         Ozturk, E. , Budak, E. * Manufacturing Research Laboratory, Sabanci University, Istanbul, Turkey * ebudak@sabanciuniv.edu  5axis milling is a common manufacturing process especially in machining of complex surfaces. In such operations, chatter is an important problem as it affects the surface quality of the finished part. The application of stability diagrams is an efficient tool to predict chatter free cutting conditions. Although several stability models have been developed for milling operations, they are limited to 3 axis milling applications. In an earlier study by the authors, a stability model for 5 axis milling was presented using single frequency solution. Due to the time varying nature of the milling dynamics, a multi frequency system response may be obtained for cases where radial depth of cut is small. These frequencies show up in the system response in the form of addition and subtraction of the chatter frequency and harmonics of the tooth passing frequency. In the present study, dynamics of 5axis milling is modelled analytically considering multifrequency effects. The existence of multi frequency response is demonstrated using experiments and numerical solutions. The effect of multi frequency dynamics on the stability diagrams are shown by the analytical solutions and time domain simulations. : 5axis milling, chatter, stability, multifrequency 1. INTRODUCTION Chatter is an important problem resulting in poor surface finish, high dynamics forces and reduced tool life. It may even be harmful for the machine tool if cutting under unstable conditions is continued for extended period of time. Thus, chatter results in poor quality, reduced productivity and increased cost. In practice, chatter is avoided by using low depths of cut and slow spindle speeds resulting in longer machining cycle times. Chatter can be suppressed using stability diagrams where stable cutting depths are given for different spindle speeds which can be used to determine the most productive stable cutting conditions for a given process. Several stability models have been developed for milling operations starting about 5 decades ago [Sridhar et al., 1968; Tlusty, 1986; Tobias and Fiswick, 1958]. Later, Minis et al. (1990) solved two