Expandable Core Chuck

1 . An expandable chuck comprising:

(a) a cylindrical housing extending along an axis,

(b) a plurality of expansion plates in the housing each supported on support structure and movable radially from a retracted position within the housing to an expanded position extending outwardly of the housing;

(c) a camshaft in the housing extending along the axis and rotatable thereabout in a first direction and a second direction;

(d) cam surfaces on the camshaft extending radially outwardly from the axis at varying distances therefrom;

(e) each support structure including cam followers which are engaged with the cam surfaces wherein movement of the cam surfaces relative to the cam followers in the first direction moving the cam followers and the expansion plates from a retracted position to an expanded position further from the axis outwardly of the housing and movement of the cam surfaces relative to the cam followers in said second direction permitting movement of the expansion plates toward the retracted position closer to the axis; and

(f) means for rotating the camshaft in the first direction and the second direction.

2 . An expansion chuck according to claim 1 wherein the housing has a plurality of slots extending parallel to the axis sized to receive therethrough the expansion plates and wherein rotation of the camshaft in the first direction moves each of the expansion plates through one of the slots.

3 . An expansion chuck according to claim 1 wherein the means for rotating the camshaft is a pneumatic motor.

4 . An expansion chuck according to claim 1 wherein the means for rotating the camshaft is an electric motor.

5 . An expansion chuck according to claim 1 further including an elastic member for urging the expansion plates back to a retracted position upon rotation of the camshaft in said second direction.