How To Adjust a Pendulum Clock

horse ornaments and wall hanging clock with swinging pendulum

Is your pendulum clock broken? has the pendulum stopped swinging? maybe the clocks hands have stopped moving. We at Tic Toc understanding that having an antique clock begin to show signs of failure can be frustrating. We offer a wide variety of repair services available at our workshop for those who would rather seek professional help. However, we have put together an in detailed step-by-step guide on how to properly service a Pendulum clock

In this post, we will discuss how to diagnose the issues you may be experiencing and how to adjust or change the speed of your pendulum clock.

Pendulum wall clock
Pendulum Wall Clock

How Does A Pendulum Clock Work?

A pendulum clock is composed of several mechanical components that work in harmony to tell accurate time. 

These are the components of a mechanical pendulum:

1. The dial or the face of the clock, which shows time through its hour and minute hand.

2. A pendulum or a bob attached to a rod.

3. A gear train that regulates the speed of power that would be used by the pendulum.

4. A set of timekeeping gears that moves the hands/ needles of the clock.

5. An escapement or anchor responsible for giving time impulses to the pendulum to continue swinging back and forth.

6. A weight that turns a pulley or a mainspring

A pendulum works by converting energy as it swings back and forth. When the bob is in its highest point(furthest from the ground), it has maximum stored energy which is the potential energy. And as it accelerates down toward its midpoint or lowest point (nearest to the surface), the potential energy will be then converted into kinetic(energy movement). So, as the pendulum swings back and forth, it repeatedly converts energy too. This process is called a harmonic oscillator, and the movement is an example of simple harmonic motion

The potential energy is what powers the gears of the pendulum clock which in turns, pull at the axle that manoeuvres the second hand which is installed on an axle driven by the timekeeping gears. This setting was designed to make all the needles remain in-sync. So, the minute needle 60 moves one place to the right when its second needle completes and the hour hand moves when the minute needle completes 60 moves. 

Whenever the pendulum swings, it rocks the escapement or lever, which locks and unlocks the controlling mechanism or gear train to let the weight fall or “escape” once every second. This locking and unlocking mechanism of the gear train made by the escapement is what produces the tick-tock sound we hear from the grandfather’s clock.

How To Change The Speed Of A Pendulum Clock

Pendulum clock swinging
isolated old-fashion wooden clock with pendulum on bamboo background

The speed of the pendulum clock depends on the pendulum itself, and you can adjust it by adjusting the nut on the bottom of the pendulum. Turning the nut from left to right will push the bob up and speed up the clock but turning it from right to left to lower the bob will slow it down.  

In other words: 

  • If you make the pendulum longer, the grandfather’s clock will run slower.
  • If you would adjust the pendulum to shorten it, the grandfather’s clock would run faster.

If you’re looking at how you can change the speed correctly, here’s a step-by-step guide for you.

  1. Check the time to see how far it is from the 24-hour period. Then, set the pendulum clock using your mobile phone. Watch your phone’s clock closely as it advances to the next minute and place the pendulum’s minute and hour hand on that location.
  2. After precisely 24 hours, recheck the pendulum clock to see if it is advanced than your phone’s watch because it means the pendulum is too fast but if it falls shortly, then it is slow. Then adjust the nut to move the bob either up or down depending if it’s delayed or fast for about a full turn for a minute a day.
  3. Recheck the clock after another 24 hours to see if it’s fast or slow. Adjust the nut again either up or down (depending on if it’s fast or slow) for about 1/2 turn for a difference of about 30 seconds a day. Then, reset the minute hand to the correct time, as mentioned above.
  4. Repeat the process above with less turn on the nut. Then, check if the pendulum is already on the correct length.

Additional Troubleshooting Tips

Sometimes, adjusting the nut down might not work possibly because the parts of an old pendulum clock such as the bob are tight or frozen, so the pendulum might still run too fast. If that’s the case, here’s what you can do to resolve the issue. 

  1. Remove the pendulum and place it backside up on a clean working surface.
  2. Add a drop of synthetic clock oil on the threaded rod located above and below the nut.
  3. Ensure that the top of the nut is in the slot.
  4. Turn the nut up and down the rod to distribute the oil evenly. Do it until the rotation feels smooth.

See to it that the bob or disk of the pendulum clock is moving up and down as you adjust the nut. Lubricating it and making sure that the top ridge of the nut is in the slot will help resolve this issue.

Common Causes For Issues With Pendulum Clocks

Your grandfather’s clock might stop swinging due to different reasons but here are the common ones that you can check out to help you diagnose and see if you can fix the problem before asking help from a repair shop. 

Pendulum Case Strike

A clock pendulum must be free from obstacles because if it touches anything, it will stop. Most of the time, when it is moved into a new location, the pendulum might hit the case, and it’s a problem because it won’t be at the sitting level anymore. You can try solving the problem by levelling it using a small piece of a flat cupboard. It’s usually done by side, but it doesn’t work, you can try doing it from back to front. 

Tangled Chains Or Weight

If the weight or chain cable gets tangled, it will cause the pendulum to stop. So, try inspecting the weights to see if there are no bunches and if it’s clear from each other as it hangs straight. 

You can also do the same for clocks composed of multiple weights or chains like cuckoo clocks. If the chain was detached from its sprocket, you might have to replace it with a brand new one to make it function again.  

Hands Stuck

The hands of a pendulum might also get stuck. You’ll notice it if you can’t hear a ticking sound when you move the pendulum back and forth with your fingers. You can try troubleshooting the hand by pushing it with your fingers to see if it touches the dial or the glass of the other hand. Then, remove the obstacle by slightly bending the stuck hand, but if both the minute and hour hands could not move, start with the minute first.

Dried Oil and Debris

A pendulum’s mechanism might also stop due to dried oil and debris. You can get rid of dust, dirt and visible dried oil by brushing it away with a soft brush. A few drops of oil dabbed in the area can also help in restarting the pendulum, and make it work again. 

Movement Needs Cleaning

One of the common causes, why a pendulum stops, is because the clock movement needs cleaning. You may also have to get it repaired or replace the shabby movement. 

How Accurate Are Pendulum Clocks

Even if the grandfather’s clock is not as famous as the sophisticated modern timekeepers today, it does not depend on a battery or electricity, unlike the contemporary ones, but still, they are accurate. The pendulum clock’s accuracy typically depends on its pendulum. If it is accurate; then the clock is accurate too. 

The most popular pendulum clock ever known was the Shortt–Synchronome clock invented in 1921 the British railway engineer William Hamilton Shortt along with horologist Frank Hope-Jones. It has an accuracy of one second per year when placed at a nearly constant temperature.  

Pendulum clocks are indeed one of the most invaluable mechanical marvels man has ever created because it led the way to many more astonishing inventions; the timekeepers we’re using today. 

We hope this guide has been helpful to you, and may it help you treasure your grandfather’s clock and the science behind it. 

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