convert watch to weight driven clock

Discussion in 'Horological Misc' started by tig1, Dec 5, 2011.

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  1. tig1

    tig1 Registered User
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    Nov 14, 2010
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    Ya,sounds pretty kooky but i wanted to try it.I thought i saw it done before but without the weight driven part,just an added pendulum. I'd be using an old english verge fusee movement.I figured i'd remove the fusee cone and replace it with something smooth,not unlike the mainspring barrel,to wrap the weight line around.Does the circumference of the barrel matter,as i can adjust the weight to get the right force.Then attach a crutch to the balance and install a suspension spring mount to the movement.
    I was just worried that the balance may require more swing to jump to the next tooth of the crown wheel than the balance has power to push it.Or in other words,it may require the pendulum to have a really large arc of swing.Can the arc of the pendulum swing be adjusted with crutch somehow? The way its mounted ,the length,something?
    I'm definitely not a watchmaker but i've been fixing watches and clocks for a few years now ,mainly my own stuff.
    Somehow this seems possible.Maybe not but if there isnt any laws of physics to be broken i'd like to try it.
    Once i get an idea in my head it's hard to get out.even if it ends in failure. :)
    Thanks for your insight.
     
  2. Tom McIntyre

    Tom McIntyre Technical Admin
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    If you want it to keep time, the pendulum has to swing as fast as the balance would. Typical verge is 4 beats per second although many are faster. Just off the top of my head, a verge needs about 22 degrees to escape and impulse, so you would need an 19 inch pendulum swinging through 22 degrees. It seems doable to me. The weight is easy, as you say, just wrap some high tension fishing line around a smooth barrel the diameter of the fusee using the great wheel of the fusee.
     
  3. tig1

    tig1 Registered User
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    Thanks Tom,so at least i know i'm not crazy for trying it.Any ideas to how long the pendulum would be? Also I'd think it'd have to be pretty light to swing that fast. And that's with a bob for speed adjustment.I have one of those novelty cuckoo clocks and the pendulum has quite a large swing to it.I guess if i use light enough material the balance should have enough impulse to keep it going. Do you think i need to remove the rest of the balance and just keep the balance staff itself? I can't see as how it would serve a purpose anymore.
     
  4. Scottie-TX

    Scottie-TX Registered User
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    While TOM suggests a possible starting point for a pendulum length, I would think amount of power - weight - would be closely related to the additional task of swinging the additional mass of a pendulum.
     
  5. Tom McIntyre

    Tom McIntyre Technical Admin
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    A detached pendulum would be about 1/2 meter effective length but there are so many variables it is hard to tell. Most of the random variables would make it need to be longer, but the escapement error is likely to be huge, so that might make it much shorter.

    These guys who work on Connecticut kitchen clocks should know how fast a short one of those beats. They might be 8 bps. I might have to wind one to find out. I normally only do that when I am expecting company that I want to either amuse or annoy. :D
     
  6. praezis

    praezis Registered User

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    Not so hard to tell if you use the well known pendulum formula. It gives 6.25 cm effective length for 4 bps. :eek:

    Regards
    Frank
     
  7. Tom McIntyre

    Tom McIntyre Technical Admin
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    Oops! I had it upside down. I was thinking 1/2 the length is 1/4 the period, but it is actually 1/4 the length is 1/2 the period.

    We use beat to mean the half period, so a seconds beating pendulum has a period of 2 seconds. For rough calculations, 1 meter is a good length and easy to remember.

    beat = C x sqrt(length) where C is a constant involving pi and gravity.

    If you need a beat of 1/4 second then the length must be 1/16 that of a 1 second pendulum (1 meter) or 6.25 cm as Frank pointed out.
     
