Lift Angle ; How Important?

Discussion in 'Clock Repair' started by Scottie-TX, Apr 17, 2014.

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  1. Scottie-TX

    Scottie-TX Registered User
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    Quite often during the course of counseling others or analyzing a problem with a DEADBEAT movement or addressing the subject of pendulum bob weight, we opine the value of or importance of lift angle. Most I believe would agree that lift angle on a deadbeat is critical, matters a lot and incorrectly set will stop the clock.
    I have always disagreed but seldom, verbally. To this end I thought it would be fun to conduct a few tests and prove this myth not true. I used a vienna DEADBEAT movement with adjustable pallets for ease of changing pallet gaps. The no name movement was first cleaned, lubed, etc., and found to be in excellent running condition as found with no alterations. The tests consisted of two factors in three phases. The two factors were an eight ounce bob and a three pound bob. The three phases were tests with impulse or lift angles of one, two, and three degrees as measured by Dave LaBounty's tangential dwg method.
     
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  2. Scottie-TX

    Scottie-TX Registered User
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    #2 Scottie-TX, Apr 17, 2014
    Last edited: Apr 17, 2014
    I began with two degrees. One was slightly off two degrees but I left it. Reliable on three pounds with an eight ounce bob I reduced power to one pound when no longer reliable. I replaced the eight ounce bob with a three pound bob and again reliable on three pounds. It did require 8 oz. more power now at minimum. It now required two pounds with the three pound bob. So; So required eight more oz to drive a bob six times heavier. Then I flipped the pallets and ground three degrees to both. Results same as two; One and a half pound minimum reliable; 8 oz more required for three pound bob.
    On to phase three, I reground the pallets to One degree, both. Just a tad different. All, same, except it required a full pound more to swing the three pounds.
    So my conclusions? 1. Lift angle is NOT critical, given that movement is otherwise in good condition with no other problems and 2. A substantially heavier bob requires very little more power to remain reliable.
    Questions? I LOVE dissenters as I ALWAYS learn from them.
     
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  3. leeinv66

    leeinv66 Moderator
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    Yep, in a perfect world you would have the angles perfect. But, in the real world close enough will work just fine.
     
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  4. shimmystep

    shimmystep Registered User

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    Nice work Scottie, great info:)
     
  5. John MacArthur

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    Scottie -- This is fine stuff. Did you find that with different lift angles, you got different degrees of pendulum arc? I think that with a smaller lift angle, you can reduce the amount of escape arc, and thus decrease the amount of circular error of the pendulum, and increase the overall accuracy of the clock. I have always assumed that this meant you would need somewhat less weight to drive the pendulum, as you would have less air resistance to overcome. Obviously, that is a smaller effect than the overall inefficiencies in the train.

    John MacArthur
     
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  6. Tinker Dwight

    Tinker Dwight Registered User

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    Hi Scottie
    One thing you didn't measure.
    How variable was the rate using the different configurations.
    The two degree swing was chosen for over swing and
    minimum disturbance of the pendulums rate. It wasn't just
    if it could be made to work.
    Tinker Dwight
     
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  7. Bruce Alexander

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    You have to "aim" for something with a worn pallet. I have to assume that the engineer/manufacturers knew what they were doing so re-establishing the original lift angle with original bob weight is what I'll continue trying to do. In the absence of an original reference I suppose a consistent angle on both pallets would be important. Beyond that, trial and error would likely be my guide.

    So Scottie, if you were trying to determine the best lift angle, are you saying it wouldn't matter whether it was one, two, or three degrees? What if you were in excess of three? What if you introduced an imbalance in the entry and exit angles?
     
  8. Randy Beckett

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    Thanks Scottie, good stuff.

    I have been doing some tests of my own recently to try to find a easy way that anyone can determine the lift angle, or lock amount, on their running clock by using the pendulum swing degrees, that is somewhat related to your test.

    If the suspension of the pendulum is made so it is on an even plane with the anchor pivot, with near zero lock and at minimum weight, the pendulum swing degrees and the lift angle should match.


    The formula I am using is ((pendulum length x 2) x3.14) / 360 = 1 degree


    So for a clock set at near zero lock, with a 26" pendulum, with a lift angle of 1 degree, the minimum swing would be about .9 inches. 2 degree lift, 1.81 inch minimum swing. 3 degree lift, 2.72 inch minimum swing.

    Does this seem to correspond to your observations?
     
  9. shutterbug

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    I'm a bit curious about how you measured your lift angles.
     
  10. LaBounty

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    Hey Scottie-

    I suspect you were testing with minimal lock and maximum drop. What did changing the lift angles do to the drops and locks and, after changing the lift angle, did you return the escapement to min-lock and max-drop?

    Does changing the lift angles make more of a difference if the escapement is adjusted for max-lock and min-drop?

    Great stuff! Keep it coming!
     
  11. R. Croswell

    R. Croswell Registered User

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    Interesting observations but I'm not sure we have all variables covered. At least theoretically with any given lift angle increasing the weight should increase the over swing. Looks like you are evaluating performance at the critical run/no run point. One generally has no control over the operating friction - suspension losses, air resistance etc. so at some point the driving force is not enough to overcome friction. Decreasing the lift angle and reducing the degrees of swing can shift the critical point back to a run situation.

    Very much like like a small car with manual transmission going up a mountain grade in high gear. When the angle of the grade gets to a certain point the engine will stall. Changing to a lower gear allows the car to keep going at the cost of lower speed. Reducing lift angle is like shifting to a lower gear at the cost of less swing. Most people don't run a clock at the critical point so we need to include amount of over swing into the equation some how.

    A few few years ago I had a Waterbury weight banjo in for service. The verge had been replaced. It was a strip pallet dead or half dead beat. It operated - good lock, not too much drop - but would not keep running reliably I spite of everything else being OK. It had a good healthy swing. The weight was the fixed variable that I could not change. Dave suggested reducing the lift angle from 2 degrees to 1.5 degrees. I did and the clock immediately ran reliably with just a little less swing. Have not seen it since. Then just recently I had a spring banjo that had too much swing and the pendulum leader was tapping the case. This was not a matter of running or not, it was running too well. Again I could do nothing about the power but reducing the lift angle a bit got the swing back to an acceptable level.

    RC
     
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  12. Tinker Dwight

    Tinker Dwight Registered User

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    Circular error percentage increase when there is a
    larger swing based on the amount of swing. In other words,
    a small change in swing of a large swing has a larger effect
    on the rate.
    A short swing caused by reduced lift means the escapement
    is driving the pendulum for a larger part of the swing. This
    means more drive error. Finding the best balance point between
    the two is how they came up with the 2 degree.
    I'm also curious as to how you determined 3 degrees and 1 degree.
    I expect they are not what you think but still useful points.
    We tend to deal with "will it run" so much, we miss the primary
    purpose of a clock, keeping time.
    Tinker Dwight
     
  13. leeinv66

    leeinv66 Moderator
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    Well, I think Scottie was pretty clear on how he measured these angles: "The three phases were tests with impulse or lift angles of one, two, and three degrees as measured by Dave LaBounty's tangential dwg method.".
     
  14. Scottie-TX

    Scottie-TX Registered User
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    Yeah that's correct Pee-Tah;
    For those not familiar, here is a crude dwg showing the radius derived from the arm span, the tangent to that circle and app. of the anchor to the dwg.

    LIFTANGLE 001.jpg LIFTANGLE 002.jpg
     
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  15. Scottie-TX

    Scottie-TX Registered User
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    JMAC; I did find that decreasing the lift angle resulted in a shorter distance from lock to lock, providing more overswing and ultimately if you choose, using less weight to achieve a smaller total arc but still reliable.
    TINK; There's a LOT of factors not considered or measured here.
    I will say with tongue lodged in cheek, "if it don't run it can't keep time."
    . . . . and BRUCE, it's also what I'll continue to do;
    So nosir. It does matter and for most efficiency, matters a lot. I wasn't trying to determine the best possible lift angles. Most agree it is apx. two. I was only trying to determine how MUCH departure from two degrees matters and concluded, "not much".
     
  16. Scottie-TX

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    #16 Scottie-TX, Apr 17, 2014
    Last edited: Apr 17, 2014
    RANDY I didn't study my results to the depth empirically as you did theoretically so can't comment on comparison.
     
