Hydraulic clamping nut

Hydraulic clamping nut for mutual axial clamping of a pair of workpiece such as a collet having a conical edge surface and a chuck embracing the collet and being provided with an external thread (6), comprising an annular housing (8), at least one pressure chamber arranged in the housing and filled with hydraulic medium, a pressure screw screwable into this chamber, an annular pressure area provided in the housing and connected to the pressure chamber and an annular piston axially displaceable in the annular pressure area, the housing (8) and the annular piston (15) having clamping surfaces (51, 53) directed inwardly and towards one another and the pressure area (13), the housing (8) and the annular piston (15) being so constructed and arranged in relation to one another that increasing pressure in the annular pressure area (13) causes an axial relative displacement of the clamping surfaces towards one another, the improvement being the annular piston (15) having as a clamping surface an internal thread (51) and being screwed onto the external thread (6) of the chuck;

• the annular piston (15) having furthermore a ring land (52) submerging into the annular pressure area (13) of the housing (8);
• the housing (8) comprising first and second sections (11, 12);
• the first section (11) being provided with said annular pressure area (13) and embracing the chuck (1) in loosely and axially freely displaceable manner;
• the second section (12) having on its side opposite the ring land (52) of the piston (15) a conical clamping surface (53) abuting the conical edge surface (18) of the collet (3).