Drill bit

#1. Field of the Invention

#This invention relates to drill bits, and more particularly relates to drill bits having removable cutter blades having hardened cutting surfaces and especially adapted for drilling earth formations, including limestone, sandstone, and shale.

#Earth formations are drilled using both rotary and percussion drilling machines. Rotary machines rotate a bit while applying pressure to the drill stem of the bit to advance the bit as chips are removed by the bit cutting surfaces. In rotary drilling, drill bits often include rotatable cone shaped cutting members. In percussion drilling, the drilling machine reciprocates the drill bit and sometimes rotates the bit as a hole is formed.

#The foregoing objects and advantages of the drill bit of the invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings wherein:

#FIG. 1 is side view in perspective of the drill bit of the invention with one of the cutter blades exploded out to illustrate the relation of the cutter blade and a wing of the body;

#FIG. 2 is a side view in perspective of the drill bit of FIG. 1 rotated from the position of the bit in FIG. 1;

#Referring to the drawings, a drill bit 10 embodying the features of the invention includes a body 11, an integral shank 12 for connection to a drilling machine, integral cutter blade mounting wings 13, and removable cutter blades 14 which are held in operating positions on the wings by roll pins 15. The cutter blades and wings are provided with hardened material over the cutting faces and the cutting edges of both the removable cutter blades and the supporting wings. The drill bit is particularly adapted for improved drilling in softer rook formations, such as soft limestone, sandstone, and shale. Typically, for most drilling applications, the bits are made in size ranges of from 3 inches to 5 inches diameter. Also, typically, three wings and cutter blades are employed.

#Referring to FIGS. 1 and 2, the shank 12 is tapered and externally threaded for securing to a drill stem of a drilling machine, not shown. It will be recognized, of course, that the shank 12 may be of uniform diameter or may have other configurations and shapes, depending upon the structure of the chuck or drill stem of the drilling machine. As illustrated in FIGS. 1, 2, and 4, the body 11 has a central cylindrical portion 20 and a lower somewhat conical portion defined by downwardly and inwardly convergent side surfaces 21 terminating at a lower end 22 of the bit body between the wings 13. The bit body has a longitudinal bore 23 extending throughout the length of the body opening through the upper end of the body and through lower end, as evident in FIG. 4, to permit a sufficient volume of drilling fluid, such as air to flow through the body. The lower conical portion of the bit body has upwardly and inwardly extending flow passages 24 which open at lower ends through the side faces 21 and intersect at upper ends with the body bore 23 for conducting drilling fluid from the central bore 23 downwardly and outwardly between wings and the cutter blades during drilling.

#As shown in FIGS. 2, and 4, the cutter blade support wings 13 are formed integral with the lower portion of the body extending downwardly and radially outwardly, as illustrated, with reference to the drilling position of the bit. As best seen in FIG. 4, the three wings are spaced apart at 120 degree angles around the bit body. Each wing has a top face 30, a forward face 31, defined in terms of the directions of rotation of the bit, a back face 32, a bottom face 33, an inside side face 34, and an outside side face 35. An inside back corner face 40 extends between the inside side face 34 and the back face 32. The front face 31, as seen in FIG. 4, lies in a plane which is vertical as illustrated in the drawings and which is parallel with the longitudinal axis of the bit body, that is the axis through the center of the bore 23, and also is a plane which includes a radius line, not shown, extending to and perpendicular to the longitudinal axis of the body. The outside side face 35 of each of the wings is a relieved face which slopes inwardly toward the bit body axis and rearwardly from the front face 31 to the back face 32 so that, as best seen in FIG. 3, as the bit rotates the side face does not engage the wall of the drill hole being cut. Each cutter blade support wing 13 has an outside side and front vertical cutting edge 41 on a rectangular insert 42 which is preferably formed of tungsten carbide, welded into the front outer vertical corner of the wing at the juncture of the front face 31 and the outer side face 35, defining a vertical side cutting edge 41. The bottom face of each of the wings 13 as seen in FIG. 4 has a mounting recess extending the length of the wing opening through the bottom face 33 of the wing aligned parallel to the front face 31 and having a rectangular cross section, as evident in FIGS. 1 and 2. The flat face 33 on each side of the mounting recess 43 provides a seat or bearing surface for the cutter blade 14 mounted on the wing. Lateral roll pin holes 44 are formed in each of the wings, intersecting the mounting slot 43, to receive the roll pins 15 for holding the removable cutter blades on the wings 13. The relief angle of the side surfaces 35 of the wings is sufficient to insure that the sides of the wings are away from the wall of the bore hole being cut so that the bit does not unduly heat during drilling. Preferably this angle is about 30.degree. degrees. The material forming the bit body including the central portion 20, the wings 13, and the shank 12, is preferably forged or cast steel having a 41-40 analysis. The insert in each wing providing the vertical side cutting edge 41 is preferably a mine grade tungsten carbide induction heat welded to the wing.