Positioning errors and accuracy of CNC machine tools

Computerized numerically controlled (CNC) machine tools are a solid foundation for modern industrial manufacturing. These machines provide linear and angular displacements in three or five axes. The accuracy of moving and positioning the tooltip relative to the work part's surface determines the final product's accuracy. Errors due to machine positioning can be linear or angular or both. This work studies the positioning errors of a vertical turning center CNC machine type. This machine has three axes, two linear X (horizontal) and Z (vertical), and one rotation axis 'C'. The travel of the spindle carrying the cutting tool along the X-axis is 1400 mm, and the travel of the carriage holding the spindle along the Z-axis is 1300 mm divided into six latches. The machine rotary table which carries the work part can rotate 360 degrees. A highly precise laser interferometer system determines the linear positioning errors in both the X and Z axes. The angular positioning errors for the 'C' rotation axis are determined accurately by an autocollimator system. The positioning error measurements are carried out based on ISO 230-2 as a measurement standard of positioning deviation, accuracy, and repeatability. The collected error measurements in linear displacements and angular rotation are analyzed, interpreted, and compared with manufacturer specifications and ISO 13041-4 allowable tolerances.