Vibrating a hairspring - would this even work?

[Geotex]

I’m interested in all the tools and techniques involved in this venture, but as a hobbyist I don’t think a full Luthy tool is in my future. I did find a lower-tech tool made by Swartchild that allows you to suspend the balance and hairspring on a transparent plate, under which you can place a watch that has the correct BPH so that its balance is visible and you can use that as a reference. I realized that I could just as easily suspend the hairspring on an iPhone screen, if I could find a video or a simulation to run as a reference. On the amazing web page by Bartosz Ciechanowski dedicated to the engineering and physics of the mechanical watch, there is a balance oscillation simulation that worked well. Here's a link:

https://ciechanow.ski/mechanical-watch/

I grabbed an unknown spare balance out of the parts box, suspended it from a pinch point a bit away from the pre-placed stud, and by adjusting the parameters of the simulation it turned out to have a periodicity of close to 0.4 seconds, which would make it an 18,000 BPH balance. I then adjusted the pinch point until the balance was matched to that specific rate in the simulation (see video). The rate of oscillation in the simulation can be changed to provide other BPH rates, so it could be useful if this would work.

My question is regarding the level of absolute precision required to place the stud, because the timing of a web-based simulation like this may not be exactly on the nose. The placement is certainly important to allow a full range of regulation, but knowing that the regulator will be used for the ultimate fine tuning, is a setup like this likely to be accurate enough to set a new hairspring into the functional zone?

Video of this setup:

https://www.youtube.com/shorts/WH58LR0AL_4

[nickelsilver]

You can certainly do it like that! You can even do it with a stopwatch just counting the beats of a suspended (but supported on lower pivot) balance, I've used that technique for odd beats like 20,222 or 19,444. Though in my case I have a Luthy tool, which makes it handy to set the balance in motion and adjust the length of the spring. With a flat hairspring you would generally stud it with a bit of extra stickout in case you need to let some out when it's in the actual watch. With an overcoil you really have to get it bang-on when vibrating as lengthening or shortening might mean the overcoil gets thrown off.

 

In any case you want your balance to stay synced with the reference balance (or video) for a good minute or you will be playing around a lot in the watch.

[Geotex]

Thanks for the info! I'll go ahead and give it a try with an actual balance needing a new hairspring. Here is the vibrating setup without the phone: