A joining tool (10) is provided for pressing a disk (12) to a shaft (14) that has opposite first and second ends. The first end (18) of the shaft (14) is received in a press table (22) and the second end (24) of the shaft (14) is received in a centering receptacle (26). A press plate (34) axially presses the disk (12) onto the shaft (14). A resilient ram (40) is provided on a side of the press plate (34) that faces toward the disk (12) and compensates for an axial run-out of the disk (12) relative to the press plate (34). The resilient ram (40) of the joining tool (10) enables the disk (12) that has an axial run-out to be pressed onto the shaft (14) in a correspondingly sloped manner, with the result that a rotor shaft (16) with a satisfactory bond is made possible.