The first step in adjusting to 5 positions is aligning the dial up (DU) and dial down (DD) rates. It doesn’t make sense to align the 3 vertical positions unless the 2 horizontal ones are alike. After all, we’ll eventually have to align the vertical and horizontal positions, and if DU and DD vary we wouldn’t know which one to align the vertical positions with.
Our current patient, the Hamilton “Fulton” 747, is -1 DU and +21 DD. We would like these to be as close as possible. In general, a difference of less than 5 seconds is good for vintage watches, and 10 seconds is probably the biggest difference would accept.
Rate and Amplitude
So why would a watch have different DU and DD rates? Basically, the balance wheel is swinging with different amplitude in the positions.
Amplitude is the balance wheel’s angular rotation, in degrees, from the neutral rest position to the point of maximum displacement.
For example, consider a traditional two-arm balance like in the figure. When the watch ticks, the wheel starts at the rest position, swings in one direction, and stops briefly before swinging in the other direction. That stopping point is the point of maximum displacement.
In watch adjusting, high amplitude is crucial for many reasons. We’ll elaborate on amplitude across this series of posts. For now, we’ll simply affirm a common standard: amplitude must be at least 270 degrees in the DU and DD positions. The balance wheel in the figure is rotating 270 degrees, which is 75% of a full circle.
Anything that affects the amplitude in the DD and DU positions will affect the rate. As amplitude increases, the rate slows. This might be counter-intuitive—when the wheel swings with more force, it seems like the watch should run faster—but it makes sense.
If you have played tennis, imagine holding the racket face up and repeatedly tapping a ball into the air. If you tap the ball lightly, the rate of the taps is faster than if you tap the ball forcefully. Tapped lightly, the ball doesn’t travel far, so the time between taps is shorter. Likewise, the arm of the balance wheel travels a greater distance when amplitude is high, so the space between ticks is greater—thus fewer ticks per minute and a slower rate.
So, if the balance wheel’s amplitude is greater DU than DD, the watch will run slower DU than DD, all else equal.
Common Causes of DU/DD Differences
What causes differences in DU/DD amplitude? Lots of things, it turns out. Both Kleinlein (pp. 56-58) and Jendritzki (pp. 86-87) give long lists of possible reasons why a watch varies DU and DD. Let’s boil them down.
The Balance Pivots & Jewels
- One pivot has too much or too little oil
- One jewel is dirty or crusty (common for older watches with hard to remove cap jewels)
- One balance jewel is cracked, loose, pitted, or out-of-flat
- The pivots have different shapes: one is relatively flatter, increasing friction and reducing amplitude
- A pivot is dirty, bent, pitted, or corroded
- The hairspring is rubbing against the balance bridge, center wheel, or balance arms
- The regulator pins aren’t parallel or flat to the regulator, causing more space in one position
- The hairspring is out of flat
- The banking pins aren’t perpendicular to the plate, so the run-to-banking varies DU and DD
- The balance wheel is scraping against a bridge in one position
- Variation in endshakes between the escape wheel, pallet, and balance wheel can create an array of DU/DD differences (e.g., rubbing of the roller jewel, roller, or pallet finger)
What To Do?
Statisticians remind us that “rare things happen rarely,” so most of the time a DU/DD difference is caused by a few common causes. In my experience, here are the big ones for vintage watches:
- The pivots differ in cleanliness or lubrication
- The hairspring is rubbing against something
- One of the balance pivots is bent, rough, or flattened
It is easy to know which position needs attention. Kleinlein points out the position with the lower amplitude is nearly always the one with the problem. After all, in this position, there is less force or more friction.
For our example Hamilton Fulton watch, here are the times and amplitudes:
- DU (dial up): -1 (291)
- DD (dial down): +21 (275)
As Kleinlein noted, the DU position has a higher amplitude (a nice 291 degrees) and a slower rate (-1). The DD position is much faster (+21), consistent with a weaker amplitude (275 degrees, just above the 270 minimum).
In this case, all it took was a good cleaning. I removed the balance, scrubbed both pivots with wood smeared with jeweler’s rouge, and cleaned and re-oiled the jewels.
After, the rates looked great:
- DU (dial up): +1 (304)
- DD (dial down): -1 (308)
Later posts will describe how to deal with some of the less common causes of DD/DU differences, but much of the time, cleaning and oiling does the trick.