  8. Tinker Dwight

    Tinker Dwight Registered User

    Oct 11, 2010
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    Hi Tom
    For a 1/4 second beat, I get a pendulum of about 2.3 inches.
    I'm not sure where your 19 inch came from?
    Dwight
     
  9. praezis

    praezis Registered User

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    Tom,
    I also have to think it over every time.
    For fast rough calculation there is an easy to remember formula (dimensionally not consistent, use 'seconds' and 'meter'):

    T=sqrt(L)
    or
    L=T^2

    Regards,
    Frank
     
  10. tig1

    tig1 Registered User
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    I think Tinker is on the right path. The mass of the pendulum,whether it's attached right to the balance staff or driven by a crutch,has to be,i would think,no heavier than the original balance.And the farther the mass is from the center of motion,the harder its going to be to move.Especially quickly back and forth. So a short pendulum is a must. And making a pendulum driven by a crutch is more components hence more mass.Unless everything is made very thin.
     
  11. Tinker Dwight

    Tinker Dwight Registered User

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    Hi
    The length I stated is from the center of the swing to
    roughly the center of the bob. For such a short pendulum,
    I'd use an arrangement like a cuckoo or better yet,
    a knife edge. A suspension spring would most likely
    be too stiff and you'd need to make the pendulum
    longer to compensate.
    As for weight, don't worry as much about the weight
    of the bob. The watch only needs to replace any
    lost energy and not anything more.
    Too light a bob and you'll not have enough inertia
    to keep the pendulum swinging. Too much weight and
    you'll have less over swing, requiring more careful
    adjustment of the verge and escapement ( what ever type ).
    Worry more about inertia of the system. A rotating
    thing like a balance wheel has quite a bit of inertia
    even if it has little weight. The pendulum will have to be
    many time heavier to be comparable.
    Consider making the crutch with small piano wire.
    Tinker Dwight
     
  12. tig1

    tig1 Registered User
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    Interesting, i've never seen a knife edge before.Now i'm not sure what you mean "from the center of the swing". I assumed it was measured from the mounting point to the bob. Also ,does that mean i should leave the balance intact to insure enough inertia and just attach the crutch to the balance?
     
  13. tig1

    tig1 Registered User
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    Hello,i have an update now. I picked a movement and stripped it down to whats needed.No balance or hairspring,no regulator,no mainspring.

    movement.jpg

    test.jpg

    pendulum parts.jpg

    pendulum made.jpg

    crutch.jpg

    mounted pendulum.jpg

    I did some weight driven tests,and after giving it a cleaning it will run steady on 3 ounces.(the pics are before cleaning!)Each weight is 1 1/2 ounces.
    The crutch is made from piano wire, just a test one to check fit. The pendulum has a nice swing to it and will actually go for a bit on its own.The knife edge really seems to work well.I left the top really long because i wasn't sure how much to leave for counterbalance of some type.
    Does anyone see something that needs changing? Any comments are appreciated. Thanks.
     
  14. RJSoftware

    RJSoftware Registered User

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    Hey Tig.

    Not to complain, but man that looks like an old keeper. An old pinned movement with nice engraving work.

    Me, I would have sacrificed a dollar watch movement or simular.

    About the anchor/crutch arrangment. When you get there, guess things will be permanent alteration.

    You could super glue some post for your anchor instead of drilling new holes.

    If you still have the lever to it, maybe you could attach your crutch there. But man it's gonna have some tourque to tear up the lever jewels if the crutch even gets the slightest pressure.

    Normally if for some reason the lever jewel lands in wrong spot the balance would just stop. Not much torque. But putting a crutch and pendulum is bound to wreak havoc on the jewels especially. Just one little bump the wrong way and "crack".

    I'd keep the balance wheel configuration and skip the pendulum and just have it weight driven.

    You could even avoid any damage if you arranged the weights strings to wrap one time arround barrel arbor or however your doing this.

    Wrap one time arround and have a small weight to hold string taunt on one side and heavier weight on other to give power.

    That way you could avoid wrapping up string in the barrel and make it a pull wind like a cuckoo.

    Pretty cool what your doing anyway. Just I would use a less historical valued movement.

    RJ
     
  15. tig1

    tig1 Registered User
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    An update: Everything went fairly easy. The crutch was a snap using piano wire,thanks Tinker. The knife edge works great ,just have to devise something so it doesnt want to walk around. I havent tested for accuracy yet,still fiddling with the pendulum rod.The top part i cut off and filed the front and back of the rod to cut the weight down.Now it's approaching the speed it had as a watch. I'm trying to work out chiming,but if not i'll at least have a passing strike.
     

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