The strong demand for increasing productivity and workpiece quality in high speed micro milling process makes the machinetool system perform close to the limit of its dynamic stability. A major obstacle that limits the productivity in machining operations is the presence of machine tool chatter. Some practices should be conducted to improve the dynamic stability limits based on predicting chatter stability accurately, e.g., variable cutter structure. In this study a numerical analysis and experimental method is present to investigate the dynamics and machining stability in micro milling with variable pitch end mills. A new approach to represent machining stability using the force output of the time domain simulation is also described. Milling cutters with variable pitch angles can be very effective in improving stability against chatter for certain speed ranges. The method can be used for process optimization for a given tool or at the design stage to predict the performance of new geometries.