Cooling medium from a main shaft (20) of a machine tool (10) is pressurized by a pump (300) and led to a nozzle (242) via a second case passage (222). A relief valve (500) is also connected to the second case passage and discharges cooling medium from an outlet port (511b) when the cooling medium pressure within the second case passage exceeds a pressure set value (Ts). At a prescribed rotational speed (Ns), the pump discharges cooling medium, at a prescribed pressure (Tr) that is higher than the pressure set value (Ts), from an outlet port (302) of the pump. The cross-sectional area (S2) of an outlet port (511b) of the relief valve is smaller than the cross-sectional area (S1) of an inlet port (511a) thereof. Therefore, at the prescribed rotational speed, a change of the discharge state of the cooling medium from the outlet port (511b) is visually observable.

A clamping device and a method for handling a workpiece or a unit comprising a workpiece and a workpiece holder. An automatic workpiece exchange is enabled by using a tool spindle. For this a spindle adapter is present that can be releasably connected with the workpiece holder. By means of the spindle adapter, the unit comprising the workpiece and the workpiece holder can be transported. The clamping device can be switched between a release condition and a clamping condition by means of a movement of an operating element. This movement can be carried out by means of the tool spindle, in that the tool spindle engages the operating element directly or indirectly by means of the spindle adapter or an operating tool.

A machining center has: a part holder for holding a part during machining; a plurality of tools; a spindle for holding an in-use tool of the plurality of tools; a tool magazine containing at least a partial remainder of the plurality of tools; and a tool changer for transferring tools between the tool magazine and the spindle. At least one of the tools is a grasper having claws shiftable between a first condition and a second condition, the second condition open relative to the first condition. Multiple other of the tools are held by respective tool holders.