Method and system for checking positioning accuracy of a CNC machine

A method for checking positioning accuracy of a CNC machine with a machine tool head and a machine table, using an x, y, z coordinate system, wherein the z coordinate is a coordinate perpendicular to a machine table surface, the method comprising the steps:

• a) arranging a plurality of vessels on the machine table, wherein the vessels are in fluid connection with each other to form a system of communicating vessels, wherein the system of communicating vessels is filled with an electrolyte solution, and wherein a vessel electrode is placed in contact with the electrolyte solution in each vessel,
• b) mounting a tool head electrode to the machine tool head, wherein a material of the tool head electrode is different from a material of the vessel electrode,
• c) positioning the machine tool head to a position perpendicular above a surface of the electrolyte solution in one of the vessels,
• d) approaching the surface of the electrolyte solution with the tool head electrode and determining the z coordinate for which the tool head electrode touches the surface of the electrolyte solution by determining an electrical potential difference between the tool head electrode and the respective vessel electrode,
• wherein steps c) and d) are repeated for each vessel to determine a respective z coordinate of the surface of the electrolyte solution.