CA1264734A - Kerfing drag bit - Google Patents

Abstract

An Improved Kerfing Drag Bit Abstract of the Disclosure Cutting a rock formation with a polycrystalline diamond rotating bit is optimized by cutting by means of a kerfing action. The polycrystalline diamond cutters are arranged and configured on the bit face to form a plurality of triads. Each triad includes two kerf cutting teeth and a clearing tooth. The kerf cutting teeth each cut a kerf into the rock formation. The two radially spaced kerf cutting teeth thus define an interlying annular space of rock. A
clearing tooth removes the interlying space. In the preferred embodiment, the radial width of the land is equal to or less than the effective cutting width of the clearing tooth, and each of the kerf cutting teeth and the clearing tooth are azimuthally offset one from the other on the bit face with the clearing tooth azimuthally disposed between the kerf cutting teeth.

Description

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n Improved Kerfing Drag ~it 3 Background of the Invention 4 Field of the Invention 5 1 The present invention relates to the field of 6 ¦ earth boriny tools and in par~icular to rotating dras bits 7 ¦ utilizing polycrystalline synthetic diamond teeth as the 8 ¦ cutting elements.
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10 ¦ Description of the Prior Art 11 ¦ One of the primary differences provided in the 12 ¦ cutting action of a rotating drag bit and a roller cone bit 13 is that the rotating drag bit cuts by sheariny action 14 whereas the roller cone bit cuts by crushing. The performance of rotating drag bits has been substantially 16 increased by the introduction of synthetic polycrystalline 17 diamond elements which can be used as the cutting elements.
18 The Assignee of the present invention has pioneered in the l9 design of synthetic diamond rotating bits and the means by which such diamond teeth are attached to, retained on and 21 exposec above the face of the bit to provide useful cuttiny 22 action.
23 Typically, diamond teeth on a rotating bit will 24 slice into or shear grooves into the rock formation in the bottom of a hole. According to designs known in the art the 26 teeth are collectively arranged on a bit face in an 27 overlapping arrangement. For example, one row of diamond

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~ 7~34 1 teeth will typically have an offset row of diamond teeth 2 disposed behind it. In some designs the offset row is

3 disposed on the bit face with a radial distribution which

4 leaves the teeth in the half spaces between the teeth of the preceding row, albeit as azimuthally displaced behind the 6 preceding row. Other designs contemplate disposition of 7 succeeding rows of teeth in o~her fractional radial 8 increments such as three rows collectively comprising a 9 cutting unit with each row radially offset from the azimuthally preceding row by one third of the intertooth 11 spacing.
12 The result is that a plurality of grooves are cut 13 by the first row into the face of the rock formation at the 14 bottom of the borehole. The next row of teeth is rotated 1 through the same given radial line and cuts the next 1 adjacent annular one-third or half space adjacent to the 17 groove cut by the first row. This cutting sequence 1 continues until the entire inter-tooth spacing is cut from 1 the rock formation. Thus, the corresponding teeth in the 2 associated rows will cut a complete annular ring from the 21 rock face. The annular rings of adjacent sets of teeth are 22 also adjacent, thereby resulting in the removal of an entire 2 layer from the face of the borehole. The progression of 2 cutting elements generally continues radially outward as 2 adjacent, consecutive, radial increments, or may be designed 2 to cut inwardly by successive radial increments .

~Z~4734 1 Although the predominant form of current cutting 2 practices is as described above, cutting through kerfing is 3 also known, although little used. One example can ~e found 4 in a soft rock cutter in Kandle, "Drill Cutting Head" U.S.
Patent 2,960,312. In Kandle two concentric annular wheels, 6 each carrying a plurality of teeth in a rotating drag bit, 7 cut two circular kerfs with the interlying land between the 8 kerfs being cut, crumbled or crushed by one of two 9 interlying clearing cutters. Although the clearing cutters are added to the design almost as an afterthought, Kandle is 11 an example of an instance where two spaced-apart kerfs are 12 cut into the rock formation and the interlying rock removed 13 by an interkerf cutter.
14 The removal of ridges which are created between adjacent kerfs, or are created by kerf cutting, has also 16 been applied to some ext~nt in rock bit or roller cone bits.
17 In Baker, "Hybrid Rock Bit" U. S. Patent 4,343,371 Stratapax 18 cutters are disposed on two opposing extensions of the bit 19 body between two opposing roller cones. The kerfs cut by the plurality of teeth on the roller cones leave raised 21 lands which are then removed by Stratapax cutters acting in 22 part as a drag bit.
23 Kerf cutting has also been used to an extent 24 within the roller cones itself as is exemplified by Youngblood, "Roller Cutter with ~ajor and Minor Insert 26 Rows", U.S. Patent 4,202,419.

