US Patent 7115082 Machine tool

A machine tool has a working spindle in which a tool receptacle for tool holders is provided. Furthermore, there is at least one tool-changing arm with a gripper in which a tool holder is held in a peripheral alignment with respect to the gripper in order to transfer this tool holder between its magazine position, which is spaced apart from the tool receptacle, and its working position, in which the tool holder can be clamped into the tool receptacle. A positioning indicator is provided for the peripheral alignment of the tool holder, the indicator indicating a misalignment between the tool holder and gripper.