How to determine watch gear's diameter and number of teeth??

AmateurFixer

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Jun 16, 2021
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Hello,

Recently I was fixing a watch and notice that the 3rd wheel is missing. I tried looking for some parts from spare movements I had, but wasn't sure which gear size would fit in and would not alter the 4th wheel. I found the right wheel size after multiple trial and error, I just randomly pick a 3rd wheel and calculate the gear ratios, but it takes a lot of time. So I was wondering how watchmakers determine the gear and pinion's pitch/full diameter and number of teeth and leaves on them?

Any info would be much appreciated.

Thank you

Best,
Rus
 

Jerry Kieffer

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Hello,

Recently I was fixing a watch and notice that the 3rd wheel is missing. I tried looking for some parts from spare movements I had, but wasn't sure which gear size would fit in and would not alter the 4th wheel. I found the right wheel size after multiple trial and error, I just randomly pick a 3rd wheel and calculate the gear ratios, but it takes a lot of time. So I was wondering how watchmakers determine the gear and pinion's pitch/full diameter and number of teeth and leaves on them?

Any info would be much appreciated.

Thank you

Best,
Rus
Rus

Great question.

This type of information is generally calculated for one or all of three reasons as follows.

(1) For tooth count and approximate OD when existing examples are being considered. (Your question)

(2) When a replacement wheel or pinion is to be machined.

(3) When constructing a movement from bar stock.

While each is similar, each has their own special considerations. One example would be when constructing a movement, one quickly learns how inaccurate and impractical a Depthing tool can be for this size work .

To answer your question, I will respond to #1, but will elaborate on the other two on request.

(1) Measure the Pitch Diameter of the existing wheel and count the teeth per the attached sketch.

(2) Divide the pitch diameter in mm by the number of teeth that will equal the tooth module of both the existing wheel and missing wheel.

(3) Measuring from the center of the missing wheel/pinion pivot hole to the pitch diameter of the existing wheel or pinion and multiply by two giving the missing pitch diameter. This can be done any number of ways, but the most accurate method I have used is with a small milling machine per two attached photos. As shown in the photos, a sharp point is used under optics from point to point utilizing the hand wheel calibration as a micrometer. If you describe how you are equipped , I my be able to make a suggestion.

(4) By dividing the pitch diameter of the missing wheel or pinion in mm by the module will give the missing wheel/pinion tooth count.

Jerry Kieffer

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Last edited:

AmateurFixer

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Hello Jeff,

This is very interesting, I remember reading about this a couple of days ago, but how will I know the missing wheel's pitch diameter if I have not found one that will fit in? I also read that you could use the gear ratio and estimate the number of teeth in the wheel that you will need, I find that a little bit tricky to do, especially counting the number of teeth and leaves in the wheels. Is this true?

Also, out of curiosity, when making a movement from scratch, how does the watchmaker decide what diameter the wheels should be, how many teeth there will be, size of the barrel, size of the main plate and etc? Is there like a standard issued chart that the watchmaker can follow when designing a movement?

This is very interesting to me btw, is there any book(s) you know that I can read about this in greater detail?

Thanks again for the info.

Best,
Rus
 

gmorse

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Hi Rus,
This is very interesting to me btw, is there any book(s) you know that I can read about this in greater detail?
The book 'Watchmaking' by George Daniels is a good source, it explains in some detail the processes of designing a watch, as well as the techniques necessary to make everything. If you want to get into the practicalities of gearing, 'Wheel and Pinion Cutting in Horology' by J. Malcom Wild is excellent, it covers the theory as well as the machining.

Regards,

Graham
 

AmateurFixer

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Hi Graham,

I've heard of those books and have been saving up to get them. I read parts of the Watchmaking by George Daniels and it is very interesting

Thanks

Best,
Russell
 

Jerry Kieffer

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May 31, 2005
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Hello Jeff,

This is very interesting, I remember reading about this a couple of days ago, but how will I know the missing wheel's pitch diameter if I have not found one that will fit in? I also read that you could use the gear ratio and estimate the number of teeth in the wheel that you will need, I find that a little bit tricky to do, especially counting the number of teeth and leaves in the wheels. Is this true?

Also, out of curiosity, when making a movement from scratch, how does the watchmaker decide what diameter the wheels should be, how many teeth there will be, size of the barrel, size of the main plate and etc? Is there like a standard issued chart that the watchmaker can follow when designing a movement?

