Parametric design is to use parameters to describe sizes of parts.When the part is designed

the shape of parts is changed by modifying characteristic parameters to achieve the sizes to drive the graphics.Cylindrical involute helical gear is a part of mechanical drives in common use

because of its complex tooth profile

it is difficult to carry out parametric design.The sizes of model and the characteristic parameters are correlated by setting up relational expression

the model of cylindrical involute helical gear are generated accurately.A new gear is generated rapidly by modifying gear characteristic parameter in expression

parametric design of involute helical gear is realized

so efficiency and precision of gear design is raised greatly.