Universal Geneve 42: Rate increases with amplitude

[patchwerk]

I am servicing a UG42 in pretty good condition. After cleaning and oiling the watch runs great...except that the rate changes over the course of the power reserve rather than staying relatively stable. Also, it goes up with amplitude which is the opposite of what I am used to. Usually rate goes down with amplitude.

What can cause this?

I have charted the rate at different parts of the wind with the corresponding amplitude to demonstrate. At near full wind it runs with 305 degrees and +44 seconds. At near end of the power reserve at 200ish the watch is close to 0 seconds. What with the balance wheel/escapement could be causing this? How do I make it more stable?

Edited October 8, 2020 by patchwerk
typo

[nickelsilver]

First thing to check is the gap between the hairspring curb pins, which should be equal to roughly twice the hairspring thickness. Then you must see that the hairspring is centered in the pins with the balance at rest.

 

What can happen is the hairspring gets bumped so that it is in contact with a pin, then as amplitude goes up it gradually pulls away during part of the vibration, spending more and more time away from the pin. If the gap is large the effect is greater.

 

Also, the hairspring must be level and well centered both overall and at the collet. In high precision timing sometimes a very slight move of the spring at the collet can give a difference of 10 seconds or so in isochronal error (or adjustment).

[Nucejoe]

Are you set up to Vid a close up  of H/S when running at high amplitude?

[JohnR725]

2 hours ago, nickelsilver said:

First thing to check is the gap between the hairspring curb pins, which should be equal to roughly twice the hairspring thickness. Then you must see that the hairspring is centered in the pins with the balance at rest.

it probably depends upon which reference book you're reading. then the particular book I'm looking at its describes slightly differently in different locations. for a flat hairspring reduced as far as possible without however gripping the hairspring. then of course the hairspring has to be centered between the pins. Which is hard to see if that their super close together. In another part of the book it comments for flat springs it should be as small as possible for example of may be made equal to the thickness of the hairspring itself. Then in over coil spring should have no clearance but the pins must not grab it.

 

[patchwerk]

14 hours ago, Nucejoe said:

Are you set up to Vid a close up  of H/S when running at high amplitude?

Here are vids at almost full wind.

Edited October 8, 2020 by patchwerk

[Nucejoe]

8 hours ago, patchwerk said:

Here are vids at almost full wind.

 

Video Oct 08, 7 21 24 PM.mov 17.8 MB · 2 downloads Video Oct 08, 7 20 45 PM.mov 28.37 MB · 3 downloads

Sorry buddy, can't open the vids, possibly or perhaps as usual domestic net problem here, thats actually good as real knowlegable members will take a look.

[praezis]

Regarding the high initial amplitude and linear change of rate w/ amplitude I have a suspicion that the mainspring is too strong and too short.

With a pin-gap-issue I would expect more abrupt changes in the rate-amplitude graph.

Frank

Edited October 9, 2020 by praezis