Two-stage drill for mechanical decoking or the like

Claim 1

A TWO-STAGE DRILL-BIT FOR CUTTING THROUGH A BODY OF SOILD MATERIAL HAVING OPPOSED TERMINAL ENDS AND HAVING A HEAD END FOR CUTTING IN A FORWARD AXIAL DIRECTION AND A TAIL END FOR CONNECTION TO A SOURCE OF ROTARY DRIVING POWER, COMPRISING TWO TELESCOPING TUBULAR MEMBERS ADAPTED FOR UNITARY ROTATION, PLURAL PILOT-DRILL RADIAL CUTTING ARMS CARRIE AT THE HEAD END OR SAID BIT AND AT THE FORWARD END OF ONE OF THE MEMBERS, SAID ARMS HAVING PILOT-BORE CUTTING EDGES UNIFORMLY REARWARDLY CANTED TO GENERATE ESSENTIALLY A FIRST SINGLE CONICAL CUT AT ONE TERMINAL END OF THE SOLID MATERIAL UPON ROTATION ABOUT THE DRILL-BIT AXIS, PLURAL AUXIALLY-DRILL RADIAL CUTTING ARMS, RETRACTABLY CARRIED BY THE OTHER OF SAID MEMBERS AT ITS REAR END, ACTUATING MEANS CONNECTING SAID AUXILIARY-DRILL CUTTING ARMS TO SAID ONE MEMBER OPERATIVE ON RELATIVE AXIAL TELESCOPING MOVEMENT BETWEEN SAID MEMBERS TO MOVE SAID AUXILIARY-DRILL CUTTING ARMS FROM ITS RETRACTED TO AN EXTENDED POSITION, SAID AUXILIARY-CUTTING ARMS BEING MOVABLE FROM A FIRST RETRACTED POSITION WITHIN THE PILOT-DRILL DIAMETER DURING THE CUTTING OF THE PILOT-BORE TO A SECOND RADIALLY EXTENDED POSITION WHEN PROJECTED BEYOND THE END OF THE PILOT-BORE AT THE OPPOSITE TERMINAL END OF THE SOLID MATERIAL, SAID AUXILIARY CUTTING ARMS HAVING EXPANDED BORE CUTTING EDGES WHICH IN EXTENDED POSITION ARE UNIFORMLY CANTED IN THE DIRECTION OPPOSITE TO THAT OF SAID PILOT-BORE CUTTING EDGES TO GENERATE ESSENTIALLY A SECOND SINGLE CONICAL CUT IN THE SOLID