Budget Watch Collecting/How a Watch Works
The crown (of a manual wind) or the rotor (of an auto wind) rotates, turning gears in the keyless works which in turn rotate the mainspring arbor, winding the mainspring. The mainspring turns the mainspring barrel, which turns the train, which supplies power to the escapement, which slows the train down to a precicesly regulated speed.
The Keyless works
In the winding position, turning the crown turns the winding pinion. Clockwise (as viewed from the crown) the winding pinion will turn the clutch wheel, which will turn an intermediate wheel and then a gear attached to the mainspring arbor. Counterclockwise, the winding pinion and clutch wheel have ramped teeth that will disengage.
In the setting position, the winding pinion moves away from the clutch wheel and towards the center of the watch where it engages an intermediate wheel that in turn engages the minute wheel.
The train consists of the center wheel, which turns at one revolution per hour. The center wheel drives the third wheel and also the motion works. The third wheel drives the fourth wheel usually at 1 revolution per minute. In direct seconds watches, the fourth wheel directly drives the seconds hand.
The Motion Works
The cannon pinion is attached with a friction fit to the center wheel. It drives thhe minute wheel, and also holds the minute hand. The hour wheel slips over the cannon pinion, and is driven by the minute wheel, using the cannon pinion as it's axle.
During setting, the intermediate wheel will be turned by the winding pinion, and will turn the minute wheel, which will make the cannon pinion slip on the center wheel shaft.
The escapement consists of the balance, hairspring, lever and escape wheel. When force is applied to the escape wheel by the fourth wheel, it will begin to turn, forcing one of the pallet jewels (referred to as jewel A) away, but bringing the other pallet jewel (B) into position to stop the movement after a 1/2 tooth rotation. The tail end of the fork will send an impulse to the balance through the impulse jewel. This will cause the balance to rotate in one direction until it is reversed by the tension of the hairspring. When the balance reverses, it will push the fork in the oppoisite direction, moving jewel B out of the way, and allowing the escape wheel to rotate. As the escape rotates, it supplies an impule to jewel B, which will again send an impulse through the tail (in the opposite direction of the first one) to the balance wheel, causing it to rotate. Additionally, jewel A will move into position to block the rotatin of the escape wheel after 1/2 tooth of rotation. Once again the balance will be reversed by the hairspring, moving jewel A agian until it can again be pushed out of the way, repeating the cycle.
The mass of the balance wheel and the length and stiffness of the hairspring combine to have a natural resonant frequency--generally between 5 and 8 half-cycles (or beats) per second on a wristwatch. Each beat will cause one jump of the seconds hand. The outside of the hairspring is held to the balance cock by the hairspring stud, while the inside is held to the balance by the collet. Generally either the stud or the collet is moveable to allow the balance to be adjusted "in beat", where the motion is centered on the fork rather than turning farther in one direciton than the other.
In most watches, the hairspring will pass through the regulator, a slot on a moveable arm. When this arm is moved closer to the stud, the working length of the spring is longer, slowing the resonant frequencey, causing the watch to run slower. Moving it away from the stud speeds the watch up. A few watches have no regulator, instead relying on moveable weights on the balance to adjust the resonant frequency and rate of the watch.