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Off topic question (clock repair)

Sorry to post this question here but I really didn't know where else to address it to. It is obviously not electronics related however I was hoping that someone could never the less help me.

I was given this really nice wall clock. The clock was missing the pendulum and the winding key when I received it. The clock is supposed to chime once on every half hour and then appropriately the correct number on every hour.

A friend who does clock repair gave me a small pendulum and a key. He said the size of the pendulum is not too critical and so he thought that the one he gave me should work. Well it does however the clock is really running slow. It sounds like it's in perfect beat though, and although I've run the pendulum up the stick pretty high now it's still a few minutes slow over a two hour period. I've tried adding some weight to the pendulum but that didn't seem to make any difference.

The clock doesn't look gummy but it is dry. I had planned to spray the movement down with a no residue cleaner and then oil every thing that moves with a light oil. I just didn't want to possibly introduce another problem into the equation before I fix the current one.

So I had some questions. i don't know what this pendulum that he gave me is from. Is the pendulum weight and length critical? My friend says no, however the loss of several minutes over the course of two hours seems really excessive. Is it possible that the incorrect pendulum is causing the current problem and that perhaps there might not even be a problem if I had the correct pendulum? Could the need for a cleaning and lubrication cause such a speed error?

The movement seems to be a fairly nice one and primarily is of brass. Above the manufacturers name, (Mason and Sullivan Co.) there is a number 75. Below that it reads: "no (0) jewels" next line: "Made in West Germany" Below that: " unadjusted" and below that : "141-070". Then on the bottom line there is the following:

29cm

----------

130.37

If anyone has some advice for me as to my questions and how to proceed with this project I would be very grateful. Thanks for any advice on this. Lenny

Reply to
klem kedidelhopper
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Weight, no; length, yes. The length alone determines the period of the pendulum. The weight just needs to be heavy enough to not be affected by air resistance, and light enough to not damage the bearings that support it.

Yes.

I suspect that the major result of crud in the works would be a tendency for the pendulum to stop, or for timekeeping to be erratic.

What did you mean by "sounds like it is in perfect beat"?

Isaac

Reply to
isw

I meant that it produces an even "Tick, Tock", as opposed to a "Tic Tic, Tock", or "Tic, Tock Tock" sound. Lenny

Reply to
klem kedidelhopper

news:alt.horology is the newsgroup for clocks & watches. You should be able to get help here.

Reply to
Michael A. Terrell

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Finally a worthwhile suggestion/comment.

Reply to
hrhofmann

The length of the pendulum should be reduced. Usual there is a nut at the underside of the pendulum. Turn the nut to get the weight closer to the clock. T = 2 Pi sqrt(L / g) where L is the length of the pendulum and g is the local acceleration of gravity. It is independent of the mass.

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Reply to
tuinkabouter

The bottom number is the length and mass of a proper pendulum. Use a search engine to find one.

?-)

Reply to
josephkk

Can't be. Almost every pendulum clock (not controlled by line frequency or a crystal) is adjustable by moving the weight along the length of the pendulum. Thus it must be the moment arm instead of the pure length. Check the units of the equations.

?-)

Reply to
josephkk

Terminology is interfering with communication. There are two 'lengths' of a pendulum. The obvious one is the physical length. The important one for timekeeping is the effective length (or as you describe it, the moment arm). This is the distance from the pivot point of the pendulum hook to the center of mass of the pendulum.

PlainBill

Reply to
PlainBill

weight makes no difference, strictly. Only the distance between the center of gravity and the pivot point controls the timing.

Hmm, that could be the correct pendulum length, maybe?

29 cm = 11.42"

There are second-order effects, though. Too light a pendulum allows the escapement to dominate the swing. But, if adding the weight high on the pendulum doesn't help, then that isn't it. (Adding the weight low on the pendulum effectively lowers the CG, making the pendulum swing slower.)

Jon

Reply to
Jon Elson

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Thanks. I knew that something wasn't getting across.

?-)

Reply to
josephkk

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Thanks for all the great advice guys. I cleaned and lubricated the bushings, it now runs great and I am slowly creeping up on the correct pendulum position. Lenny

Reply to
klem kedidelhopper

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