  17. LaBounty

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    Hey Scottie-

    Traditionally, drops are minimized and locks maximized. I realize you don't hold with tradition and try to minimize the amount of driving force needed to make a deadbeat escapement reliable. However, if you experiment at the traditional end of the spectrum, you will find the lift angles are quite critical and 1/4 degree one way or the other can cause an escapement to become unreliable.

    I've found a better indication of a healthy escapement, rather than running or not running, is the amount of over swing. Did you record the change of over swing (safety factor) during your changes in lift?

    And thanks for all of your hard work with this! It is really interesting.
     
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  18. Harry Hopkins

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    All,
    Thank you! this is the type of discussion that keeps me checking this message board every day. I will always be learning this craft and this stuff is better than any textbook.

    Harry
     
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  19. Randy Beckett

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    Ditto. I love this stuff.
     
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  20. Tinker Dwight

    Tinker Dwight Registered User

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    I guess I wasn't clear.
    I know how you determined the 2 degree. What I'm asking is how
    you determined the 1 and the 3 degree.
    There is nothing obvious about the 2 degree method that implies
    any method for other degrees of swing.
    Tinker Dwight
     
  21. shutterbug

    shutterbug Moderator
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    I get the 2° angle from David's method. What I don't get is 1° or 3°. How do you know what you have? Could be vastly different than what you expect you have. I mean we're talking about VERY minor differences here, and unless you can verify EXACTLY what angle you have, the exercise is not of great value.
     
  22. Randy Beckett

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    I think this is the link to David's instructions. http://www.abouttime-clockmaking.com/downloads/Finding%20the%20Lift%20Angles.pdf It is titled for a half-deadbeat but also applies to a deadbeat. I understand that 1/2 the distance between the pallet center and pallet pivot represents the circle radius for the tangent of 2 degree lift, 1/4 the distance for a circle of 1 degree lift, and, I assume, 3/4 the distance for a circle of 3 degree lift.
     
  23. Scottie-TX

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    #23 Scottie-TX, Apr 18, 2014
    Last edited: Apr 18, 2014
    TINK 'N SHUT, I used the same formula for one and three degrees lift. Dave goes on during his treatment of this topic - DAVE goes on to show how with simple addition and subtraction of fractional radii the same formula applies to one, three, or any fraction of them. So, "no". No the formula is not exclusively applicable to two degrees but can be used for others.
    I understand, DAVE. Makes sense and maybe just another reason I'm a minimalist locker.
    DAVE I didn't record the amount of overswing with the changes but did always make mental note and we're DEFinitely on the same page here. You taught me and I learned well the importance and value of overswing for analyzing nearly any parameter of deadbeat performance. The changes in overswing tracked the changes all the way to failure as I expected. e.g. less lift, more overswing but coupled with less power, less lift also tracked positively the changes enroute to failure. So I do understand and agree that for minimal DROPS, lift angle will be much more critical. I'm simply not a fan of minimal drops on a deadbeat as you know. THANKS!
    . . . . and keep 'em comin'
     
  24. Scottie-TX

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    #24 Scottie-TX, Apr 18, 2014
    Last edited: Apr 18, 2014
    As a sort of addendum or aside, back to LAB's statement:
    . . . and mine in post #2;
    Proper setup of the deadbeat encompasses many factors - (LAB) locks and drops, lift angles, condition of parts, i.e. preparation, pendulum system,amount of power, to name only a few. Viewing the exercise from this aspect, then ALL of these factors are or can be critical. . . . . and I'm not saying minimum drops and maximum locks is a poor choice or incorrect procedure. It is probably the preference of most clockmakers. So; If other factors render the movement with less than optimum performance - then lift angle IS critical. It could be be the proverbial straw as well as any other parameter could be.
    Another example: Is amount of power critical? Most would echo, "no" and I'd agree. However let's suppose power applied is three pounds and overswing is near zero. Let's reduce power two ounces and the clock stops. Is amount of power critical now? You get th' ideer.
     
