Abstract: A spindle carrier, which is movable vertically by an electric servo motor through a relatively long ball screw, has a substantially constant counterbalance force maintained on it irrespective of whether it is moving up or down. This prevents compression or tension of the ball screw. The counterbalance force is maintained substantially constant through sensing the load on the spindle carrier and using the sensed load to vary the hydraulic pressure applied to a piston within a hydraulic cylinder and connected through a chain to the spindle carrier to apply the counterbalance force.

Abstract: Bore holes are formed in opposite side walls of a part in alignment with each other by two separate cutting tools in two separate machine tools disposed on opposite sides of the part. One of the machine tools is a master and the other is a slave with the master machine tool being disposed at the position at which it is to form a bore hole in one of the opposite side walls. Then, the slave machine tool is moved so that the longitudinal axis of its spindle is in alignment with the longitudinal axis of the spindle of the master machine tool whereby the two bore holes will be aligned with each other and extend through the entire part. This alignment is accomplished by a laser on a spindle carrier of the master machine tool producing a laser beam in parallel with the longitudinal axis of the spindle of each of the spindle carriers and being received by a laser target on the spindle carrier of the slave machine tool.