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1 However, none of the prior art designs efficiently 2 maximize or exploit kerf cutting to any extent. In fact, 3 it remains substantially unappreciated that kerf cutting is 4 evel~ necessarily desirable or advantageous in any sense over other types of cutting action, even when kerf cutting is 6 used solely in rotating drag bits.
7 Therefore, what is needed is a design for a 8 rotating drag bit which maximizes the cutting action of the 9 rotating bit, particularly when the cutting elements are synthetic polycrystalline diamond elements.

12 Brief Summary of the Invçntion 14 The present invention is an improvement in a rotating bit having a bit face including a plurality of 16 polycrystalline diamond teeth disposed on the bit face. The 17 improvement comprises at least a first and second 18 polycrystalline diamond tooth for cutting kerfs. A third 19 polycrystalline diamond tooth, associated with the first and 2 second polycrystalline diamond teeth and disposed 21 therebetween, is provided for clearing material lying 22 between the ker$s which is cut by the first and second 2 teeth. The third tooth is azimuthally displaced with 2 respect to at least one of the first and second teeth. By 2 reason of this combination of elements, cutting by kerfins 2 with the first, second and third teeth acting in combination 27 is optimized on the bit.

7~4 I More specifically, the improvement i 5 i11~strated 2 1 in four embodiments. In the first embodiment the first and 3 ¦ second teeth are disposed on the bit face at substantially 4 1 the same azimuthal position. The first and second teeth are

5 ¦ radially spaced apart and the third tooth is a2imuthally

6 ¦ disposed behind or follows the first and second bit teeth as

7 1 defined by the direction of rotation of the rotating bit.

8 ¦ In the second embodiment the first and second

9 ¦ teeth are both radially and azimuthally offset from each

10 ¦ other. The third tooth is radially disposed between the

11 1 first and second, and is azimuthally disposed behind or

12 ¦ follows both the first and second teeth.

13 ¦ In the third embodiment the first and second

14 teeth are azimuthally and radially disposed from each other on the bit face of the bit. The third tooth is azimuthally 16 disposed behind the first tooth and in front of, or leads the 17 second tooth. ' 18 In the fourth embodiment the third tooth is 19 azimuthally disposed in front of or leads both the first and second teeth.
21 In each of the embodiments the radial spacing 22 between the first and second teeth of each triad decreases 23 as the distance of the triad from the center of rotation of 24 the bit increases.
The invention further includes a method of cutting 26 with a rotating bit having a plurality of synthetic 27 ¦ polyc sta11ine diamcnd e1eme~ts disposed on the bit . -. :
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1 comprising the steps of cutting two radially s~aced 2 ¦ concentric kerfs into a rock formation by two kerf cutting 3 teeth. The space between the kerf cutting teeth is cleared 4 with a third clearing tooth. Each of the two kerf cutting teeth have a corresponding third clearing tooth. In 6 particular the step of cutting further comprises the steps of cutting a first kerf, clearing the rock disposed between 8 the first kerf and a second kerf to be cut by an azimuthally i 9 following third clearing tooth, and then subsequently cutting a second kerf with an azimuthally following tooth.
11 These and other embodiments of the invention are 12 better understood by now turning to consider the following 1 Figures wherein like elements are referenced by like 1 numerals.

1Description of the Drawings Figure 1 is a plan view of a mining bit having the cutting teeth collectively arranged as kerf cutters 2 according to the invention~
21Figure 2 is a diagrammatic cross sectional 2 depiction of the pattern of coverage of one collective group 2 of cutters of the bit of Figure 1 as seen in a radial line 2 as the bit rotates.
2Figure 3a is a cross sectional view of a mold used 2 to dispose the cutters of Figure 2 into a matrix 2 infiltration bito 28~