  25. Randy Beckett

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    Why? I'm trying to think of an advantage and can't come up with one. Is it just a throwback way of thinking from the proper way to set up a recoil, or am I overlooking something. :confused:
     
  26. Willie X

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    #26 Willie X, Apr 18, 2014
    Last edited: Apr 18, 2014
    Thanks Scottie,

    I have always been amazed at how well some clocks would go, even though they were far from the theoretical.

    I always wanted to eliminate the impulse face completely on one side and double the width of the impulse face on the other side. This would simplify the escapement quite a bit and I've seen a few clocks where this seemed to work just fine. Might get around to it someday, might not.

    Willie
     
  27. Scottie-TX

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    #27 Scottie-TX, Apr 18, 2014
    Last edited: Apr 18, 2014
    Hey WILLIE; That's a GREAT idea. I might just give that one a go.
    Randy I can think of one reason max lock may be preferable. Others may offer more. Running locks at minimum we are always skating on thin ice - any kind of tooth or tooth gap deviation could cause mislock and that would certainly be undesirable and could stop the clock. Of course then converse is true. Those same deviations could cause loss of drop and that would also stop the clock.
    Reckon the reason is a safer failure?
     
  28. LaBounty

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    There are both advantages and disadvantages to max-lock/min-drop.

    As Scottie mentions, this will allow for a number of real world inaccuracies; varying friction due to wear, damaged or mis-cut EW teeth, slightly out of beat, barometric pressure changes, etc... which are all lumped into a term called "circular deviation". So, this is an advantage if the goal is to have a movement run reliably for as long as possible before time keeping issues arise.

    A movement with max-lock/min-drop will have a longer pendulum arc and, ideally, a large amount of over swing. This over swing is the safety factor and an ideal place to "hide" time keeping errors or circular deviation. Harrison and Graham argued the value of large -vs- very large pendulum swings with Harrison opting for the very large amplitudes requiring cycloidal cheeks to minimize circular error. He wanted his hiding place to be as large as possible :).

    Since the energy of the escapement and pendulum system is something which needs to be balanced with the energy available for the driving force, sometimes max-lock/min-drop will require more power than is available. This is, of course, a disadvantage since the movement will be prone to stoppages if there is insufficient power to push the pendulum far enough to unlock. (Shows up as very little over swing.) In this instance, the drops are increased and locks decreased until sufficient over swing is achieved.

    Another disadvantage of max-lock/min-drop would be the pendulum swinging TOO far and tapping the sides of the case. Not only is this noise obnoxious, it will also be a very poor time keeper.

    Books have been written discussing the reasons for increased pendulum swing and max-lock/min-drop is one method of achieving it.

    Hope that helps!
     
  29. LaBounty

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    O.k. I know someone is going to ask "Which books?"...

    Rawlings, A.L. "The Science of Clocks & Watches"
    Andrewes, William J.H. "The Quest for Longitude"
    Roberts, Derek. "Precision Pendulum Clocks"

    There are more but those were the first ones I thought of.
     
  30. harold bain

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    David, that is what I normally shoot for with deadbeats, deep lock and vigorous swing. I like the visuals of a healthy swing, and in my experience, the clock runs with less problems than a feeble swinging pendulum.
     
  31. Randy Beckett

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    Thanks Scottie, David, and Harold,

    There must be something I'm missing because I know better than to debate this subject with you three guys.

    For instance the clock I'm working on now. Miniature vienna, 20" pendulum (9 oz bob), 42 oz weight, came to me in running condition with near max lock and a pendulum swing of 1 1/8 inches. It took all the weight and all the swing for it to keep running.
    I evened the drops with the eccentric and adjusted the pallets for minimum lock and started reducing weight 1 oz at a time until it failed. Reliable(12 hour run) at 16 oz for just the clock, 20 oz with the snail and strike lever functions, 9/16 - 5/8 inch swing. When I got home and read these posts, I put the original 42 oz weight back on it and the swing increased back up to 1 1/8 inches, and is holding steady there as I write this. So from what I'm seeing, it seems it is set at it's most efficient place, with the maximum amount of overswing, and I can't figure out how to make it swing wider than this without adding weight.


    But I know you three guys know what your talking about. So I will continue to study and make a point to read the books David mentioned and hopefully get a better understanding on the subject.


