Development and evaluation of non-contact automatic tool setting method for grinding internal screw threads

In accuracy grinding processes of screw threads, tool setting is a significant step towards avoiding thread error and ensuring machining accuracy of screw threads. It is a challenge for grinding internal screw threads due to the narrow space limitation. This paper proposes an automatic tool setting method for grinding internal screw threads with non-contact proximity switch, which can be effectively applied into realistic situation with low cost. The geometrical features of internal screw threads in the narrow space are measured by non-contact proximity switch and used to determine the initial point of screw helix. The detailed procedures of the method are presented including preliminary adjustment for tool setting, measurement of spiral centerline for internal screw threads, calculation of the initial position of threads helix, and error compensation. Moreover, the experimental platform is developed to verify the feasibility of the non-contact automatic tool setting method. Furthermore, experiments on improved induction distance of proximity switch, axial translational speed, measurement mechanism, and robustness have been carried out to improve the accuracy of the tool setting method. The results show that the measurement mechanism with double-rising-edge level jumping is relatively better on the tool setting precision. And the improved induction distance of proximity switch is basically consistent with its theoretical one, the improved axial translational speed is - 5 mm/s, and the repeat accuracy of tool setting is up to +/- 0.002 mm. The results show the economical and effective method is applicable in the actual process of grinding internal screw threads.