In calculation of the stability diagrams, the frequency response function (FRF) at the tool tip is required which is usually measured with tap testing. In this test, a piezoelectric hammer excites the tool/workpiece and response is measured using an accelerometer as shown in Figure 1. For the response, a non-touch displacement sensor such as laser vibrometer can also be employed. By using a data acquisition system and signal processing software, displacement to transfer function, G, can be obtained.
Figure 1. Tap testing to obtain the transfer function at the tool tip