Abstract: The invention relates to rotating machine element that contains a mechanism actuated by a fluid pressure. The aim of the invention is to allow for a supply of actuation fluid also during the rotation. To this end, a non-rotating control element (2) is mounted on two fluid bearings (3) on the machine element, said bearings being spaced apart in the axial direction and allowing flows of actuation fluid to flow from one element to the other. Feed lines (R, S) in the control element are provided with a series of radially inwards facing ports (13, 14) and reception channels (17, 18) in the machine element, a series of radially outward facing orifices (15, 16) being disposed in such a manner that in every relative position both elements for every individual flow of actuation fluid are disposed such that at least one port (13, 14) is aligned with one associated orifice (15, 16).

Abstract: The chuck comprises jaws which, in addition to their radial movement, can each swivel around an axis essentially parallel to the axis of the chuck, and where this axis glides in a radial slideway of the chuck in order to allow said radial movement. This swivelling action ensures that the working surfaces of the jaws or of shoes sitting on them which are adapted to the outer shape of the workpiece will sit evenly on the workpiece even when the latter is mounted between centers and as a consequence its rotation axis does not coincide exactly with that of the chuck.

Abstract: In order to machine a workpiece on a machine-tool successively between centers and with the workpiece clamped in a chuck, the workpiece is held during at least one machining operation—and if necessary between different kinds of machining—through the axial pressure of a center pin clamped in a chuck of the machine-tool. To this end the chuck comprises an axial center pin hydraulically movable in axial direction, which can be extended for enough towards the workpiece to be gripped by the jaws of the chuck, and which is journalled in at least one expanded sleeve bearing.

Abstract: Moving parts of the chuck are enclosed in a sealed cavity which is provided with a circulating lubrication. The power which drives its flow is derived from the force needed for opening and shutting the tongs of the chuck. In a chuck with hydraulically actuated jaws, this power is delivered by the pressure differences that occur between different parts of the hydraulic circuit actuating the jaws of the chuck and the hydraulic liquid acts also as lubricant.