How mechanical movement pocket watches work
Many people of this generation do not know that there exists such a thing as a pocket watch, as such, when you mention a pocket watch they are lost and seem not to have an idea of what you are talking about.
The pocket watch was invented in the fifteenth century by a German locksmith, Peter Heinlein, and since then it has been in existence even though it has been evolving into the modern timepieces we have now.
Most of them are made of jewels and their worth can often be determined by counting the number of jewels each of the watches contain. These jewels are inserted into certain areas of a pocket watch that have the highest amount of mechanical movement in order to minimize wear and tear.
Generally, the number, seven, is considered to be the lowest number of acceptable jewel count for a quality pocket watch, and most modern watches contain up to 17 to 21 jewels - which make it highly valued and treasured. However, a quality pocket watch should have the number of jewels it contains engraved on the cover or back of the watch; to enable people to tell its worth firsthand.
Apart from other features of the pocket watch which make them look fanciful, a couple of other things are embedded in it which makes it work and tell the time - the purpose for which it was invented.
This implies that the pocket watch has a variety of components.
The pocket watch being a mechanical watch also, is powered by mechanical energy, hence it possesses a mechanical component that consists of a mainspring, a gear train, a balance wheel, an escapement mechanism, and a clock face.
All these parts perform distinct functions that make the whole work effectively.
Let's see the various works performed by each of these parts:
The Mainspring Part
This is primarily the element that drives the pocket watch. It consists of a flat spring-steel band that is stressed in coupling or bending. It works in such a way that whenever the watch or other spring-driven part is wound, the curvature of the spring is increased and energy is stored. As a result, the energy that is generated is transmitted to the oscillating section of the watch, otherwise known as the balance, by the wheel train and escapement - the motion of the balance itself controlling the release of the escapement and consequently the timing of the watch. Also, a friction drive permits the hand to be set.
However, for early pocket watches, there were some defeats in them of which one was the variation in the torque exerted by the mainspring. This implied that the force of the mainspring was greater when fully wound than when it was almost run down. And since the timekeeping of a watch fitted with a verge escapement was greatly influenced by the force driving it, this problem was quite serious.
The problem was eventually solved by the application of the fusee, a cone-shaped, grooved pulley used together with a barrel containing the mainspring. With this arrangement, the mainspring was made to rotate a barrel in which it was housed; a length of catgut, later replaced by a chain, was wound on it, the other end being coiled around the fusee. When the mainspring was fully wound, the gut or chain pulled on the smallest radius of the cone-shaped fusee; as the mainspring ran down, the leverage was progressively increased as the gut or chain pulled on a larger radius. With correct proportioning of mainspring and fusee radii, an almost constant torque was maintained as the mainspring unwound.
The going barrel, in which the mainspring barrel drives the wheel train directly, is fitted to all modern mechanical watches including the pocket watch and has superseded the fusee. With better quality mainsprings, torque variations have been reduced to a minimum, and with a properly adjusted balance and balance spring, good timekeeping is ensured.
The Gear Train
The gear mechanism of a pocket watch in its simplest form is used as a means of transferring power from the mainspring to the escapement; which, as we have previously seen, prevents the energy from escaping all at once.
The gears function to scale up the speed of the slow-turning mainspring, allowing it to power the watch for several days before it needs to be wound again—and its to the mainspring that the first wheel in the gear train is attached. The spring turns, causing the wheel to rotate, which then, in turn, moves three successive wheels.
This is where the second main function of the gears comes into play. The second wheel in the sequence is attached to the minute and hour hands, while the fourth wheel—the last in the train—drives the escapement, which returns the energy in regulated amounts and enables the watch to keep accurate time.
Most mechanical watch movements are standardized, without much variance in the parts and technique used. Its a feat of engineering that took mankind thousands of years to master; without gears, the earliest clock makers would have had much more trouble releasing their ideas.