    Thanks again,
    Randy
     
  32. shimmystep

    shimmystep Registered User

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    Would increasing the lock help Randy to increase the swing? The swing would have to increase to allow drop off? as long as it had the power from the impulse.
     
  33. leeinv66

    leeinv66 Moderator
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    That is not what I shot for. I associate deep locks and exaggerated swings with recoil rather than dead beat escapements. But that's just me;)
     
  34. R. Croswell

    R. Croswell Registered User

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    Not just you. I do not believe that performance can be based on any single parameter (swing, over swing, lock, drop, etc.). I'm no egg-spurt on this matter, but it seems to me that there should be a mathematical equation that would yield a "performance" or "quality" value. The absolute degrees of over swing and the absolute degrees of total swing alone seem irrelevant but perhaps we should be looking at the ratio of over swing to total swing, or over swing to critical operating swing?

    RC
     
  35. Randy Beckett

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    #35 Randy Beckett, Apr 19, 2014
    Last edited: Apr 19, 2014
    Even though the clock came with max lock with the same total swing, I think it would be unfair, and possibly inaccurate, of me to say "no difference" at this point, because the drops were also far from equal. So I will revisit the max lock setting, at first opportunity, with equal drops and see the effect on the total swing.
     
  36. harold bain

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    Viennas are a whole different ball game when it comes to pendulum amplitude. They are usually happiest on a small swing. Having sufficient overswing is the important thing.
    Most of the deadbeats I work on are Seth Thomas, and their similar variants made by IBM. The pallets are only adjustable by moving the anchor up and down, anything else requires delicate bending of the anchor.
     
  37. Randy Beckett

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    I have just been lucky I guess with the limited number of deadbeats with fixed pallets I have had opportunity to adjust. I just adjusted the depth until the drops were equal and they worked, with a nice smooth action and good swing. But I know my time will come when one comes along when this won't work, and hopefully I'll know how to correct it by then. That's why threads like this are so good, to expose one to problems and solutions they haven't encountered in real life, yet.


    Thanks Harold and thanks again to Scottie for the thread,


    Randy
     
  38. Tinker Dwight

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    I see no reason why it can't be made to work. The loss of energy on
    the non-impulse part would mean the clock would use more
    energy to run but since the impulse was half as often, the clock
    should be more accurate.
    "Rob Peter to pay Paul".
    Tinker Dwight
     
  39. Willie X

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    One thing I can say for sure, clocks have to have over-swing. If it doesn't have a decent over-swing don't let it out of your door. If you do, that clock will come back to see you a lot sooner than you would like!

    Willie X
     
  40. Rob P.

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    I'd hazard a guess that lift angles are important when it comes to power. With enough power you could probably get a brick to impulse smoothly. The question becomes, what happens when the power drops off?

    For weight driven movements, power loss happens when the movement gets dirty and worn. For spring driven movements, power loss happens as the spring winds down as well as when dirt/wear are injected into the equation.

    So proper lift angles are most likely a compromise for best performance under horrible running conditions. Not optimum ones.
     
  41. Tinker Dwight

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    I don't see anything other than adding weight that will
    increase the swing, as you have empirically determined.
    The amount of energy is really related to the lift angle and
    the weight. The amount of swing is tied to the amount of
    energy. Excessive lock only means you are reducing
    over swing by that amount ( the reliability of keeping the
    clock running ).
    Tuning for equal drops and minimum lock should require
    less weight to run but for the same over swing, the same
    weight.
    I think what you determined is that if the clock is running
    with the designed weight and is set for minimum locks, that
    won't run, you have power loss in the train. Fiddling
    with the escapement won't help.
    Equal drops is more an issue of clearance. Minimum locks
    is more an issue of making it run, with over swing.
    This is what I'd expect.
    Tinker Dwight
     
  42. LaBounty

    LaBounty Registered User
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    This may be a good time to define drops and how they relate to pendulum swing...

    Drop is the amount of free rotation of the escape wheel after an EW tooth is released from the pallet and another tooth is caught. This motion is wasted energy which could have gone to moving the pendulum. Minimizing the drops means there is more energy given to moving the pendulum, resulting in an increased pendulum swing. If the drops are adjusted so they are as large as possible, the result will be a decrease in pendulum swing.

