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  1. #1
    Registered User RobertG's Avatar
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    Default Geneva stop, or what is this?

    Before I take down this small movement for cleaning, I want to be sure I understand what the mechanism noted by the two arrows does. I have been told that it is a "Geneva stop", but the explanation of that mechanism that I have found is that a Geneva stop converts a continuous rotary motion to an impulse rotary motion. That sounds more like an escapement than the device shown here, which is obviously part of the winding/spring mechanism.

    Not that the bottom arrow designates a flat bottomed notch in the lower star wheel with the other notches being more rounded. The upper arrow points to the largest of the five arms on the upper star wheel. What are the purposes of these two differences?

    Is there anything I should make particular note of in regards to these pieces before I remove them, such as their relative positons to each other or toward something else?

    Thank you for your input.

    RobertG
    Attached Thumbnails Attached Thumbnails Pocket watch clock Geneva Stop 1-12-08.jpg  

  2. #2
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    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Geneva stop :

    http://www.flying-pig.co.uk/mechanis...es/geneva.html

    The mechanism works like a fusee clock - taking the best bit of the power in the train and using it over 7 days or so to keep the clock running at a steady, even pace which should keep the time even as well.

    The clock is wound up a bit then the stops are placed so it 'locks' at this point when wound down. When you wind the clock up you can only wind against the stop again to stop the spring getting fully wound up.

    This means you are getting the 'middle' part of the spring power and a steady run down for better timekeeping.

    Hope this helps.

  3. #3
    Registered User RobertG's Avatar
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    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Oldticker:

    Thank you. When I release the click and let the spring down, it releases until the large arm (left arrow) and the flat bottom notch (lower arrow) mesh. They then lock and then the let down ceases.

    This tells me the spring is still under power even though the click is released. So, I must remove the star wheel from around the winding arbor before the spring can be let down all the way.

    How do I know how to align these two star wheels properly, and have the spring sufficiently wound, during reassembly so the Geneva-stop works appropriately in conjunction with the spring tension?

    RobertG

  4. #4

    Default Re: Geneva stop, or what is this? (RE: RobertG)

    "Stop works are added to a movement for either of two distinct purposes: First, as a safety device, to prevent injury to the escape wheel from "over winding", or to prevent undue force coming on the pendulum by jamming the weight against the seat board ; or , second, to use as a compromise by utilizing only the middle portion of along and powerful spring, which varies too much in the amount of its power in the up and down positions to get a good rate on the clock if all the force of the spring were utilized in driving the movement.

    With weight clocks, the stop work is a safety device and should always be set so that it will stop the winding when the barrel is filled by the cord; consequently the way to set them is to wind until the barrel is barely full and set the stops with the fingers locked so as to prevent any further action of the arbor in the dirction of the winding and the cord should then be long enough to permit the weight to be free. Then unwind until within a half a coil of the knot of the cord and see that the weight is also free at the bottom of the case, when the stops again come into action.

    On a spring barrel, it may be taken for granted that the barrel contains more spring than is being wound and unwound in the operation of the clock and it becomes important to know how many coils are thus held under tension, so that we may put it back correctly after cleaning. Wind up the spring and then let it slowly down until the stop work is locked, counting the number of turns and writing it down. Then hold the spring with the letting down key and take a screw driver and remove the stop from the plate; then count the number of turns until the spring is down and also write that down. Clean the spring and put it back the way that it was." REF: The Modern Clock by Goodrich

    Geneva stops are found on what I think are the better quality antique movements made by American manufacturers. Most of these do not use the "middle portion of a long & powerful spring" but use most, if not all of the mainspring. They are set so that when winding the mainspring you can only wind so far and then no further. As we know, clocks can't be "overwound" and this lets you know where the definite stopping point is.

    On modern grandfather clocks they are normally set to prevent jamming the weight into the seatboard and only allowing the weights to descend until there is a turn of cord/cable or less on the winding drum.

    You will notice a long "finger" on one of the geneva stop gears and a wider gap on the other. You set these up so that when the proper number of turns are completed the long finger meshes with the wide gap, thus preventing any further turning. Sometimes these are difficult to properly set up and someone may have a better explanation as to how that's done.

    In fact, on many antique clocks these have been removed because the repair person didn't know what to do about properly setting them up.

    Regards,

    Richard T.


    [edit=2214=1200179638][/edit]
    [edit=2214=1200180109][/edit]
    Best,
    Richard T.

