Pendulums, crutches, and pivot points.

[Brian Decker]

I don't want to dive into an overly technical discussio n - so I'll try to stay above water on this.  In GM the top of the pendulum attaches to the pallet shaft.  In all metal movements and most wood movements the pendulum shaft is hung from a spring or suspended from a separate pivot and the impulse is transmitt ed via a crutch which is attached to the pallet shaft.  To keep the calculati ons correct is the pendulum length kept the same regardles s of its suspensio n point?  In other words is the pendulum length the same using a crutch and separate pivot point as it is when attached directly to the pallet shaft?

[ArtF]

Brian:

   In a word, yes. While a virge can be used instead of hanging to the pendulum shaft, its really more a way of "beating" in the clock. Bending the virge one way or the other will cause the "tick" and "tock" to be equal in volume. At that point it usually means your hitting the lock face on either pallet at the same point. I hang on the pendulum shaft simply as its the best way to show it...and in my clock I acutally do it tht way. For me its because its plastic, and friction will hold it snug to the shaft, yet allow me to move it slightly back or forth on the shaft while the pawl is held still, this basically does the same thing as a verge.
   The virge ( or crutch) can be placed further up or down the shaft to change the pendulum arc limit, but generally this doesnt change the
gravitic constant which really dictates the timing as the virge should be set just far enough down to ensure the pawl pivots the full amount it should, which is the point at which the deatbeat hits a lockface on each pallet when the drop occurs. The deadbeat should not hit the pallet directly, if so, the virge is too far up..if the virge is too far down, the pawl will be forced too far into the tooth..so you pick a point at which the deadbeat pins safely hit the lockface before sliding down onto the pallet. Stay with a pendulum of appropria te length though, as this adjustmen t shouldnt affect timing. The period of swing will be ( or should be) the same no matter the amplitude ( arc) of the swing. Think of it as Amplitude of swing is a function of virge and pawl mechanics, and Time of swing is gravitic constant applied to the length formula. ( Which GM does for you. ). A virge is very helpfll to Beat in the clock as you just never know how level the clocks mount will be, the virge corrects for that non-levelness by allowing you to adjust for center properly.
   As to hanging on a pivot, I do that on my wooden clock because the arc had to be shorter than actual swing, and the virge wire can do that well by moving up and down. Some now use a sping steel ribbon to hold it as the spring helps the return swing get up to speed.

 Hope it helps,
Art

[Brian Decker]

I cut and assembled a simple escapemen t test last night - note to self the pallet is not omnidirec tional   A 50% shot at being wrong made 100% certain by haste lol.

[ArtF]

Brian:

  LOL..happ ens to the best of us..

Art

[Brian Decker]

Hopefully I can get in the shop tomorrow and get some parts cut.  I drew up a quick crutch in PW and will post some pics.   

[BobL]

Brian;

 I enjoy seeing those pictures, thanks for sharing.

Cheers
Bob

[John T]

Unless there is a significa nt distance between the pallet pivot point and the pendulum pivot point, my experienc e is that the length of the verge does not affect the size of pendulum arc.

  The reason for separatin g the pendulum pivot and pallet pivot is so that the pendulum can easily be removed when the clock is transport ed.  As well when the pallet arbor is used as the pendulum suspensio n the weight of the pendulum will "weigh" on the pallet pivot and can cause significa nt problems  with friction and will make the clock require more weight (power) to operate.

In clocks that I have experimen ted with the weight reduction to make the clock run reliably can be only half when the pendulum has its own suspensio n point and is driven by a verge.

[dansfoundry]

Could someone guide me to a picture showing what the different parts are I know what a pendulum is Thanks DAN

[ArtF]

John:

   Good points. Its why I say Im no expert, while Ive built a few clockwork s, I dont have enough empiracle data to show such things. Good to have more experienc e in the mix. Luckily in my clock the pendulum will simply twist off for
moving it, but a virge and proper hanging would typically be lower friction. Mine hangs directly off a good bearing so it wasnt important in this one.
  My wooden clock though uses a pivot assembly to hang on, much lower friction. .

Art

[Brian Decker]

This is a typical pendulum and verge (crutch) assembly:


A- the crutch or verge
B- verge fork - this is where the pendulum and pallet pivot actually interface
C- suspensio n spring hang point - ideally this is placed on the same horizonta l plane as the pallet pivot shaft
D- suspensio n spring - a flexible piece of metal that helps to isolate pendulum vibration from the rest of the clock as well as slow and accelerat e the pendulum swings
E- suspensio n spring/pendulum rod attachmen t point
F- pendulum rod

Hope this helps

[John T]

A couple more part definitio ns.

Arbor:
  The axle upon which a clock's pinions and wheels are mounted. The arbor carrying the balance or pallets is often called a staff.

Pivots:
Are the holes in the plates (frame) into which the arbors fit.

Pallets:
The pallet is the actual face of the "rocker" that makes contact with the escape wheel teeth.

[BobL]

Brian;

 Nice clip of a typical pendulum and verge. May I use this clip in our tutorial?

Cheers
Bob

[Brian Decker]

Anything I post here is up for grabs   Bob and Art I owe you more than you know - this software is revolutio nizing how I develop my projects.  I can't believe the user community is so small - care if I do some advertisi ng on the shopbot forums?  (not real advertisi ng as it is banned but more along the lines of "hey look at this great stuff I designed in GM!)

[BobL]

 Hi Brian;

 Thanks for the great comment and feel free to share your view point to who ever and when ever. As you probably know Art and I  have always tried to steer the developme nt part around users needs and requireme nts, so it is folks like you, our users, that help us make this software package better all the time. To all of you out there, never stop dreaming and thanks for sharing your ideas with us..

Cheers
Bob

[dansfoundry]

Thank you Brian, John for the education, and thanks to Art for the latest video. soon I will begin a clock project. Dan