This article presents research conducted to study the dynamic behavior of the assembly of a horizontal milling CNC machine spindle at the speed of 10 000 rpm and 50 000 rpm. This step aims to determine the critical rotation speeds of the complex system “spindle – bearings”, by drawing Campbell diagrams. The rotor is a subset of these machines, consisting of a shaft, in which the one or more discs, and which executes a rotating motion around the axis propyl. The curve Campbell contours in the diagram represents the variation of natural pulsations of spindle system, depending on the speed bearing spindle.