Reversible pattern-tracing control for a duplicating milling machine

Claim 1

In combination with a duplicating milling machine which includes a work-supporting table arranged for transverse movement beneath a longitudinally and vertically movable, rotary cutting tool and a pattern-tracing unit disposed in laterally spaced relation to said cutting tool but coupled for vertical and longitudinal movement with said cutting tool; that improvement which comprises: means for stationarily supporting a three dimensional pattern beneath the pattern-tracing unit of said machine; a reciprocative hydraulic motor connected with the pattern-tracing unit of said machine and operable to reciprocate said unit in a direction transverse to the longitudinal direction of movement of said cutting tool; pump means connected with the work-supporting table of said machine and hydraulically connected to transfer fluid under pressure to and from said motor in response to movement of said work-supporting table, said motor and pump means comprising cylinder-piston units of equal volumetric displacement connected in a closed hydraulic circuit; and a selector valve connected in the hydraulic circuit between said motor and pump means and operable selectively to reverse the direction of flow of fluid to and from said motor and pump means, and thereby to cause said milling machine to produce either a direct image or a mirror image of a pattern stationarily supported beneath the tracing unit of said machine.