How do Grandfather Clocks Keep Time?

Grandfather clocks easily impress with their ornate appearance and melodious chimes. However, the complex mechanisms that can be observed moving inside them create the impression that these clocks are intimidating and complex to maintain. It is true that the system used by grandfather clocks to keep time is elaborate. However, all any grandfather clock needs to continue running and accurately measuring time is one simple action that is completed at regular intervals.

All grandfather clocks keep time using a system of one or more weights whose controlled motion is propelled by the swinging of a pendulum. Each swing of the pendulum marks one second. With each swing of the pendulum, a gear is moved which drops the weight by one increment, moving the hand or hands of the clock. Most grandfather clocks need their weights to be reset daily or weekly to remain accurate.

The ornate decorations and intricate detailing of grandfather clocks often distract from the elegant systems that keep them running. While it is possible to see inside many grandfather clocks, it is not always clear how each of the components work together to keep them running. Understanding that all grandfather clocks rely on a few variations of the same foundation helps to demystify their workings and explain why they have been such an enduring apparatus for timekeeping.

grandfather clock

The Origins of the Grandfather Clock

Different iterations of what we know as a grandfather clock have existed for centuries. While some variations have been made, a grandfather clock can be characterized by a long pendulum and weight driven movement. They are always self-contained within a housing that is typically wood. Over time these clocks came to feature ornate decoration. Later cases often utilized glass to allow for observation of the complicated movements inside the timepiece.

Long Case Clocks

Most records suggest that what we now refer to as a grandfather clock appeared during the mid 1600s. The development that paved the way for grandfather clocks was the implementation of the pendulum. A pendulum swings back and forth at a consistent pace. Further innovation helped to keep pendulums swinging at a stable pace for longer periods of time and increase useability. The addition of a pendulum to timekeeping systems helped to tremendously increase the accuracy of clocks. 

At first, these heavy clocks with their wide swinging pendulums presented practical challenges that limited use. The development of a pendulum that required a smaller swinging range resulted in a more compact model. This design also conserved energy, which meant the clocks could run for longer periods between resetting the weights. A longer pendulum was required to make this design viable, which is how these clocks gained their characteristic height.

These evolutions made it possible for the clocks to be housed in the familiar wood cases, which also aided stability. The main development leading to the development of the grandfather clock as we know it was the creation of the anchor escapement. This mechanism helped to control and maintain the movement of the clock components by providing a small push to the pendulum each time it would swing.

Earlier Terms for Grandfather Clock

During this period, grandfather clocks would have been known as long case clocks. Other terms that emerged include floor clocks and standing clocks. The name “grandfather clock” would not emerge in popular culture until the turn of the twentieth century. A song from the late 1800s called “My Grandfather’s Clock” inspired the popular moniker that we still know them by today.

Read more about why they’re called grandfather clocks here.

What keeps Grandfather Clocks Running?

The interval of time a clock can run accurately with the momentum provided by the descent of the weight is referred to as the movement. At the end of a movement, the weights need to be raised to the top position.

From here, the weights could restart the cycle and keep the clock running consistently. Cable driven movements and chain driven movements are the two most common forms found in grandfather clocks.

Innovations in movements allowed them to conserve more energy and require less frequent resets. Eight-day movements became the standard for grandfather clocks. The typical low-cost alternative was the thirty-hour clock, which required more frequent intervention to continue running.

Cable Driven vs. Chain Driven

Two styles of grandfather clock have prevailed over the centuries. In the first, the weights of cable driven clocks are reset by rewinding them to their original position. The mechanism is accessed by inserting a winding key, also called winding crank, into an opening in the face of the clock and turning it. More complex clocks require the winding of multiple weights.  Meanwhile, chain driven mechanisms are reset by pulling the chain the weights are attached to, which will manually bring them back to their start position.

Eight-Day Clocks vs. Thirty-Hour Clocks

If a clock is not reset at the end of the movement, it may stop running entirely. Most grandfather clocks run at either eight-day or thirty-hour intervals. Thirty-hour clocks needed to be reset approximately every thirty hours. These clocks required more frequent maintenance and were typically less expensive. These clocks were usually simpler in their design and relied on one weight to both keep time and power the striking mechanism. These clocks were often disguised to imitate their longer running, costlier counterparts.

Eight-day clocks, as the name suggests, only needed their weights to be set around once per week. These clocks typically had separate weights to control the timekeeping mechanism and striking mechanism. These clocks were more technically complicated, but they were easier to keep and therefore sold at a higher premium.

Improvements in Timekeeping

Over time, functions were added to clocks. The first long case clocks kept time using only an hour hand. However, as these accurate timekeeping devices became commonplace and allowed for more standardized timekeeping, it became possible and later necessary to measure even smaller units of time.  An hour hand was supplemented by a minute hand. Some clocks even began to feature a seconds hand to allow the tracking of even smaller intervals.

The striking mechanism, which created a sound to announce passing time using a bell or chimes, was likewise elaborated. Early striking mechanisms would have only marked each hour as it began. Starting in the 20th century, clocks began to feature a more elaborate chiming system that distinctly marked each hour, half hour, and quarter hour. This was made possible by the addition of a third weight, which controlled the interval chiming between each hour.

Legacy of the Grandfather Clock

The advent of what we refer to as the grandfather clock revolutionized timekeeping. Timekeeping, in turn, revolutionized the grandfather clock. Still, the way that grandfather clocks keep time has remained largely the same over three hundred years.

Read more about the accuracy of grandfather clocks here.

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