When adjusting to 5 or 6 positions, the first step—adjusting the dial up (DU) and dial down (DD) positions—is usually the hardest. Kleinlein’s approach to adjusting emphasizes that these two horizontal positions must be similar before we can turn to the four vertical positions.
Bent balance staff pivots are a common cause of DU/DD differences. Pivots get bent when a watch is dropped or jolted. For watches made before the advent of shock protection, bent pivots are ubiquitous.
As we have explained elsewhere, anything that causes frictional differences in the DU and DD positions—like a pivot bent like a hitchhiker’s thumb—will cause rate differences. In this post, we’ll look at how to diagnose and deal with bent balance staff pivots.
A Typical Tale
As an example, let have a look at this charming 12-size Hamilton 912 pocket watch. This watch was a rare bargain. A local consignment store was dumping a batch of flawed pocket watches, and this one was missing a crown and a crystal but otherwise ran.
I took it home, wound it up, and checked it out on the timing machine. Here is what the dial down (DD) timing results looked like. Not much to complain about here: the amplitude is good, and the traces are stable and clean.
And the pendant up (PU) position, not shown here, was nearly identical. Could this be an easy one?
Such hopes were quickly dashed when I looked at the dial up (DU) rates. These timing traces are not for the faint of heart.
The amplitude is terrible, and the traces are all over.
After some troubleshooting, we can see that a bent pivot is to blame. Notice that the upper pivot is both bent and squashed. The balance rests on this pivot when the watch is dial up (DU). The pivot juts to the side, and the cone-like shape is completely gone.
If a pivot is bent, your trusty timing machine will usually show erratic traces, although not always as bad as these. Many things can cause ugly traces, of course, but a pivot that is bent enough to cause timing problems is usually easy to spot visually.
Sometimes, of course, a pivot is too bent for the wheel to rotate. The balance wheel on this 12-size Illinois pocket watch, for example, was stuck in place, and it’s easy to see why. The upper pivot looks comically bent.
Fixing Bent Pivots
Just as there is a simple way to go faster than the speed of light that doesn’t work, there are some simple ways to straighten bent pivots.
One approach involves thick tweezers designed for straightening bent pivots. The steps involved are heating the tweezers, gripping the bent pivot, pulling outward, and after a few rounds, giving up in despair.
Another approach uses a Seitz pivot straightening tool. This is probably the most elegant and expensive way to break a balance staff yet devised by the Swiss, so we won’t delve into using it here.
Replace the Balance Staff
Most bent pivots—like our Hamilton 912’s pivot—are bent beyond straightening. Others—like the Illinois 12s pivot—could perhaps be straightened, but they will rarely be perfect enough to be adjusted to the kind of close time we aspire to. Bent pivots usually mean the balance staff has been weakened or deformed, so it is time to start over.
Your best option is to replace the balance staff, so long as a replacement is available. Putting in a new staff takes less time than fiddling around with the straighteners, and it will yield a better final result.
This blog focuses on watch adjusting, not general-purpose watchmaking, but we might do a post on replacing balance staffs one day. Our textbooks describe how to do this, especially Fried’s book. Should you have a copy, The Watchmakers’ Staking Tool by Lucchina and Perkins has an excellent discussion. This video is helpful, too.
As an aside, I like how Mark dismisses static poising and gets right to dynamic poising.
And as another aside, an old-timer step not shown in the video is to run the watch at “half time.” The wheel, staff, and roller—but not the hairspring—are placed in the watch. It should “tick” if the clearances are right: the pallet fork will fling the roller jewel, which should bounce off the outside of the pallet and return with enough force to unlock it, continuing the cycle for a few ticks.
If the watch runs at half time in all positions, it will run well with the hairspring. If not, you’ll find it easier to identify the escapement problem without the hairspring.
Replacing the balance staff did the trick for our Hamilton 912. With a new staff, it had great amplitude DU and DD, and the DU/DD rate difference was around only 3 or 4 seconds.
Check Your Jewels
If your balance staff pivot is bent, be sure to inspect all the balance jewels. The impact that bent your pivot may have caused pitted or chipped cap jewels, themselves a common cause of DU/DD errors. The hole jewels, too, may have problems. The uneven force of the bent pivot can cause the hole to wear out-of-round or to crack. Our Illinois “Santa Fe Special” is a good example of the havoc a shock can wreak on jewels.
Truly, shock protection was one of the great innovations in watchmaking.