above the rigid gear has an involute tooth profile and is shown at a position rotated by the angle u03c6 10 u00b0 with respect to the wave generator with a coordinate system o x y fixed thereon so that its y axis passes through the center of the tooth space also shown in fig1 are the flexible gear the cutter blade c k and the imaginary rolling contact plates p r and p f it should be noted that the path of contact shown is that for the left tooth flank defining the coordinates of the point c in the x y system as x c y c and those in the y y system as x c y c it follows that equ18 where x c and y c are obtained from equation 22 defining the angle between the common tangent the blade c k of the two tooth profiles and the y axis as u03b1 k the angle u03b1 k is obtained by the following equation where the angles u03b3 r and u03b1 b are obtained from equations 15 and 16 where there are alternative signs the upper one is for the left tooth flank and the lower one for the right tooth flank the tooth profile will be generated if the cutter blade c k is held at the position shown in fig1 i e at the position relative to the coordinate.