Design of nonstandard spur gears cut by a hob

Abstract

A numerical technique has been developed for determining the individual hob offsets for a pair of spur gears designed to operate at a nonstandard center distance with the maximum ratio of recess to approach action or to balance tooth strengths of the pinion and gear. The numerical technique is based on determining the limit to which the hob is offset to create a full recess-action gearset, to balance the tooth strengths, to maintain a desired contact ratio, and to avoid undercutting. The values of the hob offsets from these design criteria are calculated, and the limiting value selected to produce an acceptable gearset. In this paper, backlash is incorporated into the solution method and a new numerical technique is employed to solve the optimum hob offsets. This paper presents the formulation of the equations for each of the design criteria and the corresponding solution methods, which include backlash, that are used to determine the optimum hob offsets. These design criteria have been incorporated into a Basic program. Example problems and results from the program are presented.