I have a question about the pendulum swinging distance ?

Discussion in 'Clock Repair' started by Jmurrell, Nov 20, 2018.

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  1. Jmurrell

    Jmurrell Registered User
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    I am working on a Urgos grandfather movement. I have taken this movement apart and installed the needed bushings. The clock time train seems to have plenty of power and runs great.

    I purchased a replacement pendulum for this clock and after many adjustments it is keeping good time.

    My concern is that the pendulum doesn't have a very wide swing to it. I have measured the distance of the swing and it is around 1 3/4". Is this a normal swing?

    If not do I have to move pallets closer to the escape wheel to create a wider arc or do I move them further away from the escape wheel?

    John Murrell

    101_1155.JPG 101_1156.JPG 101_1158.JPG
     
  2. shutterbug

    shutterbug Moderator
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    Closer will create a bigger swing. If you go too far though, the swing will be too wide for the impulse to carry the pendulum far enough to unlock. Make small adjustments until you're happy with the swing.
     
  3. Jmurrell

    Jmurrell Registered User
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    Shutterbug do you have any idea if this amount of swing is enough?
    John
     
  4. Willie X

    Willie X Registered User

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    Just about any GF clock will do a 3" swing. Some will go over 5". This is total, left to right, measured at the tip of the rating rod. The main thing is the 'overswing' if you have easily observable overswing, all will be well ... really no need to try for more. Willie X
     
  5. Jmurrell

    Jmurrell Registered User
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    Thanks to both of you for the information.

    John
     
  6. kinsler33

    kinsler33 Registered User

    Aug 17, 2014
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    Thanks. I'd always guessed about 7cm, which agrees with the others.

    If the swing can't be improved by adjusting the escapement, try bushing the verge and escape-wheel pivots. These may seem okay from a shake standpoint, but even the slightest bit of lost motion, especially in the verge, can really decrease the pendulum motion. It's very hard to see when it happens, so I generally make a habit of bushing the verge and escape wheel on most clocks.

    M Kinsler
     
  7. rgmt79

    rgmt79 Registered User
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    If it's running ok and keeping good time, why play around with the swing?

    Richard
     
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  8. kinsler33

    kinsler33 Registered User

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    Because a clock with a pendulum swing that's too small is correspondingly easy to stop, say, if the floor vibrates at just the wrong time due to a passing truck.

    A wider pendulum swing means that more energy is being transferred from the escape wheel to the pendulum. A pendulum with lots of energy moves with higher speed through its lowest position. A slow pendulum can be stopped with only a very small external force, while lots more external force is needed to stop a speedy pendulum.

    Now, we also want some overswing: that is, we hear the tick as the escape wheel releases, but the pendulum continues to move in the same direction for a while longer. This overswing is not, oddly enough, closely related to the amplitude of the pendulum's swing--that is, we can have good overswing even with a small pendulum swing.
     
  9. Willie X

    Willie X Registered User

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    Overswing is absolutely directly related to pendulum amplitude (swing). Every degree of overswing equals 2 degrees of extra pendulum amplitude. Willie X
     
  10. R. Croswell

    R. Croswell Registered User

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    Johh, I have a questions;

    1) Is the replacement pendulum significantly larger and.or heavier than the original?
    2) How much pendulum swing did you have after the bushings were installed using the original pendulum?
    3) on what did you base your conclusion that "the clock time train seems to have plenty of power"?

    A larger pendulum swing does not always indicate a healthier or better adjusted clock., in fact some of the best precision regulators have very small pendulum swings. A large pendulum arc actually has a greater circular error, and forcing a clock to swing the pendulum wider can in some cases actually increase instability and the chance that the clock could stop unexpectedly. As Willie and others have pointed out, "over swing" is the property to observe, but more isn't always better. Adequate is the desired amount.

    I assume that this movement has a deadbeat escapement. Each end of the verge has two pallet faces - the dead face and the impulse face. As the name implies, the impulse face delivers the power to the pendulum. The duration of the impulse is constant and determined by the physical geometry of the pallet. The distance the pendulum moves during the impulse (during the delivery of power to it) is a function of the length of the impulse face and the lift angle. If the escapement is adjusted properly the escape wheel teeth land on the dead face and then transitions to the impulse face. The general belief that moving the verge closer to the escape wheel will increase pendulum swing is somewhat misguided as it applied to dead beat escapements. In a recoil escapement increasing the lock (moving the verge closer to the escape wheel) also increases the duration of the impulse and may deliver a wider pendulum swing. In the dead beat escapement if the escape wheel teeth are landing on the impulse face (insufficient lock) the escapement will run as a recoil escapement (if it runs at all) and increasing the lock will in deed increase the impulse duration and pendulum swing. But in normal operation (escape wheel teeth landing on the dead face) moving the verge closer to the escape wheel cannot change the duration of the impulse and if the lock becomes excessive it will introduce additional friction and instability.

    Step one should be to check that the escape wheel teeth are clearly locking on the dead face just a bit past the division line between the dead and impulse face and the pendulum swing will be what it will be. Step two is to make sure the pendulum continues to swing in the same direction some little distance more after each tooth is released (the over swing that's already been described). If the escapement is locking on the dead face and there is obvious over swing then its OK. If the escapement is adjusted properly as above and there is very little over swing then there is a power problem, and in this case, the prime suspect(s) would be a tight or crooked bushing or perhaps a bent pivot.

    RC
     
  11. Willie X

    Willie X Registered User

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    RC has covered the bases. Some late1960s thru about mid 1980s Urgos movements had some funky escapewheels on their auto-beat models. The tooth tips were tiny and very susceptible to misadjustment and wear. It is impossible to adjust these clocks proberly, even with some moderate wear in the escapement pivots. What RC and Kins said.

    A good photo of the escapement would tell us exactly what you are working with there. Willie X
     
  12. kinsler33

    kinsler33 Registered User

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    Well, yes: overswing is measured at each end of the pendulum travel, and so there'd be two overswings per stroke of the pendulum.
    And that would be true if the pendulum was swinging two inches or ten inches. But a pendulum with a wide swing has lots of momentum at its highest speed, which occurs at the bottom of its swing, and so it would require a proportionally larger external force (say, a wind gust or floor vibration) to stop it.
     
  13. kinsler33

    kinsler33 Registered User

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    RC's explanation of the dead-beat's operation is excellent, and I read it several times.

    I might observe that it isn't so easy to determine if the tooth tip is really landing safely in the dead-face zone or on the impulse face, for there's always something in the way when you're looking at it, and that long, thin tooth tip frequently seems to land maddeningly close to the boundary between the two faces if you're not looking at the thing correctly as the clock is running.
     
  14. shutterbug

    shutterbug Moderator
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    Another thing about auto beats: Unlike most other anchors, you can't set them too deep. If they bottom out on the wheel rim when they're trying to lock and impulse, they will eventually die. There's a sweet spot where they are comfortable, and you have to find that spot.
     
  15. R. Croswell

    R. Croswell Registered User

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    I bought one of those inexpensive bore scopes that helps sometimes. One indication that you are on the dead face is that there should be no perceptible recoil. That of course won't let you how much dead lock you have or if the lock is on the dead/impulse interface, but if there IS recoil you know the lock is on the impulse face. RC
     
  16. Willie X

    Willie X Registered User

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    If the clock has a direct coupled second hand, you can actually see what's going on with the escapement just by studying how the second hand moves during the normal operation of the clock. Willie X
     

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