1 3L~47;3~ 1 1 ¦ Fisure 3~ is a cross-sectional view of a mold for 2 the remaining tooth of the collective group depicted in 3 ~ Figure 2.
4 Figure 4 is a diagrammatic plan view of a firs~
5 ¦ embodiment of the kerf cutting teeth.
6 ¦ Figure 5 is a diagrammatic plan view of a second 7 ¦ embodiment of the kerf cutting teeth.
8 ¦ Figure 6 is a diagrammatic plan view of a third ¦ embodiment of the kerf cutting teeth.
10 I b I Figure 7 is a diagrammatic plan view of a fourth I e -~ Od ~
11 ¦ emt~ro~YRt of the kerf cutting teeth.
12 ¦ Figure 8 is a diagrammatic plan view of a 13 ¦ petroleum bit utilizing the selective disposition of kerf 14 cutting teeth of the invention.
Figure 9 is a diagrammatic cross sectional view 16 taken through line 9-9 of Figure 8 showing a profile of the 17 petroleum bit.
18 Figure 10 is a diagrammatic plot diagram of the 19 teeth as disposed on the petroleum bit of Figures 8 and 9.
The invention and its various embodiments are now 21 best understood by considering the detailed description as 22 illustrated by the Figures described above.

24 Detailed Description of the Preferred Embodiments 2 The invention relates to a design wherein kerfing 28 ; a~ti OD in synthetic polycrystalline diamond rotating bit ~ 4734 1 ¦ is optimized. In the preferred embodiment the cutting teeth 2 of the bit are associated in triads. The first two teeth of 3 1 the triads are particularly adapted and arranged to cut 4 parallel kerfs. The third tooth of the triad is particularly adapted and arranged to cut into the interlying 6 space in the rock formation between the first two teeth or 7 to remove the interlying land between the kerfs cut by the 8 preceding first two teeth of the triad. The last tooth is 9 arranged and configured to act as a hammer or chisel and to provide a broad surface of cutting contact than the 11 corresponding first two teeth of the triad. It has been 12 determined according to the invention that the azimuthal and 13 radial disposition of each of the teeth, which collectively 14 forms a triad of cutters, is of material importance to 1 maximize cutting efficiencies through kerfing action. The 16 invention, its operation and various embodiments may bettPr 17 be understood by now turning to the plan view of a mining 18 bit shown in Figure 1.
1 In Figure 1 a coring mining bit, generally denoted by reference numeral 10, is characterized by an outer gage 21 12 and inner gage 14. Bit 10 is divided into six 60 degree 22 segments as delineated by radial waterways 16. At least one 23 and generally a plurality of polycrystalline diamond teeth 24 18 are disposed near or on the edge of each waterway 16.
Teeth 18 may in fact be any cutting elements now known or 26 later devised in the art although they are described here as 27 synthetic polycrystalline diamond teeth such as incorporated ~, ., ~tj4~34 l in the various designs of bits sold under the trademark 2 BallaSet marketed by Norton Christensen, Inc. of Salt Lake 3 City, Utah.
4 Teeth 18 are collectively arranged to form groups of triads. For example, teeth 18a form a leading pair of a 6 first collective triad of teeth of which tooth 18b is the 7 third tooth. As depicted in the plan view of Figure 1, 8 tooth 18b is radially disposed in the half space between 9 teeth 18a and azimuthally displaced behind tooth 18a ~y a predetermined angle, in this case approximately 60 degrees.
ll Teeth 20a serves substantially the same purpose with respect 12 to tooth 20b. Thus, teeth 20a and 20b collectively forming 13 a kerfing triad. Additional teeth, such as gage defining l teeth 24 may also be provided on bit 10 to provide cutting l assistance in a conventional fashion.
l Turn now to Figure 2, which shows the pattern 1 of coverage of a single triad of teeth in a cross-sectional l view in enlarged scale as would be seen in a fixed l longitudinal plane as the bit rotates. The triad, comprised 2 of teeth 18a and b, are depicted by way of example in Figure 2 2. First teeth 18a will traverse any given plane cutting 22 ¦ two parallel circular kerfs. Thereafter the next tooth 23 ¦ encountering the fixed longitudinal plane will be tooth 18b 24 which is disposed approximately in the half space between 25 1 teeth 18a. In the embodiment of Figures 1-3, each of the 26 ¦ teeth are shown as triangular in cross section, such as 22 would be the case when triangular polycrystalline synthetic _9_ ~ .`^ , .

~ 7;~4 l ¦ diamond teet}~ are used, such as manufactured by General 2 ¦ Electric Co. under the trademark "G~OSET". However, as will 3 ¦ be illustrated in the additional embodiments described 4 1 below, the invention is not restricted or limited to the us~
of any particular profile of tooth or cutting element.

