Anti-tracking feature for rock bits

Abstract

The harmful effects of tracking are reduced for a drill bit having roller cones with at least one of the outermost rows of active teeth containing one or more teeth having a height that does not extend to the height of at least one of the outermost rows on another roller cone on the bit. The crest on this tooth may have a length in a circumferential direction that is wider than an overall width of the tooth in the outer to inner direction. The invention may be used on any cutter row, not just the outermost row. The design may be used on a different roller cone or row, or more than one cutter row. The anti-tracking feature may be located between the leading and trailing edges of the tooth on one or more roller cones.

1 . A drill bit for reducing harmful effects of tracking, comprising:
 a bit body having bit legs with bearing pins;   a roller cone mounted to each of the bearing pins to define a plurality of roller cones, each roller cone having an axis and rows of active teeth, each of the active teeth having a radial height, an outer end and an inner end that define a length, a pair of flanks that define a width and a crest at which the ends and flanks converge;   spaces between the active teeth that define a depth of cut for the roller cones; and   an anti-tracking element on at least one of the rows of active teeth and having a second radial height that is less than the radial height of the active teeth and extending into a range of the depth of cut, such that the anti-tracking element engages and removes formation that remains as a result of uncut formation left behind by the active teeth.   
   
   
       2 . A drill bit according to  claim 1 , wherein the anti-tracking element is in an outermost row of one of the roller cones. 
   
   
       3 . A drill bit according to  claim 1 , wherein the anti-tracking element has a crest with a width extending in a circumferential direction that is wider than the width of the active teeth. 
   
   
       4 . A drill bit according to  claim 3 , wherein the crest has a length in an axial direction that is less than an axial length of one of the active teeth. 
   
   
       5 . A drill bit according to  claim 4 , wherein the width of the crest of the anti-tracking element in the circumferential direction is greater than the length of the crest of the anti-tracking element. 
   
   
       6 . A drill bit according to  claim 1 , wherein the anti-tracking element comprises a plurality of anti-tracking elements located on more than one row of the plurality of roller cones. 
   
   
       7 . A drill bit according to  claim 1 , wherein the anti-tracking element comprises a heel row of a plurality of anti-tracking teeth having a higher count than any other row on the plurality of roller cones. 
   
   
       8 . A drill bit according to  claim 7 , wherein the plurality of anti-tracking teeth comprise tungsten carbide inserts. 
   
   
       9 . A drill bit according to  claim 7 , wherein the heel row comprises an integrally-formed anti-tracking element in a shape of disk having a plurality of slots formed therein to define the plurality of anti-tracking teeth, and the slots extend radially in a symmetrical configuration. 
   
   
       10 . A drill bit according to  claim 7 , wherein the plurality of anti-tracking teeth have wear pads on outer surfaces thereof opposite a next row of active teeth. 
   
   
       11 . A drill bit according to  claim 1 , wherein the anti-tracking element comprises a scallop extending between two adjacent active teeth. 
   
   
       12 . A drill bit according to  claim 11 , wherein the scallop tapers radially with respect to the axis of the roller cone, and tapers in width in a circumferential direction. 
   
   
       13 . A drill bit according to  claim 11 , wherein the anti-tracking element has a greater circumferential width than the active teeth, and crests of the anti-tracking element maintain an active tooth pitch on the row with other ones of the active teeth. 
   
   
       14 . A drill bit according to  claim 1 , wherein the anti-tracking element forms an integral portion of one of the active teeth and is curved on a leading or trailing edge of said one of the active teeth. 
   
   
       15 . A drill bit according to  claim 14 , wherein the anti-tracking element tapers radially with respect to the axis of the roller cone, tapers in width in a circumferential direction, such that the anti-tracking element has a greater circumferential width than the active teeth, and the tapers converge in a crest that is formed at multiple radii or non-uniform radii. 
   
   
       16 . A drill bit for reducing harmful effects of tracking, comprising:
 a bit body having bit legs with bearing pins;   a roller cone mounted to each of the bearing pins to define a plurality of roller cones, each roller cone having an axis and rows of active teeth, each of the active teeth having a radial height, an outer end and an inner end that define a length, a pair of flanks that define a width and a crest at which the ends and flanks converge;   spaces between the active teeth that define a depth of cut for the roller cones; and   a plurality of anti-tracking elements located on more than one row of the plurality of roller cones, with at least one of the anti-tracking elements located on an outermost row of active teeth and having a second radial height that is less than the radial height of the active teeth and extending into a range of the depth of cut, such that the anti-tracking element engages and removes formation that remains as a result of uncut formation left behind by the active teeth.   
   
   
       17 . A drill bit according to  claim 16 , wherein the anti-tracking elements have crests with a width extending in a circumferential direction that is wider than the width of the active teeth. 
   
   
       18 . A drill bit according to  claim 17 , wherein the crest has a length in an axial direction that is less than the length of the active teeth, and the width of the crest of the anti-tracking element in the circumferential direction is greater than the length of the crest of the anti-tracking element. 
   
   
       19 . A drill bit according to  claim 16 , wherein the anti-tracking element comprises a heel row of a plurality of anti-tracking teeth having a higher count than any other row on the plurality of roller cones. 
   
   
       20 . A drill bit according to  claim 19 , wherein the plurality of anti-tracking teeth comprise tungsten carbide inserts. 
   
   
       21 . A drill bit according to  claim 19 , wherein the heel row comprises an integrally-formed anti-tracking element in a shape of a disk having a plurality of slots formed therein to define the plurality of anti-tracking teeth, the slots extend radially in a symmetrical configuration, and the anti-tracking teeth have wear pads on outer surfaces thereof opposite a next row of active teeth. 
   
   
       22 . A drill bit according to  claim 16 , wherein the anti-tracking element comprises a scallop extending between two adjacent active teeth. 
   
   
       23 . A drill bit according to  claim 22 , wherein the scallop tapers radially with respect to the axis of the roller cone, and tapers in width in a circumferential direction. 
   
   
       24 . A drill bit according to  claim 23 , wherein the anti-tracking elements have greater circumferential widths than the active teeth, and crests of the anti-tracking elements maintain an active tooth pitch on the row with other ones of the active teeth. 
   
   
       25 . A drill bit according to  claim 16 , wherein the anti-tracking element forms an integral portion of one of the active teeth and is curved on a leading or trailing edge of said one of the active teeth, the anti-tracking element tapers radially with respect to the axis of the roller cone, tapers in width in a circumferential direction, such that the anti-tracking element has a greater circumferential width than the active teeth, and the tapers converge in a crest that is formed at multiple radii or non-uniform radii.