Combination ring and central drill bit drilling equipment

Claim 2

IN ROCK DRILLING APPARATUS ADAPTED FOR DRILLING COAXIAL BORES OF TWO DIFFERENT DIAMETERS WITH BOTH AXIAL PERCUSSIVE MOTION AND ROTARY MOTION, THE COMBINATION WHICH COMPRISES A PERCUSSIVE RING DRILL BIT HAVING CUTTING EDGES DISPOSED THEREAROUND DEFINING THE DIAMETER OF THE LARGER OF SAID BORES AND AN OPEN CENTRAL PASSAGE AXIALLY DISPOSED THROUGH SAID RING DRILL BIT, A CENTRAL PERCUSSIVE DRILL BIT HAVING CUTTING EDGES DISPOSED THEREAROUND DEFINING THE DIAMETER OF THE SMALLER OF SAID BORES, THE DIAMETER OF SAID CENTRAL DRILL BIT BEING LESS THAN THE INTERNAL DIAMETER OF SAID AXIAL PASSAGE IN SAID RING DRILL BIT FOR FREE AXIAL MOVEMENT AND RETRACTION OF SAID CENTRAL DRILL BIT THROUGH SAID PASSAGE, A BIT ADAPTOR CONNECTED TO SAID CENTRAL DRILL BIT AND COAXIALLY DISPOSED WITH RESPECT THERETO IN SAID PASSAGE, MEANS ON SAID BIT ADAPTER FOR TRANSMITTING AXIAL DRILLING PERCUSSIONS TO SAID CENTRAL DRILL BIT, COOPERATING AND ENGAGING SUBSTANTIALLY TRANSVERSE SURFACES ON SAID BIT ADAPTOR AND SAID RING DRILL BIT FOR TRANSMITTING AXIAL DRILLING PERCUSSION TO SAID RING DRILL BIT ONLY IN A DRILLING DIRECTION, SAID BIT ADAPTOR BEING FREELY AXIALLY RETRACTABLE FROM SAID RING DRILL BIT IN THE OPPOSITE DIRECTION, AND ENGAGING MEANS ON SAID BIT ADAPTOR AND SAID RING DRILL BIT FOR TRANSMITTING ROTARY MOTION FROM SAID BIT ADAPTOR TO SAID RING DRILL BIT AND BEING FREELY AXIALLY DISENGAGEABLE UPON RETRACTION OF SAID BIT ADAPTOR FROM SAID RING DRILL BIT.