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Mechanical Watch Mainspring: A Winner or a Loser?

January 8th, 2010 Posted in Orient News | 15 Comments | Comment and Win a Free Orient Watch Comment and Win a Free Orient Watch

Everyone is familiar with the game of tug of war: a battle between two resisting sides connected by one common thread, a rope. Some relate mechanical watches to a constant game of tug of war: the mainspring and barrel vs. the balance and hairspring.

All of these parts are important in the functioning of a mechanical watch, but this article’s focus is on the mainspring. So although the war continues, the mainspring has won the battle in this case. Before getting into the function of a watch mainspring, it is helpful to understand some simple mechanics.

Where does energy come from?

Energy in any system may take on various forms, such as potential, light, and kinetic. The Law of Conservation of Energy states that “energy may neither be created nor destroyed.” The formula that represents this law is: E=PE + KE (E is for energy, PE is for potential and KE is for kinetic). This rule is actually a special case within a more general rule, the law of conservation of mass and energy, which has to do with Einstein’s famous relativity formula E=MC^2.

For simplicity’s sake, an example commonly used to highlight the law of conservation of energy is a swinging pendulum. According to this law (and common sense), a pendulum will not swing higher without an external force pushing it, and it won’t stop swinging as long as there’s no friction.

The energy of conservation only works in theory because of friction. So in the case of mechanical watches, it’s necessary to store energy in order for them to operate over an extended period of time.

What is the function of a watch mainspring?

The watch mainspring is important in storing the energy in a mechanical watch system.

A watch mainspring is a flat, thin band of metal at least 14 inches long, curled into a spiral. As the watch is wound (manually or automatically) via the arbor attached at its center, the tension in the mainspring increases, tightening the spiral and thus, increasing potential (i.e. stored) energy.

A watch mainspring is contained inside a small drum called a mainspring barrel. The mainspring barrel acts as the first gear in the watch’s train and has toothed gears on the outside edge that mesh with the movement gear trains. Once wound, the mainspring naturally tries to regain its original shape by uncoiling. The barrel rotates as the spring uncoils, and then the once stored energy is transmitted to the oscillating balance through the wheeltrain and escapement.

A fully-wound mainspring can store enough power reserve for about two days, which allows automatics to keep running even while off the wrist.

To see how a mainspring is assembled, watch this video:

The mainspring is powerful; and like anything (or one) with lots of power, if left unchecked, it will spin things–in this case, the hands of the watch–out of control. At first, the hands would go fast, but eventually, they would slow and eventually stop as the watch mainspring unwound. The escapement is the mainspring’s balance of power. It allows the energy from the watch mainspring to “escape” in short, equal intervals. The escape mechanism is driven by the going train, which is also responsible for turning the hands of the watch.

As aforementioned, a mechanical watch’s system is like a game of tug of war. If it weren’t for the escapement, the mainspring and barrel would pull the balance and hairspring into the mud.