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correct pendulum weight

jpbar70+nawcc

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Sep 23, 2021
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Hello,
I recently restored a small clock which had no pendulum. I calculated the length by the formulas in the site and installed a new pendulum.
The lenght should be ok, because the case is closed but has a small window where one can see the pendulum, it it fits nicely.
The problem is that it is running faster around 30min per day and I suspect that the pendulum is too light. I could bring the pendulum bob down but then, it will be out of the see through window.
Could the weight be the problem? How should I check the correct weight? By trial and error?
Thank you for your help.

joão pedro
 

wow

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Jun 24, 2008
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The weight has very little to do with the rate. Since it is 30 minutes off, I suspect that the movement has been changed at some point or the anchor is skipping a tooth on the escape wheel ocassionally. A video of the clock running would help us.
 
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Dick Feldman

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Many/most of the pendulum calculations are based on theoretical pendulums. Those pendulums have one dimension, length. Theoretical pendulums are devoid of friction, etc. The calculations are useful in getting only a reasonable estimate of proper pendulum length.
In the real world of pendulums, the correct pendulum is the one that will make the clock keep time. (The rate of the hands will be correct) That sounds like doublespeak but in the real world it is true. After a pendulum is installed, it is normally necessary to adjust length to make the hands perform properly.
Proper time keeping is a relationship between the speed of the escape wheel and the clock hands. It is evident your escape wheel is turning faster than it should. Good sense and experience tell me that the verge is occasionally skipping a tooth, your calculations were in error or there is something else wrong. The gain you are experiencing is excessive and I do not believe length adjustment will be the solution.
As was mentioned, pictures or a video would be most helpful.
JMHO
Dick
 

Uhralt

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Sep 4, 2008
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How light is the bob in comparison to the mass of the complete pendulum? To slow down the clock (assuming there is not a problem with the escapement as Will and Dick mentioned), you need to lower the center of gravity of the complete pendulum. If the pendulum bob is very light this can be done by adding mass to the bob.

Uhralt
 
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Dick Feldman

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The variation you are seeing will not be affected much by changing critical mass, the thickness of the suspension spring, etc.
Something else is way wrong.
JMHO
Dick
 
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c.kugle

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Jul 15, 2021
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Hello,
I recently restored a small clock which had no pendulum. I calculated the length by the formulas in the site and installed a new pendulum.
The lenght should be ok, because the case is closed but has a small window where one can see the pendulum, it it fits nicely.
The problem is that it is running faster around 30min per day and I suspect that the pendulum is too light. I could bring the pendulum bob down but then, it will be out of the see through window.
Could the weight be the problem? How should I check the correct weight? By trial and error?
Thank you for your help.

joão pedro
"Normaly" weight has little effect on ratebut when you crunch the variables ie pendulum length, escapement wheel diameter and gear to spring ratios it will come down to weight. When I was restoring a New Haven regulator I asked the same question and received the same answers you have-longer pendulum length and others.. I hung the heaviest bob I had and started adding fishing sinkers one ounce at a time. In the end I bought a nice 14.5 oz. bob and now the clock is dialed in and keeping perfect time down to less than a minute a month deviation.. So weight does matter since you cant use a feather nor a brick...
 
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Willie X

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Feb 9, 2008
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First, "a small clock" doesn't tell us to much. :???:

Try a pair of 1 ounce stick-on wheel balancing weights on the back of your pendulum bob, near the bottom edge, just to see what happenes. This will lower your center of gravity a bit and thus slow your clocks rate. This together with maxing out your down position on the rating nut is about all you can do, short of making a longer pendulum rod, or using a SMALLER but heavier bob.

Note, very few pendulums swing in the center of the door, or viewing portal. So don't go by this.

Willie X
 
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ChimeTime

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Look up the formula for a pendulum. You'll see that Weight is not even a component of the formula. Only Length, acceleration due to Gravity, and some other minor considerations.

Drop the bob 1/2 inch (~13mm) and see what happens.
 
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shutterbug

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Lowering the bob will probably still allow it to be seen in the window. As Willie said, they rarely run centered in the window.
 
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Fitzclan

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Many times the pendulum doesn’t show in the window but that was probably not the original intention.
Over the course of a clocks life, the suspension spring may very well have been changed.
A stiffer (thicker) spring will cause the clock to run faster as will a shorter one.
Add these together and your pendulum will have to be adjusted down to compensate for the faster rate and the pendulum will no longer show in the window.
I have found that it is easy enough to use a longer and thinner suspension spring to bring things back into order, even while raising the pendulum.
Admittedly 30 min/day is a lot to overcome and you may have other issues, but it’s worth a shot.
Sometimes you run across a marriage where the movement and case were not born together and just won’t mate.
Photos and or video will help to get your problem diagnosed and solved.
 
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jpbar70+nawcc

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Hi all. Sorry for the delay and lack of information. I'm quite new at this and didn't received the notifications correctly.

The mechanism is from "essa" brand, from Germany I guess.

I uploaded videos here 3 new photos by João Pedro Ben Barreiros

So, by the replies I guess that the easier things to do are : 1st and easiest, lowering the bob, then put a height on the Bob.

The bob is quite light. I guess it's even a quartz clock Bob.

Thanks for your support.

João pedro
 

wow

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Your clock is out of beat which will affect the rate somewhat but your best option is to lower the bob until it keeps good time. Then see where the bob swings.
 
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Willie X

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Need to find a similar size, or slightly smaller, German style pendulum with a regular rating rod and nut. That will do it.
Willie X
 
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shutterbug

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Yeah, I think you have a quartz clock pendulum. Too light for your movement.
 

Fitzclan

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Looks like someone did a homemade job on the suspension spring.
That hand nut on the right looks like it may be hitting the post. It is in an unfortunate spot.
I don’t think the pendulum is the problem at all. The spring and rod are makeshift.
 
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shutterbug

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I think the long suspension spring an attempt to lower the center of gravity. A proper pendulum with a heavier bob would accomplish that better.
 

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