To predict the process machine interactions in high speed machining, models of the speed dependent behavior of the spindle tool system are required. Parameter identification of these models can be achieved by utilizing measured frequency response functions of the rotating system. If an impact hammer is used to conduct the excitation of the structure, frictional forces may occur in the contact zone between hammer tip and rotating spindle. To evaluate the measured frequency response functions it is necessary to estimate the amount of the frictional forces and to ascertain what influence they have on the measurement results.