The invention includes a method of generating a tooth profile for an extended contact harmonic drive assembly having an oval wave generator having a major axis and a minor axis, a flexspline and a circular spline, which includes the steps of: fabricating a tooth profile on both the mating flexible spline and the circular spline so as to permit full engagement therebetween at a major axis of interen gagement of the flexible spline, and no engagement between the teeth at a minor axis of the flexible spline; forming the tooth profile so as to avoid interference between the flexs pline and circular spline teeth at any point between the major axis and the minor axis by forming the tooth profile to avoid that interference otherwise incurred due to the tooth inclination at points between the major and minor axis. The method also includes the step of manufacturing the tooth profile so as to allow the inclination of up to 2 degrees for the teeth precessing on the flexspline as the oval shaped wave generator sweeps therepast.