Instability of internal damping due to collet chuck holder for rotating spindle–holder–tool system

Instability of internal damping due to collet chuck holder for rotating spindle–holder–tool system is investigated using transfer function approach as well as Routh–Hurwitz criteria with complex coefficients. Firstly, modal parameters of system including mass, stiffness, external damping and internal damping are extracted through three types of experimental modal analysis. Then, the effects of interference fits and clamping lengths between holder and tool on internal damping and instability are elaborated using experimental and numerical results, respectively. Finally, the internal damping instability is investigated through eigenvalue analysis and transfer function analysis in detail. The critical internal damping and phase “Jump” speed are derived. The former can be used to identify the instability mode (forward or backward modes), and latter can be applied to judge in advance whether the instability occurs. These results can be used to design and optimize the novel spindle, holder, and tool system with high damping in high rotating speed milling or deep-hole drilling process.