Grandfather’s Clock: How It Works

Grandfather’s Clock: How It Works

Everyone was probably looking at the grandfather clock, thinking that it is a piece of workmanship of some people with mysterious and secret knowledge. Many questioned how it could happen that those weights, hanging on the chain, are making the clock’s hand turn and show the time. Moreover, that secret mechanism ‘tells’ us the time. Every hour it strikes the gong with an exact number of hours, and every half an hour just once informs that another 30 minutes passed. Therefore, this type is most common but not that sophisticated. There are other clocks, which play some simple or quite complicated tunes; others are equipped with calendar, showing moon phase, and the most complicated showing others astronomical values that even hard to understand without special knowledge. It is truly amazing. The pure mechanical device, without any processors, quartz oscillators and electronics shows accurate time. Moreover, some of them are doing that for centuries. It is widely accepted that first mechanical clocks appeared on Town Hall towers in medieval Europe during Renaissance. Not many people know the fact that mechanical clockworks devices were known already in the Ancient Greece. Divers discovered the Antikythera Mechanism over a hundred years ago. Even badly corroded, it demonstrates a complex device that is still investigated by an international group of scientists from Greek, UK and the U.S. institutions. The mechanism research tells us that it was designed for complex astronomical calculations and often called the first analog computer. It is too sophisticated to discuss now and mentioned only to show how old the history of clockworks is. Therefore, the next part of the paper will examine how much simpler and widely known mechanism works. The grandfather clock is something what everyone most probably has seen at home or while visiting relatives or friends.

Main Components

Every mechanism needs an energy source to make it run. It could be either thermal energy from the fuel combustion, or electrical energy from battery cells and generators, or nuclear energy, or mechanical energy. The energy should be stored for later conversion into kinematic energy in moving mechanism. If the speed of mechanism is to be kept at certain desired values or stable and permanent, some regulating device should control the speed of the mechanism. The speed that is possible to obtain directly from energy conversion of the source may not match, as it happens in the most cases, the speed needed at the end device. Hence, some gear must be present to transform initial speed to the required value, either increasing or reducing it. The end device is any part where the initial energy finally converted to some process that performs designated work, i.e. car wheels or the drill chuck for example. All these components present in mechanical clock too. There always is an energy source, a regulator that contains two components, a train that contains wheels and an end device that usually realized in hands, but there were also moving dials used in some clocks in the past, and even some animated figures performing some actions at desired time. The most known are cuckoo-clocks, but there were much more sophisticated clocks with many figurines moving, such as singing birds in cages or dancing groups of people. Furthermore, all major components of the clock are realized in a specific way.

Energy Source

Two energy sources are used in clocks in the most of the cases. The first one is a weight that stores potential energy accumulated from winding clock by man hand’s power. The second one is the spring that accumulates the energy from the same source but in a different way, as a spring tension. The usage of the spring allows making clock more compact. In addition, watches would never exist without the invention of the spring as energy source plus another device that will be briefly mentioned later. Yet, springs are affected by natural factors such as aging and fatigue. The classic grandfather’s clock has another energy source. It is a weight. The gravity is the stable force that depends on the planet mass and slightly differs by latitude. As the clock is not supposed to be often moved, the gravity force considered as a constant in every location and could be utilized as a stable energy source. The energy is stored by lifting the weight, thus, converting the gravity into potential energy. The gravity is constant, but accumulated energy depends on weight and height. That is why weights are quite heavy, and grandfather clocks are placed in big cabinets staying on the floor. However, if one makes an experiment with attaching some weight to the thread bobbin, put it on a pen or toothpick and release, it will go down uncontrolled, until the weight reaches an obstacle. Hence, some regulating device is needed.

Regulator

Each clock regulator contains two components, the escapement and controller. The escapement is a specially designed wheel and pallet device that allows only a small portion of the energy to be released with every swing of the controller. The controller is an oscillating device. It can be actuated by inertia or the energy from another spring called hairspring. That spring is widely used in mechanical watches and newer clocks, but the stability of its oscillations is a very complicated task. Although many improvements achieved since its invention for making portable watches and clocks accurate, the stability of pendulum controller is hard to achieve. The answer is simple; the pendulum is operated by the same gravity force used to store energy. Another simple experiment with the same thread and weight can show that the oscillation period of the pendulum does not depend on the weight and amplitude but only the length. Even if this is true for the pendulum without friction and air resistance; for the real pendulum, it assumed to be correct with small amplitudes. The length of the pendulum can be adjusted to have constant period, thus, causing the escapement wheel to have stable speed. For simplicity, it is recommended to assume that one turn per minute. In this case, the second hand attached directly to the escapement wheel axis will show seconds. However, we need to see minutes and hours. In addition, even to show minutes directly, the pendulum must be about ?60 = 7.75 times longer, as the pendulum’s period of oscillation is proportional to the square root of length. That is practically achievable only with a tower clock. Hence, we need a reduction gear.

Train and Hands

The clock gear assembly is called a train. The train is an assembly of wheels and pinions that serve two purposes. It reduces the speed of rotation of the main wheel 60 times, thus, making the minute hand, attached to the main wheel, to have exactly one revolution per hour. Usually, the clock train contains four wheels. An escapement wheel is engaged to the second wheel that in turn engaged to the intermediate, or third one. An intermediate wheel is engaged to the main or center wheel. Another purpose of the train is reducing the force required from the regulating device to control much higher forces from the energy source. The gear ratio calculated in such way that 60 turns of the second wheel will make the main wheel turn once. The number of wheels is determined by practical reasons. With only two wheels, the diameter of the main wheel must be 60 times bigger than the pinion on the same axis with escapement wheel, considering the second making one revolution per minute. It is clear about a minute hand, but the explanation about hours should be better given.

Another gear serves for hours’ indication. It is located on the same side with the dial and hands. It contains the cannon pinion planted onto center wheel axis in such way that there is enough friction to rotate the wheel by the clock mechanism, and it could be rotated by human’s hand on the axis, allowing clock setting without disturbing other parts of clockwork. The cannon pinion is engaged with a minute wheel that, in turn, is engaged with an hour wheel, planted on top of the cannon pinion and rotating freely on it. The gear ratio is usually 1:12, but sometimes also 1:24, thus making possible to display time in 24 hours’ scale.

This brief informative description discussed the principle of grandfather’s clock operation. The detailed description requires much more words and time. Many different types of escapements are a matter of separate discussion. Nothing had been said about ratchet and click, small but important device preventing the drum from the rotation in opposite direction. The chime mechanism is another complex part requiring separate description as it contains its own energy source, train, and counting device, that, in turn, could be of two major kinds, a counting wheel, and a snail type.

Lesley Glover, an online marketing consultant, freelance writer at professional article writing service, blogger and social media enthusiast who enjoys photography, tennis, and hiking.