The mechanical clock pendulum length

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The mechanical clock pendulum length

A pendulum clock without a pendulum is a shame for sure. Hence, getting the mechanical clock pendulum length correct does take some diving into the clock world.

If there is no idea what pendulum it would take, this is a basic guide. Of course, this is a basic guide to narrow it down to the best pendulum for the clock. This will cover most situations, without special equipment to figure out the length.

The movement CM or PL stamp

On the back plate of the clock movement usually, there are some numbers and or letters for identification. Likewise, there may be an indication of how long the pendulum should be in the mix of these numbers.

It may say CM or PL and this stands for centimeter or pendulum length. Subsequently, this would be the length where it should keep approximate time. Generally, there are a few different ways to measure this depending on the country of origin.

Mechanical Clock Pendulum Length for German made movements

Most mechanical German made clock movements are easy to figure out the pendulum length. In essence, the numbers will let us know or the stamp will clearly state the CM or PL number. If it is German, keep in mind the CM length is not the actual pendulum length.

Altogether, German units measure this length from the top of the clock movement, and this includes the three components of the pendulum all in one length, in centimeters.

This length will include the pendulum itself, the leader that it hooks to, and the suspension spring on the top that the leader hooks on to, all in one CM measurement. To clarify, CM stands for centimeter and PL stands for pendulum length.

If no stamp try to convert

When there is no stamp with the CM on the movement, there are some additional steps that need to happen. You will need to cross reference The numbers on the back plate to the pendulum length that you need. The first step is to identify the manufacturer of the clock movement by using the movement numbers.

The movement numbers indicate who the actually manufacturer is of the movement. Various clock retailers may have a stamp of their name on it, but the numbers are always true to the manufacturer.

Converting numbers to CM length

Moreover, some movements do not have an indication of the pendulum length on the back plate. The unit will have a number that would need to be found on this website first to find out what the correct CM length is for it.

Conversion number example

Generally speaking, let's say that the movement has no CM stamp on the movement and only shows the Urgos number UW32319.

Go to the identification page to look at the movement number examples. In this example, we see that it is a Urgos. Now it is possible to go to the Urgos page and find the number to see what the pendulum length is.

In this example, the pendulum length would be 80cm, representing the full length with the size including the size of the bob.

German grandfather movements

Almost all grandfather clock movements are going to be German if made after 1950. The first thing we need to do is get the numbers off of the back plate of the movement. This is the only way, and we can't cheat by looking at the paperwork or clock case.

It has to come right off the back of the clockworks. The manual and the sticker on the case is of no use to get the pendulum.

American clocks

The American mechanical clock movement manufacturers refer to the pendulum length as a "drop". The drop is the length of the pendulum from the hand shaft all the way down to the bottom of the pendulum rating nut threads.

It is a different way of measuring the pendulum length then the German made way. The basis for both ways are on the smallest bob diameter. If the bob is larger or heavier, the length would be longer than what the stamp indicates.

No luck

If everything fails for one reason or another, the best chance for a pendulum is the wood stick style. This is the only style of pendulum that can be easily modified because it can be cut down.

These types of clocks are usually antiques, or of Asian origin, and information such as pendulum length is simply not available. Sometimes it takes a good guess on where the manufacturer meant to have the bob sit. To do it this way, you only need a pendulum with a stick that is way too long to begin with.

Chop it, try it, chop it, try it. Each time slowly cut an inch and half off of the sticks length and hang it back on. It will only take a couple of times, and if starting way too long it can always go shorter.

Clock makers method for Mechanical Clock Pendulum Lengths

There is another way, which is known as setting the beat rate. This is a more complex way and is usually just done by clock makers. It involves a beat detecting device that counts out the beats per hour, or the beats per minute. To do this, first figure out what the beat rate is suppose to be for that particular movement.

Then keep adjusting the pendulum length until it keeps time. There are cell phone apps out there these days that will tell the beat rate and the cell phone will listen and say if the clock will keep time with that pendulum. Go longer or shorter until the phone says the beat rate is set.

Contacting us for help with Mechanical Clock Pendulum Lengths

Please email the movement numbers from the back plate, and explain what part you need. The email address to send this information to is [email protected]. We always welcome pictures but they are not a necessity. If emailing pictures please include the back side of the clock movement where the markings are.

