A New Method for Thread Calibration on Coordinate Measuring Machines

This paper presents a new method for the calibration of thread gauges on coordinate measuring machines. The procedure involves scanning of thread profiles using a needle-like probe, achieving traceability by substitution of different thread portions with corresponding paths on a calibrated sphere. The feasibility of applying the method to calibrate a parallel thread gauge with respect to all the relevant thread parameters was demonstrated experimentally using a precision CMM. Application of the comparator approach as described in ISO DTS 15530-3 gave measuring uncertainties comparable to the values from usual calibration methods on dedicated equipment, e.g. a measuring uncertainty of 1.8 μm was achieved for measurement of the pitch, and 2-2.5 μm for diameter measurements.