Pallet Angle Span vs Reqquired Power

Discussion in 'Clock Repair' started by Scottie-TX, Jun 13, 2014.

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  1. Scottie-TX

    Scottie-TX Registered User
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    When it was inventented the original deadbeat pallet span was 138 degrees . Since then for various reasons the square escapement has replaced it with ninety degrees believing it more efficienet - whatever that means. I have my own opinion. I'd like to canvass yours. Do you think the square escapement is more efficient and for the purpose of my question, "efficient" means less weight to drive it.
     
  2. shutterbug

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    I can't pretend to know escapements and pallet spans like you do, Scottie. However, I can just about guarantee that any change from original design was not for efficiency concerns. Always follow the money. It was probably cheaper to make the 90° version. :)
     
  3. Randy Beckett

    Randy Beckett Registered User
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    It seems that the wider the span, the farther the distance is from the pallet to the anchor arbor. This would give the impulse more leverage to the crutch. The wider span would be more efficient, in my opinion.
     
  4. eskmill

    eskmill Registered User
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    I don't think pallet span of the dead-beat escapement design affects the amount of impulse delivered to the pendulum.

    A well designed escapement goes beyond the geometry of the anchor and pallets, the design has to include the driving force delivered to the escapement and the requirement imposed by the mass of the pendulum.

    Too, is the effectiveness or efficiency of the mechanism linking the escapement to the pendulum. Likely the usual crutch wastes a measurable amount of force.

    In theory, the most efficient dead-beat escapement is the one that provides only the minimum force to the pendulum and requires the least amount of feedback force from the pendulum to unlock the escapement.

    Not to be overlooked is practicality. The most efficient escapements loose their effectiveness from external causes, the environment.

    I recall reading of a laboratory study comparing the driving force required the dead-beat escapement and a recoil escapement. The test bed, a carefully designed dead-beat astronomical quality regulator. Precise measurements were carefully recorded, then the escapement was altered to recoil. The difference in the amount of force was minor as I remember.

    I think Bernie Tekippe's design took into consideration most of the factors that contribute to efficiency in a practical pendulum regulator.
     
  5. Jay Fortner

    Jay Fortner Registered User

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    Something else to ponder is the relationship of pivot points on the anchor and pendulum. If you raise the pend. pivot point above the anchor pivot point it requires less power to push it and the pend. swing is decreased in relation to the crutch swing,vice-versa if the pend pivot is lowered. If you were to use a wide span anchor with a pend. point quite a bit higher than the anchor point you could swing a heavy pend. with a small amount of weight on the train. The pend. won't have a wide swing but a very consistent one.
     
  6. Tinker Dwight

    Tinker Dwight Registered User

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    There are a number of factors. One is that if the pallets are
    closer to 180 apart, the escapement wheel needs to slide the pivots
    to the opposite side of the escapement on each power stroke.
    When closer together, there is less need to slide.
    Wider spans have the advantage that the same pendulum swing
    can be had with a shallower angle of the pallets.
    David's 1/2 escapement wheel method creates faces on the pallets
    that are 30 degrees. The width of the anchor would set how much
    this angle was translated to the pendulum angle.
    The angle of the next wheel down to the pallets arbor has an effect
    on friction as well.
    The number of teeth on the escapement would also be a factor in the
    choice of the span angle.
    Tinker Dwight
     
  7. Scottie-TX

    Scottie-TX Registered User
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    'Thanks y'alls for your opinions, both general and specific.
    Sorry for the late opinion; I've been sporadic here lately as I'm having health problems as well but here goes. RANDY we agree but few authors on escapemens do not. I'll think this a tad more thoroly but give time to compose
     
  8. shutterbug

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    I just returned from the two-day suitcase workshop on constructing and setting recoil strap verges. The instructor said very much the same as what Jay posted above - that the wider pallets will produce a smaller arc, but much improved timekeeping. He applied that equally to recoil or deadbeat styles.
     
  9. Scottie-TX

    Scottie-TX Registered User
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    Here's what I think; Of all treatments on this subject by those I regard as competent and qualified all agree the square escapement is the most efficient but here's where we don't disagree but rather are not using the same definition of efficiency. Theirs is one of optimum overall operation and regulation. Mine was as the title implies. How much weight and for that - minimum weight. From MANY tests of this definition clearly it requires less weight but operation is not optimal
     
  10. Jay Fortner

    Jay Fortner Registered User

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    Minimum weight = wide span + raised pivot point. I think most wieners have their pendulum pivot well above the the anchor pivot,most have light weights and quite heavy bobs for the amount of weight driving it.
     
  11. shutterbug

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    You're concentrating on minimum weight, Scottie. While less weight might seem to imply better efficiency, in reality it may be detrimental to the optimal efficiency of the clock. It's comparable to a spring powered clock that is way under powered. It will run, but may not keep the best time. There's a 'sweet spot' that you have to find for the best operation ... and that is not always going to be the lesser weight.
     
  12. leeinv66

    leeinv66 Moderator
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    You would have to define "well above" Jay. I wouldn't have thought that was the case.
     
  13. Jay Fortner

    Jay Fortner Registered User

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    About 1/2" - 1"
     
  14. leeinv66

    leeinv66 Moderator
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    What are you calling the pendulum pivot Jay? From where the pendulum hangs or from where the suspension spring flexes?
     
  15. Jay Fortner

    Jay Fortner Registered User

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    The point where it flexes is the pivot point.
     
