Accuracy vs number of Jewels

[finiteguy]

Hi All: I have been collecting Waltham Pocket Watches for about 2 years now. I have a Riverside 12 Size 19 J which is supposedly a high grade and it has relatively mediocre accuracy. I recently picked up a 6 Size 7-15j (I can't tell how many perhaps someone could advise me on how to determine this) and this watch is extremely accurate, as accurate as a quartz. This particular watch was made in 1890.
Is there supposed to be a correlation between number of jewels and accuracy? I haven't seen this to be the case.
Robert

[finiteguy]

Hi All: I have been collecting Waltham Pocket Watches for about 2 years now. I have a Riverside 12 Size 19 J which is supposedly a high grade and it has relatively mediocre accuracy. I recently picked up a 6 Size 7-15j (I can't tell how many perhaps someone could advise me on how to determine this) and this watch is extremely accurate, as accurate as a quartz. This particular watch was made in 1890.
Is there supposed to be a correlation between number of jewels and accuracy? I haven't seen this to be the case.
Robert

[John F]

The theory is that accuracy is enhanced by using jewels because they reduce friction, wear, etc. But, even a fully jeweled watch won't keep good time if it's dirty, has an old & tired mainspring, isn't properly oiled, etc.

The theory is pretty well borne out in practice, too. Get your Riverside serviced, and I'll bet a box of donuts that it'll run with a high degree of accuracy.

[Tom McIntyre]

If a watch has been mishandled in its history, it will not keep good time. Most of the time the problem will lie in the escapement and a good overhaul by a competent watchmaker will bring it back to its original specification.

An inexpensive watch can also have remarkably good performance. A flat hairspring can be fully isochronous by accident. Modern mainsprings deliver remarkably uniform force over their operating length, etc.

However, if you keep records on large numbers of watches of various grades, the advantages of jeweling will eventually show up.

In the 19th century there were stories in the news from time to time of ship's captains navigating with duplex pocket watches when the ships chronometer was out of order or stopped working properly.

[Don Dahlberg]

There is more to it than cleaning the watch and friction.

First, using jewels improves time keeping of a watch in two ways. With jewels there is less wear, so the watch will keep better time over more years of use. Second, the lower friction with jewels, the better the isochronism, the rate of the watch for the first 12 hours of a wind compared to the rate for the second 12 hours on the same wind.

When a watch is dirty, all time keeping bets are off. Warn, mushroomed or bent pivots, broken jewels and etc will also decrease accuracy. These things need to be corrected in a normal cleaning and overhaul.

Even a clean, highly jeweled watch will not keep good time if the balance is out of poise or the hairspring is not true. "Poised" is what you have done to your tires when you have them "balanced". The balance needs to be balanced or poised. The hairspring must be flat and symmetricly round. Most watchmakers will not poise the balance and true the hairspring unless you ask them to do it. Done properly, the watch is timed, and if it does not pass standards, then more poising and truing work needs to be done. It is a very time consuming process, especially if it had previously been attempted by someone who was not good at the process. The time needed to properly adjust a watch is why a watch adjusted for 5 positions cost more than one adjusted to 3 or fewer positions.

So if you want to spend the time, you can make a 7 jewel watch keep excellent time. Eventually even with frequently cleaning, there will be enough wear that major work will be required to keep it that way. With a 17 jeweled watch, wear is minimal with properly cleanings. The one exception is eventual wear of the mainspring barrel by the barrel arbor. This is why the 19 jewel watch with the barrel jeweled was sold. Twenty-one jewels involve using cap and olive jewels and conical pivots to reduce friction versus straight pivots and hole jewels. This is more for isochronism than anything (but not exclusively).

So the more jewels:
The better the isochronism
The better the timekeeping for decades/centuries with proper cleaning and minimal repair.

Still the watch needs to be cleaned and adjusted at proper intervals. I have a 21 jewel Sangamo from 1907. It was properly cleaned, overhauled, poised and trued about 8 years ago. Now I clean it about every 2 to 3 years , since I wear it 90% of the time. I have not had to repoise the balance and do minimal adjusting of the hairspring each time. It keeps time to within 7 seconds over six positions and to about 5 seconds per week. I do change the rate about four times a year due to the changing temperature.

Don