gear wheel

A gear wheel is a mechanical component with teeth cut or formed around its outer rim, designed to mesh with another toothed wheel to transmit rotational power and motion. The teeth engage in a controlled, repeating contact pattern that converts torque from one rotating shaft to another, or alters the speed and direction of rotation between two axes.

The teeth are the critical feature. They are typically evenly spaced around the wheel's circumference and cut to a specific profile, most commonly an involute curve. The pitch diameter, module (or diametral pitch in imperial systems), and pressure angle determine whether two wheels will mesh smoothly. When a driving gear rotates, its teeth push sequentially against the teeth of the driven gear, creating a mechanical advantage. The ratio of teeth between wheels sets the speed ratio: a 40-tooth gear meshing with a 20-tooth gear will produce a 2:1 speed reduction.

Gear wheels come in several types based on their geometry and axis arrangement. Spur gears have straight teeth cut parallel to the axis and are used for parallel shafts. Helical gears have angled teeth that produce smoother, quieter engagement and higher load capacity. Bevel gears have conical teeth and transmit motion between shafts at an angle, often perpendicular. Worm gears interact with a threaded shaft to achieve very high speed reductions.

Materials and wear patterns

Steel is the standard material for gear wheels that must carry high loads; cast iron is used where weight and cost matter more than precision. Tooth wear, tooth breakage, and pitting of the tooth flank are the primary failure modes. Poor lubrication, misalignment, or overloading accelerates all three. Backlash, the small gap between meshing teeth, must be carefully controlled: too little causes friction and heat; too much causes impact and noise.

In assembly, gear wheels are mounted on shafts via bores, keyways, or splines, and spacing between wheels must be precise enough that teeth engage smoothly without binding. Modern gear wheels are often manufactured by hobbing or shaping, allowing high accuracy and consistency. The term "gear wheel" is sometimes used interchangeably with "gear", though "gear wheel" emphasizes the wheel form as distinct from, for example, a rack or a worm.