  16. Scottie-TX

    Scottie-TX Registered User
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    #16 Scottie-TX, Jun 22, 2014
    Last edited: Jun 23, 2014
    If we fully understand your def of suspension then for optimum operation the pendulum should be suspended on the same axis as the anchor. However despite the rule, one here ran just as accurately and same amount of weight as one on center. Also SHUT, anther here runs very accurately on 3oz. Another rule broken.
     
  17. leeinv66

    leeinv66 Moderator
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    Thank's Jay! Then no, my Viennas do not fall into the "pendulum pivot well above the the anchor pivot" category. Of the eight I have, only one fits that description.
     
  18. Jay Fortner

    Jay Fortner Registered User

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    I'm definitely no vienna regulator guru, they don't seem to be that popular in my neck of the woods. I think I've worked on a total of three with one of them being one I owned then sold. That one I remember quite well. It had the suspension mounted on the movement holder and it was about 5/8" above the crutch pivot. It was spring wound but had very light springs,almost as light as a frenchie. The pend. was about 24" long. The other was mounted in the same manner but only about 1/2" above the crutch pivot and a much larger clock with I'd say 30" of pend. and small weights. The third had the pend. mounted to the movement and at the crutch pivot point it was spring wound. All three had the wide span anchors. The big one had the second fine tuning rating nut and is a terrific time keeper. It will be back in soon for it's two year oiling.
     
  19. leeinv66

    leeinv66 Moderator
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    Ah okay, now I know why we are reporting different results. Yes, spring driven Viennas are a different ball game. And yes, their pendulum pivot point is often above the anchor pivot. But, that is not normally the case with weight driven Viennas in my experience.
     
  20. Tinker Dwight

    Tinker Dwight Registered User

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    These that are off center may have been done as part of the
    thinking to help regulate the size of the swing. The friction
    goes up as the swing increases. Also, as the swing of an unrestrained
    pendulum get larger, the pendulum slows in rate. With added
    friction restraining the swing, it would tend to shorten the swing
    for a given amount of drive. This would increase the rate some
    even though it were swinging a greater amount.
    I think the only way to test how much it improved or not would be
    to have two similar clocks, one centered and one with the inflection
    point above and vary the drive strength by the same percentage.
    Then note the difference in the rate.
    Just measuring a normally running clock would have little variation
    anyway.
    Tinker Dwight
     
  21. shutterbug

    shutterbug Moderator
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    Yep. One thing I've learned is that in clocks there are no hard rules :)
     
  22. Jay Fortner

    Jay Fortner Registered User

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    Sometimes hard knocks!
     
  23. Neuron

    Neuron Registered User

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    Getting back to the original question, I found on p.204 of Gazeley's Watch and Clock Making and Repairing (2nd Ed.) these comments on the Graham DB:

    "It was made originally with the pallets spanning 14 teeth, but this has been superseded by an escapement having the same principle in which the pallets span eight teeth. The former requires less power to keep it going, and thus the slightest thickening of the oil affects the rate. The arrangement whereby the pallets span eight teeth require more power to keep it going, and, as such, the thickening or thinning of the oil is less troublesome, although still a factor to be reckoned with. The vibration must be kept as small as possible, and, as a regulator requires the slightest amount ofsupplementary arc, this type of escapement is ideal."
     
  24. Randy Beckett

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    So, is Mr. Gazeley saying that the wide span is more efficient, since it requires less power to operate, but the narrow span should be favored since it operates better on a gummed up escapement? With all due respect to him, I don't think that is a valid arguement. A deadbeat operating on minimum power should disrupt the natural oscillation rate of the pendulum the least. This should result in the clocks most accurate potential. Any change, whether it be thickening oil, added friction, or something else should make the clock stop, not change it's rate and keep running.
     
  25. Neuron

    Neuron Registered User

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    Randy,

    Gazeley does say that the 14-tooth span is more efficient than the 8-tooth span because it requires less power to keep it going, but that doesn't mean the clock will go with less weight. Goodrich, in The Modern Clock (p.112-113) discusses this in greater detail, and particularly the other mechanical/environmental issues (and Goodrich also mentions dirt and gummy oil).

    Your comment that: A deadbeat operating on minimum power should disrupt the natural oscillation rate of the pendulum the least. This should result in the clocks most accurate potential. Any change, whether it be thickening oil, added friction, or something else should make the clock stop, not change it's rate and keep running.

    makes perfect sense, since if it's operating at the minimum sustaining power, with the smallest possible vibration, any added friction would eventually stop it.


    So Goodrich does give a more complete discussion of this issue than does Gazeley, and indicates that the shorter pallet span was developed for practical reasons, essentially a compromise that worked well in real world clocks.
     
  26. Randy Beckett

    Randy Beckett Registered User
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    Possibly the meaning of "efficient" is interpreted differently. My interpretation is "the most work done with the least amount of effort". This could either be that a clock will swing a given pendulum on the least amount of power or that a clock will swing a heavier pendulum on a given amount of power.

    I think the wider span anchor is more efficient than the shorter span only if the pallet angle is the same on both, which would result in a smaller(but stronger) degree of impulse on the crutch with the wide span. However if the grind on the pallets on both was such that the crutch of each would have the same degree of impulse, it would be hard to prove one was more efficient than the other.

    About a 2 degree crutch impulse seems to be a generally accepted "standard" and is easily attained by either wide or short span. However when the desired degree of impulse gets less than this(primarily viennas and jewelers regulators), the margin for wear on the escape wheel and anchor pivots becomes much more critical on the short span.


    As far as the shorter span being developed for practical reasons, I understand that, as they work fine on the vast majority of pendulum clocks, and are probably simpler to make. It's just in special applications that one would realize benefit from the wide spans increased efficiency.
     

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