Underdrilling bit

Claim 1

AN IMPROVED ROTARY PERCUSSION BIT FOR DRILLING BOREHOLES IN THE EARTH COMPRISING A MAIN BIT BODY, ROTARY PILOT DRILLING MEANS ON THE BOTTOM OF SAID BIT BODY WHOSE CROSS SECTION IS SMALLER THAN SAID BIT BODY, WHOSE CENTRAL AXIS IS OFFSET FROM THE CENTRAL AXIS OF SAID BIT BODY AND WHICH TERMINATES IN A GENERALLY FLAT, HORIZONTAL SURFACE, A NONCUTTING SURFACE FORMED ON THE LOWER END AT THE SIDE OF SAID ROTARY PILOT DRILLING MEANS FURTHEST FROM SAID AXIS OF SAID BIT BODY, SAID NONCUTTING SURFACE SLOPING INWARDLY TOWARD THE AXIS OF THE BIT BODY AND FORWARDLY WITH RESPECT TO THE DIRECTION OF PENETRATION OF SAID BIT AND ADAPTED TO FORCE SAID ROTARY PILOT DRILLING MEANS INWARDLY TOWARD SAID AXIS OF SAID BIT BODY, AT LEAST ONE FIRST ROTARY PERCUSSIVE CUTTING MEANS LOCATED ON THAT HALF OF SAID PILOT DRILLING MEANS NEAREST THE CENTRAL AXIS OF SAID BIT BODY EXTENDING FROM ADJACENT THE AXIS OF SAID PILOT MEANS TO THE INNER EDGE OF THE SAID PILOT MEANS AND ADAPTED TO CUT A CYLINDRICAL PILOT HOLE WITH SUBSTANTIALLY VERTICAL SIDES WHOSE CIRCUMFERENCE ACCOMMODATES THE OUTER MOST EXTENSION OF SAID NONCUTTING SURFACE WHEN SAID AXIS OF SAID ROTARY PILOT DRILLING MEANS COINCIDES WITH THE CENTRAL AXIS OF SAID BOREHOLE, AT LEAST ONE SECOND ROTARY PERCUSSIVE CUTTING MEANS LOCATED ON THAT HALF OF SAID PILOT DRILLING MEANS FURTHEST FROM THE CENTRAL AXIS OF SAID BIT BODY, THIRD ROTARY PERCUSSIVE CUTTING MEANS ON THE BOTTOM SURFACE OF SAID BIT BODY ABOVE SAID ROTARY PILOT DRILLING MEANS AND HAVING AT LEAST ONE CUTTING EDGE ADAPTED TO CUT AN ANNULAR SECTION OF THE EARTH IMMEDIATELY SURROUNDING SAID PILOT HOLE AND TRAILING SAID PILOT HOLE WITH RESPECT TO THE DIRECTION OF PENETRATION OF SAID BIT, AND SAID FIRST AND SECOND PERCUSSIVE CUTTING MEANS ON SAID PILOT DRILLING MEANS LEADS SAID THIRD PERCUSSIVE CUTTING MEANS ON SAID MAIN BIT BODY BY A DISTANCE BETWEEN 0.15 AND 1.25 TIMES THE MAXIMUM WIDTH OF SAID BIT BODY.