Balance staff replacement

clayb1970

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Jul 26, 2021
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Thanks for letting me join your extremely knowledgeable forum. I've recently purchased one of these pocket wathes which is a 10s size approx 38mm. I looked a some Ronda data and order a staff for the 764 series going of Rantff and some Ronda catalogues. I couldn't find any specific reference to the 729 so went by ligne and with etc. Basically I had a choice of two staffs. Any way on fitting I ran into problems with it not gripping on the balance spinning around and made a mistake of getting it stuck in the stake so it eventually broke. I've checked the diameters and there may be and slight difference. Any info would be helpful. I'll get back with the staff Ronda numbers although the differences seem to be just length rather the the balance seating rim diameter. Has anyone done one of these or can offer info on this top winder Cyma calbre. Thanks
 

Skutt50

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Mar 14, 2008
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Welcome to the forum.

I've recently purchased one of these pocket wathes
Do you mean Cyma 729? (When I googled it came up as a wrist watch........)

It sounds like you have the wrong staff and that it is too short....... Just make sure you don't have a busted end stone making the staff look too short. When a pivot breaks it sometimes takes the jewel(s) with it.

You should try to find the correct staff for the caliber of the movement. The size of the movement is not a good way to select a staff.
Generally there are signs or certain dimmensions that can be taken from the old staff to help in the selection process. Make sure your replacement staff has the same dimmensions as your old staff. If I am not sure I test fit before I rivet the staff permanently.

On some rare occatons when I can't find the correct staff there is one that is close and where some dimmensions are the same. It is one possibility to get one of these and to modify to fit the movement. If not there is always the option to cut a new staff from scratch but that is a more complicated story.
 

roughbarked

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Dec 2, 2016
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Apparently they all use the same staff. According to Ranfft.
Breguet hairspring
differences not known between 764, 766

family/generations:
hunter / open face (old designation) respectively
H= 3.85mm:
704,706 / 705,707 (17'''30): 3 train cocks
784,786 / 785,787 (17'''18): 1 train cock
796 / 797: bigger barrel
H= 5.05mm:
764,766 / 765,767 (17'''6): 3 train cocks
768 / 769: 3 train cocks, negative stem mechanism
734,774 / 735,775 (17'''7): 2 train cocks
736,776 / 737,777 (17'''7): 1 train cock
778 / 779: 1 train cock, negative stem mechanism.


This is a riveted staff. Your problem may be that you haven't riveted a staff before?
 

John Runciman

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Aug 13, 2003
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very important rule to follow when staff is the following. Always measure the old staff all the dimensions. Always helpful when ordering a staff to hopefully get the correct one. Then always measure the new staff compare make sure that everything is the same avoid unpleasant surprises later on.

order a staff for the 764 series going of Rantff and some Ronda catalogues. I couldn't find any specific reference to the 729 so went by ligne and with etc.
my confusion in my reading skills are we looking for a 764 or a 729? Then it's always nice if you would give us a picture of the watch so we are all on the same page talking about the same watch hopefully.

That I have a link to a site where you can look for balance staffs and I snipped out an image for the 764


Balancestaffs.com - cyma balance staff

staff 764.JPG
 

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