Chip relief for rock bits

Abstract

This invention relates to roller cone, air circulation type rock bits. Means are provided on the rock bit body as well as on the shirttail portion of each of the legs extending from the body to provide a relief to pass rock chips from the borehole bottom and up the drill string as the air circulation roller cone bit works in a formation.

I claim: 
     
       1. An air circulation, air lubricated, roller cone rock bit comprising: a rock bit body having a first cutting end and a second threaded pin end .Iadd.having a shoulder.Iaddend., said body forming a chamber therein, said chamber communicates with said circulation air through an opening formed in said second pin end, said pin end being connected to a drill string,   at least a pair of legs extending from said bit body, each leg forming a shirttail portion and a bearing, each bearing serves to support a roller cutter cone at said first cutting end of said bit, cutting elements adjacent the largest diameter of each roller cone form a gage of a borehole in a formation,   at least one nozzle formed in said bit body in communication with said chamber, said nozzle directs air past each roller cone into said borehole to lift detritus material out of the bottom of the borehole, and   relief means formed by said legs, said relief means serves to pass said detritus material from the bottom of said borehole by the rock bit body and out of said borehole by providing an annular space between an outer surface of said legs and walls formed by said borehole, said annular space, in a plane perpendicular to an axis of said bit, about adjacent an exit end of said at least one nozzle, is thirty-five percent or more of the .Iadd.annular .Iaddend.area .[.formed by.]. .Iadd.between the shoulder of the threaded pin end and the walls of .Iaddend.said borehole .[.through said plane.]., said annular space progressively enlarges in perpendicular planes between said exit end of said at least one nozzle and a shoulder formed in said bit body, said shoulder forms a thread termination base end for said second threaded pin end of said rock bit.   
     
     
       2. An air circulation, air lubricated, roller cone rock bit comprising: a rock bit body having a first cutting end and a second threaded pin end, said body forming a chamber therein, said chamber communicates with said circulation air through an opening formed in said second pin end, said pin end being connected to a drill string,   at least a pair of legs extending from said bit body, each leg forming a shirttail portion and a bearing, each bearing serves to support a roller cutter cone at said first cutting end of said bit, cutting elements adjacent the largest diameter of each roller cone form a gage of a borehole in a formation,   at least one nozzle formed in said bit body in communication with said chamber, said nozzle directs air past each roller cone into said borehole to lift detritus material out of the bottom of the borehole, and   relief means formed by said legs, said relief means serves to pass said detritus material from the bottom of said borehole by the rock bit body and out of said borehole by providing an annular space between an outer surface of said legs and walls formed by said borehole, said annular space progressively enlarges in perpendicular planes between said exit end of said at least one nozzle and a shoulder formed in said bit body, said shoulder forms a thread termination base end for said second threaded pin end of said rock bit, said relief means formed by said legs include channel grooves formed in the sides of the leg in a leading edge and a trailing edge of said shirttail portion of said leg, said relief means formed by said legs further include a space formed between said shirttail portion of each of said legs and said wall of said borehole, said space is formed by relieving the surface of said shirttail substantially paralleling said borehole wall, said leading and trailing edge grooves and said relieved portion of said shirttail portion paralleling said borehole wall serve to enhance the removal of relatively large detritus material from the bottom of said borehole, a cross-sectional area of said annular space measured in a plane through said .Iadd.at least .Iaddend.one .[.or more.]. nozzle exceeds thirty-five percent of the cross-sectional annular space .[.defined by.]. .Iadd.between .Iaddend.said shoulder of the second threaded pin end and the borehole wall .[.and increases as the bit cross section approaches said shoulder of said second pin end of said bit.].. .Iadd.   
     
     
       3.  An air circulation, air lubricated roller cone rock bit comprising: a rock bit body having a first cutting end and a second threaded pin end for connection to a drill string;   a shoulder on the bit body forming a thread termination base for the second threaded pin end of the rock bit;   an interior chamber in the body communicating with circulation air from the drill string through an opening formed in the second pin end of the bit body;   at least a pair of legs extending downwardly from the bit body, each leg including a shirttail portion at the outside of the bit body and adjacent to the wall of a bore hole drilled by such a rock bit, each leg also comprising a bearing supporting a roller cutter cone at the first cutting end of the bit, such a roller cone including cutting elements adjacent to the largest diameter of the roller cone for forming the gage of a bore hole drilled by such a rock bit;   at least one air nozzle in the bit body in communication between the chamber and the exterior of the bit body for directing air past each roller cone into a bore hole to lift detritus material out of the bottom of the bore hole; and   an annular space between the outer surface of the bit body and walls formed by such a bore hole drilled by the rock bit for passing the detritus material from the bottom of the bore hole past the rock bit body and out of the bore hole, the cross-sectional area of the annular space between the outside surface of the rock bit body and the walls of the bore hole in a plane at the exit end of such a nozzle being at least 35% of the cross-sectional area of the annular area between said shoulder of the threaded pin end and the bore hole wall, the cross-sectional area of the annular space progressively increasing in successive planes perpendicular to the axis of the rock bit from a lower portion of the shirttail to the shoulder. .Iaddend. .Iadd.4. A rock bit as recited in claim 3 further comprising a longitudinally extending channel groove in each of the leading edge and trailing edge of the shirttail portion of each leg. .Iaddend. .Iadd.5. A rock bit as recited in claim 4 wherein each of the channel grooves progressively increases in size from the lower end of the shirttail portion toward the pin end of the rock bit. .Iaddend.