6 ¦ Figure 3a is a cross-sectional view of a mold 7 ¦ corresponding to line 3a-3a of Figure 1 in which the pair of 8 ¦ teeth of the triad, such as teeth 18a would be disposed.
9 ¦ The triangular diamond element is disposed in a l0 ¦ correspondin~ triangular indentation 26a or b machined into ll graphite mold 28. Mold 28 is then backfilled with a 12 ¦ conventional tungsten carbide powder matrix and the entire l composite is infiltrated by a conventional process to form 14 an infiltrated matrix bit. In the illustrated embodiment, l each tooth 18a is inclined at a selected angle within mold 16 28. For example, indentation 26a for one of teeth 18a is 17 inclined at an angle of 11 d~grees with respect to 18 centerline 30.
l9 Figure 3b illustrates a second section taken from mold 28 corresponding to the position of tooth 18b and teeth 24, 2l corresponding to line 3b-3b of Figure 1. Teeth, such as 2 teeth 18b, 20b and 22b of Figure 1, will be disposed within 2 indentation 36 and gage teeth 24 are disposed within 2 indentations 38. Tooth 18b is generally perpendicularly 2 disposed with respect to the bit face 40 and teeth 24 extend 2 outwardly at an angle of 27 degrees with respect to the 2 vertical. Only a small portion of teeth 24 is exposed (0.070 ~ 734 l inch) as compared to the exposure of teeth 18a and 18b 2 (0.180 inch). The teeth, disposed in mold 28 and as 3 depicted in the radial dispositions illustrated in Figures 4 3a and 3b, collectively combine to cut an azimuthal swath or form a pattern of coverage as diagrammatically depicted by 6 Figure 2.
7 Turn now to Figure 4 where another embodiment of 8 a mining bit, generally deno~ed by reference numeral 42, and 9 which is a variation of the tooth pattern as depicted in Figures 1-3, is shown in plan view. Face 44 of bit 42 is ll divided into three 120 degree sectors as defined by radial 12 waterways 46. A triad of teeth 4~a and 48b are disposed ~3 within each sector, beginning at an azimuthal displacement 14 of approximately 45 degrees behind the preceding waterway 46. The triad is comprised up a pair of teeth 48a and a 16 following single tooth 48b. Teeth 48a include a generally 17 triangular prismatic polycrystalline synthetic diamond 18 elements such as manufactured by General Electric under the l9 trademark "GEOSET" in a tooth structure such as those found in the BallaSet bits manufactured by Norton Christensen of 21 Salt Lake City, Utah. However, it is entirely within the 22 scope of the invention that other tooth structures now known 23 or later devised could be substituted with equal facility.
24 In any case, pair of teeth 4Ba are disposed on bit face 44 2 on the same azimuthal position, but are radially displaced 2 by predetermined distance. The triangular cutters of teeth 27 ~ 4~a tangentially set, na~el~ haviny an apical rldge ~47;~4 l generally paxallel to the tangent of the radius at the situs 2 of the tooth placement. Teeth 48a thus cut two parallel 3 circular kerfs into the underlying rock formation.
4 Behind teeth 48a is a third tooth 48b which is comprised of a cylindrical axially mounted synthetic 6 polycrystalline diamond such as is sold by the People's 7 Republic of China. The radial distance between teeth 48a is 8 equal to or less than the diameter of cylindrical tooth 48b.
9 Tooth 48b is azimuthally displaced behind pair of teeth 48a and in the interlying radial gap between teeth 48a. Thus, ll after the pair of kerfs are cut by teeth 48a, tooth 48b 12 follows to hammer, chisel or otherwise remove the inter-13 lying land in the rock formation left between the two kerfs.
14 Each sector of bit 42 may also include a plurality of gage protecting cutters 50 which generally maintain or 16 protect the gage, but do not coact with the triad of cutters 17 48a and 48b to cut by kerfing. Each of the triad of cutters 18 in each of the sectors are radially disposed on bit face 44 19 ~ to provide a complete coverage across the radial sweep of the bit face as seen by any given longitudinally fixed plane 21 in the rock formation. For example, the triad of teeth 52 22 sweep through a portion of bit face 44 nearest outer gage 23 54, while a triad of teeth 5G sweep through a middle 24 portion, and triad of teeth 4Ba and 48b sweep that portion nearest inner gage 58. Each of these portions are 26 overlapping, although no kerf line of any one tooth lies 27 identically on the same line of any other tooth of the bit.
2~

1~ 7~4 l For example, in the illustrated embodiment of Fig~re 4, 2 outermost triad 52 scribes its outermost kerf at 3 approY~imately 0.12 inch (3.05 millimeters) from outer gage 4 54 while the center of the outermost kerf line of triad 56 is scribed at 0.15 inch (3.81 millimeters) from ou~er gage 6 54. The center of the outermost kerf of triad 48a and 48b is 7 scribed at 0.19 irlch (4.83 millimeters) from outer gage 54.