  5. #5
    Registered User RobertG's Avatar
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    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Richard T.:

    Thank you very much for that explanation and the reference for more reading. I will try that let down counting procedure. I can understand why you want to count the turns after the Geneva stop has activated, but I don't see why counting windings from full wind to Geneva stop activation is necessary. I will count both just to be sure and maybe it will become evident as I do it or as I re-install it.

    Thank you again.

    RobertG

  6. #6
    Registered User Tom Kloss's Avatar
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    Default Re: Geneva stop, or what is this? (RE: RobertG)

    For what it's worth, and at the risk of getting flamed.

    I've always felt that "Geneva stop" is a term that is used too loosely in applying it to these stopping devices. The link given by OLDTICKER shows what a Geneva stop is.

    The Geneva stop can be modified to perform the action of a stopping the winding process at a given point. And, indeed you do see them from time to time. I have seen stop work on movements that are a modified Geneva stop devices.

    These devices in this post pictures are IMHO, "stop work", that will stop the clock from being "over wound". And, we all know that can not be done.

    I've included a picture of a Geneva style stop work. It's on an alarm mechanicsm

    But then again, a rose by any other name would smell the same.

    Donning my flame retardant vest.

    Tom

    [colour=blue]“Sometimes you really don’t know if your being rewarded or punished”[/colour]

    Attached Thumbnails Attached Thumbnails stop.JPG  
    "Find a need and fill it". Henry J. Kaiser


  7. #7

    Default Re: Geneva stop, or what is this? (RE: RobertG)

    I think part of the problem is terminology. It seems that the terms "Geneva Stop" and "stop work(s) are used interchangeably. Several references list geneva stops as...."see stop work"..........



    Richard T.
    Best,
    Richard T.

  8. #8

    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Klossee is correct. Geneva stops are a modified form of Geneva gearing which are designed to convert continous rotary motion to indexed stop/start rotary motion. I believe Geneva gears form the guts of film projectors allowing the film to pause at each frame and quickly index to the next.

    Both pictures in this thread show stop work but only one is a picture of Geneva stops.

    Fusees are not at all similar to stop work. Fusees are designed to equalize the power applied to the clock over the run. There is stop work in a fusee clock (the stop iron) whose main purpose is to prevent the gut or chain from being wound past the fusee.

    Rich McCarty, GradBHI & West Dean College
    http://www.restoredclocks.com

  9. #9
    Registered User Tom Kloss's Avatar
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    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Quote Originally Posted by Richmccarty
    ...I believe Geneva gears form the guts of film projectors allowing the film to pause at each frame and quickly index to the next....

    Rich McCarty, GradBHI & West Dean College
    http://www.restoredclocks.com
    Rich

    Yes. The mechanism used in a film projector, is called a Geneva intermittent movement. Very precision machining as they run a high speeds. The clock stops are a variation of that movement.

    As aside, did you ever notice that many movements that have stop work, half of the work will be missing. [colour=red]My guess is that a lot of clock repair people just don't know their purpose, just throw them away or they don't know how to set them up. Sigh, throw them away and you don't have to deal with them. [colour=black]

    Tom

    [colour=blue]“Sometimes you really don’t know if your being rewarded or punished”[/colour]

    "Find a need and fill it". Henry J. Kaiser


  10. #10
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    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Quote Originally Posted by Richmccarty
    Fusees are not at all similar to stop work. Fusees are designed to equalize the power applied to the clock over the run. There is stop work in a fusee clock (the stop iron) whose main purpose is to prevent the gut or chain from being wound past the fusee.

    Rich McCarty, GradBHI & West Dean College
    http://www.restoredclocks.com
    Can you clarify where the fusee is not at all similar to the clock design in the original post?

    Both have stop mechanisms.
    Both are wound up a bit then 'locked' with power on.
    Both utilise the middle part of the mainspring power "- designed to equalize the power applied to the clock over the run".
    Both cannot be overwound.

    The ONLY difference is the fact the fusee doesn't have a 'geneva type stop.

  11. #11

    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Robert,

    If the spring is not broken you can let it down until the stop comes into play. Then remove one of the stars and COUNT the remaining turns as you let it down the rest of the way. When reassembling, wind the spring to the previous point and reinstall the star.

    When replacing a broken spring YOU will need to establish the working area of the new spring.