    The effect of varying the amount of drop on the amplitude of the pendulum can be most easily seen by watching the rate of the clock. Max-drop would increase the rate (shorter pendulum swing) while min-drop would produce a slower rate (longer pendulum swing).

    As a side note: Adjusting the drops effects the locks so minimizing the drops results in maximizing the amount of lock. The only way to vary the lock without changing the drops is to change the lift angles.

    Hope that helps!
     
  43. Randy Beckett

    Randy Beckett Registered User
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    (i) Got it.

    Thanks, David
     
  44. Tinker Dwight

    Tinker Dwight Registered User

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    Only true for fixed pallets. Adjustable pallets can be separately adjusted
    for lock.
    Drops are wasted energy. Drops on a deadbeat are for clearance of
    the teeth. Teeth thickness is for strength.
    Adjusting drops on fixed pallets with depth also effects locks. Deeper
    engagement means larger locks at the expense of reducing exit drop.
    Deeper engagement increases entrance drop. The only way to independently
    Adjust both drops, more or less each, together on a deadbeat is to change
    the thickness of the pallets( they are not the same as recoils ).
    Tinker Dwight
     
  45. Scottie-TX

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    #45 Scottie-TX, Apr 19, 2014
    Last edited: Apr 19, 2014
    I don't think so SHIM;
    I don't think so SHIM because I see total swing as cutting a pie. The pie consists of lock, drop, and overswing. You can slice large pieces of lock leaving smaller pieces of drop and overswing, etc. etc. The only way I can see of increasing total swing is to have a larger pie and that ingredient is power. More power will increase RANDYs swing.
    Don't think you'll elicit an argument here, RC;
    Now it won't provide a "Q" factor but should be described in degrees and not linear inches because for a little frenchie with a five inch pendulum, a thirty second of an inch may be excellent overswing while for a seconds beat pendulum would be very poor. Rather, measuring in degrees or as a ratio is a MUCH more meaningful term. For a little frenchie, a thirty second overswing may be ten degrees or 20 per-cent ratio of total swing. For a seconds beat pendulum a thirty second may be only a quarter of a degree or less than 1 per-cent of total swing.
    Terms mean everything in analysis.
     
  46. Scottie-TX

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    #46 Scottie-TX, Apr 19, 2014
    Last edited: Apr 19, 2014
    ROB, I really think the value of overswing becomes important here moreso than lift angle. With adequate overswing, the movement is able to overcome variations induced by wearing parts, departing lubes, etc.
    Now if you believe lift angle is a factor in overswing ( it is ) then lift does matter but;
    Is it critical?
    Again; No argument here for me. You just described my pie.
     
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  47. Scottie-TX

    Scottie-TX Registered User
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    #47 Scottie-TX, Apr 19, 2014
    Last edited: Apr 19, 2014
    LAB; I understand that during drop no work is being done. No motion is being imparted to moving the pendulum but;
    With larger locks, drops are smaller and anchor must travel further to unlock. Question is, " is this period of further travel contributing to moving the pendulum?" I think not. As I see it the only period dedicated to moving the pendulum is duration of lift - the time it spends on the lift face.
    While maxing drops DOES increase overswing and makes it POSSIBLE to have good overswing with less power I fail to see that decreasing locks alone, makes swing smaller. To say that increasing or decreasing drops alone changes amplitude of swing is the same as saying it changes the size of the pie. Is this so? Does the pie in fact change size without adding or reducing power?
    Regardless of which pallet is moved I believe the change is distributed equally between the pallets.
     
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  48. LaBounty

    LaBounty Registered User
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    Hey Scottie-

    You don't have to take my word for it. Experiment with it and see if the rate varies. Let us know what you find out!
     
  49. Scottie-TX

    Scottie-TX Registered User
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    "the rate"? Timekeeping - regulation? Oh yes! I believe that does change.
     
  50. Tinker Dwight

    Tinker Dwight Registered User

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    The only way to make the locks unequal is to either put it out of
    beat or have different left angles on the pallets. We've see both
    from messages on this MB.
    Tinker Dwight
     

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