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May 22, 2011 at 9:54 am #48067estanek70Participant
I have been asked by an antique dealer that I work with to install a missing pendulum on a Frech clock. The movement is mounted in what looks like a vase. The movement is 3 inches in diameter and the pendulum hangs on a loop of string that is mounted on a post that extends from the back plate off the movement. I have found a length and weight that alllows the clock to run in beat through trial and error but I cannot figure out how to adjust the beat. The crutch extends through the back of the case but I cannot get to the verge without taking off the back plate. Since I have never worked on a french clock before, I am reluctant to do this. Does anyone have any info on how to adjust the beat on this type clock? Thanks for any help you can provide.
Ed StanekMay 22, 2011 at 10:27 pm #50710Bob TascioneModerator
I believe what you are referring to is what’s called a silk thread suspension. One end of the thread attaches to the post and the other end passes through a hole on the post and extends down to and wraps around an arbor. The pendulum rate is adjusted by rotating this arbor which either shortens or lengthens the effective length of the pendulum by winding or unwinding the thread. The silk thread suspension was found on most early french movements. If the movement has a Brocot escapement, ie; one that has the pallets and escape wheel on the outside of the dial, then it should have a clutch type beat adjustment. You could just push the pendulum to one extreme or the other to set the beat. If not a Brocot then my guess is that the crutch may need to be bent in the correct direction. Your cautious approach is a wise one as forcing the pendulum can easily bend the delicate teeth. There is often another way to adjust the beat in these clocks. These round movements are mounted in the case by slipping into a drum or ring and are secured in place by tightening the screws that hold the back door onto the clock. If the adjustment needed is a minor one then loosen these screws, start the pendulum swinging and slowly turn the front bezel while listening for a steady beat. When you think you have it let it run for a minute or so until the pendulum settles down to a normal swing. If it sounds good then tighten the screws and your all set. These movements are very high quality and generally show little wear after many years of use. The plates are thick and the pivots, pallets etc. are hard and highly polished. Beautiful movements! If you decide to repair it then pay particular attention the the small pivots when assembling. As I just mentioned, they are hardened and can break if not lined up in the holes when tightening down the plates. As long as you don’t force anything you should be fine. They actually assemble quite easily and are a pleasure to work on.
Hope this helps Ed,
BobMay 23, 2011 at 7:20 am #50711estanek70Participant
Hi Bob, thanks for your response. On this clock, there are no escapement parts outside the dial. The back of the movement is held in place by four pins. There are also two arbors extending through the face for winding main springs. One seems to work fine, but the other does not feel right so I did not try to wind it. I can see where the silk thread could extend down but the crutch has a rectangular piece that is at right angles to the crutch and that the pendulum shaft must fit inside. A thread through this piece would move at least 1/8th of an inch before contacting either side of the opening. It looks like a solid pendulum shaft would be required. The clock is still at the store so I don’t have any pictures.
I did experiment with short rods at the store and I did get the movement working and it was in beat without any adjusting. I will be going to the store this morning and will try to get some pics that I will try to post here. Thanks again.
EdMay 23, 2011 at 7:59 am #50712Bob TascioneModerator
The pics might help me to figure out what you’re describing. From how I visualize your descriiption though (I could be way off) I think all that you need to do at this point is hang your pendulum from the thread loop. The loop doesn’t extend down through the crutch. The silk thread loop design was eventually replaced by a suspension spring which passed through a brass block or chops that could be moved up and down the spring for regulating. The adjustment for the silk thread just raises or lowers it a little for regulation. Anyway, if you get some pics of the clock please do put them up here or email them to me and I’ll throw them up here for you. Sounds like a nice clock.
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