A quick setting and release actuator for cooperating with an axially movable chuck for holding a tubular workpiece in fixed position includes an anchor member (12) that is mounted in fixed relationship relative to a housing of a machine tool (20) and a thrust member (42) carried by a pivotally mounted carrier member (38) that pivots towards and away from the anchor member to drive the thrust member (42) into engagement with the end wall (44) of a multi-segment collet (26) to cause the collet to ride along its segment bearing surfaces (30) in a radial direction to engage the periphery of a workpiece (24) to be retained in the machine tool (20). Thrust member (42) may be pivotally mounted by a pivot connection (48) on the carrier (38) so that the thrust member will align itself with the end wall (44) of collet (26) even when the carrier is not precisely parallel with the collet end wall. In an alternative arrangement, rounded thrust pins may be used to transmit axial force to the collet (26) and this arrangement may include a thrust transmitting spacer (86). A lever (50) and cam (52) arrangement is provided to exert positive force on the carrier (38) at its terminal pivoted position by means of a thrust rod (54) cooperating with a thrust nut (58) connected to the thrust rod. A quick release pivot connection (40) may be provided to enable quick separation of the carrier (38) from its normal operating position adjacent the anchor member to thereby permit quick changing of the collet in the tool.