Roger - Got it! Watched Chris Abell's video and another video (among other watch repair videos) showing a hairspring being vibrated on a digital vibrator.

On the digital vibrator, the balance was swung and after 15-20 seconds it settled into a 18003 bph rate. For the next 80 seconds the balance held that beat rate even though the swing arc kept getting shorter and shorter and shorter (reducing amplitude). Quite convincing!

Now for the final question:

Will the regulator pins in the watch contact the hairspring in about the same location as it was clamped in the machine . . .

and do the regulator pins effectively determine the hairspring length in the watch (I assume they do) . . .

and knowing that the regulator pins must be a slip fit over the hairspring, is the effective hairspring length changed during the fraction of time the hairspring is not contacting either regulator pin (I assume it is)?

I guess that's actually three questions . . .

And finally, I always heard the term 'vibrating the hairspring', when actually it is 'vibrating the hairspring and balance wheel assembly' to determine it's natural resonant frequency at a given hairspring length. Right?

That hairspring - the heart of a well running watch - the little devil!

Joe,

As far as nomenclature, I have always heard it stated as vibrating the hairspring. Not sure if there is a more technically accurate term. The idea is to set the regulator in the middle and use the clamping position from the machine so that the regulator pins are at that point in the watch. Yes, there is a timing issue as the hairspring moves from one pin to the other. It is actually an adjustment that can be made. Closing the pins speeds up the watch, opening them slows it down, BUT that is not a primary adjustment for timing purposes and great care must be taken when working around these pins and the hairspring. There are entire books dedicated to watch timing alone.

Thanks Roger. The term 'vibrating the hairspring' is not totally self-explanatory, is it? Now I know what the process is. Thanks again.

This has been quite a thread. A lot has been learned - at least by me. I originally simply tried to answer Paul's actual question on how to safely stop a balance wheel for whatever reason he asked it. This is something I have done routinely in the past when stopping and starting a watch to sync it to the time standard. I realized the risks in doing it, I felt I had developed a reasonably safe method that I could handle, and I never had a problem. I still feel I can safely handle stopping a balance wheel using my method.

However, I don't think I am going to be stopping a balance wheel in the future. There have been several good options (and reasons not to stop the wheel) laid out in this thread which I am eager to try. I now have better options to explore thanks to everyone's input.

What I didn't realize is that by offering my method (which is inherently risky, and I was aware of that whenever I did it) to others, that they may not fully appreciate the risk they are taking. They might think it is perfectly safe because someone else who they presume to be knowledgable (me, and I'm not) has been doing it with no problems (up to this point in time, anyway).

I shouldn't be offering options to others which may turn out disasterous for them.

Thanks, everybody, for getting me up to speed on this issue, especially what to say to who, when and where.

In general terms, a properly timed Hair spring-Balance wheel assembly is "vibrated" so that the forces to coil and recoil the hair spring are "in balance" with the weight and moment of inertia of the balance wheel. This causes the hair spring/wheel assembly to "Oscillate" (That is the correct definition) at the desired Beat/hour speed of the watch (16,200 for "slow train", and 18,000 for "fast train" movements).

The oscillation involved is no different than a tuning fork reacting to a strike. You can hear the amplitude ("loudness") slowly go down as the subsiding energy of oscillation reduces the amplitude of the fork arms vibration, BUT there is NO CHANGE in the pitch (frequency) of the sound.

So, with oscillating balance wheels, the same applies in an "ideal" * situation, as the power of the train and escapement system goes down, so will the amplitude (arc of rotation) of the balance wheel, BUT, the "Beat goes on" at 18,000 until it stops completely.

* Sadly, the friction in watches will make this relationship a little "less than ideal", so as watches get dirty and mainsprings get tired, the watch will run faster or slower depending on the circumstances of its condition.