A novel measuring tip for thread functional diameter: error compensation of the effect of lead angle and curvature radius

To obtain a method for measuring thread functional diameter, a new probe based on the synthetic measurement principle is designed to quantify the practical effect of each parameter in all axial sections. The probing element is an axial slice of a standard thread with a certain thickness; hence, the slice has a determined lead angle and curvature radius. When threads with different diameters are measured by slices, the maximum error caused by the lead angle and curvature radius can approach 99 μm according to the simulation results. To solve this problem, a measurement error model is established by analyzing the relationship between the contact points of the measuring tip and thread. By simulations and experiments, our results show that most of the effect of lead angle and curvature radius can be compensated. Using six slices with different pitches, a precise detection of 192 kinds of threads is achieved after error compensation within the range of M65-M300.