Abstract: A hydraulic double acting chuck motor comprising a hollow cylinder and piston mounted at the rear end of a working spindle of a lathe operates a collet or chuck by pushing or pulling on a hollow operating shaft. The chuck motor is arranged in an enclosed housing attached to the rear end of the head stock of the lathe and which is fitted with a drainage connection. The hollow piston of the chuck motor is operatively controlled through a hollow cylinder extension attached to the cylinder and which is provided with a pair of fluid supply ducts, each of which communicates with a chamber of the chuck motor. The ducts open on the outer peripheral surface of the cylinder extension. A slidable annular collar surrounds the cylinder extension and defines therewith an annular space. The collar is connected by a conduit to a source of fluid under pressure and is axially shiftable by a control means into communication with one or the other of the openings to the ducts leading to the chambers of the chuck motor.