The wheels, together with the pinions, are vital components of the gear train. The wheels are commonly made of huge brass material while the pinions are tiny gears out of steel. They are interconnected and go hand in hand in the gear train. The one cannot function without the other.
Generally, you call the large gears as wheels and the small gears the pinions. Wheels and pinions are the technical horology term to describe the two differentiations of gears used in watch making. Large gears or the wheels usually do the driving of the small gears called the pinions. They are riveted together and when combined as one piece is now referred as the major wheel.
The wheels are constantly rotating while the watch is running. A friction is created that in the long term results to mechanical wear. To reduce the negative effects of mechanical wear, the wheels and pinions are made out of two different materials. Brass is used for wheels and steel is used for pinions. Steel is most appropriate for pinions because they are used as axis for the wheel’s rotation thus they pivot very hard.
Due to the fact that the diameter of wheels is usually large, they have spokes. The spokes help in reducing their weight so that the strength is maintained. The spokes are trimmed in a process called crossing out. In fact, the number of spokes in the wheels helps identify what type of wheel it is. There are also cases where spokes are made decoratively.
Manufacturing pinions is very complex. Its teeth are called leaves and cutting them needs a milling machine. Afterwards, they undergo hardening, tempering, and polishing stages. Before they are riveted to the wheels, they are trimmed accordingly.