Getting Familiar with the Nomenclature of Gears

According to Wikipedia, gears are rotating machine parts that have teeth and mesh with another toothed part to transmit torque. Devices with gears are able to change the speed, torque and direction of a power source. This function is quite important in many different industries today, especially where machines are used.

With the increasing demand on gears, Kore Industries have improved and set the standards on plastic gears, producing end results with the highest quality. However, many do not understand and get confused with the process of gear production.

In order to fully understand how gears are produced, how they can help different industries and what spur gears are used for, let us first familiarize ourselves with the different terminology used in the gearing process and the nomenclature of gears.

Gear Nomenclature


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There are so many terms related to the subject of gears that many can easily mistake for another. A worm gear can be confused for a rack and pinion, for instance. This is why it is important to have even just basic knowledge on gears to be able to understand its production and function.

Having said this, here are the basic gear nomenclatures:

  • Four circles of the gear:
  • Addendum circle – the circle touching the outermost points of the teeth of a circular gear wheel.
  • Pitch circle – the imaginary circle concentric to a toothed wheel, along which the pitch of the teeth is measured.
  • Base or root circle – the circle bounding the spaces between the teeth, in a right section of the gear.
  • Dedendum circle – the circle touching the bottom of the spaces between the teeth of a gear wheel.
  • Other parts of the tooth profile:
  • Addendum – the height by which the tooth of a gear projects beyond the standard pitch circle or pitch line.
  • Dedendum – the radial distance for which the tooth profile is extended inward from the pitch circle.
  • Pitch Point – the point of tangency of two pitch circles and is on the line of centers.
  • Line of Action – a line tangent to the base of circles of mating gears, through the pitch point and thus the path of tooth contact.
  • Pressure Angle – the angle formed between the line of action and a line tangent to the pitch point.
  • Tooth Thickness – the thickness of the gear tooth measured along the pitch circle.
  • Circular Pitch – defines the width of one tooth and one gap measured on an arc on the pitch circle; or the distance on the pitch circle from a point on one tooth to the corresponding point on the adjacent tooth.
  • Face Width – the length of teeth in an axial plane.
  • Tooth Face – the mating surface of a gear tooth between the addendum circle and the pitch circle.
  • Tooth Flank – the mating surface of a gear tooth measured between the pitch circle and the base circle.
  • Backlash – the amount of clearance between mated gear teeth.

Gears are quite important, there is no doubt about that. We might not know it, but we use plastic helical gears, spur gears and more in our everyday lives, even in the simplest devices. And being familiar with the terminology used with gears can help us understand why they are formed the way they are and to be able to maximize their application.

If we understand gears terminology better, we will be able to articulate our specifications and requirements for our gears. And Kore Industries would then be able to effectively produce the tools of the appropriate specifications.

It's worth noting that the standard pressure angles are 14.5 and 20 degrees. The significance is the time and costs it takes to manufacture the gears. Any variations from the standard pressure angles would result in higher costs and longer time.

If there are still some things you don’t understand about gears, simply get in touch with Kore Industries via the Contact Us button. We will be glad to help you out without any obligation on your part.

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