Modified tooth surfaces of one of the members of the straight bevel gear set were proposed in order to low the installation error sensitivity and improve the stability of contact patterns. Profile modification was carried out by changing the trajectory of the cutter from line to parabolic; tooth trace modification was carried by changing the roll

so the modifield tooth surface with drum shape could be obtained and the gear set could mesh with point contact. In order to further improve the meshing stability

the optimization model for tooth surface modification was proposed. The two modification coefficients were used as optimal variables; the Gauss curvatures of two meshing surfaces at contact points were controlled to construct the objective function

and the principal curvatures of the ease-off tooth surface at the contact point were controlled to ensure that the length of the instantaneous contact ellipse is at least 1/3 of tooth width. Finally numerical example of design of straight bevel gear drives was included to illustrate the advantages of the proposed geometry. A cutting and rolling experiments validate that the patterns maintain good stability with amount of the total axial misalignment and total axial separation accounted for 30% of the normal module.