FHF 96-4 erratic rate and amplitude after service

[SPIGGOTT]

I am new to the hobby and only on my 4th service of a watch.  The first 3 have gone without any issues.

The latest one being a FHF ST96-4 movement. 

I put it on the timegrapher (Weishi 1900) to check it after servicing and to regulate.  All looked good at first then i adjusted the rate and beat error as it was loosing a little.  During this the balance wheel stopped (i did not touch it), so i move the levers back and it started again with a very poor amplitude.   Small adjustment and all started working again.

When it runs now there is no consistency in the rate or amplitude.  can go from -6 to -36 every few seconds.  the amplitude also changes from 284 to 295. The Beat error is 0.0ms.  The change is not dramatic like -6 to -36 in one go but runs steady for about 20 seconds then changes to 0 gain for 4-5 seconds when it resumes the rate goes lower.  Odd is at some times it gains and goes back to -6 as though it was resetting itself.

 

This is the output from the timegrapher.   I am assuming at this point it is an issue with the balance wheel / CAP Jewels???

 

 

 

Below is another one i have done showing normal results after regulating.

[Nucejoe]

Periodic eraticity if correspondes to the period of a gear in the train, either on its own teeth or pinion or both ,imperfect jewel or bent/damage arbour, damage may not be noticable under normal eye loupe magnification. 

 

 

[SPIGGOTT]

Since the erratic nature did not show before I started to regulate, I figure it must have something to do with the balance wheel.   Just took it out to inspect under microscope but could not see any damage to pins, spring or impulse pin.

I have a spare movement (not serviced) with a complete balance.  Swapped it out and put back on timegrapher.  All looks ok.  -18s/d, 251 amp and 0.5ms beat error. Nice consistent reading.

 

Again, I can not see any difference or faults when comparing both of them under a microscope.  

[JohnR725]

53 minutes ago, SPIGGOTT said:

Again, I can not see any difference or faults when comparing both of them under a microscope

Often times people with microscopes can see the dust on the pine needles in the forest but can't see the trees.

Then interesting on the timing machine you appear to have two separate lift angles?

Then what happens if you rotate the microphone so the crown is facing down what is that look like On the timing machine?

 

[Nucejoe]

2 hours ago, SPIGGOTT said:

Since the erratic nature did not show before I started to regulate, I figure it must have something to do with the balance wheel.   

Imperfections across the terminal curve of hairspring, might change its coil configuration, causing intermitent sticking, fouling ....etc. 

Genterate more data please in various positions.

 

[Nucejoe]

2 hours ago, Nucejoe said:

Imperfections across the terminal curve of hairspring, might change its coil configuration, causing intermitent sticking, fouling ....etc. 

Genterate more data please in various positions.

 

So configuration of the coil might have changed as you moved the regulator arm, unlevel, coning so on.

Have you checked coil levelness from side view?

[Colditz]

I would check the balance with a poising tool this will show any irregularity with the arbors and any imbalance.

[SPIGGOTT]

Thanks everyone for the guidance.  I figured out the issue after watching some of Mark’s tutorials on the Unitas 6489.

He noticed that after servicing a new movement a few times he had the same issue with the balance.   It appears that it was not the balance at all but a few marks where it attaches to the main plate.  Basically screwdriver twists in the mainplate that lifted the balance slightly.

so when screwed down it was too tight and pushing against the cap jewels and springs.  This is why it was erratic. Must have put some further down pressure when I turned the regulator arms.

 

 

 

 

[jdm]

1 hour ago, SPIGGOTT said:

when screwed down it was too tight and pushing against the cap jewels and springs. 

That is called endshake, very important to be right at least on the balance and escapement.

[SPIGGOTT]

what a difference a day makes....