The content of this website is copyright by Clockworks and written by James Stoudenmire in year 2022

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David Turner
David Turner
2 months ago

I have a Hermle clock that I need to replace the pendulum and bob. I know the pendulum needs to be 94cm but I am not sure how to determine the bob size. I read one place that you measure the inside of the clock waist and subtract 4 inches. My clock waist is 9 1/2″. Based on this I would need a 5 1/2″ bob. Is that right or is there a better formula?
Here are the numbers on the movement. 81 Hermle 451-050H 94cm/66. (what does the 66 mean)? Thanks for any help you can offer.

David Turner
David Turner
2 months ago

Would be there be any problem in ordering the 4.5 inch instead of the 5.5 inch bob? It is mainly a cost issue, but I want to make sure the clock works properly.

Kenneth Wright
Kenneth Wright
3 months ago

I have a Herman Miller grandfather clock that I bought without a pendulum. The works are German and have 93cm stamped on the plate. I now know that I have to measure this distance from the top of the suspension spring. But where is the end of the 93cm? Is it at the bottom of the bob or its middle or the rod itself or some other distance?

Simon Carter
Simon Carter
10 months ago

I will put up the other working parts to clock No 1 sorry not a very good photo.

Kind regards Mr Simon carter

Clock No 1.jpg
Simon Carter
Simon Carter
10 months ago
Rating :
     

Good afternoon Sir/madam, I have two clocks with no Pendulums I have the numbers in which there is no PL or CM. Can you please help with pendulums and the weight required please? If you can help I would be very grateful I would like of sent more photos but would only let me send one if you would like the rest ie the clock faces of both clocks and the other clock workings please send me an e-mail and I return by attachments.

Clock 1 (2373 48)
Clock 2 (3209 46)

Thank you for any help Kind regards Mr Simon Carter

Clock No 2.jpg
Robert Louzek
Robert Louzek
1 year ago

I replaced the Regula 34 movement in my cuckoo clock with the exact movement. The original pendulum (19.5 cm) that came with the clock is not long enough to adjust the time correctly. The clock runs fast. How is the best way to correct the problem. Would additional weight on the pendulum work or a longer pendulum?
Thank you
Robert

Steve B
Steve B
1 year ago

Hi,
I’m trying to find the correct movement for an Ansonia Ledger no. 1. The clock i have is just the box and dial, and I need a time only movement. I think it would be one of two that I’ve found online. One is stamped with an “A” and the other is stamped with a “12”. I think the number/letter may tell if it is a long drop or short drop but I’m really not sure. Either would work, but a long drop would look much better. Any information would be appreciated. Thank you!

Mr B Edgeworth
Mr B Edgeworth
1 year ago

Hi, I am trying to find a pendulum for a smiths grandaughter clock. stamped on the back of the movement is the smiths logo and K6P 575. Your help would be much appreciated. Kind regards Brian

George Kruse
1 year ago

any idea on pendulum length of a Colonial Clock Company movement 64

George Kruse
1 year ago

The movement says Jauch 96

Rich
Rich
1 year ago

Can I shorten the length of a pendulum and still keep the correct time

Subhash Bhola
Subhash Bhola
1 year ago

I need time chain ratchet wheel for cuckoo clock German made .It is Regula 25-v ,64 teeth (ccw) if you see the brass wheel

Maria nogueira
Maria nogueira
1 year ago

I need to know the size of the pendulon for a Barkwick clock/howard miller model 475884

Dom
Dom
2 years ago

I was trying to find a Pendulum for a Howard Miller 625-409 clock

Robin Morton
Robin Morton
2 years ago

hi I have an 1939 haller grandmother clock that was a gift to my grandmother and grandfather on their wedding day it does not have a pendulum and im wondering if you could help

Craig Conrad
Craig Conrad
2 years ago

Hello, I need a pendulum for a movement I obtained. It is a Hermle 1161-853 but it was made for Sligh and does not have the CM stamped on it. It actually says Made in the USA 8710 A-415-015 but for sure it is a Hermle 1161-853 I also need weights for it, but not sure the specs for that either…

Daniel
2 years ago

Hello,

I have a Sligh clock, model 2071-850. I am trying to find a pendulum for it. The stamp in the back says 114cm/60.

Could you help me find the proper pendulum to order?

Thank you

Carl Radino
Carl Radino
3 years ago

I have a Franze Hermle 151-080 Clock Movement. I need to replace the pendulum. According to the stamp on the movement, it is a 21cm length pendulum. Can you provide a replacement? It is a brass pendulum.

Daniel warner
Daniel warner
3 years ago

I have a 1906 Ingraham Landua wall clock with a Gilbert Clock company mechanism. Can you help determine the correct pendulum and bob? There are no markings on the front or back of the mechanism.

Dan

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