Gear train

The gear train (also called the going train; German Räderwerk) is the sequence of meshing wheels that transmits energy from the mainspring barrel through the escapement to the hands. It is the mechanical connection between energy store and timekeeping oscillator — and at the same time the gear reduction that turns the slow rotation of the barrel into the fast oscillation of the balance and the correct speeds of seconds, minutes and hours hands.

Layout of the standard going train

A classical going train consists of four wheels counted from the barrel toward the escapement:

• Barrel wheel. The toothed barrel itself, typically with around 80 teeth.
• Centre wheel. Carries the minute arbor and therefore the minute hand; usually at the centre of the movement.
• Third wheel. Drives the fourth wheel.
• Fourth wheel. Rotates once per minute and on many calibres carries the seconds hand.
• Escape wheel. The last wheel in the chain; delivers energy to the pallet fork.

The gearing ratios are chosen so that the centre wheel turns once per hour, the seconds or fourth wheel once per minute, and the escape wheel reaches the high rotation rate needed to supply the escapement at 4 Hz.

Other gear trains in the movement

Beyond the pure going train a modern movement contains further wheel sequences:

• Winding train. Connects the crown or rotor with the mainspring barrel.
• Date and complication trains. Drive date display, day, moon phase, chronograph and other complications.
• Sub-dial wheels. Small seconds, power-reserve indicator, GMT wheels.

In highly complicated movements several dozen wheels can interact. The Lange 1, for instance, needs more than 60 wheels and pinions to drive the combination of outsize date, off-centre dial and power reserve.

Materials and bearings

Wheels are typically brass, steel or gilded brass; the pinions (small toothed wheels on the wheel arbors) are made from hardened steel. Each arbor turns at both ends in a jewel — synthetic ruby — which minimises wear. On a classical three-hand watch around 14 of the 17 jewels sit in the bearings of the going train and escape wheel.

Wear and service

At our atelier in Munich, gear-train problems typically appear as erratic rate, audible play or stoppage in certain positions. Common causes:

• Contaminated bearings — dust and aged oil raise friction.
• Bent pinions after a shock.
• Damaged teeth on an individual wheel — rare but possible, for example after work by an uncertified repairer.

During a complete service the gear train is disassembled, each wheel and pinion is inspected under the microscope, then cleaned and re-oiled. A well-maintained gear train lasts decades without component replacement.