Underdrilling bit

Claim 1

IN EARTH BOREHOLE DRILLING, AN IMPROVED ROTARY PERCUSSIVE DRILL BIT HAVING A CENTRAL LONGITUDINAL AXIS COMPRISING AN UPPER BIT SECTION HAVING A FIRST DRILLING FLUID PASSAGE MEANS THERETHROUGH, ROTARY PILOT PERCUSSIVE DRILLING MEANS EXTENDING DOWNWARD FRROM SAID UPPER BIT SECTION, SAID PILOT DRILLING MEANS HAVING A MAXIMUM WIDTH WHICH IS SMALLER THAN THE MAXIMUM WIDTH OF SAID BIT AND HAVING A CENTRAL LONGITUDINAL AXIS WHICH OFFSET FROM SAID CENTRAL LONGITUDINAL AXIS OF SAID BIT, A SLOPING NONCUTTING SURFACE FORMED ON THE LOWER END AT THE SIDE OF SAID ROTARY PILOT DRILLING MEANS FURTHEST FROM SAID AXIS OF SAID BIT, SAID NONCUTTING SURFACE SLOPING INWARDLY TOWARD THE AXIS OF SAID BIT AND FORWARDLY WITH RESPECT TO THE DIRECTION OF PENETRATION OF SAID BIT AND ADAPTED DURING DRILLING TO FORCE SAID ROTARY PILOT DRILLING MEANS INWARDLY TOWARD SAID AXIS OF SAID BIT, FIRST PERCUSSIVE CUTTING MEANS HAVING CUTTING EDGES LOCATED ON THE LOWER PART OF SAID PILOT DRILLING MEANS AND ADAPTED TO CUT A CYLINDRICAL PILOT HOLE HAVING A SUBSTANTIALLY CIRCULAR VERTICAL WALL WHOSE CIRCUMFENCE WILL ACCOMMODATE SAID PIOT DRILLING MEANS WHEN THE AXIS OF SAID PILOT DRILLING MEANS COINCIDES WITH THE CENTRAL AXIS OF SAID BOREHOLE, SECOND ROTARY PERCUSSIVE CUTTING MEANS LOCATED ON SAID UPPER BIT SECTION ABOVE SAID FIRST ROTARY PERCUSSIVE CUTTING MEANS AND ADAPTED TO CUT AN ANNULAR SECTION OF EARTH SURROUNDING SAID PILOT HOLE AND TRAILING SAID PILOT HOLE WITH RESPECT TO THE DIRECTION OF PENETRATION OF SAID BIT, SAID FIRST PERCUSSIVE CUTTING MEANS LEADING SAID SECOND PERCUSSIVE MEANS BY A DISTANCE OF AT LEAST TWO INCHES, SAID PILOT DRILLING MEANS HAVING A SMOOTH CYLINDRICAL OUTER SURFACE HAVING SUBSTANTIALLY THE SAME CURVATURE AS THE WALL OF THE PILOT HOLE DRILLED BY SAID FIRST PERCUSSIVE CUTTING MEANS AND EXTENDING ABOVE SAID SLOPING NONCUTTING SURFACE FOR A DISTANCE OF AT LEAST TWO INCHES ABOVE THE CUTTING EDGES OF SAID FIRST PERCUSSIVE CUTTING MEANS AND LOCATED ON THE SIDE OF SAID PILOT DRILLING MEANS FURTHEST FROM SAID CENTRAL AXIS OF SAID BIT, SAID SMOOTH CYLINDRICAL OUTER SURFACE FORMING AN ANGLE WITH VERTICAL OF BETWEEN ZERO AND TWO DEGREES NEGATIVE AND FOR MING AN ARC EQUAL TO AT LEAST 30 DEGREES OF SAID PILOT HOLE, SECOND DRILLING FLUID PASSAGE MEANS EXTENDING THROUGH SAID PILOT DRILLING MEANS AND ADAPTED TO CONDUCT DRILLING FLUID FROM SAID FIRST DRILLING FLUID PASSAGE MEANS IN SAID UPPER BIT SECTION EXTENDING PILOT HOLE, AND THIRD DRILLING FLUID PASSAGE MEANS IN SAID PILOT DRILLING MEANS AND SAID UPPER BIT SECTION EXTENDING FROM THE LOWER END OF SAID PILOT DRILLING MEANS TO A POINT ABOVE THE TOP OF SAID PILOT HOLE DRILLED BY SAID PILOT DRILLING MEANS AND ADAPTED TO CONDUCT DRILLING FLUID FROM SAID PILOT HOLE TO SAID BOREHOLE.