In a direct-drive high-power A/C-axis bi-rotary milling head

torque is transferred by two parallel connected rotary direct drive motors of C-axis

therefore

the length of the transmission components of C axis are considerably large

and they are borne high torque.Through analyzing the twist stiffness of the transmission components of C axis by using finite element method

the increase of scale of the sleeve’s reverse deformation in transmission components of C axis is been found.In the structural design permitted extent of C axis

the stiffness of transmission components of C axis is increased effectively through shortening its length and increasing its external diameter.