Base curves of involute cylindrical gears via Aronhold’s first theorem

The subject of this paper is the synthesis of the base curves of involute cylindrical gears, for uniform and non-uniform transmission ratio, by means of Aronhold’s first theorem and the return circle. The base curves can be generated in several ways, as reported in the literature, but this approach comes from the kinematics fundamentals; it is, thus, more straightforward than the alternatives for the case of non-uniform transmission ratio, which leads to non-circular gears. The base curves of circular and non-circular gears are obtained by intersecting, at each pitch point, the corresponding return circle with the line of action for a given pressure angle. This is possible for involute cylindrical gears since the tooth profile of the rack is represented by a line, and the conjugate profiles of the two meshing gears can be generated by its envelope.