Involute gear
The
involute gear profile, originally designed by Leonhard Euler, is the most commonly used system for gearing today, with cycloidal gearing still used for some specialties such as clocks. In an involute gear, the profiles of the teeth are
involutes of a circle. Irrespective of whether a gear is spur or helical, in every plane of the involute gears the contact between a pair of gear teeth occurs at a single instantaneous point where two involutes of the same spiral hand meet. Contact on the other side of the teeth is where both involutes are of the other spiral hand. Rotation of the gears causes the location of this contact point to move across the respective tooth surfaces. The tangent at any point of the curve is perpendicular to the generating line irrespective of the mounting distance of the gears. Thus the line of the force follows the generating line, and is thus tangent to the two base circles, and is known as the Line of Action. When this is true, the gears obey the Fundamental Law of Gearing: The angular velocity ratio between two gears of a gearset must remain constant throughout the mesh.