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Thread: Hair Springs

  1. #1
    Craftsman
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    Hair Springs

    Just wondering Guys.What governs the size and number of coils in a hair spring in a watch? Is there a mathematical formula? Can a hair spring from one watch be used in another?

  2. #2
    Master Webwatchmaker's Avatar
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    Quote Originally Posted by lew07 View Post
    Just wondering Guys.What governs the size and number of coils in a hair spring in a watch? Is there a mathematical formula? Can a hair spring from one watch be used in another?
    You need to read George Daniels 'Watchmaking'.
    From a hogs hair to Invar, a non magnetic steel with low coefficient of expansion, the evolution of the hairspring is fascinating.
    Nivarox SA will send you info if you ask them.
    Sent from my SM-G900F using Tapatalk
    Last edited by Webwatchmaker; 10th November 2019 at 15:20.

  3. #3
    Craftsman
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    Size and number of coils depends on the design. The spring is matched to the balance inertia to give the required oscillation frequency, which in turn is decided by the train. The actual length of the spring depends on its material/shape etc which give the spring its springyness so for instance a stiffer material might need a longer spring to give the same period as a weaker one (danger Will Robinson, beware of the massive generalisation)
    Yes there are formula, although I donít know them - if I need them Iíll look them up. More likely I would find a balance complete that had the required frequency and make the rest of the watch train work to that.
    Yes you can in theory switch hairsprings, but itís not as simple as just swapping it over. Itís very unlikely the balance inertia will match, which will give you an error in the period, and so the watch would run fast /slow. Swapping a balance complete between related movements will also probably work.

    Dave

  4. #4
    Craftsman
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    Thanks Guys.Its amazing isnít?We take for granted that these springs are going to work correctly all day everyday for its working life!!!

  5. #5
    To answer part of your question, yes you can calculate the stiffness required and the number of coils / coil thickness using a formula.

    You know the mass/inertia of a given balance wheel, so can calculate and design a spring to give the required frequency.

    Any 2 watches with identical balance wheel mass and inertia would have the same spring stiffness for the same beat rate.

    Differences in moment design however mean they are seldom the same, as mounting points, geometry around the ends etc tend to vary.

    Edit - As Dave said above, but beat me to it!


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  6. #6
    Master Webwatchmaker's Avatar
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    The formula.
    This will keep you out of the pub:



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