Interim check and practical accuracy improvement for machine tools with sequential measurements using a double ball-bar on a virtual regular tetrahedron

This study proposes a method for a quick, simple interim check and practical accuracy improvement of machine tools using just a double ball-bar. The double ball-bar is used to measure sequentially the length of the six sides of a virtual regular tetrahedron within the workspace of the machine tool. Then, the scale and squareness errors of and between the three linear axes are calculated from the length results, and the measured lengths and the calculated errors can be used as criteria for the interim check. The calculated errors can also be compensated for to improve the accuracy of experimented machine tools practically. A sample machine tool was subjected to experimental interim checks applying the proposed method; it showed primarily large length deviations for the six sides due to geometric errors mainly. To improve the geometric accuracy practically, the calculated errors were compensated for and the measurements were repeated, showing significantly improved length deviations for the six sides. The main advantage of the proposed method is that it requires only a double ball-bar and sequential measurements; thus, it is a simple procedure with a measuring time of ∼5 min for a virtual regular tetrahedron. Additionally, the size of the virtual regular tetrahedron can be readily modified by changing the nominal length of the double ball-bar, increasing measurement flexibility. Thus, the proposed method is suitable for quick, simple, cost-effective daily and periodic interim checks, with practical improvement of machine tool accuracy.