8 The exposure above bit face 44 of the leading pair of teeth, 9 such as teeth 48a of the triad 48a and 48b is at least 0.150 inch (3.81 millimeters) above bit face 44, while gage ll protecting teeth 50 and the third tooth of the triad, such 12 as tooth 48b have a lesser exposure, for example 0.105 inch 13 (2.67 millimeters).
14 In each of these triads the spacing between the kerfs cut by the teeth of the triad may vary among the 16 teeth. For example, the outermost triad 52 may have a 17 inter-kerf spacing of approximately 0.25 inch l6.35 18 millimeters), triad 56 an inter-kerf spacing of 0.31 inch l9 (7.87 millimeters) and triad 48a and 48b in inter-kerf 2 spacing of 0.38 inch (9.65 millimeters). Thus, near the 21 outer gage 54 where linear speeds of bit 42 are greater, the 22 inter-kerf spacing is less. This spacing increases as the 23 radial distance of the triad from the center of the drill 24 string decreases. In this way compensation is made for the 2 greater rock-cutting rate imposed upon the third tooth of 2 the triad, such as tooth 48b, as one moves outwardly from 28 he center of the bit to outer e 54. In fect, if desired, ~ 47~s4 l the inter-kerf spacing can be made inversely proportional to 2 the radial distance of the third tooth, such as tooth 48b.
3 Turn to Figure 5 wherein a plan view of a second 4 embodiment is illustrated. The bit, generally denoted by reference numeral 41, is again divided into three sectors of 120 degrees by radial waterways 47. Each sector includes a 7 triad of cutters. ~or example, the radially innermost triad 8 is comprised of a pair of teeth 49a and an azimuthally 9 following tooth 49b radially disposed between pair of teeth 49a. The mid-radial triad 57 and outermost triad 53 are ll similarly constituted. Gage protection teeth 51 are also 12 disposed on the inner and outer gages.
13 The second embodiment of Figure ~ differs from 14 that of Figure 4 in that the second tooth of pair 49a of teeth is azimuthally disposed approximately 15 degrees behind the leading face of the first tooth of ~ r 49a.
17 Third clearing tooth 49b is azimuthally disposed l approxim~tely 30 degrees behind the leading face of the 1 second tooth of pair 49a.
2 Turn now to Figure 6 wherein another embodiment of 21 the invention is illustrated, showing in plan view a minins 22 bit, generally denoted by reference numeral 60. Once again 23 mining bit 60 is divided into three sectors as defined by 24 radial waterways 62. Gage protecting teeth 64 are provided 2 as before, however, within each sector the triad of teeth 2 are arranged so that the first kerf cutting tooth 66 is 2 followed by the clearing tooth 68 and hence by the second I ~tj47;~ j 1 1 kerf cutting tooth 70. In the embodiment of Figure 6, 2 ¦ leading kerf cutting tooth 66 is the radially innermost 3 1 tooth of the triad of teeth 66-70, while the second kerf 4 ¦ cutting tooth 70 is the radially outermost tooth of the triad.

