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Types of Gears: A Summary
A gear is a type of machine element featuring teeth cut along a cylindrical or cone-shaped surface. By combining two gears, they are able to transmit rotations and forces from the driving shaft to a driven shaft. Gears can be classified by many characteristics, such as their shape, shaft position, and more. There are a wide range of gear types, but the most common, and the ones we will cover in this blog, are spur gears, helical gears, bevel gears, screw gears, worm gears, and internal gears.
Any gear with a cylindrical pitch surface is considered a cylindrical gear. Spur gears are a type of cylindrical gear with a parallel shaft and teeth that are straight and parallel to the shaft. They are the most widely-used type of gear and are able to achieve high accuracy with a relatively simple production process. Spur gears’ unique characteristic is their lack of thrust load, or load in the axial direction. In a spur gear configuration, the larger of the two is called the gear and the smaller is called the pinion.
Helical gears, similar to spur gears, are used with parallel shafts and are cylindrical gears. However, they have winding tooth lines which provide better meshing than spur gears and allow them to transmit higher loads while operating more quietly. During use, helical gears create thrust force in the axial direction, meaning they require the use of thrust bearings. Helical gears come in both right- and left-hand twist and require opposite hand gears to create a meshing pair.
Bevel gears are cone-shaped gears used to transmit force between two intersecting shafts. Bevel gears have a cone for their pitch surface with its teeth cut along this cone. There is a broad range of bevel gear types, including straight bevel gears, helical bevel gears, spiral bevel gears, miter gears, angular bevel gears, crown gears, zerol bevel gears and hypoid gears. Screw gears are like-hand helical gears with twist angles of 45° on non-parallel, non-intersecting shafts. Because their teeth are the primary contact point, they have a very low load-carrying capacity and are not ideal for large power transmissions. Additionally, it is critical to pay regular attention to their lubrication levels.
Worm gears consist of a screw shape cut on the shaft and mating gear combined together on a non-intersecting shaft. Unlike other gears, these are not limited to a cylindrical shape. Some worm gears have an hourglass shape, which increases the contact ratio but makes production more difficult. The sliding contact of the gear surfaces make it necessary to reduce friction. Because of this, a hard material is used for the shaft (worm), and a soft material is used for the mating gear (worm wheel). Though worm gears are less efficient, they operate quietly and smoothly.
Lastly, internal gears are a type of gear with teeth cut on the inside of the cylinder. These are paired with external gears and mainly used for planetary gear drives or gear-type shaft couplings. Due to involute interference, trochoid interference, and trimming problems, there are limitations in the acceptable number of teeth differences between the internal and external gears. In internal gears, the rotational directions of the internal and external gears in mesh are the same, while two external gears in mesh will have an opposite rotational direction.
For gears of all types and much more, look no further than ASAP Aero Supplies, a trusted supplier of parts for a wide range of industries. We are an online distributor of aircraft parts as well as parts pertaining to the aerospace, civil aviation, defense, electronics, and IT hardware markets. We’re always available and ready to help you find all the parts and equipment you need, 24/7-365. For a quick and competitive quote, call us at 1-714-705-4780 or email us at sales@asapaerosupplies.com.
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