Abstract: The influence of vortex motion of spinning drilling shaft is investigated, which caused by the hydro-force between the workpiece hole and the drilling shaft. First, it established the mathematic model of spinning drilling shaft concerning about the nonlinear reactive force of liquid acted on the drilling shaft. Then it acquired equation of vortex motion buckling condition and instability on drilling shaft. It proves that main reason of instability on spinning drilling shaft is the self-excited vibration and sub-resonance is the side effect. By analyzing the relation between the instability and the moving parameters of drilling shaft, the rules of selecting cutting parameters are derived. The theoretical result is consistent with practical data used in the factory, so has significant guidance to the production.

Key words: BTA deep-hole processing, Drilling shaft, Motion stability, Vortex motion