Bevel Gears and Their Types

A gear is a device made of toothed wheels that transfer mechanical power between two elements. They are found throughout machines used for industrial processes, such as production lines in drive systems. However, they are also used in a wide range of sectors such as mining, aerospace, pharmaceuticals, textiles, and more. This blog will focus specifically on a certain type of gear: the bevel gear.

Bevel gears are gears that use two cone-shaped, toothed wheels to transfer power between axes cut within the same space. The teeth of a bevel gear can be either straight or spiraled, also known as a conical helix. Different types of gears are commonly classified based on their tooth width, the tooth face width, or the center’s circular pitch. There are four classifications of bevel gears: helical bevel gears, hypoid gears, straight bevel gears, and spiral bevel gears.

Helical bevel gears are used to transfer motions between axes that intersect on the same plane by combining a right- and left-handed helix. These gears reduce the speed of a shaft at a 90-degree angle. Helical bevel gears are usually found in car’s rear axle transmissions and are known for their low noise generation. The main difference between these and straight gears is that the edges of the teeth are angled instead of being parallel to the axis of rotation.

Hypoid gears are relatively uncommon, and can actually be considered a type of helical bevel gear. However, the main difference is that these gears feature a speed-reducing pinion that has few teeth and a gear that has many teeth. Hypoid gears are ideal for use in scenarios where the shafts are perpendicular but not in the same plane. Apart from being used in industrial applications, these are highly popular in the automotive industry where they are used in rear-wheel drive vehicles to connect the wheels and driveshaft together. Hypoid gears use a type of oil lubricant characterized by its high pressure. Regardless of their popularity in low-speed applications, hypoid gears can exceed 1,000 revolutions per minute.

Straight bevel gears feature teeth with milled outer surfaces placed on bevel surfaces. Gears of this type are useful in verifying the transmission of the motion that is generated between axes that intersect within a single plane, nearly always at a 90-degree angle. Despite the fact they are only used to achieve a speed reduction in shafts placed at right angles, they can also operate at 45, 60 and 70 degree angles. Contrasting from helical bevel gears, straight bevel gears have a very minimal mating surface.

The last type of bevel gear, spiral bevel gears, operated at very steep and varying planes. They are set apart from other bevel gears by their meshing, as the pinion’s teeth are wider than those of the main gear. This makes it easier for them to transfer very high torques with minimal wear, because the pinion’s teeth are able to mesh with the main gear’s teeth. Their low wear also enables them to be used at very high speeds. As such, spiral bevel gears are commonly found in motorcycle and bicycle gears.