6 In the illustrated embodiment, the first kerf 7 cutting tooth 66 is azimuthally displaced behind the center 8 of waterway 62 by approximately 35 degrees. Clearing tooth 9 68 is then azimuthally displaced behind the leading edge of tooth 66 by approximately 30 degrees. Finally, the second 11 kerf cutting tooth 70 has its leading edge azimuthally 12 displaced behind the center of clearing tooth 68 by 13 approximately 20 degrees. As described before in connection 14 with the embodiment of Figure 9, the radial displacement of 1 teeth 66, 68 and 70 is adjusted so that clearing tooth 68 1 lies in the halfspace between the kerf cutting teeth 66 and 1 70. The radial displacement between azimuthally offset 1 teeth 66 and 70 is equal to or less than the radial 1 effective cutting width of clearing tooth 68, which may be slightly larger or smaller than the actual physical radial 21 dimension of clearing tooth 68. For the purposes of this 22 specification, "effective cutting width" of a tooth is 23 defined as the maximum radial dimension of rock land between 24 two concentric kerfs or kerf cutting teeth, which a cutter 2 can remove in a single pass. Thus, the magnitude of 2 effective cutting width will depend on tooth design, the 2 nature of the rock and other drilliny parameters. The 1~t~4734 1 inter-kerf distance between teeth 66 and 70 i5 similarly 2 adjusted to compensate for the greater cutting rate 3 experienced near outer gage 72 as contrasted to that 4 experienced near inner gage 74 as previously described in connection with the embodiment of Figure 4.
6 Finally, the annular swath cut into the rock 7 formation by the triad of teeth 66, 68 and 70 overlaps with the swath cut by the triad of teeth 76 and 78 also disposed ~ on bit face 80 of bit 60 in a manner similar to that discussed above.
11 Turn now to Figure 7 where yet another embodiment 12 of the invention is illustrated. Here a mining bit, 13 generally denoted by reference numeral B2, again is 14 organized into three sectors defined by radial waterways B4.
Each sector includes a plurality of gage protection teeth 16 86. Here, clearing tooth 92 azimuthally precedes the 17 following kerf cutters. For example, the leading kerf 18 cutting tooth 88 is associated with a second kerf cutting 19 tooth 90 and a leading clearing tooth 92. Again, teeth 88 and 90 are tangentiallly set BallaSet type teeth, and 21 clearing tooth 92 is a axially or stud mounted cylindrical 22 polycrystalline diamond cutter. In the illustrated 23 embodiment, clearing tooth 92 is azimuthally displaced 24 behind its preceding waterway by approximately 30 degrees.
The leading edge of the second kerf cutting tooth 90 is 26 azimuthally displaced behind clearing tooth 92 by 27 approximately 20 degrees, while the first keri cutting tooth ~ 7~

l 88 has its leading edge azimuthally displaced in front of 2 ¦ second kerf cutting tooth 90 by approximately 35 degrees.
3 1 As in the embodiments of Figures 4-6, kerfing 4 ¦ teeth 88 and 90 are tangentially set BallaSet type teeth, 5 ¦ while clearing tooth 92 is a stud set, cylindrical, 6 1 polycrystalline diamond element. Teeth 96 form a second 7 ¦ triad and teeth 98 a ~hird triad in a similar manner. Each 8 1 of the triad of teeth 98, 96 and 88-92 are, as described 9 ¦ before, radially disposed across bit face ~4 to cut 10 1 overlapping annular swaths rangins from outer gage 100 to 1l inner gage 102. The triads are also characterized by the 12 ¦ variable inter-kerf spac~ns across bit face 94 as previously 13 described.
14 Mining bits 41, 42, 60 and 82 as depicted and 1 described above in connection with Figures 5, 6 and 7 16 respectively, were test drilled into rock and a drilling 17 rate established. In the test run in question, the design 18 of mining bit 60 of Figure 6 exhibited the highest drill l9 rate, bit 41 of Figure 5 a drilling rate approximately two thirds less, and the design of bit 82 of Figure 7 the lowest 21 driling rate. It is not entirely well understood why the 22 triad placement of bit 60 is dramatically better than the 23 triad placements of bits 41, 42 and 82. In fact the 24 superior performance of an "in-between" design such as illustrated by bit 60 of Figure 6 is surprising, since 2 conventional notions of kerf cutting would suggest that the 2 design of bits 41 or 42 should have been optimal on t~he 1 ~2~73~ 1 1 ¦ ground that the clearing tooth would he able to remove an 2 ¦ unsupported and fully defined land between the kerfs.
3 ¦ Turn no~ to Figure 8 which shows a diagramatic 4 ¦ plan view of a petroleum bit incorporating the invention.
5 ¦ The petroleu~ bit, generally denoted ~y reference numeral 6 ¦ 104, includes an inner crowfoot 106. The hydraulic fluid 7 ¦ flows outwardly through spiral waterways 108 to a plurality ¦ of junk slots 110 defined into outer gage 112. Between 9 ¦ waterways 108 are collectors 114. Collectors 114 and 10 ¦ waterways 108 in turn define spiral lands 116 upon which the 11 ¦ cutting elements are disposed (not shown in Figure 8).
12 ¦ A profile of petroleum bit 104 as depicted in 13 Figure 8 and seen in cross-sectional sideview taken through 14 line 9-9 of Figure 8 is shown in Figure 9. Crowfoot

