Hello Mechanical Engineers. Gears are generally used for power transmission. As it transmits almost full power Gear transmission is termed as positive transmission drive whereas there is some loss of power in transmitting it through belt drive and chain drive. To be able to design the gears you should first of all know the basic gear terminology.

Image source : www.wikipedia.org

And here we are with the basic Gear Terminology.

The main paramaters are as follows:

Root Diameter : The Diameter at the bottom of the tooth is Root Diameter.

Outer Diameter : The overall Diameter or Adendum Diameter of the Gear is said as Outer Diameter.

Base Diameter : The diameter where involute of the Gear profile gets generated is known as Base Diamter.

Pitch Circle Diameter : It is defined as diameter of pitch circle. Pitch circle of one gear touches the pitch circle of another gear while transmitting the motion. It is the circle on which gear is designed.

Chordal Pitch : Distance between two adjacent teeths along pitch circle.

Pressure Angle : Angle formed at pitch point between line normal to tooth surface and surface tangent to the pitch circle diameter. It is generally taken as 14.5 or 20

Addendum (a) : Its defined as radial distance between pitch circle and top of the gear.

Dedendum (b) : The radial distance between root and the pitch circle of the gear.

Face Width : Its the length of teeth in axial plane.

So its the basic terminology that we should have knowledge about. In the next post we will learn how to design a gear. The design of gear is very important factor and remember the above facts it would be helpful for the next post.