Abstract: Pressurized hydraulic fluid for energizing the collet unclamping mechanism of a machining center is supplied through a first solenoid valve from an accumulator which is charged by a piston pump. The piston pump is attached to the machining center between the Z axis slide and the Z bed so that as the Z axis slide is moved to a home position at the outset of a tool change cycle, the pump charges the accumulator, allowing pressurized hydraulic fluid to be admitted into the collet unclamping cylinder through the solenoid control valve in response to machining center control system commands. Following pressurization of the unclamping mechanism from the accumulator, both the unclamping mechanism and the piston pump drain to the oil sump to reduce any drag on the Z axis slide or on the unclamping mechanism itself.