Geometric interference in cylindrical worm gear drives using oversized hob to cut worm gears

• We introduced geometric interference in cylindrical worm gear drives.
• Examination of the interference by using surface separation topology is presented.
• Examination of the boundary of the initially occurring area of interference is presented.
• Characteristics of the interference were investigated through numerical examples.
• The involute and Klingelnberg types of worm gear drives are chosen for the illustration.

This study examined the geometric interference of cylindrical worm gear drives using an oversized hob to cut the worm gear. The instantaneous line contact of a fully conjugated gear set becomes an instantaneous point contact when an oversized hob is used. In this type of worm gear drive, however, an edge contact can occur between the worm and worm gear. The edge contact is caused by geometric interference, and it occurs regardless of the presence of elastic deformation, misalignment, and transmission error. Aspects of the interference are presented through graphical illustrations. For examining the interference based on the differential geometry, two methods are proposed. The first method is for determining the surface separation topology between the tooth surfaces of a worm and a worm gear for an entire meshing cycle, and the second method for determining the boundary of the initially occurring area of interference when the hob oversize changes from zero to a nonzero value. By using the presented methods, the influence of various design parameters, such as the lead angle of the worm, the oversize of the hob, and the normal pressure angle, on the interference are examined and discussed through numerical examples.