Terminology of gear
The following are the important terms used for gears:
A Pitch circle is an imaginary circle that will contact the pitch circle of another gear when in a mesh.
Pitch circle diameter
The pitch circle diameter is the diameter of the pitch circle. Usually, the size of the gear is defined by its pitch circle diameter. It is generally denoted by the letter “D”.
Pich point is the point of contact of the pitch circles of gears in mesh.
The angle made by the common normal at the pitch point and the common tangent at the pitch point is called the pressure angle.
Face of tooth
The part of the tooth above the pitch circle is called the face of the tooth.
The part of the tooth below the pitch circle is called the flank.
The profile is the curve formed by the face and the flank of the tooth. In short, it is the shape of the tooth. Cycloidal and involute are the two main types of gear profile.
The Face width is the width of the tooth when measured parallel to the axis of the gear.
The topmost part of the tooth is known as the top land.
The distance of the tooth from one flank to another flank of the same tooth or the distance of the tooth measured along the pitch circle is the tooth thickness.
The distance or space between two adjacent gear teeth when measured along the pitch circle is known as the tooth space.
The distance from one point on one tooth to the same point on the adjacent tooth, when measured along the pitch circle, is known as circular pitch.
Diametral pitch is the ratio of the number of teeth (N) of gear to its pitch circle diameter (D).
Mathematically, Diametral pitch = N / D
The circle drawn such that it passes through the top of the teeth and is concentric with the pitch circle is called the addendum circle.
The radial distance between the addendum circle and the pitch circle is known as Addendum.
The circle drawn such that it passes through the bottom of the teeth of the gear and is concentric with the pitch circle is known as the Dedenddum circle.
The radial distance between the dedendum and the pitch circle is known as Dedendum.
The radial distance between the addendum and the dedendum is the total depth.
The total depth is the sum of the addendum and the dedendum of the gear.
Module is defined as the ratio of pitch circle diameter (D) to the number of teeth (N).
Mathematically, m = D / N
When 2 gears are in mesh, then the radial distance between the top of the tooth of one gear to the bottom of the tooth of another gear is called clearance.
Backlash is the difference between tooth space and tooth thickness when the distance is measured along the pitch circle.
Backlash in a gear helps prevent jamming of the gear. It also acts as clearance for thermal expansion and allows a thin film of lubricating oil. Manufacturing errors in gear also lead to the formation of backlash between the gear.
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FAQ on gear terminology
What is a module in gear?
A module in gear is the ratio of the pitch circle diameter of gear to the number of teeth on the same gear.
What is gear terminology?
Gear terminology are the terms related to a gear that helps in the design of it and describes the shape and size of gear.
What is an addendum and dedendum?
An addendum is the radial distance between the pitch circle and the addendum circle whereas the distance from the pitch circle to the dedendum circle is the dedendum.