1-1 Types of Gears

There are many types of gears such as spur gears, helical gears, bevel gears, worm gears, gear rack, etc. These can be broadly classified by looking at the positions of axes such as parallel shafts, intersecting shafts and non-intersecting shafts.

It is necessary to accurately understand the differences among gear types to accomplish necessary force transmission in mechanical designs. Even after choosing the general type, it is important to consider factors such as: dimensions (module, number of teeth, helix angle, face width, etc.), standard of precision grade (ISO, AGMA, DIN), need for teeth grinding and/or heat treating, allowable torque and efficiency, etc.

Besides this page, we present more thorough gear technical information under Gear Knowledge (separate PDF page). In addition to the list below, each section such as worm gear, rack and pinion, bevel gear, etc. has its own additional explanation regarding the respective gear type. If it is difficult to view PDF, please consult these sections.

It is best to start with the general knowledge of the types of gears as shown below. But in addition to these, there are other types such as face gear, herringbone gear (double helical gear), crown gear, hypoid gear, etc.

Spur Gear
The most common and easy to produce parallel shaft cylindrical gears. Of a pair of gears, the larger one is called a gear and the smaller one a pinion.
spur gear

Helical Gear
Quiet and able to transmit larger torque than spur gears. Cylindrical gears with spiral shaped tooth trace.
helical gear

Gear Rack
Changes rotary motion to linear motion. A set consisting of rectangular or circular rod shaped gear with mating small gear.
gear rack

Bevel Gear
Cone shaped gears used in intersecting shaft applications. There are also bevel gears with spiral shaped tooth trace called spiral bevel gears.
bevel gear

Spiral Bevel Gear
Cone shaped gears used in intersecting shaft applications. There are also bevel gears with straight shaped tooth trace called straight bevel gears.
spiral bevel gear

Screw Gear
Used in offset shaft application. Shape wise, they are the same as helical gears.
screw gear

Miter Gear
Type of bevel gears in which the pair is made of same number of teeth and used where speed reduction or increase is not needed.
miter gear

Worm Gear
Used when a large speed reduction is needed. Worm and worm gear set. Normally, different materials are used for worm and worm gear.
worm gear

Internal gear
Gear teeth are cut on the inside surface of hollow cylindrical forms and used in planetary gear systems. The gear teeth are cut using gear shaper machines.
internal gear

overview of gears

(Important Gear Terminology and Gear Nomenclature in this picture)

  • Worm
  • Worm wheel
  • Internal gear
  • Gear coupling
  • Screw gear
  • Involute spline shafts and bushings
  • Miter gear
  • Spur gear
  • Helical gear
  • Ratchet
  • Pawl
  • Rack
  • Pinion
  • Straight bevel gear
  • Spiral bevel gear

There are three major categories of gears in accordance with the orientation of their axes

Configuration :

  1. Parallel Axes / Spur Gear, Helical Gear, Gear Rack, Internal Gear
  2. Intersecting Axes / Miter Gear, Straight Bevel Gear, Spiral Bevel Gear
  3. Nonparallel, Nonintersecting Axes / Screw Gear, Worm, Worm Gear (Worm Wheel)
  4. Others / Involute Spline Shaft and Bushing, Gear Coupling, Pawl and Ratchet

The difference between a gear and a sprocket

Simply said, a gear meshes with another gear while a sprocket meshes with a chain and is not a gear. Aside from a sprocket, an item that looks somewhat like a gear is a ratchet, but its motiion is limited to one direction.

Classification of types of gears from the point of positional relations of the attached shafts

  1. When the gears’ two shafts are parallel (parallel shafts)
    Spur gear, rack, internal gear and helical gear, etc.
    Generally they have a high transmission efficiency.
  2. When the gears’ two shafts intersect each other (intersecting shafts)
    Bevel gear is in this category.
    Generally they have a high transmission efficiency.
  3. When the gears’ two shafts are not parallel or intersect (offset shafts)
    Worm gear and screw gear belong in this group.
    Because of the sliding contact, the transmission efficiency is relatively low.

Precision class of gears

When a type of gears is grouped by accuracy, precision class is used. The precision class is specified by the standards set by ISO, DIN, JIS, AGMA, etc. For example, JIS specifies each precision class’ pitch error, tooth profile error, helix deviation, runout error, etc.

Existence of teeth grinding

Existence of teeth grinding greatly affects the performance of gears. Therefore, in considering types of gears, teeth grinding is an important elememt to consider. Grinding the teeth surface makes gears quieter, increases force transmission capacity and affects the precision class. On the other hand, the addition of teeth grinding process increases cost and is not suitable for all gears. To obtain high precision other than by grinding, there is a process called shaving using shaving cutters.

Kinds of tooth shape

To broadly classify types of gears by their tooth shape, there are involute tooth shape, cycloid tooth shape and trochoid tooth shape. Among these, involute tooth shape is most commonly used. They are easy to produce and has the characteristic of being able to correctly mesh even when the center distance is slightly off. Cycloid tooth shape is mostly used in clocks and trochoid tooth shape is mainly in pumps.

Related Links :
Gear Types and Characteristics – A page of The ABCS of Gears – B
Gear Types and Terminology – A page of Gear Technical Reference
齿轮类型 – 中文页