We have successfully developed a tooth profile which enables a spur gear having zero relative curvature at contact points under the engagement through the concave/convex pattern of contact and further enables a single flank of the tooth profile to have the infinite number of points where the relative curvature and specific sliding are zero values. We have given a name of “LogiX” to this tooth profile. A W-N (Wildhaber-Novikov) tooth profi¨le has been known as that having the concave/convex pattern of contact. The tooth profile, however, is applied only to a helical gear due to its feature of a point contact. While, on the LogiX tooth profile, an improvement has been made so that a pair of spur gears having the tooth profile may contact each other through the concave/convex pattern of a line-contact which cannot be achieved by the W-N tooth profile. Therefore, the LogiX tooth profile has realized a spur gear whose surface durability is as high as that of the W-N tooth profile. Since the results of durability tests show slightly higher than an involute one, it is expected that a new type heavy duty gear of this tooth profile puts into practical use. Furthermore, the tooth profile will have the possibility of creating the new era in the history of tooth profile theory.

A new W-N gear tooth profile is developed. The gear developed has an addendum of circular arc and a dedendum of involute curve. This particular tooth profile is believed to solve the problem of conventional W-N gear profile—that is, the profile is sensitive to center distance variations. No pitting on the gear was observed even after 1 × 107 revolutions cycle during the laboratory test using a pair of gear having specified values of Mn (normal module) = 4, β (helix angle) = 30 deg, and Lloyd’s K factor at 8 MPa.

Gear tooth tips are frequently chamfered to prevent nicks or scuffing on the tooth surface. Some of the hob cutters and pinion cutters can be chamfered but many types of cutters should be used for a particular range of tooth numbers since the amount chamfering largely varies depending on the tooth number. However, intensive efforts in the design have made it possible to produce cutters with little variation of chamfering amount for a wide range of tooth numbers. The error in the amount of chamfering by a single cutter designed by the above method can be maintained within ±10 % for gears with tooth numbers ranging from 16 to 94. It was found that three cutters of the conventional design are required for keeping the error within the same range for cutting gears within a given range of tooth numbers. The paper describes the tooth design method of the hob cutter with little variation of chamfering amount along changes in number of teeth to be machined and demonstrates that chamfering errors are maintained within practically allowable ranges for profile shift cutting or helical gear cutting with the use of this cutter.