Abstract:Spindle system tool point frequency response function (FRF) is an important indicator of NC machine tools which measures and evaluates the cutting stability. So obtaining the tool point FRF has great significance in effectively drawing up processing technology and evaluating the overall performance. The semi-theoretical method, a combination of theoretical and experimental methods are adopted to predict the spindle system tool point FRF. Firstly, the prediction principle of semi-theoretical method is introduced. Then the process of applying this method in predicting FRF is researched, including calculating the receptance matrix at the free end of the tool by Timoshenko beam, setting up the test system of spindleholder FRF, testing the FRF of spindle-holder system with the short cylinder, calculating tool point FRF by the semi-theoretical method and experiment validation. Finally, as a research object, the spindle system of a vertical machining center is used to predict the tool point FRF by the proposed method, then the effectivity can be verified by comparing with the experimental results.