Robotics is increasing its presence in the machine tool sector. One interesting application for robot assisted machining involves a robot locally increasing the stiffness of a thin walled part to suppress regenerative vibrations and minimize part deformations during machining. Simulating the dynamics improvement achieved when coupling the robot and the part is of high concern, in order to guarantee the appropriate performance of the assisted machining. Receptance Coupling Substructure Analysis (RCSA) technique for High Speed Machining (HSM) dynamics simulation has been expanded to derive the frequency response of the assembled system composed by the coupling of the thin walled part and the robot.