Understanding movements

Thread: Understanding movements

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  1. #1
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    Understanding movements

    Hi all. I'm very new to watches and I'm trying to understand how to calculate the size and ratios for the wheels. I'm a member of the BHI and will be taking all the courses (I don't plan to make money from watches, I plan for them to be a diversion from daily work), and I have read George Daniels book.

    I guess what I'm asking is which way do you work? An 18,000 VBH escapement with a 15 tooth escapement wheel will mean that wheel turns at 20rpm right? From that I could work backwards and design a train. The design of the mechanics is what I find fascinating.

    I have built a basic workshop - lathe, mill, micro CNC for cutting wheels, and I'm learning the basics of metalwork. I have 20 years before I retire, maybe more. At that point I want something to do that occupies my hands and my mind. Pocket watches and motorcycles are it

    I'm from the UK. I've spoken to a few repairers and one clock maker but they thought I was competition so weren't entirely friendly.

    Cheers.

  2. #2
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    Re: Understanding movements

    Quote Originally Posted by P1505C View Post

    ...I'm trying to understand how to calculate the size and ratios for the wheels. *

    ...I guess what I'm asking is which way do you work? **

    ...An 18,000 VBH escapement with a 15 tooth escapement wheel will mean that wheel turns at 20rpm right? From that I could work backwards and design a train. ***

    I'm from the UK. I've spoken to a few repairers and one clock maker but they thought I was competition so weren't entirely friendly. ****
    * Ratios according to parameters in your display (h, m, s, day, date, moon, etc) and train parameters such as power source, power reserve, oscillator frequency...among others. Size, in part, takes into consideration the target size for the finished product...but also must take into consideration the power source and transmission as it relates to arm/torque...and so actual point of contact between each tooth...and transmission of power through the entire arc of contact.

    **It depends on what your objective is. Work with an existing design and resolve issues such as accuracy, power reserve, servicability, scale up/down...or design something completely new to register the passage of time...

    ***Yes and yes. I think I'd call that working from the middle, though. Starting with the oscillator would be working backwards...and power source would be working forwards (at least from me).

    ****Probably has nothing to do with competition. Watchmaking attracts introverts...we have problems with social skills to begin with. Compound that with years of naive questions from folks wanting simple explanations for complex issues which may have required years of study and experience to reasonably understand, and whatever extroversion we can summon is looking for a place to hide... Besides that...most of us repair and restore...and while interested in design we are not usually involved in design...except to the extent that a perversion of engineering is required to effect a "repair" (and based on the specimens that arrive at my bench...such field engineering must be more common than I ever imagined)...

    I'd start with a good education in the operation, repair, problems with current designs...then set my objectives...then implement (innovative) solutions.

    This conveys the general idea much better than I could ever attempt with language: https://www.youtube.com/watch?v=9Oo8sK9ER28

    Regards, BG

  3. #3
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    Re: Understanding movements

    Daniels covers it pretty well. The ratios tend to range between 1:9 to 1:6, you see 1:7.5 pretty often. Some books list sample trains with ratios (tooth counts), but best is to get some decent basic vintage movements and count the trains, study the ratios and try to figure out why they are what they are.

    On a really basic level, the barrel diameter is a bit less than half the movement diameter. In an 18,000 bph watch the balance in a nice one would be somewhat smaller than the barrel, like you could fit it loosely into the empty barrel. The escape wheel is about half the balance diameter, often. The wheels in between get a little bigger each step until you're back at the barrel. In theory they don't really have to be a certain size as it's the ratio that matters, but practically it makes sense to keep the movement layout manageable and so their pinions clear the next wheel without having everything at different heights. Also pivot sizes reduce and inertia becomes a factor as you approach the balance; a watch train increases in speed as you move from barrel to balance and decreases in power so smaller pivots mean less friction.

    In an 18,000bph watch the escape wheel makes a rotation every 6 seconds, so 10rpm. Each tooth makes two 'tics' as it passes the pallet fork.

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