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Source of Large Positional Variation?


Giannifive
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I've just serviced a previously running Seagull ST36, as part of Level 2 of Mark's watch repair course.  Prior to servicing, the rate in all positions was between -6 and +6 s/d and was steady for each position.  After servicing, there is a large positional variation between dial-up and dial-down.  In addition, in one position the rate takes one of two distinct values.

Dial-up, the rate is about +30 s/d.  Dial-down, it starts at -10, but will eventually switch to +30.  I find that if I tap the movement with my finger in dial-down, it will immediately switch rates from -10 to +30.  In all other positions the rate is a steady +30 or so, and the amplitude in all cases is between 270 and 290.  Interestingly, when the rate switches from -10 to +30 the timegrapher shows the beat error changing from 0.8ms to 0.1, although I don't know if this is an artifact.

What could be the source of this behavior?  Could it be improper oiling of the balance jewels?  I've had difficulty getting them perfectly oiled as per Mark's instruction, even after several attempts.  I can see a circle of oil in the upper jewel, although the width is a bit below Mark's recommended 50%.  The lower jewel appears to be slightly over-oiled, with oil extending to the edges of the jewel for about half the circumference.

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8 minutes ago, Giannifive said:

I've just serviced a previously running Seagull ST36, as part of Level 2 of Mark's watch repair course.  Prior to servicing, the rate in all positions was between -6 and +6 s/d and was steady for each position.  After servicing, there is a large positional variation between dial-up and dial-down.  In addition, in one position the rate takes one of two distinct values.

Dial-up, the rate is about +30 s/d.  Dial-down, it starts at -10, but will eventually switch to +30.  I find that if I tap the movement with my finger in dial-down, it will immediately switch rates from -10 to +30.  In all other positions the rate is a steady +30 or so, and the amplitude in all cases is between 270 and 290.  Interestingly, when the rate switches from -10 to +30 the timegrapher shows the beat error changing from 0.8ms to 0.1, although I don't know if this is an artifact.

What could be the source of this behavior?  Could it be improper oiling of the balance jewels?  I've had difficulty getting them perfectly oiled as per Mark's instruction, even after several attempts.  I can see a circle of oil in the upper jewel, although the width is a bit below Mark's recommended 50%.  The lower jewel appears to be slightly over-oiled, with oil extending to the edges of the jewel for about half the circumference.

Magnetism could be the issue. But more likely some issue with a pivot. Tapping and the watch rate changes might be a pivot slipping back into the jewel. As well, you may have a sticky hairspring and the tap releases it. Is it magnetized or perhaps some oil on the hairspring. Have a close look or videotape in slowmo with your iPhone and have a look. 

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Thanks for the suggestions.  Demagnetizing didn't have an effect, so I cleaned the balance again.  I used One Dip this time instead of naphtha like I had been using, and that did the trick.  The hairspring must not have been fully clean.

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1 hour ago, Giannifive said:

Thanks for the suggestions.  Demagnetizing didn't have an effect, so I cleaned the balance again.  I used One Dip this time instead of naphtha like I had been using, and that did the trick.  The hairspring must not have been fully clean.

Good job. Amazing how a gummed up hairspring impacts positional error

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1 hour ago, Giannifive said:

I used One Dip this time instead of naphtha like I had been using, and that did the trick.  The hairspring must not have been fully clean.

just to be clear rinsing solved all your problems?

then are you really using naphtha or lighter fluid?

then also helpful if you give us a picture of your timing machine results because sometimes we can see things in the graphical display that you might not see.

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