Referring now to Figures 3 and 4, t

Referring now to Figures 3 and 4, the derivation of the curves defining the tooth profiles of the flexspline 26 and the circular spline 28 will now be explained in connection therewith. Figure3 depicts one tooth 60 of the flexspline 26 at a point of contact P'(x1,y1) with the face 62A of a tooth 62 of the circular spline 28. The tooth 60 has an upper face profile curve at 60A and a lower flank profile curve at 60B joined by a straight line transitional profile at 60C. The movement locus of the flexspline 26 describes the path of a point on the flexspline neutral surface or plane 68 as it is rotated by a wave generator (not shown). The movement locus is designated 54 and is shown by dotted lines. Dashed lines 68 delineate the neutral surface or plane of the flexspline 26 which does not change length as the flexspline is distorted by the wave generator (not shown). When the origin of the flexspline is moved from q(0,0) to a point q'(x0,y0)on its movement locus; the point P(x2,y2) on the tooth profile face 60A moves to the contact point P' (x1,y1) with the face 62A of circular spline 28.