15 ¦ openings 106 here are seen inclined outwardly and in or

16 ¦ near nose 11B of bit 104. Generally flat portion or flank

17 ¦ 120 extends from nose 118 to shoulder 122 where the bit face

18 ¦ extends into outer gage 112. A triad of teeth, collectively

19 ¦ denoted by reference numeral 124, is diagrammatically depicted in enlarged scale on flank 120 where two BallaSet 21 ¦ type teeth 126 with an interlying cylindrical cutter 128 is 22 shown in cross section. The disposition of teeth according 23 ¦ to the invention across the face of petroleum bit 104 can 24 ¦ now be understood by turning to the plot detail as shown in 25 ¦ Figure 10.
26 ¦ In the illustrated embodiment of Figure 10 the 27 ¦ triad design of Figure 6 is implemented although any. one of 28 l 1~47~4 l ¦ the embodiments could be employed through suitable 21 substitution of BallaSet type teeth for cylindrical cutters 3 1 and vice a versa. The plot detail of Figure 10 is a 41 diagrammatic depiction of the disposition of teeth acrGss 5 ¦ the entire surface of bit 104 including the gage. The plot 61 is taken as if the bit were cut from the outer gage to the 7 ¦ center along any given radius and then laid out and 8 stretched to form a flat strip. Therefore, in the 9 ¦ projection of the plot detail of Figure 10 some distortion lO ¦ of proportion is unavoidable. Therefore Figure 10 must be ll ¦ understood as showing a logical relationship only and no 12 ¦ implication should be drawn from the illustrated 13 ¦ proportionate dispositions.
14 Petroleum bit 104 is divided into three sectors 130, 132 and 134. Each sector 130-134 includes two spiral 16 lands 116a and 116b in the case of section 130, lands 116c 17 and 116d in the case of section 132, and 116e and 116f in 18 the case of section 134.
l9 Turn now to section 130 which shows a plurality of tangentially set BallaSet type teeth such as tooth 136 and a 21 plurality of cylindrical synthetic polycrystalline stud 22 mounted teeth, such as tooth 138 disposed on land 116a and 23 tooth 148a on land 116b. In addition to these types of 24 teeth, a plurality of surface-set natural diamonds 140 are also included in the nose area 118 and in shoulder portion 2 122 as well as through out gage 112. Surface-set diamonds ~ 47~4 1 ~ 140 are conve~tional and are provided for abrasion 2 ¦ protection in a manner well noted in the art.
3 ¦ Now consider the first triad of kerf cutting teeth 4 ¦ in section 130 beginning from nose 118. The first kerf 5 ¦ cutter, tooth 136 leads and is radially disposed outward 6 ¦ with respect to the interlying cylindrical cutter 138. The 7 ¦ next kerf cutter of the triad is BallaSet type tooth 142 8 ¦ which is the radially outermost tooth on second land 116b.
9 ¦ The second triad of teeth al o includes tooth 142, 10 ¦ cylindrical polycrystalline diamond ~pcd) tooth 144 and 11 ¦ BallaSet type tooth 146 on land 116a. The triad of teeth 12 ¦ continue to be interlaced between lands 116a and 116b toward 13 shoulder 122. For example, the third triad also includes 14 ¦ BallaSet tooth 146, cylindrical tooth 148 and BallaSet type tooth 150 each forming with respect to the other the type of 16 relationship as depicted in Figure 6. The fourth triad 17 includes BallaSet tooth 150, cylindrical tooth 152 and 18 BallaSet type tooth 154 on land 116a. Thus, each BallaSet 19 type tooth doubles as forming a kerfing cutter in adjacent triads of cutting teeth.
21 The disposition of teeth is completed ~y 22 enumerating the following triads; BallaSet tooth 154, 23 cylindrical tooth 156, and BallaSet tooth 158; BallaSet 2 tooth 158, cylindrical tooth 160 and BallaSet tooth 162;
BallaSet tooth 162, cylindrical tooth 164 and BallaSet tooth 26 166; BallaSet tooth 166, cylindrical tooth 168 and BallaSet 2B¦ ooth 170; BallaSet tooth 170 lindrical tooth l72 and ~ i473~

l BallaSet tooth ~74; BallaSet tooth 174, and an omitted 2 cylindrical tooth due to the presence of the junk slot, and 3 BallaSet tooth 176; BallaSet tooth 176, cylindrical tooth 4 178 on land 116a, and finally BallaSet tooth 180.
In addition to the triad specifically listed above 6 in section 130, additional cylindrical teeth, such as 7 cylindrical cutters 182 on land 116a and BallaSet tooth 184 8 on the leading edge of land 11 6a may also be included to 9 provide redundant cutting coverage according to conventional design principles.
ll Each of the sections 132 and 134 on bit 104 are 12 similarly provided with triads of kerf cutting teeth on 13 their paired lands in the same manner as described in 14 connection with section 130. Furthermore, as described in the embodiments of Figures 4-7, the triads on adjacent 16 sections 130-134 are offset with respect to the triads in 17 the other sections to provide overlapping annular cutting 18 swaths into the face of the rock formation, thereby l9 ultimately providing cutter coverage from the center of the bit to the gage.
21 Many modifications and alterations may be made by 22 those having ordinary ski.ll in the art without departing 23 from the spirit and scope of the invention. For example, 24 although the plot diagram of Figure 10 as been illustrated in connection with the embodiment of Figure 6, a similar 26 diagram could have been derived with respect to the triad 27 embodiments illustrated in Figures 4, 5 or 7 as well.

