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Adjusting a Pendulum From Slow to Fast

In weight-operated grandfather clocks, the force of gravity acting on the weights drives the clock mechanism. But the time is regulated by the uniform, tick-tock swing of the pendulum. The rate of the swing, known as the pendulum's "period," is directly related to the length of the pendulum and the position of the weighted disk, called a "bob," on the pendulum shaft. Pendulum swing varies by the size of the clock, and large grandfather clocks may have a period as long as 2 seconds. The pendulum bob on a grandfather clock is adjusted by a nut on the shaft underneath the bob. Most properly maintained grandfather clocks can be adjusted to deliver an accuracy of plus or minus 1 minute per week.

Instructions

- 1
  Set the grandfather clock to the accurate time as shown on a reliable timepiece or online source.
- 2
  Recheck the time on the grandfather clock 24 hours later, and determine if the clock is running slow or fast.
- 3
  Check manufacturer's instructions, if they still exist, to determine if the clock is constructed so each turn of the pendulum nut equals 1 minute faster or slower per day. If so, simply adjust the nut accordingly, rotating the pendulum nut one turn counterclockwise to make the clock run 1 minute slower per day or one turn clockwise to make it 1 minute faster. If no instructions exist, continue to the next step.
- 4
  Turn the adjuster nut underneath the pendulum knob counterclockwise to lower the bob, if the clock is running fast. Turn the adjuster nut underneath the pendulum knob clockwise to raise the bob, if the clock is running fast.
- 5
  Maintain a record of how far you turned the adjuster nut each day and what effect it had on the time. Over a period of several days, you should be able to zero in the pendulum period to produce an accuracy of plus or minus 1 minute per week.
- 6
  Check the accuracy of the clock every 7 days going forward. Make minor adjustments to the pendulum nut to further increase accuracy.

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