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Clocks that run too fast--what to do?

jboger

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This is a question I've had for some time. Other than adjusting the length of the pendulum, how can a clock that runs too fast be brought back on line? I don't have a specific clock in mind other than typical spring-driven American clocks like Gilberts, Sessions, Seth Thomases, and a whole host of late 19th C ogees and kitchen clocks. Some I've had could be adjusted by the pendulum, others no. My question is directed to the latter, Can anything be done for those clocks?

John
 
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shutterbug

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Some have adjustments you can access with a key in the front dial. They function using chops (look that up) which can be lowered or raised with the key to increase or decrease the BPH settings. Most also have a suspension rod which is a wire with a suspension spring on top. Often these break and are replaced by people who don't really understand how clocks work. So they could make them too long or too short to adjust. If that's the case, you have to replace them with a proper length unit. Naturally, if they are too long they can just be cut shorter at the loop end.
If you replace one, the chops should be set to center position and the length of the suspension rod adjusted to where it's very close to keeping good time. Then use the chops for fine adjustments.
 
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jboger

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Thanks, Shutterbug. Let me check into this "chops. I've noticed them before but have done little with them. I looked at one recently on a Sessions that I dismantled. If I'm not mistaken (probably am), this little mechanism adjusts the length of the pendulum rod from its pivot point (the top) down to the point where the rod makes contact with the crutch. That length affects the BPH?
 

shutterbug

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Yes. Some adjust the length and others just choke up on the spring. The effect is the same. The more spring showing under the chops, the slower it runs.
By the way, if you need a new rod, here's a link.
 
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Robert Horneman

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If the fan is slipping on its arbor that could cause the strike train to run too fast. The fan needs to be loose enough so it slips a little when the train stops.
 

jboger

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Again, thanks. Most of my clocks don't have the chops; they're early 19th C triple deckers or wood works clocks. I've noticed this adjustment but never thought much about it. It's on two French slate clocks I have, one of which I recently got but haven't cleaned yet.

May I hazard a guess? Clocks with short pendulum drops are more sensitive to this adjustment than those with longer pendulum drops. That is, a small adjustment can have a bigger effect on these clocks than those with longer pendulum rods.

Have a good holiday.

John
 

shutterbug

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May I hazard a guess? Clocks with short pendulum drops are more sensitive to this adjustment than those with longer pendulum drops. That is, a small adjustment can have a bigger effect on these clocks than those with longer pendulum rods.
That would be a correct guess ;)
 

Ralph

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No one has mentioned, too strong of a suspension spring, being the cause.. It’s a common problem.

Ralph
 

jboger

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Ralph:

Yes, I could see that. Too stiff a suspension spring could/would change the vibrational frequency of the pendulum and thus cause the clock to run fast. Given that we often don't know the repair history of these clocks, who's to say if the original rod is "in there".

John
 

ChimeTime

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John -
I have limited understanding and experience with clock movements, but my grasp of the physics of pendulums is much better, so maybe I can help you.

First of all, it may help you to mentally separate the pendulum from the time train. They are actually 2 separate and discrete simple machines, forever locked in a co-dependent relationship. The time train by itself would loose energy far too fast if it were not moderated by the pendulum. On the other hand, the pendulum would eventually loose energy and stop swinging if it were not for the tiny amount of power the time train imparts to it. So they work together, the time train stores the going power, and the pendulum slowly meters out the release of that power. Therefore if the rate is too fast, look to the pendulum.

The pendulum works by swinging back and forth, and the time of its swing (the period) is set only by its Length and the local strength of gravity. That bit is common knowledge. Pendulum "Length" is then the distance from the point of rotation to the Center of Gravity of the swinging weight. At the upper end is typically a suspension spring acting as a pivot point. The exact point of rotation is hard to pin point, but what is clear is that shortening the spring, shortens the active pendulum length.

However, the bottom of the pendulum is where the greatest confusion is found. The CG of the pendulum is not the center of the bob, it is the Average location of ALL the weights that comprise the weight of the pendulum. In other words: the CG of the leader and its distance to the pivot, PLUS the CG of the bob and its distance to the pivot, PLUS the CG of the rate nut and its distance to the pivot, PLUS the CG of the rate nut washer and its distance to the pivot.... all divided by the total number of elements (in this case 4).

This position of the CG can cause curious things to happen. If you replace a plain grandfather clock pendulum leader with a fancy brass lyre or 9 wire compensating type, even though the pendulums are both the same physical length, the clock will speed up. This is because weight was added between the existing bob and pivot, which moved the average CG of the entire pendulum upward. Conversely, If your clock is too fast and your rate nut is on its last thread, you can add voids to the top of the bob, thus moving the CG lower on the pendulum and thereby slowing the clock.

This last method was used to slow a recent repair. By removing the top of the bob weight, the CG for the bob moved ~1/4" lower, thus helping to slow a runaway clock.

Hope this helps.
IMG_20210809_180637692.jpg
 

shutterbug

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The factory suspension rod can usually be made to work OK. The length is more important than the thickness of the spring, as long as the thickness allows enough swing.
 

Ralph

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Yes, I could see that. Too stiff a suspension spring could/would change the vibrational frequency of the pendulum and thus cause the clock to run fast. Given that we often don't know the repair history of these clocks, who's to say if the original rod is "in there".

John
John,

The goal is that the suspension should not affect the rate at all. The theoretical pendulum you see in physic books, has a frictionless suspension point. The suspension spring is a necessary evil, if it is selected as the suspension method, It must be strong enough to support the weight of the pendulum bob securely, but weak enough to have minimal effect on the rate. I would say the suspension springs for the clocks you described, should be .003” or even less in thickness.

Ralph
 
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Willie X

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That point about the 'to strong' suspension rod/spring, that David L made, is especially true for one piece 'made in India' suspension rods.

They are not made correctly and should be avoided. Use the 3 piece ones .003" thick, they are also from India but work fine.

The original one piece springs were rolled to the correct thickness and annealed (left soft) very few of these are left. The Indian replacements are rolled and left to thick and work hardened.

Many of these one piece Indian rod/springs have been used as an effort to keep originally, which would normally be a good thing but not in this case.

This has been going on for a long time.

Willie X
 

shutterbug

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You can thin the spring part with emery paper, a file, or even a bench grinder. Then you'll know if the thickness is causing the issue or if it's something else.
 

jboger

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Thanks, folks. More good advice.
 

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