Method and apparatus for impact drilling of overburden

Claim 1

THE METHOD OF MAKING A STRAIGHT BOREHOLE IN OVERBURDEN WHICH COMPRISES IMPRESSING AN ANNULAR BIT BODY HAVING A CENTRAL PASSAGE AND A PLURALITY OF RADIALLY ALIGNED CUTTING EDGES DEPENDING FROM SAID BODY INTO THE GROUND UNDER A STEADY PRESSURE APPLIED TO A RIGID DRILL PIPE FIXED TO SAID BODY SUCH THAT EACH INCH OF TOOTH EDGE SUPPORTS AT LEAST 400 POUNDS DEAD WEIGHT WHILE DELIVERING ENERGY OF IMPACT TO SAID BIT BODY BY REPEATEDLY IMPACTING A HEAVY MASS AXIALLY ON THE UPPER END OF SAID DRILL PIPE TO ABRUPTLY INCREASE THE STRESS IN THE CONTACT ZONES ADJACENT SAID TOOTH EDGES, SAID ENERGY BEING SUFFICIENT TO FRACTURE BRITTLE OBJECTS ENCOUNTERED BY SAID BIT BODY AND TO DISPLACE FRAGMENTS AXIALLY AND LATERALLY OF SAID ANNULUS, AND BEING AT LEAST 500 FOOT POUNDS PER BLOW PER INCH OF BOREHOLE DIAMETER.