Antique Clocks/Sth Thomas 124 clock speed
QUESTION: I have a Seth Thomas mantle clock with the #124 movement. The clock has been in storage for a long while and seems to run fine, the Westminster chimes all work properly, but the clock loses about 10 minutes in 30. I have tried different pendulum bobs, adjusting them from minimum to maximum length, and in desperation run the clock with the bob removed and with the movement ticking away like crazy. The clock still loses about 10 minutes in 30. How can this be? I am not unfamiliar with these clocks, having rebuilt a few and getting them to work well again. But this is a mystery and I hope that perhaps you can give me a clue?
ANSWER: Assuming the clock has been lubricated after being removed from storage, the problem has to be the pendulum is too long. The period of oscillation of a pendulum varies little, if any, with the weight of the bob. To lose 10 minutes in 30 the pendulum would have to be shortened about 40%. As the period of oscillation goes as the square root of the length.
There is no other thing that affects the beat rate of a pendulum clock to the extent of error you are experiencing other than pendulum length. The amount of push provided by the main spring has a very slight effect, lack of lubrication generally causes them to simply stop although it could have a slight effect.
I recently acquired a clock which had no pendulum. I have been experimenting with pendulum lengths. I am using a small weight and a piece of wire to get an idea how long the pendulum should be. You could do the same thing. Of course I have not been able to get the clock to keep accurate time as I have no means of precision adjusting the pendulum length. On my next order to Merritts (www.merritts.com) I will obtain the correct length pendulum.
I hope this information will be helpful to you.
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QUESTION: In your answer you suggest that "There is no other thing that affects the beat rate of a pendulum clock to the extent of error you are experiencing other than pendulum length." In my question, I said that "I have tried different pendulum bobs, adjusting them from minimum to maximum length, and in desperation run the clock with the bob removed and with the movement ticking away like crazy. The clock still loses about 10 minutes in 30.."
So my question remains the same: Even with NO PENDULUM BOB on this clock and the pendulum stem "beating" at a crazy-fast rate, the clock still runs as slow as it does with the pendulum bob attached.
There is a possibility your clutch which causes the center wheel to rotate the minute hand staff may be slipping. However, when this happens the minute hand simply moves to one of the points where the chime cam contacts the follower and then stops completely. I would have expected, as you did, when the pendulum rod is swinging rapidly the minute hand would also move rapidly. Gaining time instead of losing time. I have experienced problems with clutches and this generally requires complete disassembly of the clock. this happens because one of the pressed on collars gets oxidized and loses its grip on the staff. The clutch spring then pushes the collar away. My experience has been the amount of time loss varies greatly and often results in the minute hand not moving at all. You can tell the clutch is defective because the minute hand is very easy to turn.
Let me know if this is of help.