Microend milling offers the ability to machine microparts of complex geometry relatively quickly when compared with photolithographic techniques. The key to good surface quality is the minimization of tool chatter. This requires an understanding of the milling tool and the milling structure system dynamics. However, impact hammer testing cannot be applied directly to the prediction of tool tip dynamics because microend mills are fragile, with tip diameters as small as . This paper investigates the application of the receptance coupling technique to mathematically couple the spindle/micromachine and arbitrary microtools with different geometries. The frequency response functions (FRFs) of the spindle/micromachine tool are measured experimentally through impact hammer testing, utilizing laser displacement and capacitance sensors. The dynamics of an arbitrary tool substructure are determined through modal finite element analyses. Joint rotational dynamics are indirectly determined through experimentally measuring the FRFs of gauge tools. From the FRFs, chatter conditions are predicted and verified through micromilling experiments.