see a big assortment for sale.
Timing screws are simply replacement screws for a balance wheel. They are sized for different watch sizes and manufacturers, as the picture shows.
These screws vary significantly in size: some are as big as the OEM screws in your balance, but most will be smaller. Here are some screws marked as “Elgin 0’s HEAVY.”
Uses for Timing Screws
Timing screws are a useful way of making big changes in weight. Typical methods, like undercutting a screw or adding a timing washer, are good for small changes. If you find yourself needing to make changes around the order of 300 or more seconds, you might consider changing a screw.
Here are some common ways to use timing screws:
Lighten a balance by swapping a smaller screw. If one screw is notably too heavy, you can pick a slightly smaller timing screw instead of deeply undercutting.
Replace a gouged or dimpled screw with a smaller screw. The desire to remove a lot of weight drives people to desperate measures. You often see screws with deep dimples from accursed screw cutters. I recently handled an Illinois pocket watch with screw heads filed so deeply that they lacked screwdriver slots. Clearly, someone was trying to make a heavy screw light. In these cases, the skunked screw can be replaced with a small timing screw, which will be both more functional and attractive.
Greatly slow down a watch by adding a pair of screws. If a watch is running monstrously fast (yet has good amplitude), you can slow it down by adding a pair of small timing screws. Compared to the huge timing washers that would be necessary, the timing screws will be discreet and visually consistent.
Needless to say, if you add a pair of screws, pick two screws of identical size and weight and place them exactly opposite each other on the balance wheel. Otherwise, your poise will go from bad to calamitous.
Change the rate without changing the regulator or mean-time screws. In some cases, adding or swapping timing screws can allow you to bring a watch close to a zero rate without shifting the mean-time screws (if the watch has them) or regulator index. This gives you more room for subsequent fine adjustments.