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BGF 866 movement - timing - beat error

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I've just completed a clean and re-build of this movement. The hair spring was a little messed uo but managed to get it back into reasonable shape. I adjusted the hair spring collet to get the roller directly inbetween the banking pins and facing right at the pallet fork pivot hole before assembly.

You can see the tomegrapher readings. This is the best I can get and cannot improve the beat error. These are not sophisticated movements of course but could I improve it? Note I have the timegrapher set at 44 degrees for lift angle which I beleive to be correct for this movement.

Thoughts appreciated.





Edited by Edifred
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Does your watch have a fixed stud holder?  or

mobile stud carrier?  otherwise called beat adjustor arm.  no need to adjust hairspring collet for BE if your watch is a latter vesion, just move the adjustor arm.

 In old   ( fixed stud holder )  versions, smallest reshaping of hairspring coil , throws the balance complete out of beat, just a tweak and its out of beat.  Yours look fixed stud, shouldn't expect nice BE out of it.


Edited by Nucejoe
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Yah- looks like the fixed stud kind. I’ve gone a handfull of Baumgartners with both fixed and moveable studs. Jon’s posts on these are everything you need to know. I’ll second the above comments- don’t expect nice straight lines from these, timegraphs can give funny readings from pin levers and they were cheap to begin with. You’re close to 2ms which many find acceptable. Does it keep time? is maybe the next best question…

Yours looks to be in fine condition- pivot holes look round and these respond well to modern oils- I don’t think they saw much lubrication when they were new…

If you’re using this as an experiment to test your skills- as I recall there’s no impulse jewel but can you adjust the metal roller thingie to reduce the beat error? I never tried it…Jon also shows how you can put a tiny bit of oil on the face of it to improve things a bit.


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