Direct flank geometry calculation for face gears

Face gear drives with a 90° shaft angle represent special types of angular gear units. In these gearings, a spur or helical involute cylindrical pinion meshes with a face gear. They offer the possibility for high transmission ratios in small construction spaces. An involute pinion-type cutter typically generates the face gear. Several geometry generation approaches exist. These approaches include the determination of a cutter envelope during generation by either direct application of the law of gearing or via special analytical methods for face gears. Usually, the resulting surface is not limited to the boundaries of the active flank (i.e. fillet, tip and inner/outer radius). For these methods of generation, post-processing is necessary to receive the flank geometry within its limits. These operations are needed due to the implicitness of the governing equations in the analytical approaches, but lead to discretization errors. The present study offers a direct calculation method for the pointwise geometry of the face gear flank. This novel method generates the face gear geometry for all combinations of the helix angle and the centre offset. By limiting the calculation to the boundaries of face gears, deviations based on the calculation are minimized. The paper compares the developed calculation method to gear calculation software. Eventually, the calculated geometry is compared to the geometry of manufactured face gear teeth.