    Joe

  12. #12

    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Klossee-

    I think one of the reasons that Geneva stops are often missing on carriage clocks is that slop in the barrel arbor bushings can cause the Geneva stops to prematurely stop the clock because of the close clearances involved. So instead of properly fixing the bushing, which requires a lathe and some knowledge, some 'repairmen' just throw out the stop work.

    Oldticker -

    Stop work does not compensate for changes in the power of the spring as it winds down, which is the primary purpose of the fusee. The radius of the fusee gets larger as the gut winds down, thus compensating for the reduced spring force.

    Torque = radius X force

    The idea is that as the force of the spring decreases, the radius of the fusee increases, thus equalizing the torque appied to the fusee arbor. Also, there is a (variable) gear ratio between the spring barrel and the fusee. Typically, 16 turns of the fusee will give 7 or 8 turns of the barrel. Stop work is incorparated into the fusee mechanism primary as a safety device as winding the gut past the fusee groove can be disasterous.

    By the mid-late 18th century springs were available that were consistant enough to obviate the need for the fusee. The French knew this, but due to conservative nature of British clockmaking, the British continued to make fusee clocks all the way through the 19th century. A modern (ish) sping combined with stop work will give good results by using the middle of the spring wind, as you suggest.

    Rich McCarty, GradBHI & West Dean College
    http://www.restoredclocks.com

  13. #13

    Default Re: Geneva stop, or what is this? (RE: RobertG)

    I am always use caution when giving advice on this type of question. The answers assume either the clock was never taken apart or that during previous repairs the stop gears had been assembled correctly or the spring hasn't aged.

    I have quite a number of 8 day ST clocks with dual springs and use the following procedure to set the stops.

    Remove the stops and fully wind the springs. Run the clock. At the end of the first 24 hours, rewind the springs counting the number of turns. This number gives the turns per hour which we will use later.

    Next, rewind the clock and using a Microset timer record the rate every 24 hours until the clock stops. This data will give you the dynamic spring rate over the running period of the clock.

    Plot a curve of the clock rate data on graph paper ( rate vertically and hours or days horizontally ). Select a 192 hour (8 day ) segment that is most linear and if not linear a segment that is a good average of fast and slow.

    The beginning of that linear segment is where we want the stop works to jam. Using the graphed data determine the elapsed time (hours) from fully wound to that start point on the curve.
    On the graph determinine how many hours that increment of time is and using the turns per hour from above paragraph crank it into the spring. Then install the stop work gears to jam at that point.

    We now have the stopworks set at the point to run the clock most accurately over the full running of the spring
    [edit=846=1200251804][/edit]

  14. #14
    Registered User RobertG's Avatar
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    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Thank you, everyone. This has turned into a very interesting discussion.

    The spring on my clock is not broken, so I don't have that variable to contend with, and I do have a Microset time, so I can follow Sherm's advice as well.

    It might be interesting to do a comparison of the two methods and see if one has better results than the other.

    Here is a photo of the stop works when it is activated, "jammed" as described above.

    RobertG

    Attached Thumbnails Attached Thumbnails Geneva stop activated 1-12-08.jpg  

  15. #15

    Default Re: Geneva stop, or what is this? (RE: RobertG)

    Quote Originally Posted by Sherm
    I am always use caution when giving advice on this type of question. The answers assume either the clock was never taken apart or that during previous repairs the stop gears had been assembled correctly or the spring hasn't aged.

    I have quite a number of 8 day ST clocks with dual springs and use the following procedure to set the stops.

    Remove the stops and fully wind the springs. Run the clock. At the end of the first 24 hours, rewind the springs counting the number of turns. This number gives the turns per hour which we will use later.

    Next, rewind the clock and using a Microset timer record the rate every 24 hours until the clock stops. This data will give you the dynamic spring rate over the running period of the clock.

    Plot a curve of the clock rate data on graph paper ( rate vertically and hours or days horizontally ). Select a 192 hour (8 day ) segment that is most linear and if not linear a segment that is a good average of fast and slow.

    The beginning of that linear segment is where we want the stop works to jam. Using the graphed data determine the elapsed time (hours) from fully wound to that start point on the curve.
    On the graph determinine how many hours that increment of time is and using the turns per hour from above paragraph crank it into the spring. Then install the stop work gears to jam at that point.

    We now have the stopworks set at the point to run the clock most accurately over the full running of the spring
    Sherm, you are a purist, aren't you! Bless your heart for that! I wouldn't be above removing the stops altogether in spring driven clocks, and will refrain from doing that due partly to good examples like you

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