How To Regulate A Pendulum Clock

Mechanical clocks are inherently inaccurate and therefore cannot be compared to electronic clocks. People have to keep in mind that antique clocks are often hundreds of years old. Each antique clock was made by hand without using electric tools and without the aid of computerized machines.

Today, modern mechanical clocks are manufactured with machines that can cut gears with incredible precision. In contrast, antique gears were cut using hand tools and often took many hours to make. With that being said, an antique clock that is accurate to within a couple minutes per week really needs no adjusting. Unless you are a clock expert, accuracy greater than that is difficult to attain.

Every time your clock pendulum makes a complete swing back and forth, two teeth on the escape wheel are released and the minute hand advances – ultimately one sixtieth of a minute. The faster the pendulum swings, the faster the minute hand will turn.

A basic principle of physics is that the length of a pendulum will determine how fast it swings. A shorter pendulum swings faster than a longer pendulum. You can change the effective length of a pendulum by either rising, or lowering, the pendulum bob. The pendulum bob is located on the pendulum rod. If you raise the bob, the clock will run faster. Likewise, if you lower the bob, the clock will run slower. This is comparable to a dog’s tail; shorter tails always wag faster than longer tails.

Antique and modern pendulum clocks are regulated by adjusting the length of the pendulum. Most are regulated by turning a nut on the bottom of the pendulum but some are regulated by using a double ended winding key or thumb screw from the dial. Both ways will be shown below.

Regulating Clocks With Nut On Bottom Of Pendulum

ADJUSTING THE TIME

Check the clock against an accurate source like a cell phone or digital clock. After 24 hours make note of any discrepancy in the time. Stop the pendulum and use the adjusting nut on the bottom of the pendulum to move the pendulum bob up or down to change the pendulum’s effective length. If the clock is running fast, move the bob down or turn the nut to the left. If the clock is running slow, move the bob up or turn the nut to the right. Restart the pendulum and reset the clock hands to the proper time.

How much to adjust the bob depends upon both the error and the length of your pendulum. In general, a British grandfather clock can be changed one minute per day with one revolution of the nut.

After the adjustment, synchronize your clock and repeat the process. As your clock becomes more accurate, switch from recording every day to recording every week. Continue the process until the clock is accurate to within two minutes per week. When you are satisfied with the accuracy of your clock, simply correct the time every time you wind your clock.

Regulating Clocks With Key

Antique mantel clocks mainly use this method of time regulation. If your clock has a double ended winding key as shown below most likely you will regulate the clock from a hole located on the top or bottom of the dial.

Look on the dial of the clock and see if there is a hole with S and F on each side. It could be located by the 12 or 6. The one below is near the 6.

ADJUSTING THE TIME

Check the clock against an accurate source like a cell phone or digital clock. After 24 hours make note of any discrepancy in the time. If the clock is running slow, insert the small end of the key into the hole and turn a quarter turn toward the F to speed up the clock. If the clock is running fast, turn the key a quarter turn towards the S to slow down the clock. After the adjustment, synchronize your clock and repeat the process. As your clock becomes more accurate, switch from recording every day to recording every week. Continue the process until the clock is accurate to within two minutes per week. When you are satisfied with the accuracy of your clock, simply correct the time every time you wind your clock.