~tj47;:~4 l ¦ Similarly, although the triad embodiments of Figures 4-10 2 ¦ each contemplate two BallaSet type cutters with a 3 ¦ cylindrical cleariny cutter, the invention is not limited to 4 ¦ particular types of teeth or cutters for any one or all of 5 l the triad of cutting teeth. Furthermore, the a~imuthal .
6 spacing specifically described in connection with the 7 ¦ embodiments of Figures 4-7 is illustrative only and the 8 ¦ actual spacing may vary with each application or within a 9 ¦ single bit such as shown in the embodiment of Figure 10.
Therefore, the illustrated embodiment has been set forth ll only by way of example and should not be taken as limiting _ ¦ e invention as defined in the f~llowing cl~ims.

Claims (6)

1. An improvement in a drag bit having a bit face including a plurality of polycrystalline diamond cutting teeth comprising:
a plurality of triads of cutters, substantially all of said cutting teeth on said bit being included in at least one of said triads, each triad comprising:
first and second polycrystalline diamond teeth for cutting kerfs, said first and second teeth being azimuthally and radially displaced from each other on the face of said bit; and a third polycrystalline diamond tooth associated with said first and second polycrystalline teeth and disposed therebetween for clearing substantially all of the material lying between said kerfs cut by said first and second teeth, said third tooth being azimuthally displaced with respect to at least one of said first and second teeth.
whereby cutting by kerfing with said first, second and third teeth acting in combination is optimized on said bit.

2. The improvement of Claim 1 wherein said third tooth is azimuthally displaced behind said first tooth and in front of said second tooth.

3. The improvement of Claim 1 wherein said third tooth is azimuthally displaced behind both said first and second teeth.

4. A rotating bit comprising:
a bit body;
a bit face defined on at least a portion of said bit body;
and a plurality of synthetic polycrystalline diamond cutting elements disposed on said bit face, at least three of said plurality of polycrystalline diamond cutting elements disposed to form a kerf cutting triad, said kerf cutting triad comprised of a first and second kerf cutting tooth and a third clearing tooth, said third tooth being azimuthally disposed on said bit face behind said first kerf cutting tooth, in front of said second kerf cutting tooth, and radially disposed between the radial position of said first and second teeth on said bit face, wherein the radial distance between said first and second teeth is equal to or less than the effective cutting width of said third tooth;
whereby cutting action of said triad through kerfing is optimized.

5. A drag bit for drilling rock comprising:
a bit body;
a bit face defined on at least a portion of said bit body;
and a plurality of synthetic polycrystalline diamond cutting elements disposed on said bit face, at least three of said plurality of polycrystalline diamond cutting elements disposed to form a kerf cutting triad, a first and second kerf cutting tooth and a third clearing tooth, said third tooth azimuthally disposed behind at least one of said first and second kerf cutting teeth and radially disposed between the radial position of said first and second teeth on said bit face;
wherein the radial distance between said first and second teeth is equal to or less than the effective cutting width of said third tooth so that said clearing tooth removes substantially all of said rock between said first and second kerf cutting teeth;
wherein said third tooth is azimuthally disposed on said bit face behind said first and in front of said second tooth of said triad, whereby cutting action of said triad through kerfing is optimized.

6. A method of cutting with a drag bit having a plurality of synthetic polycrystalline diamond elements disposed on said bit comprising the steps of cutting a plurality of annular swaths into a rock formation, each swath concentric with another swath and lying in a partially overlapping relationship, said step of cutting each annular swath comprising the steps of:
cutting a first narrow knife-like kerf in a rock formation by applying a shearing force with a first kerf cutting tooth;

cutting a second kerf with a narrow knife-like second kerf cutting tooth azimuthally following said first kerf cutting tooth; and clearing a substantially greater volume of rock than was included in said first knife-like kerf with a third azimuthally following tooth by applying a shearing force.