Chuck for axially clamping two machine parts which are releasable from each other

In a chuck for releasably axially clamping first and second machine parts along a central clamping axis, said chuck including one of a conical and a cylindrical hollow centering attachment provided on the first machine part, means for defining an axially facing contact surface surrounding said centering attachment and extending perpendicularly to said central clamping axis, means for defining an annular groove on the inside of said centering attachment which includes a groove flank tapering conically radially inwardly towards a free end of said centering attachment, means for defining a holding bore in the second machine part adapted to axially receive said centering attachment, means for defining on the second machine part an axially facing end face which radially surrounds said holding bore and extends perpendicularly to said central clamping axis and against which said contact face is pressable, means for defining a further annular groove in said holding bore which includes a further groove flank, several clamping jaws arranged substantially parallel to said central clamping axis in said holding bore of the second machine part, and means for yieldably supporting each said jaw at a first end thereof against said further groove flank of said further annular groove, a clamping sleeve which is axially movable in said holding bore of the second machine part and arranged radially within the clamping jaws and which includes clamping cone means engagable with respective second ends of said clamping jaws for moving said second ends of the clamping jaws radially outward against said groove flank of said centering attachment when said clamping sleeve moves axially, the improvement comprising:

• additional clamping cone means provided on said clamping sleeve and engagable with said first ends of said clamping jaws for, during axial movement of said clamping sleeve and in cooperation with said first-mentioned clamping cone means, moving said clamping jaws radially outward in mutually parallel relationship when said axial movement of said clamping sleeve occurs in a first direction and permitting said jaws to move radially inward in mutually parallel relationship when said axial movement of said clamping sleeve occurs in a second direction, said clamping jaws including at both said first and second ends thereof means for defining clamping surfaces respectively adapted to engage the associated said groove flank, each said clamping surface having an angular orientation relative to said central clamping axis and said associated groove flank which permits continuous surface contact between each said clamping surface and said associated groove flank.