📌 Introduction:
Gears are one of the most important elements in Theory of Machines (TOM) and Machine Design. They are widely used in automobiles, machines, gearboxes, clocks, and industrial equipment to transmit motion and power between shafts.
Therefore to understand gears properly, you must first learn Gear Terminology, which defines all basic parts and dimensions of a gear system.
In this article, you will learn:
- All important gear terms
- Simple definitions (exam-friendly)
- Diagram explanation
- Key formulas
- MCQs for practice
⚙️ What is Gear Terminology?
Gear terminology refers to the standard set of terms used to describe different parts and dimensions of a gear tooth and gear system. Gear Terminology is fundamental for understanding design, manufacturing, and operation of gears, which transmit motion and torque between shafts.
However These terms are essential for:
- Exam preparation (Diploma, B.Tech, GATE)
- Machine design understanding
- Viva questions
- Mechanical interviews
Diagram of Gear Tooth:
Important Gear Terminology (Explained Simply):
Pitch Circle (Reference Circle): Imaginary circle that rolls without slipping against the mating gear’s pitch circle. It defines the gear’s theoretical size.
Addendum: Radial distance from the pitch circle to the top (tip) of the tooth.
Dedendum: Radial distance from the pitch circle to the bottom (root) of the tooth.
Addendum circle: The addendum circle is the theoretical circle that passes through the outermost tips of gear teeth, concentric with the pitch circle
Dedendum circle: The dedendum circle (or root circle) is an imaginary circle passing through the bottom or base of the gear teeth, concentric with the pitch circle.
Whole Depth: Total tooth depth = Addendum + Dedendum (including clearance).
Clearance: Extra space at the root to prevent interference with the tip of the mating tooth.
Tooth Thickness: Thickness of the tooth measured along the pitch circle (usually half the circular pitch).
Base Circle: Circle from which the involute tooth profile is generated.
Flank (Tooth Face): Side surface of the tooth that contacts the mating gear.
Fillet: Curved transition at the root of the tooth (reduces stress concentration).
Module: The gear module of a gear is defined as the ratio of the pitch diameter (D) to the number of teeth (T) of a gear’
Circular pitch: It is the distance from a point of one tooth to the corresponding point on the next tooth measured on the circumference of the pitch circle.
Diametral pitch: It is the ratio of number of teeth to the pitch circle diameter.
Backlash: It is the small clearance (gap) between mating teeth to allow for lubrication, thermal expansion, and manufacturing tolerances.
MCQs on Gear Terminology:
Q1. Pitch circle is:
A) Real circle
B) Imaginary circle
C) Outer circle
D) Root circle
✅ Answer: B
Q2. Backlash is:
A) Gear failure
B) Gap between teeth
C) Gear ratio
D) Tooth height
✅ Answer: B