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Discussion in 'American Pocket Watches' started by Jskirk, Nov 8, 2019.
If a watch has a cut balance wheel, does that always mean it is adjusted to temperature?
The folks in the Watch Repair forum can do a better job answering your question, but I've attached a page from a Navy book, i.e. Navy, Instrumentman 1 & C. that gives you the basics on how a bimetallic balance wheel functions.
Although, a watch may have a cut bimetallic balance wheel, it is not necessarily adjusted to the proper temperature. The screws in balance wheel are used to fine tune the balance to temperature as described in the attached page.
The Hamilton, 18 size, 924, has a cut balance wheel, but is not adjusted to temperature per factory specifications.
A bimetallic cut balance wheel is compensated for temperature but not necessarily adjusted to temperature.
In addition to the excellent source Robert posted, Olof Ohlson describes the compensating balance and method of temperature adjustments in Helpful Information for Watchmakers. The excerpt below is from the 3rd edition, published in 1918, but this booklet was published in a variety of editions for many years.
The entirety of the 3rd edition is available online, and is an excellent resource for studying primary watchmaking principles:
Helpful Information for Watchmakers (3rd Edition, 1918) | PWDB Digital Archive
From the Time and Timing Section:
“One difficulty encountered in the first attempt to make accurate timepieces was the variation in the dimensions of metals caused by difference in temperature. All metals, with the exception of recently discovered alloy of steel and nickel (64 parts of steel and 36 of nickel), have the property of expanding with increase of temperature, - the different metals showing a somewhat different rate of change. As the length of the pendulum is the all-important factor in the timing of clocks, so also is the diameter of the balance and the length and resiliency of the hairspring in a watch. It is absolutely necessary to devise some means of compensating for changes in temperature before a reliable timepiece of either form can be made. So far as this problem applies to clocks, the mercury pendulum proves to be a very satisfactory solution, at least so far as accuracy is concerned. The bob of this pendulum is composed of one or more tubes of glass or iron, and these tubes are filled with mercury to a certain height. When of proper dimensions, the expansion and contraction of this column of mercury rises or lowers its mass to exactly compensate for the change in the length of the pendulum rod due to variations in the temperature. This method, although very satisfactory for clocks, cannot, of course, be applied to watches, for obvious reasons, but for this purpose we make use of the property of the metals alluded to above, namely, the difference in the ratio of expansion in different metals. Brass, for example, expands more than steel from a given increase in temperature, so in making a compensating balance it is common to use steel for the arms and the inside of the rim, and brass for the outside of the rim, the brass being fused to the steel, so as to make a perfect union. This rim is cut off in two places, as shown in the illustration, so as to make each half of the rim free to bend, as it naturally will tend to do, as a result from any change in temperature. A number of holes are drilled radially through this bi-metallic rim, and these holes are tapped to receive the balance screws.
Usually about twice as many holes are made in the rim as the number of screws used in the balance; this is done to give opportunity for moving the screws in the final adjusting to temperatures. The object in using screws in the balance rim is twofold: first, to provide the necessary weight (mass) in the rim, and second, to have this weight movable for temperature adjustments, as stated above.
We will now understand from what has been said that when a compensating balance is exposed to a higher temperature, every part of it expands, or grows larger, but as a result of the combination of the two metals in the rim, and the ends of the rim being free to move, each half of the rim will curve inward, carrying its weight toward the center of the balance, and thus compensate for the lengthening of the arms and the weakening of the hairspring. If a balance is exposed to a lower temperature, the action will, of course, be in the opposite direction.
When a watch is to be adjusted to temperatures, it is run 24 hours, dial up, in a temperature of 90° F., and its rate compared with a standard. It is then run 24 hours, dial up, in a temperature of 40° F. If it shows a gain in the 40° temperature, as compared with the running in the 90°, it is said to be under-compensated. This is remedied by moving some screws nearer the free ends of the rim. This will, of course, result in a greater compensating effect, because the screws which we move nearer the ends of the rim must travel a greater distance in or out in relation to the center of the balance when the balance is exposed to changes of temperature. After the screws have been moved, the movement is tried again the same length of time, and so on, until it runs the same in both temperatures. When a screw is moved in one side of the balance, it is, of course, necessary that the corresponding screw in the other side should be moved the same. A modern compensation balance, combined with a correctly proportioned steel Breguet hairspring, which has been hardened and tempered in form, constitute a time-measuring device of marvelous accuracy.”
No, a cut balance is not any guarantee a watch was adjusted to temperature. The Hamilton 976 uses the same balance as the 974 but the 976 was sold as unadjusted. Plus, there are many watches that were made to look like expensive watches but in fact were extremely inferior as timekeepers.
All adjustments entailed moving the masses around the balance rim. For temperature, this was done by distributing the mass in
reference to the free end of the balance arm to equalize the rate at low and high temp.
For positional adjustment, the masses would be altered to equalize the rates in the various positions the watch could be found.
For a Hamilton RR watch, it could take 3 months to adjust the watch. For something like the 976, it might be a week. It is the time required to adjust a watch that accounts for the bulk of the price difference. With the exception of one jewel, the 976 is constructed from parts that very well could have wound up in a 974.
So temperature and positional adjustments are all achieved with the balance wheel?
So if you have a pile of different balance wheels , how can you tell which ones are or have been adjusted for position. I think the presence of the bi metal shows that it is temperature compensated?
You cannot without putting them into a watch and checking its performance. And you are onto something with your observation about both adjustments being achieved via the balance masses.
In watches,temp comp is secondary to positional performance because it is kept at a pretty consistent temp (on wrist or in pocket). In navigational pieces (chronometers and deck watches), it is positional adjustment which is secondary since the instrument will not be carried on the person exposing it to wide temp ranges and is kept in one position (dial up).
When this was first posted I was going to move this to watch repair but the OP was asking
and educational question rather than a repair question. They asked
"If a watch has a cut balance wheel, does that always mean it is adjusted to temperature?"
I have been asked to move it to repair but I think the question has been answered here
in an intelligent manner already and I do believe it's relevant to understanding American Pocket watches.
Thanks Rob and thanks to others who posted, I really appreciate the input, i read through this a few times and read through the attached links. This helped me understand that the balance is the brain of the watch, and is the principal part of a movement and how much it affects the precision. I really look more closely at regulators and the balance when looking at watches.