Ok, now an escapement "swap" question

Discussion in 'Clock Construction' started by Rob P., May 16, 2013.

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  1. Rob P.

    Rob P. Registered User

    Dec 19, 2011
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    Ok, remember it's my first time.... Be gentle and go slow...

    FOR STARTERS, I DO NOT have any actual parts. I'm just looking for knowledge.

    Let's say you have a mantle clock movement with, say, an escapement with 38-42 teeth and a short pendulum. IF you wanted to convert it to a longer pendulum, say maybe 1 meter, could you just replace the existing escapement with one with fewer teeth and and get it to keep time?

    I think this would NOT work but can't wrap my head around the concepts involved. My sticking point seems to be that the gearing appears to require that the escapement rotate X number of times per minute. If the number of teeth are reduced to the point it rotates 1 time per minute with a seconds beat pendulum length, the gearing is off for correct time keeping.

    So, this means either the gearing would have to be changed along with the escapement (more pinon leaves/teeth) OR the escapement would have to have even fewer teeth. (Say 28 rather than 30.) Since existing depthing and tooth profiles prevent pinion tooth count changes, the only viable way to make this work is by using an escapement with fewer than 30 teeth.

    The other alternative is that regardless of the number of teeth on the escapement, an escapement ALWAYS ALWAYS ALWAYS only rotates 1x per minute. Which makes no sense because there are lots of different gear tooth counts in different movements. However, they all add up to 3600 at some point regardless of the beat frequency.

    So, where am I making my conceptual mistake?
     
  2. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    Hi
    Escapements don't always rotate once per minute.
    If the escapement wheel is changed, one also has to change
    the pallets as well.
    Many manufactures designed their clocks to take different
    escapement/pallet pairs for different length pendulums.
    With an escapement that rotates once in a minute, it would need
    to be 30 teeth to use a one second beat pendulum.
    With an escapement that was not 1 rotation per minute,
    there may not be a number of teeth that would allow
    a one second beat pendulum.
    I hope that helps.
     
  3. David S

    David S Registered User
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    Dec 18, 2011
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    Rob, I did the exact thing recently. I had two Hermle movements with different chime hammer configurations. The one that I wanted to use had too short a pendulum. The other one had a longer pendulum. I transplanted the E/W and the two wheels below it from one clock to the other, and all is well.
     
  4. leeinv66

    leeinv66 Moderator
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    #4 leeinv66, May 17, 2013
    Last edited: May 17, 2013
    The total tooth count of the time train you are working with is the limiting factor when you want to change the length of a pendulum. As David has pointed out, you would need to change more than just the escape wheel to gain the sort of change in pendulum length you are looking for. Have a play with this pendulum length calculator that is available from the home page.

    http://www.nawcc-index.net/CalcPendulumLength.php
     
  5. tok-tokkie

    tok-tokkie Registered User

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    Going the other way makes this explanation slightly simpler.

    1 second pendulum with 30 tooth escape wheel does 1 rev per minute. The rest of the train is geared to suit that.
    Change to a 1/2 second pendulum & it would do 2 revs per minute. So change to a 60 tooth escape & pallets to match & the escape wheel will do 1 rev per minute. No need to change any of the train.

    The escape wheel must be changed in proportion to the BPM of the 2 pendulums. As Tinker says - the proportion needs to be an integer so it is only possible for certain BPM combinations.
     
  6. sharukh

    sharukh Registered User
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    I don't know how much this will help or if it will muddy the waters even more.

    A couple of weeks ago, I saw a clock at a flea market with a long pendulum. On looking closer, some smart chap had removed four (opposing) escape wheel teeth to be able to use a longer pendulum. I might be going back and if the clock is still there, I'll shoot a couple of pics if anyone is interested. The clock was keeping good time and the pendulum swing was pretty smooth. I wonder what sort of wear problems it would throw up due to the irregular forces in action.

    Sharukh.
     
  7. Tinker Dwight

    Tinker Dwight Registered User

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    I'd just seen a manufactured clock with just such
    an escapement wheel on this MB. It also had some
    type of lever to reduce the inertia of the escapement
    as it rotated.
    Tinker Dwight
     
  8. Rob P.

    Rob P. Registered User

    Dec 19, 2011
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    This is what my brain is telling me. As long as the EW rotates the correct number of times, the number of teeth on the EW isn't that critical. Just make the BPM/tooth count give the required RPM on the EW. So, if you have an EW that needs (for ex) 1.2 RPM, then putting a seconds beat pendulum on with a 28 tooth EW would make the EW rotate 1+ times per minute and the clock would keep time with nearly a seconds beat.

    The thing that got me thinking of this is the thought that technically, you could snip off every-other tooth of a 60 tooth EW/half seconds movement and then stick on a seconds beat pendulum. Of course the drop would be horrific with the stock anchor/pallets. To cure that problem another one crops up. Namely that the anchor needs to be modified in some manner to reduce the drop and still give good lock and impulse.

    At some point you wind up redesigning the EW/anchor to work together and quickly get to the point where it's probably easier to just buy a movement with the correct parts in it. BUT, the engineering aspect is interesting. (At least this week it is - who knows what idiocy I'll think of next week.)
     
  9. riccardo

    riccardo New Member

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    Hi Rob
    I read with great interest your response.
    Could you explain in a simple way how you do the math changing the teeth of the EW leaving unchanged the length of the pendulum?
    thanks
    Riccardo
     
  10. Tinker Dwight

    Tinker Dwight Registered User

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    #10 Tinker Dwight, May 20, 2013
    Last edited: May 20, 2013
    The ratio of the wheels and pinions between the center wheel and the
    escapement determine how fast the escapement wheel must turn
    to make the center arbor rotate once per hour.
    One can do teeth counting to determine the ratios.
    As an example if one wheel meshes with another pinion
    and the wheel has 48 teeth with the pinion having 6,
    the ratio is 48 to 6 or reduced to 8 to 1.
    What this means is that every time the wheel rotates
    once, the pinion has to rotate 8 times.
    To determine the total ratio from the center wheel
    to the escapement, on needs to multiply all the wheels
    between the center wheel together and then divide by
    all the pinions ( multiplied together ). The escapement is
    considered to be one of the wheels.
    One has to be careful to not introduce other wheels
    or pinions that are not in the path between the
    center wheel and the escapement.
    If this ratio is then multiplied by 2, that gives
    the beat rate per hour.
    Why 2?
    That is because each tooth on the escapement wheel
    gets used twice. Once on each pallet.
    The right length pendulum can be calculates using
    one of the web pendulum length calculators.
    Tinker Dwight
     
  11. shutterbug

    shutterbug Moderator
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    #11 shutterbug, May 22, 2013
    Last edited: May 22, 2013
    I think an easier way to think of this is to calculate the beats per hour you currently have, and then by counting the teeth you can calculate beats per revolution of the EW (two ticks per tooth). Now, using pendulum theory, you can calculate the BPH with the new pendulum length, and then how many beats per revolution you need. The revolution of the new EW MUST match the revolution of the old one. Get a matching EW and anchor and install them. I forgot to mention that the number of pinion teeth must match the old one too[MARQUEE=75] :)[/MARQUEE]
     
  12. Tinker Dwight

    Tinker Dwight Registered User

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    That works fine if the BPH stated is an integer number. It might be a little confusing
    if not.
    The calculated number of desired teeth would still have to be an integer number.

    nT = nB * oT / oB

    oT = Old escapement Tooth count
    oB = Old Beat
    nT = number of new Teeth ( must be integer )
    nB = New Beat ( BPS, BPH or BPD must be the same units as oB )

    Tinker Dwight
     

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