Patent ID: 7017919

Claim:
A chuck comprising: a holder body having a shank portion for insertion into a spindle of a machine tool, a gripping flange formed at one end of said shank portion, and a chuck sleeve that extends from said flange in a direction away from said shank portion in alignment with an axis of said shank portion, said chuck sleeve having a tapered outer circumferential surface whose diameter decreases from a bottom end adjacent to said flange to a tip end of said chuck sleeve; a clamp sleeve fitted onto the outer circumference surface of said chuck sleeve such that said clamp sleeve is rotatable and axially movable relative to said chuck sleeve, said clamp sleeve having a tapered inner circumferential surface whose diameter decreases from a bottom end adjacent to said flange toward a tip end of said clamp sleeve; needle rollers disposed between the outer circumferential surface of said chuck sleeve and the inner circumferential surface of said clamp sleeve over the entire circumference, said needle rollers inclining in the circumferential direction at a predetermined angle with respect to the center axes of said chuck sleeve and said clamp sleeve, and said clamp sleeve being rotated to cause said needle rollers to revolve spirally along the outer circumferential surface of said chuck sleeve while rotating about their own axes in order to decrease and restore the diameter of said chuck sleeve; and a thrust member disposed between an end surface of said flange opposite said shank portion and a corresponding end surface of said clamp sleeve, wherein said thrust member is held by means of a thrust-member holder of an annular flat shape, said thrust-member holder having at a central portion an opening for allowing passage of said chuck sleeve therethrough, and an end of said thrust-member holder being accommodated in an annular groove formed in the end surface of said flange, wherein said thrust-member holder includes an elastic member which is provided on the end of said thrust-member holder accommodated in the groove and engages with a wall surface of the groove so as to restrict movement of said thrust-member holder in the axial direction.