Incremental hob shift mechanism

Claim 1

IN A HOBBING MACHINE, A HOB SUPPORT, A HOB CARRIAGE ON SAID SUPPORT, A HOB SPINDLE ON SAID CARRIAGE, SAID CARRIAGE BEING MOVABLE ON SAID SUPPORT IN A DIRECTION PARALLEL TO SAID SPINDLE, DRIVE MEANS FOR SAID SPINLE OPERABLE IN ALL POSITIONS OF SAID CARRIAGE ON SAID SUPPORT, INCREMENTAL HOB SHIFT MECHANISM OPERABLE TO SHIFT SAID CARRIAGE BY INCREMENTS FROM A STARTING POSITION TO A FINAL POSITION AND TO RETURN SAID CARRIER RAPIDLY IN A SINGLE MOVEMENT TO STARTING POSITION, SAID MECHANISM COMPRISING A FIRST FLUID PRESSURE ACTUATED PISTON AND CYLINDER DEVICE CONNECTED BETWEEN SAID SUPPORT AND CARRIAGE, A SHIFTING DEVICE CONNECTED BETWEEN SAID SUPPORT AND CARRIAGE AND COMPRISING A SCREW AND A HALF NUT ENGAGEABLE WITH ONE SIDE OF SAID SCREW AND MOVABLE RADIALLY OF SAID SCREW INTO AND OUT OF THREAD ENGAGING RELATIONS WITH REFERENCE TO SAID SCREW, MEANS FOR EFFECTING INCREMENTAL RELATIVE ROTATION BETWEEN SAID SCREW AND HALF NUT IN TIMED RELATION TO HOBBING OPERATIONS TO SHIFT SAID CARRIAGE BY INCREMENTS FROM SAID STARTING TO SAID FINAL POSITION, AND MEANS RESPONSIVE TO ARRIVAL OF SAID CARRIAGE AT FINAL POSITION TO MOVE SAID HALF NUT RADIALLY OUT OF THREAD ENGAGING RELATION WITH RESPECT TO SAID SCREW AND TO APPLY FLUID PRESSURE TO SAID FIRST PISTON AND CYLINDER DEVICE TO RESTORE SAID CARRIAGE TO STARTING POSITION, THE MEANS FOR MOVING SAID HALF NUT RADIALLY OF SAID SCREW COMPRISING A SECOND FLUID PRESSURE ACTUATED PISTON AND CYLINDER DEVICE.