Addendum Shifting in Gears

Addendum shifting, also known as profile shifting or addendum modification, is a technique used in gear design to modify the shape of gear teeth. This modification is achieved by intentionally shifting the basic rack datum line, which is a theoretical line used to generate the gear tooth profile, relative to the reference diameter of the gear.

Why Addendum Shifting is Used

• Undercut prevention: When gears have a small number of teeth, the standard involute tooth profile can lead to undercutting, where the tooth tip becomes pointed and weakens the gear. Addendum shifting can be used to modify the tooth profile and prevent undercutting.

• Center distance adjustment: By shifting the addendum of one or both gears, the center distance between the gears can be adjusted without changing the gear ratio. This can be useful in situations where the desired center distance is different from the standard center distance for the given gear pair.

• Load distribution: Addendum shifting can be used to redistribute the load between the teeth of a gear pair, which can improve the load-carrying capacity and reduce wear.

Types of Addendum Shifting

Positive Addendum Shift (+): Increases the addendum length, moving the teeth slightly outward. This is done to increase the gear's load capacity or avoid undercutting in smaller gears. It can improve tooth strength and reduce bending stress.

Negative Addendum Shift (-): Reduces the addendum length, moving the teeth slightly inward. This can be used to reduce interference between mating gears and allow for a more compact gear design.