The Balance Wheel
The balance wheel is the heart of the oscillating system of a compact portable timepiece such as a pocket watch. The vibration of the balance wheel is used to measure time and is one of the main specifications of a movement. The balance wheel produces a temporal defined movement, rotating back and forth, which is then transmitted through the gear train of the watch movement into a movement of the hands. It serves the same function as the pendulum in a clock, but it is much more compact and works largely independent of the position of the watch.
The balance wheel keeps time for the watch. It consists of a weighted wheel which rotates back and forth, which is returned toward its center position by a fine spiral spring, the balance spring, or "hairspring". The wheel and spring together constitute a harmonic oscillator. The mass of the balance wheel combines with the stiffness of the spring to precisely control the period of each swing or 'beat' of the wheel.
One major historic issue with balance wheels is the fact that changes in temperature can affect the accuracy of the movement. For this reason, a major area of research and development throughout the 20th century revolved around improved balance wheel materials and construction. To maintain its oscillation, the balance wheel escapement is periodically excited by the mainspring.
The balance wheel can also be regulated by changing the effective length of the balance spring: There is typically a lever that can be rotated to change the frequency of the wheel.
The Escapement Mechanism
The escapement is a device in the pocket watch that releases the watch's wheels to move forward a small amount with each swing of the balance wheel, moving the watch's hands forward at a constant rate. The escapement is what makes the 'ticking' sound which is heard in an operating mechanical watch.
This is to say that the escapement has the dual function of keeping the balance wheel vibrating by giving it a push with each swing and allowing the watch's gears to advance or 'escape' by a set amount with each swing. Also, the periodic stopping of the gear train by the escapement makes the 'ticking' sound of the mechanical pocket watch.
The fourth wheel also drives the escape wheel of the lever escapement. The escape wheel teeth alternately catch on two fingers called pallets on the arms of the pallet lever, which rocks back and forth. The other end of the lever has a fork which engages with an upright impulse pin on the balance wheel shaft. Each time the balance wheel swings through its center position, it unlocks the lever, which releases one tooth of the escape wheel, allowing the watch's wheels to advance by a fixed amount, moving the hands forward. As the escape wheel turns, its tooth pushes against the lever, which gives the balance wheel a brief push, keeping it swinging back and forth.
The Clock Face
The pocket watch also has a part called the clock face. Its responsibility is to display the time through the use of a fixed-numbered dial or dials and moving hands. In its most basic form, the clock face is the symbol of recognition of watches throughout the world. The periphery of the dial is numbered 1 through 12 indicating the hours in a 12-hour cycle, and a short hour hand makes two revolutions in a day.
The clock face is so familiar that the numbers are often omitted and replaced with applied indices (undifferentiated hour marks), particularly in the case of watches. Occasionally, markings of any sort are dispensed with, and the time is read by the angles of the hands.
So with the clock face of the pocket watch, one can easily look at the watch and be able to accurately tell what time it is, provided the time is set and the watch works appropriately.
So in summary, the mainspring is attached to a cylindrical barrel with gear teeth. The barrel's gear teeth turn the gear train, which consists of four separate wheels attached to one another with additional gear teeth. The barrel is directly attached to the center wheel, also known as the balance wheel; which is then attached to the escapement mechanism. The escapement mechanism is a pendulum that rocks back and forth with each rotation of the center wheel. One end of the escapement mechanism is attached to an upright pin on the balance wheel. The movement of the escapement mechanism causes the balance wheel to advance at regular intervals, thereby allowing the watch to keep time. Attached to the balance wheel is a cannon pinion that attaches to the minute wheel. The cannon pinion also drives a small 12-1 gear reduction mechanism that rotates the hour wheel once for every 12 rotations of the minute hand. Both the hour and minute wheels contain shafts going through the clock face and attaching to the watch hands.
Since pocket watches depend upon the stored energy in the mainspring to power the movement, it is therefore required that it is wound daily in order for it to work effectively.