Distortion-free expansion/contraction arbor or chuck assembly

A distortion-free contraction chuck assembly, for holding a workpiece or tool having a body portion or shaft of a given outside diameter in alignment with a machine axis, comprising:

• a chuck body positioned in alignment with the machine axis, said chuck body having a linear body portion with inner surfaces facing radially inwardly relative to the machine axis and a contraction portion with inclined faces facing inwardly at an inclined angle to the machine axis;
• a contraction member positioned radially inwardly of said chuck body and being movable relative to said chuck body in reciprocal directions in parallel with the machine axis, said contraction member having a linear body portion with outer surfaces facing radially outwardly toward the inner surfaces of said linear body portion of said chuck body and a contraction portion with inclined faces at an inclined angle to the machine axis facing outwardly in sliding contact with the inclined faces of said chuck body, said contraction portion being contracted radially inwardly into pressure contact with the outside diameter of the body portion or shaft of the workpiece or tool for holding the same securely when said contraction member is moved relative to said chuck body in a contraction direction, and being released from pressure contact therewith when moved relatively in a release direction;
• and
• a ball bushing disposed between, the outer surfaces of said linear body portion of said contraction member and the inner surfaces of said linear body portion of said chuck body and being configured and dimensioned for a slight interference fit to provide substantially zero clearance of said outer surfaces of said contraction member and said inner surfaces of said chuck body and for substantially frictionless movement therebetween.

A method for holding a workpiece or tool, having a given inside or outside diameter, in alignment with a machine axis, comprising the steps of:

• positioning a mounting body in alignment with the machine axis, said mounting body having a linear body portion with surfaces facing in a radial direction relative to the machine axis and an expansion or contraction portion with inclined faces facing at an inclined angle to the machine axis;
• positioning an expansion/contraction member radially between said mounting body and the inside or outside diameter of the workpiece or tool, said expansion/contraction member being movable relative to said mounting body in reciprocal directions in parallel with the machine axis, said expansion/contraction member having a linear body portion with surfaces facing radially toward the surfaces of said linear body portion of said mounting body and an expansion/contraction portion with inclined faces at an inclined angle to the machine axis facing in sliding contact with the inclined faces of said mounting body, said expansion/contraction portion being pressed radially into pressure contact with the inside or outside diameter of the workpiece or tool for holding the same securely when said expansion/contraction member is moved relative to said mounting body in an expansion/contraction direction, and being released from pressure contact therewith when moved relatively in a release direction;
• and
• providing a ball bushing between the surfaces of said linear body portion of said expansion/contraction member and the surfaces of said linear body portion of said mounting body, said ball bushing being configured and dimensioned for a slight interference fit to provide substantially zero clearance of said surfaces of said expansion/contraction member and said mounting body and for substantially frictionless movement therebetween.