Capability assessment of CNC machining centres as measuring devices

This paper deals with application of CNC machining centre as a measuring device for measuring of length dimension with workpiece touch probe. Capability determination of machine tool as a measuring device is verified based on the proposed procedure using a laser interferometer. The current value of the position of workpiece touch probe and the length of the measured object is obtained directly from the machine control system. The position of the workpiece touch probe, or the length of the measured dimension, is verified by the laser interferometer connected to the machine control system. Based on the obtained positions and lengths of inspected dimension (standard length) from the machine control system, the accuracy of measurement with workpiece touch probe can be determined and the applicability limit of the machine tool as a measuring device can be assessed. Using the machine tool as a measuring device would reduce idle times necessary to move the workpiece to the inspection point at the measuring device, its inspection and potential new fixing of a workpiece on the machine. Shortening of idle times or elimination of entire measurement operations at the coordinate measuring machine is a major contribution of the presented procedure. Use of the proposed procedure of assessment of the machine capability by capability indexes cg and cgk is demonstrated on a small machining centre.