The gear has been classified through a lot of methods. The classification that is most popular is through the different position of the gear axis. This time we introduce the methods through different position of gear axis and manufacturing.
Classifications by the position of gear axis
(1) Parallel axis gear (The teeth are parallel to axis)
A) Spur gear
This is Cylindrical gear. Tooth trace is parallel to axis. This is a highly demanded gear, which is easy to manufacture and to assemble.
B) Helical gear
This is a Cylindrical gear. Tooth trace has helix curve. Helical gear provides more strength, less oscillation and lower noise level compared with Spur gears. However Helical gear provides a thrust load to axis direction. If changed rotating direction, thrust load is reversed.
C) Internal gear
This is a cylindrical gear ring with teeth formed at the inner diameter. The most popular demand for Internal gear is used for mechanism of planetary gear train. There are two types of Tooth trace, one is parallel and the other is helix to axis. However, gear with parallel axis has higher demand.
D) Straight Rack
It is thought that radius of spur gear grew infinite to become a straight line. It can be matched with Spur gear to convert between the rectilinear motion and the rotary motion.
E) Helical Rack
It is thought that radius of Helical gear grew infinite to become a straight line and Tooth trace is also straight line. It can be matched with Helical gear to convert between the rectilinear motion and the rotary motion.
F) Double helical gear
The shape looks like two Helical gear joined together. Therefore, this type of gear does not have thrust load to axis during operation.
∗ Other types of gear designs used for parallel axis such as non-circular gear and Eccentricity gear are available but omitted this time.
(2) Intersecting axis gear
G) Straight bevel (Miter) gear
This is gear with Tooth trace, which is a straight line in the same direction as surface element of Pitch cone. Miter gear has shaft angle of 90° and gear ratio of 1:1.
H) Angular straight bevel gear
Angular straight bevel gear which does not have shaft angle of 90°.
I) Spiral bevel gear
Tooth trace is described as a curve with spiral angle. Spiral bevel gear has advantage over Straight bevel gear for gear strength, oscillation and noise level. Disadvantage of Spiral bevel gear is axial thrust load. Therefore, proper bearing location and firm support are needed.
J) Angular spiral bevel gear
Angular spiral bevel gear does not have shaft angle of 90°.
K) Zerol bevel gear
Zerol bevel gear, similar to Spiral bevel gear with zero spiral angle. The Tooth trace is described as a curve with spiral angle of zero degree. (Occasionally, spiral angle 10° or below are also called Zerol bevel gear.) The force of tooth action is the same as Straight bevel gear.
L) Face gear
is Face gear. A Toothed disk gear, can be matched with Spur or Helical gear. There are two types of Face gear with shaft angle 90°, intersecting axis and Non intersecting axis.
(3) Skew gear (Non-Intersected Gear)
M) Cylindrical worm gear
This is a Worm gear pair consisting of Cylindrical worm gear and Worm wheel. Meaning of Cylindrical worm gear is that the thread has one or more starts. This Worm gear pair provides high speed reducing ratio and low noise level. Disadvantages are low efficiency and generation of heat.
N) Crossed helical gear (Screw gear)
This is a Gear pair for transmission between Nonparallel and Non-intersecting axes of Cylindrical gears as pair of Helical or Spur gear. Due to spot contact in theory, design of transmission should be light load.
O) Hypoid gear
This is a gear for transmission between Non-parallel and Non-intersecting axis of conical gear. This gear is similar to Spiral bevel gear. Most popular usage is for Deferential gear for automotive.
∗ Others including Enveloping worm, Spiroid and Helicon gear types of gear designs are available for Non-parallel and Non-intersecting axis but omitted this time.
(4) Machine elements compared with gear for similar shape and purpose of usage.
P) Sprockets
This is Sprocket wheel used for matching with bushed chain and Ladder chains. Usage is for transmitting a power over long distances between axes.
Q) Ratchet gear
This is Ratchet gear, which looks like the teeth of saw formed at external wheel used for positioning (indexing) and preventing inversion.
R) Timing Pulley
This is Timing pulley using matching timing belt (belt with teeth). Usage is for transmitting power over long distance between axes.