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  1. How Do Grandfather Clock Pendulums Work?

How Do Grandfather Clock Pendulums Work?

by: Michael O'Brien

How Do Grandfather Clock Pendulums Work?

One of the most important discoveries in timekeeping was the swinging pendulum. The pendulum made it possible for the development of tall case and grandfather clocks. Thanks to the innovative thinking of the Italian physicist Galileo Galilei, the pendulum revolutionized clock making, making clock more accurate. Though his concept would not be incorporated into clock making until twenty years after his death, there is no doubt the Galileo’s original calculations help to propel clock making and timekeeping into a whole new era.

Dating back to sometime around two hundred CE, the pendulum was developed in China. A pendulum is defined simply as a weighted object that is suspended from a fixed point. The movement of the pendulum is driven by the forces of gravity and inertia. A common clock pendulum consists of a rod connected to a circular piece called a disk or bob. The pendulum rod is connected to the clock. The movement of a pendulum helps to regulate the movement of the clock and is receives its power from the mainspring.

The cycle time or vibration for the same length pendulum will vary depending on where there are located on the planet. For example, the cycle time a pendulum located on the Earths equator will decrease if the pendulum is moved towards either the North or the South Pole.

Clock makers have always looked for ways to preserve the uniform length of the pendulum. Referred to as regulator clocks, the pendulum rod is made up of a frame consisting of rods made from different metals. The rods are arranged in such a way that some of the rods expand downward and others expand upward, which maintains the mean length of the pendulum.

There are antique and vintage pendulum clocks that make use of what is called a mercurial pendulum. The mercurial pendulum has a single rod design and a very unique pendulum weight. Unlike many grandfather clock pendulums, the weight or bob of a mercurial pendulum contains mercury. As the rod lengthens, the mercury expands upward. As the rod shortens, the mercury expands downward maintaining the length of the pendulum.

In spite of many technological innovations in grandfather clock design, the basic components in a pendulum and weight clock movement have not changed much over the years. The basic parts of the movement include a weight or spring, which supplies the power for the movement. In a weight system, weights are attached to a chain or cord that is wound around a drum. As one weight descends, the unwinding of the chain transfers movement to the gears. The motion is regulated by the motion or vibration of the pendulum. In a mainspring movement, a spring, along with gravity, supplies the power that keeps the pendulum swinging.

A very critical piece of the movement is the escapement which connects a balance wheel or pendulum to the movement. Galileo is said to have designed an escapement while he was very ill and going blind. An escapement is used in all mechanical clocks and watches.

Through a train of gears and rods, movement is transmitted to the hands of the clock. As motion is transmitted to the movement, a pinion gear attached to the escapement connects with cogs that are sometimes referred to as leaves. The leaves are on a larger wheel whose pinion connects with another large wheel and so on. This system of wheels produces a rotation. The rotation, once every twelve hours, is carried to the hour hand. Another wheel attached to the minute hand, makes a complete rotation every hour. The movement of the wheelworks is controlled by the swinging of the pendulum.

A grandfather clock can be made to run slower or faster by lengthening or shortening the length of the pendulum rod. Most grandfather clocks have a threaded adjusting rod at the bottom of the bob or pendulum. This finely threaded adjusting rod aids in making very precise adjustments to the speed at which the pendulum swings.

About the Author

Michael O'Brien is Staff Writer for Grandfather Clock

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