Abstract: A power drawfinger system for selectively locking and releasing a toolholder or arbor in the socket of a power driven machine tool spindle. The system includes a collet device actuated by a power drawbolt using hydraulic means for expanding said device and a resilient member for contracting same to disengage or engage the toolholder. The collet device and drawbar mechanisms are constructed to be fail safe in event of breakage of the collet or loss of power.

Abstract: A counterbalance mechanism for a vertically movable machine tool headstock in which the net counterbalance force applied to the headstock is the same for both upward and downward movement of the headstock so that the accuracy of the spindle alignment is not disturbed by such movement. The counterbalance mechanism includes a hydraulic control system which automatically provides a greater pressure to a hydraulic counterbalance cylinder during raising movement of the headstock than during lowering movement so that difference in forces exerted by the counterbalance cylinder as a result of said pressure differential compensates for frictional resistive forces in the counterbalance mechanism and thereby enables the same net counterbalance force to be applied to the headstock.