Changing BPH from 21600 to 18000

[ftwizard]

I have a Ronda 1217-21 with a damaged balance. I have a spare 1213 movement with a good balance, but it is a 18000 mph movement. The 1217-21 is 21600.

Is the escape wheel the only other part I need to change to complete the change to 18000.

[Tiktok]

Presuming it's the same movement just a different train count and the parts will fit I would think all of the train wheel will need changing and possibly the barrel, this can easily be checked by counting the teeth on all of the wheels and pinions to see if they are the same number. The pallet may need changing as well.

it is possible to time a watch up perfectly on a timing machine with a wrong traincount wheel in and the watch will gain or loose time even though the timing machine shows perfect in all positions.

[matabog]

http://watchguy.co.uk/repair-heuer-autavia-buren-12/

[ftwizard]

That's the problem I've been chasing. The timegrapher says it's running fast, but it loses about 10 minutes an hour. I finally realised that the balance is from a faster beat movement. Most of the parts are interchangable, apart from the balance and escape wheel.


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[matabog]

change the 4th wheel, see what happens!

[matabog]

then set your timegrapher to the current escapement frequency. then watch how the watch indicates the time.

[ftwizard]

Using the Borel charts, it seems I need to change the escape and fourth wheel. This is good learning for me.


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[matabog]

please count the teeth on the escape wheels,I think they have both 15, in which case, it makes no sense to change them.

 

If you change the escape wheel, though, change the pallets, too - the escape wheel and pallets usually are paired (IMHO small adjustements are made for each pair)

Edited April 3, 2017 by matabog

[Tiktok]

If you have a wheel with the wrong amount of teeth/pinions fitted (wheel from different bph) then even if you time it perfect in all positions the watch will gain or loose.

When you time up a watch say at 18000bph the microphone is listening to the escapement and in theory will oscillate at 18000 times an hour.

If you have a wrong wheel fitted the ratio of the other wheels are turning at the wrong rate meaning the wheels/hands aren't turning at the correct speed, although the timing machine says it's timed up it is only actually confirming the escapement is running bang on at 18000bph because that's all the timing machine can listen too.

If you count the teeth on all of the wheels and pinion there is a fotmula to work out the beats per hour, if your answer is not 18000 or 21600 then you have a wrong wheel fitted, it's just a matter of working out which one.

Hope your good at maths

[ftwizard]

Thanks. That's what I'm gonna do. Compare the wheel train of each movement and see where the difference is.


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[ftwizard]

OK. The only difference was in the fourth wheel, as suggested above. Around 60 teeth on the 18000, and 76 on the 21600.

All other wheels and pinions were the same. I'm a bit confused as to why the pinions on the escape wheels were the same on both, as they have to mesh with the fourth wheel. Also, Borel list them as incompatible. Maybe someone had been doing a bit of swapping sometime in the past.

It certainly runs much better now, just need to check if it runs to time as well.