Can someone tell me the problems and or symptoms associated with a Movement that has a balance wheel out of Poise. Any long term effects on the jewels or staff? Thanks for any replies.

Frank

Frank Juchniewicz

Frank,

I know very little about the dynamics of the balance but I believe the watch would not maintain the same rate in different positions.

John D. Duvall
Vice President, Education

John's right.... A balance wheel that's not "balanced," will produce different rates in different positions, and those will vary depending on balance amplitude. Obviously, the degree of rate error is directly proportional to the degree of poise error.

After an extended period of time, a balance that is badly out of poise will tend to wear the staff pivots in an elliptical shape, but that takes a long, long time.

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Steve Maddox
Past President, NAWCC Chapter #62
North Little Rock, Arkansas
IHC Charter Member 49

John, Steve

Thanks for the information.I just re-staffed one of my aquisitions,a 18s Elgin,when I checked the Poise of the balance wheel I was surprised how far out it was. There is an equal amount of screws in counter positions around the wheel.They all seem to match as far as size goes,judging only by eye.But laid on the poising tool,there is a pronounced imbalance.Poised checked with only the wheel and roller attached to the staff.

Frank Juchniewicz

Frank,

Once you get it poised, the fun starts! Chances are, the watch will run either too fast or too slow when you get it back together. You must then add or subtract weight in identical amounts or the watch will be out of poise again.

I've never adjusted a watch for heat and cold yet but if someone has modified the factory weight adjustments at the cut end of a compensated balance, you would have even more work to get it timed correctly.

John D. Duvall
Vice President, Education

John,thank you for that information.This would be my first time tampering with screws on the balance rim.I have been lucky, in sofar as I have never had to put a balance wheel in poise after changing a staff,usually when I checked it, it would be in poise(not that I have done all that many).What I think I will do is to study-up on the balance wheel/screw relationship and exactly how they interact,before getting into that problem.I like to know what I am doing,before I do it,so there are no surprises waiting for me.

Frank Juchniewicz

Frank,

Before adding or removing weight from or to any of the balance screws, I'd recommend swapping some of the screws from one side to the other to see if you can improve the overall poise. That might seem like a lot of trouble, but it really is one of the better ways to go about the problem. It has the great advantage of not altering the overall moment of inertia of the wheel, which means that you should be able to avoid having to use timing washers, etc., to bring the wheel to rate again.

BTW -- Most American pocket watches (of quality manufacture) will have a few balance screws that are "hollowed" out on the bottom to reduce their weight, without altering their appearance (or more importantly, their aerodynamic qualities). That job is accomplished with a "balance screw undercutter," and you'll need to look for a set of those if you plan to do any serious, high-quality watch work.

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SM

Steve,thank you again for the advice. I took a look at the balance again,and there are,besides the one size screws,some screws that I would call 1/4 size. They being about 1/4 the size of the larger screws. Would I be correct in assuming that they are a"fine adjustment" to the wheel. And I have one more question,as regards the balance wheel in question. Assuming, who ever worked on this before had the balance poised, what would cause it to go out of poise.

That last question sounds like I just set myself up

Frank Juchniewicz

Frank,

Removing an old staff by driving it out instead of cutting it out with a lathe, will enlarge the hole in the spoke arm. As the hole enlarges, the metal around it stretches in the weakest point, and that allows the spoke to bend in one direction or the other. Needless to say, that's a major cause of poise errors. Other causes can include staffs whose rivets fail to expand evenly all the way around, etc.

It's rare to be able to change a staff (especially a riveted one) without having to make numerous corrections to the balance wheel, including poise adjustments. Obviously, the first thing one needs to do is use a wheel truing caliper to make certain the wheel is as perfectly flat and as perfectly round as possible. Once that's accomplished, the poise should be checked, and perfected as necessary. It's almost unbelievable how critical the poise of a balance wheel really is. Just the weight of an eyelash will throw the wheel badly out of poise, and result in positional timing errors of several minutes per day.

It is not an exaggeration to say that whenever a wheel is straightened or manipulated in ANY way, the poise will always be affected. If a wheel is made as perfectly round and flat as possible, then perfectly poised, and its subsequently bent, even the most expert work in making it as nearly round and flat again as possible, will ALWAYS leave some residual poise errors. Regardless of what work is done to a balance wheel, the last thing should always be a final check of the poise, and correction as necessary.

As I've noted previously, intentional poise alterations can be made to adjust for certain positional errors, but that's generally not a good practice. The reason is that poise errors that result in a positional gain when the balance amplitude is high, will reverse and produce a positional loss when the balance amplitude falls as the watch winds down. In automatic, or self-winding watches, where the power remains more constant through the course of daily wear, poise alterations are less likely to produce bad results, but it still isn't generally considered a good practice. In 99.9% of watches, the ideal situation is to have the balance wheel as perfectly poised as possible.

The small screws in your balance rim were probably necessary in order to bring the watch to time with a particular hairspring. In my experiences, I've found screws of that type used more frequently in Elgins than in any other brand, but I know that other brands did occasionally use them as well, when circumstances warranted.

As always, I hope this helps!

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SM

Steve

Thanks for taking the time to follow-up on my querry. You have been a great help. It has pointed me in the right direction.


I find this is a great site to get expert advice on anything to do with watches.


Frank

Frank Juchniewicz