The range of tasks performed by industrial robots has become increasingly comprehensive in recent decades.This includes pick-and-place tasks with low to medium handling weights, as well as material processingtasks with medium to high processing forces. Milling in particular involves high-frequency excitation of thematerial, which results in vibration phenomena and therefor affects the surface quality of the product. Theseeffects were investigated by milling tests at characteristic positions and in different orientations of the millingspindle, using aluminum. For this purpose, based on an experimental modal analysis, a prediction model ofthe robot's natural frequencies in dependence of the joint positions was developed. This allowed thedetermination of characteristic milling positions and milling spindle orientations. Subsequently, the millingresults were related to a causal connection and were analyzed regarding the natural frequencies.