Chuck for machine tools, in particular for lathes, having a chuck body defining a chuck axis and having in its front end face several guide grooves extending radially to the chuck axis for receiving clamping jaws, each guide groove having assigned thereto a driving jaw unit which has a base body which can be moved parallel to the guide groove between an inner and an outer end position in a guide pocket formed in the chuck body behind the guide groove and comprises a driving jaw held on the base body and movable relative thereto in the axial direction, which can be brought into engagement with a corresponding counter-toothing of a clamping jaw via a front toothing, a chuck piston axially movable in the chuck body, movable between a front end position and a rear end position in the chuck body and coupled via a coupling mechanism to the base bodies of the driving jaw units to convert an axial movement of the chuck piston into radial movements of the driving jaw units, wherein at least one notching mechanism is provided with a disengaging element which is movably arranged in the chuck body relative thereto and is coupled to at least one driving jaw in order, by moving the disengaging element, to move the driving jaw between a rear jaw change position in which the toothing of the driving jaw is lowered out of the guide groove to such an extent that a jaw change is possible, and a front working position in which a jaw change is not possible, wherein a safety mechanism is provided and designed in such a way that a movement of the disengaging element from a first position corresponding to the working position of the driving jaw into a second position corresponding to the jaw change position of the driving jaw is only possible when the chuck piston is in a defined axial securing position, and the chuck piston is locked in the securing position when the disengaging element is in its second position, in particular the securing position of the chuck piston corresponding to its front end position, wherein each driving jaw unit has assigned thereto precisely one disengaging mechanism with a disengaging element, wherein each disengaging element is mounted so as to be rotatable about a respective axis of rotation lying transversely, in particular radially to the chuck axis, and is coupled to the associated driving jaw in such a way that a first rotational position of the disengaging element corresponds to the working position of the associated driving jaw and a second rotational position of the disengaging element corresponds to the jaw change position of the associated driving jaw, characterized in that each disengaging element is mounted rotatably in the chuck body. a chuck body defining a chuck axis and having in its front end face several guide grooves extending radially to the chuck axis for receiving clamping jaws, each guide groove having assigned thereto a driving jaw unit which has a base body which can be moved parallel to the guide groove between an inner and an outer end position in a guide pocket formed in the chuck body behind the guide groove and comprises a driving jaw held on the base body and movable relative thereto in the axial direction, which can be brought into engagement with a corresponding counter-toothing of a clamping jaw via a front toothing, a chuck piston axially movable in the chuck body, movable between a front end position and a rear end position in the chuck body and coupled via a coupling mechanism to the base bodies of the driving jaw units to convert an axial movement of the chuck piston into radial movements of the driving jaw units, wherein at least one notching mechanism is provided with a disengaging element which is movably arranged in the chuck body relative thereto and is coupled to at least one driving jaw in order, by moving the disengaging element, to move the driving jaw between a rear jaw change position in which the toothing of the driving jaw is lowered out of the guide groove to such an extent that a jaw change is possible, and a front working position in which a jaw change is not possible, wherein a safety mechanism is provided and designed in such a way that a movement of the disengaging element from a first position corresponding to the working position of the driving jaw into a second position corresponding to the jaw change position of the driving jaw is only possible when the chuck piston is in a defined axial securing position, and the chuck piston is locked in the securing position when the disengaging element is in its second position, in particular the securing position of the chuck piston corresponding to its front end position, wherein each driving jaw unit has assigned thereto precisely one disengaging mechanism with a disengaging element, wherein each disengaging element is mounted so as to be rotatable about a respective axis of rotation lying transversely, in particular radially to the chuck axis, and is coupled to the associated driving jaw in such a way that a first rotational position of the disengaging element corresponds to the working position of the associated driving jaw and a second rotational position of the disengaging element corresponds to the jaw change position of the associated driving jaw, characterized in that each disengaging element is mounted rotatably in the chuck body.