Check smooth shaft torsional stiffness is calculated shaft torsional deformation of the work, is the twist per meter axial length of the angle amount. Smooth shaft torsion deformation to affect their work performance and accuracy, such as the internal combustion engine camshaft torsional angle is too large, will affect the proper valve opening and closing time; gantry crane movement mechanism to reverse the shaft angle will affect the driving wheel of the synchronization ; on the risk of torsional vibration occur from the shaft and the axis control systems, require greater torsional rigidity.