The main reasons for fixture errors in CNC lathe operation are the low manufacturing accuracy of fixture components, the low installation accuracy and the wear and tear of fixture appearance during operation. Fixture errors will directly affect the orientation accuracy and scale accuracy of the workpiece surface, and the orientation accuracy of the machined surface will be more affected.

     Under the effect of cutting force, transmission force, inertia force, clamping force and gravity, the general process system will deform correspondingly, and then destroy the correct orientation between the adjusted cutter and the workpiece, resulting in a few shape errors and scale errors of the workpiece.

     For example, when turning slender axle on NC lathe, under the effect of cutting force, the workpiece presents the phenomenon of "letting the knife" because of elastic deformation, which causes the cylindricity error of waist drum shape of the workpiece. For example, when grinding holes on an internal grinder with transverse cut-in method, because of the bending deformation of the spindle of the internal grinder, the holes will appear cylindricity error with taper.

    In the production practice of NC lathe, some useful methods are often adopted: reducing the surface roughness value of the touch surface diameter; increasing the touch area; properly pre-tightening; reducing the touch deformation and improving the touch stiffness; reasonably placing ribs and improving part stiffness; adding auxiliary support to improve the stiffness of the workpiece, such as using the center frame or the heel frame to improve the stiffness of the workpiece when turning slender axles; reasonably installing the workpiece stiffness; Clamp workpiece, reduce clamping deformation, such as when processing thin-walled sleeve, choose open transition ring or special claw clamping.