In Part 1, we repaired and serviced an Illinois 12s “Santa Fe Special.” This nice little pocket watch had fallen on hard times, with cracked jewels, a mangled hairspring, and a broken balance staff. Now that it has been running for a while, let’s see if we can adjust it to keep close time in all 6 positions.
I’m expecting this watch to be a trial. Remember that we swapped the hairspring, and this rarely goes well. Hairsprings are “vibrated” to match the balance wheel. Balance wheels vary in their weight but must have the same number of beats per hour. The factory hairspring was chosen and vibrated—pinned, formed, clipped, and studded—so that its thickness and length would cause the wheel to beat at the proper vibration rate (usually 18,000 beats per hour).
If you swap hairsprings, the new spring won’t match the balance. As a result, it will either be too short or too long, causing the watch to run freakishly fast or slow. Adjusting such a watch is tedious.
The proper thing to do is to vibrate a new hairspring, but I simply lack the training and tools to do it. But I’ll get there eventually. If you’re curious, you can read about vibrating hairsprings here and here.
Taking Baseline Readings
So let’s steel ourselves and see how this watch runs. “Freakishly fast” was the winner. The humble Timegrapher showed a rate of ++++, which means the watch was running more than 1000 seconds fast per day. Out of curiosity, I put hands on it and let it run, and the watch was running around 17 minutes fast per day. Yikes. The balance wheel is simply far too light for the new spring.
We need to slow that sucker down. When we need to add a quarter of an hour, timing washers won’t do it. Instead, we need to add screws to empty spots on the wheel.
I have a couple 12s Illinois parts watches, but neither one had screws that would fit the Santa Fe Special—the threads were different. This was unexpected, and I began to get a looming sense that this watch was going to be tricky.
Fortunately, I remembered my big stash of timing screws, which we described in a recent post. After trying a few out, a stash of screws labeled for Elgin 0s movements (of all things) fit. I matched a pair of screws for size and weight. Adding two screws to opposite sides of the balance wheel didn’t slow it enough, so I added another matched pair.
Knocking, Knocking, Endless Knocking
After adding 4 timing screws to slow down the watch, what rates did we have in the 6 pocket watch positions? None, in a way—we had knocking, ceaseless and relentless knocking.
As we explained in an earlier post, knocking is a consequence of unusually high amplitude. The balance wheel rotates so far that the roller jewel hits the other side of the pallet, which is locked against a banking pin. Obviously, a watch won’t run well when the balance is careening between collisions with the pallet fork.
Our post on knocking described some ways to cure it. The best way is to use a weaker mainspring. I had put in a widely available mainspring, Illinois part #47344. This spring is 2 mm wide and .18 mm thick. A mainspring’s force, all else equal, is a function of its thickness, often called its strength.
A weaker (thinner) mainspring will deliver less force and hence less amplitude, so the balance wheel should stop knocking.
After a bit of hunting, I found a weaker option: Illinois part #47343. Its strength is .17 mm. This is only .01 mm less than other one, but a mainspring’s force is the cube of its thickness, so it should notably reduce amplitude.
With the new spring, the amplitude was reduced by around 35 degrees and knocking was reduced—.01 mm makes a big difference!
Back to the Baseline Readings
After the watch ran for a day or so, it was time to take some baseline readings. Beforehand, the watch was demagnetized and had its regulator set to the middle of the FAST/SLOW index. The rates looked grim, with huge deviations in the vertical positions. (Keep in mind that pendant right and left are defined from the dial side, but we’re viewing the watch from the movement side, so PR and PL are reversed.)
Adjusting such bad rates will take some time. The good news is that the dial up (DU) and dial down (DD) positions are close, which is the first step in adjusting to positions.
Adjusting to 6 Positions
But the adjusting process is the same regardless of how bad it looks. We need to find the heavy spot in the balance wheel, so we run it at low amplitude, around 140-160, and then find the fastest position. The heavy spot is directly below the balance staff when the watch is at rest in this position.
The watch was fastest in this position, the diagonal between PU and PR:
The heavy spot is directly below the balance staff, right where a big ol’ screw sits.
So, do we add weight or remove weight? In this case, we should remove weight for a few reasons:
- when a watch is running slow, removing weight aligns the horizontal positions (DU and DD) with the vertical ones. Adjusting to 3 to 6 positions requires that all of them are similar.
- although a historic preservation approach prefers only adding weight, which is reversible, I can tell that many of the screws have already been heavily undercut. And, of course, we’ve replaced some key parts, such as the hairspring.
- the mean-time screws are already most of the way in, so we couldn’t use them to make the watch run fast and then add weight.
- we know that the wheel is too heavy because of the 4 timing screws.
In the first round, I removed some weight from the heavy spot with a screw undercutter, which is a clean and discreet way to remove weight.
In most of our example watches, I have described alternating between low wind and full find: we take the rates at full wind, find the heavy spot at low wind, make an adjustment, and then take the rates at full wind again to see the results. The virtue in seeing the effects you caused is that you quickly build your tacit, intuitive knowledge of how much weight to add and remove.
But you needn’t wind it fully in between adjustments. You can do several rounds at low wind, which saves time when poise is terrible.
This watch took around a dozen rounds of adjusting. In all cases, that same general position—the region between PU and PR—had the heavy spot. Toward the end, I would move the mean-time screws or regulator to shift the DU/DD rates to be slightly slow. This allowed me to remove a tiny amount of weight (by deepening the screw slots with a screw slot file). When removing weight, it is better to remove too little and do another round than to carve off too much. Taking it slow gives a better result.
After a few rounds of adjusting at low wind, we ended up here: better, but bad in the vertical positions.
And after a few more rounds, we got here: the rates are starting to converge.
And after yet a few more rounds, we arrived here: pretty good, frankly.
And, finally, after a few more, we stopped here: a great result.
This watch took a lot of work. Between the new staff, repairs, cleaning, and tedious adjustment, it was a trial. But all’s well that ends well: this watch is clean, shiny, and running accurately. It was originally adjusted to 5 positions, and it is most accurate in those 5. But even the 6th position (PD) is pretty good.
I’m going to let this one run for a few days before casing it up, just to monitor the stability of the adjustment. If all goes well, I’ll post a picture soon of our newly sleek and shiny Santa Fe Special.
One lesson from this watch: I need to learn to vibrate hairsprings. If I had the skill, it would be faster to vibrate a new hairspring than to adjust a mismatched balance wheel over a dozen times. It turns out that among its many great offerings, the NAWCC hosts a 3-day workshop on hairsprings. Interesting….