A spindle assembly useful at high rotational speeds including a tool holding and releasing collet mechanism operated by an axially movable drawbar held in its tool holding position by a spring the force of which is overcome by a piston movable between first and second positions. A plurality of arms pivotally secured at one end thereof to a housing with a second end thereof engaging said piston and having a cam surface intermediate the first and second ends thereof engaging an actuator positioned to engage said drawbar, overcome said spring and move the collet mechanism to its tool releasing position. The ratio of the distance between the pivot point and cam surface with respect to the distance between the pivot point and the second end thereof being such to magnify the force of the piston sufficient to overcome the spring force.