Gears are toothed cylindrically shaped components that mesh with others to transmit power from one shaft or source to another. They are mainly used to change torque as well as the speed of the driving or driven shafts. Gears fall into four main categories. To make them work more effectively, gears are often used with gear racks. The racks are used to help convert rotary motion to
linear motion. The racks are often modified with tapping mounting holes, and matching ends to create continuous lengths. Gears and gear racks fall into five main categories: 1. Spur gears: These gears help transmit power in the same plane when the driving and driven shafts run parallel to each other. The teeth are cut parallel to the axis of shafts so that power is transmitted in the same direction to the driving axis. If connected to helical gears, power is transmitted at an angle. 2. Helical gear: The helical gears are designed with teeth cut at an angle from the axis. The gears have cylindrical rollers featuring helicoid teeth. The main advantage of helical gears over the spur gears is that they are less noisy because power is transmitted both in the parallel and non-parallel shafts. If the pinion is cut with right-handed teeth, the driven gear is made with left-handed teeth. 3. The double helical gear: This type of gear is designed with both left and right-handed teeth on one gear. It is used to provide an additional shear area on a gear that is further required for higher torque transmission. 4. Bevel gear: This type of gear is used to transmit torque between two perpendicular shafts. The gear is made with spiral or helical teeth on a conical shaped geometry. 5. The rack and pinion gear: This gear is used in automotive steering. In this case, the teeth are cut on straight rectilinear geometry referred to as rack and pinion. The gear helps to transmit rotary to linear motion.