When machining high-precision mechanical components, prevention and avoidance of self-excited chatter vibrations are crucial. In internal turning, the boring bar is usually the most flexible element of the machining system, which is characterized by the ratio of boring bar overhang L to boring bar external diameter D. The critical ratio (L/D)cr can be defined as the maximum admissible ratio L/D assuring stable cutting conditions in the considered configuration. Regarding this topic, incomplete and poor experimental results are reported in literature, mainly focused on theoretical and numerical approaches. In this paper, an experimental study on the critical ratio dependence on boring bar material (steel and high-damping carbide), boring bar external diameter D, workpiece material cutting pressure ks and tool nose radius rε is presented. Statistical analysis of the experimental data was performed, and a mathematical model able to predict the critical ratio (L/D)cr in internal turning for different toolholder materials and geometries, as well as for different cutting insert geometries and workpiece materials is proposed.
