Abstract: A method is disclosed of controlling a hydraulic chuck of a rotary machine tool, the chuck clamping a workpiece to be machined and being actuated by a double-acting clamping/unclamping actuator. A clamping pressure controlled in accordance with a clamping pressure set point is applied to at least one chamber of the actuator and the clamping pressure is maintained in the corresponding chamber if the control pressure upstream of the actuator suddenly falls due to a malfunction. The clamping pressure is controlled by a closed loop and is modified in the chamber to disable the aforementioned maintaining of the pressure for a predetermined time period in response to an operator request to modify the clamping force applied to the workpiece. The disabling is being at least equal to the time necessary for the control system to stabilize.

Abstract: The invention relates to a clamping chuck. The clamping parts of the jaws are connected to support pieces sliding radially inside the body by means of bolts sliding axially inside these support pieces and provided with teeth.An axially sliding operating ring causes the jaws to clamp by acting on the support pieces by means of levers for example. The bolts are operated by actuating members.To avoid undesired clamping when the clamping parts are disassembled or adjusted, means lock the operating ring when an actuating member is in the position corresponding to retraction of the bolt, preferably before this retraction can be performed.