How to Adjust an Antique 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.

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.

 Adjusting Clock Rate (Speed)

First synchronize your clock with an accurate time source - like a digital clock. After twenty-four hours, record how many minutes your clock is off. Then adjust the bob up, or down, to change the pendulums effective length. If you clock is running fast, lower the bob. If your clock is running slow, raise the bob.

How much to adjust the bob depends upon both the error and the length of your pendulum. In general, a modern grandfather clock can be changed 1/2 minute per day with one revolution of the nut.  Antique grandfather clocks are usually adjusted at a rate of 1 turn (360 degrees) to 1 minutes every 24 hours.

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.

 Adjusting Hourly Strike Count

What to do when your clock strikes a different count to the hour hand indication? The most common cause is that the hour hand is out of position to the inner workings of the clock mechanism.  The hour hand is attached to the hour post by friction.  It is free to rotate without a fixed gear locking it to the clock's internal hour counting mechanism. Therefore, it is possible for the hour hand to get out of sequence with the clock mechanism.

To fix this move the minute hand around until it is in the 12 o'clock position and the clock starts striking the hours. Count the numbers of hours struck.  Then rotate the hour hand until it corresponds with the correct number of hour strikes. The clock hands are now in synch with the internal clockworks. The final step is to rotate the minute hand clockwise stopping at each quarter and/or half hour letting the clock run through its sequence until the clock reads the correct time.

Adjusting "The Beat"

What if your clock only runs for ten minutes then stops? Most times this happens because the clock is not "in beat". A clock is "in beat" when the time between each tick/tock cycle is evenly spaced. To determine if your clock is out of beat, start the pendulum swinging and carefully listen to the tick and tock. If it the time between each tick/tock is uneven your clock will not run correctly. If the time between the ticks and the tocks is even your clock is "in beat".

If your clock is not "in beat", there are several things you can try to correct the beat. If your clock is mounted on a wall by a single point, move the bottom of the clock case left or right until the clock sounds "in beat". The clock has been adjusted so that when the case is level, the escapement is "in beat". 

Mike's Clock Repair
Centennial, Colorado 80112
www.eclockfixer.com
(720) 333-6309
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