The geometry transmission errors of modified helical face-gear drive was investigated in the paper.A new version of face-gear drive geometry was proposed as envelopes of two parabolic racks of the pinion and shaper in the profile to improve the continuity and stability.The results show the transmission errors of helical face-gear drive with only modified helical pinion is an asymmetric one
and symmetric function parabolic transmission errors
no matter alignment or misalignment
were caused by the new geometry with tooth surfaces modified
while the factors of parabolic a1
as and parameter u0 of parabola apex were designed.