The Difference Between Addendum and Dedendum: Clearance

Introduction:
In mechanical engineering, the terms "addendum" and "dedendum" are used to describe specific parts of a gear tooth profile. The addendum refers to the portion of the tooth that extends beyond the pitch circle, while the dedendum refers to the portion of the tooth that lies within the pitch circle. The difference between the addendum and dedendum is known as clearance.

Clearance:
Clearance is defined as the difference between the addendum and the dedendum of a gear tooth. It represents the space between the top of one tooth and the bottom of the mating tooth in the gear set. Clearance is essential in gear design to ensure proper functioning and prevent interference between the mating gears.

Importance of Clearance:
Clearance plays a crucial role in gear design for the following reasons:

1. Smooth Engagement: The clearance allows for smooth engagement and disengagement between the gear teeth. It prevents jamming or binding of the gears during operation.

2. Thermal Expansion: Gears experience temperature variations during operation, resulting in thermal expansion. The clearance accommodates this expansion, preventing the gears from locking up or seizing.

3. Manufacturing Variations: During the manufacturing process, there can be variations in the gear tooth dimensions. The clearance provides tolerance for these variations, ensuring proper meshing and functioning of the gears.

4. Lubrication: Clearance allows for the presence of lubrication between the gear teeth. Lubrication reduces friction and wear between the gears, enhancing their lifespan and efficiency.

Other Gear Parameters:
Apart from clearance, there are other important parameters that define the gear tooth profile:

1. Backlash: Backlash is the amount of free movement or play between two mating gears. It is the result of clearance and manufacturing tolerances. Backlash can affect the accuracy and precision of gear systems.

2. Tooth Space: Tooth space refers to the width of the gap between two adjacent gear teeth. It is calculated by subtracting the addendum and dedendum from the whole depth of the tooth.

3. Flank: Flank is the side surface of a gear tooth.

Conclusion:
In summary, the difference between addendum and dedendum in gear tooth profiles is known as clearance. Clearance is crucial for smooth gear engagement, accommodating thermal expansion, compensating for manufacturing variations, and allowing lubrication. Understanding these parameters is essential in gear design to ensure efficient and reliable operation of mechanical systems.