This is very interesting to me btw, is there any book(s) you know that I can read about this in greater detail?

Thanks again for the info.

Best,
Rus
Rus
Calculating the pitch diameter of the missing wheel or pinion is covered in item #3 post #2

Interestingly, I have only met three people who have successfully constructed movements where each part was machined from bar stock. Even of more interest, two did not consider themselves watchmakers nor were they certified watchmakers by anyone.

Of course, movement construction is more complicated than can be covered here. Those who I have met who have accomplished this, did not use charts or utilize exact copies of original parts as they wished to be able to say the design or arrangement was of their own. After spending hundreds or thousands of hours on a project, little accomplishment is realized if you copy the work of others.

I suspect each person who has ventured into this has had their own approach that was at the very least slightly different from each other. I also suspect those who have developed the capabilities and skill levels to accomplish a properly functioning movement will wish to do things their own way regardless of what others have done.

My personal method of starting has been to utilize a 18000 beat per hour balance that allows the calculation of the various wheels and pinions in the train. However when doing your own thing, calculation is often thrown to the wind in favor of trial and error to achieve the highest level performance.

Building a movement from bar stock is a very long and hard road requiring the utmost determination.

Years ago, I built a very basic 16s, 19 jewel movement from bar stock for educational purposes. It is my personal feeling that every student who spends time and money has a right to see work examples of everything they may encounter from an Instructor. A completed and properly functioning movement should cover all of the bases for those interested in watch movements. The movement is mounted in a container that allows a student to inspect and evaluate almost all parts.

For those who have a interest in machining parts for movement repair or movement construction, NAWCC workshops WS-117, WS-119 and WS-120 covers all of the procedures utilized in the Construction of the movement mentioned above.

In addition, one of the things also covered is machining cutters that duplicate existing tooth forms. Unless I have missed it I have not seen this covered in any of the publications on wheel and pinion cutting.

While I see your from Canada, the School is located in Columbia , PA USA and has had many Canadian students over the years.

However, the School has not yet resumed classes from the Virus shut down, but I think perspective students are getting on a list to be notified when classes resume.

Jerry Kieffer
 

DeweyC

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Hi Rus,


The book 'Watchmaking' by George Daniels is a good source, it explains in some detail the processes of designing a watch, as well as the techniques necessary to make everything. If you want to get into the practicalities of gearing, 'Wheel and Pinion Cutting in Horology' by J. Malcom Wild is excellent, it covers the theory as well as the machining.

Regards,

Graham
Graham,

I agree; especially about the Wild book (not the pamphlet). The Wilder book gives actual recipes for how to accomplish the job and I would recommend it over Daniels who often left Easter Eggs that you had to find.

Not to mention the ubiquitous You Tubes on any subject that are available today. FOr anyone who wants to see professional horological machining in action, I recommend Steffen Gotteswinter:

 

gmorse

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Hi Dewey,
I would recommend it over Daniels who often left Easter Eggs that you had to find.
I agree on both counts, although I do know of someone who's made a tourbillon watch following George's descriptions in his book.

Regards,

Graham
 

Jerry Kieffer

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Until you have trained yourself to think for yourself and built the confidence to act on your thoughts, not much will happen especially watch movement construction.
Having only ever had a brief discussion with George Daniels, I suspect that his publications were purposely written the way they are written.

Those who have equipped themselves and developed the skills to build a movement, will get the general idea and wish to apply their own solutions to the various challenges that arise.

Jerry Kieffer
 

DeweyC

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Hi Dewey,


I agree on both counts, although I do know of someone who's made a tourbillon watch following George's descriptions in his book.

Regards,

Graham
Graham,

I spent the evening with him, Tony Randall, Jonathan Betts and Catherine Cardinale at the Earnshaw Symposium at Harvard in 93. He had no patience for those who did not know what they were talking about or those who just wanted bragging rights. He made it clear his writing was for those would commit to figuring it out.

Have no idea how I got assigned to that table, but I was one observant puppy! Kept MY mouth shut and just listened.
 

gmorse

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Hi Dewey,

That must have been quite a conversation to listen in to! I never had the privilege of meeting George, but I know he could be prickly, and certainly didn't suffer fools gladly. Jonathan on the other hand is far more approachable, (he's also technically a member of my BHI branch and has delivered talks to us on several occasions).

Regards,

Graham
 

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