Patent ID: 8726772

Claim:
A self-centering steady rest for clamping and/or holding a workpiece on a turning machine, wherein three holding elements are mounted in a housing of the steady rest and held adjustably in a common plane, two outer ones of said holding elements being configured as swivelling angled levers supported in the housing and in a mirror-image arrangement with one another, wherein the middle holding element is guided in the housing by means of a drive unit and a middle piece in a driveable connection with the drive unit such as to be axially moveable in the direction of the workpiece, control surfaces provided on the middle piece, the two outer holding elements being adapted to interact with the control surfaces by means of inner ends of the holding elements wherein the drive unit is driven by an electric motor and rotational movements of the electric motor are converted by the drive unit into at least two different axial advance speeds of the middle piece with resulting force components vectored onto the workpiece, and in order to set a corresponding advance speed of the middle piece between the middle piece and the electric motor, a clutch with a constrained action is provided, by means of which the drive unit can be changed over automatically into two different shift positions; and wherein the drive unit comprises a shaft and a hollow shaft enclosing said shaft in areas in a longitudinal direction of said shaft, and said shaft and said hollow shaft are in a force-locking, or releasable form-locking, active connection by means of said clutch; wherein said clutch is configured as a spring-loaded pin, the pin being arranged in a hole disposed in said shaft and aligned at right angles to a longitudinal axis of the steady rest, and a recess is provided in the inside of said hollow shaft, in which the pin engages during advance and return movement of said three holding elements, and the pin is moved out of the recess whilst said holding elements clamp the workpiece.