Cutter element with expanded crest geometry

A cutter element for a drill bit. The cutter element has a base portion and an extending portion and the extending portion has either a zero draft or a negative draft with respect to the base portion. The non-positive draft allows more of the borehole bottom to be scraped using fewer cutter elements. The cutter elements having non-positive draft can be either tungsten carbide inserts or steel teeth.

FIELD OF THE INVENTION
 The invention relates generally to earth-boring bits used to drill a
 borehole for the ultimate recovery of oil, gas or minerals. More
 particularly, the invention relates to rolling cone rock bits and to an
 improved cutting structure for such bits. Still more particularly, the
 invention relates to a cutter element having an expanded crest geometry
 which extends up to and beyond the envelope of its base portion.
 BACKGROUND OF THE INVENTION
 An earth-boring drill bit is typically mounted on the lower end of a drill
 string and is rotated by rotating the drill string at the surface or by
 actuation of downhole motors or turbines, or by both methods. With weight
 applied to the drill string, the rotating drill bit engages the earthen
 formation and proceeds to form a borehole along a predetermined path
 toward a target zone. The borehole formed in the drilling process will
 have a diameter generally equal to the diameter or "gage" of the drill
 bit.
 A typical earth-boring bit includes one or more rotatable cutters that
 perform their cutting function due to the rolling movement of the cutters
 acting against the formation material. The cutters roll and slide upon the
 bottom of the borehole as the bit is rotated, the cutters thereby engaging
 and disintegrating the formation material in its path. The rotatable
 cutters may be described as generally conical in shape and are therefore
 sometimes referred to as rolling cones. Such bits typically include a bit
 body with a plurality of journal segment legs. The rolling cone cutters
 are mounted on bearing pin shafts that extend downwardly and inwardly from
 the journal segment legs. The borehole is formed as the gouging and
 scraping or crushing and chipping action of the rotary cones remove chips
 of formation material which are carried upward and out of the borehole by
 drilling fluid which is pumped downwardly through the drill pipe and out
 of the bit.
 The earth-disintegrating action of the rolling cone cutters is enhanced by
 providing the cutters with a plurality of cutter elements. Cutter elements
 are generally two types: inserts formed of a very hard material, such as
 cemented tungsten carbide, that are press fit into undersized apertures or
 similarly secured in the cone surface; or teeth that are milled, cast or
 otherwise integrally formed from the material of the rolling cone. Bits
 having tungsten carbide inserts are typically referred to as "TCI" bits,
 while those having teeth formed from the cone material are known as "steel
 tooth bits."
 The cutting surfaces of inserts are, in some instances, coated with a very
 hard "superabrasive" coating such as polycrystalline diamond (PCD) or
 cubic boron nitride (PCBN). Superabrasive materials are significantly
 harder than cemented tungsten carbide. As used herein, the term
 "superabrasive" means a material having a hardness of at least 2,700 Knoop
 (kg/mm.sup.2). Conventional PCD grades have a hardness range of about
 5,000-8,000 Knoop, while PCBN grades have a hardness range of about
 2,700-3,500 Knoop. By way of comparison, a typical cemented tungsten
 carbide grade used to form cutter elements has a hardness of about 1475
 Knoop. Similarly, the teeth of steel tooth bits may be coated with a hard
 metal layer generally referred to as hardfacing. In each case, the cutter
 elements on the rotating cutters functionally breakup the formation to
 create new borehole by a combination of gouging and scraping or chipping
 and crushing.
 The cost of drilling a borehole is proportional to the length of time it
 takes to drill to the desired depth and location. In oil and gas drilling,
 the time required to drill the well, in turn, is greatly affected by the
 number of times the drill bit must be changed in order to reach the
 targeted formation. This is the case because each time the bit is changed,
 the entire string of drill pipe, which may be miles long, must be
 retrieved from the borehole, section by section. Once the drill string has
 been retrieved and the new bit installed, the bit must be lowered to the
 bottom of the borehole on the drill string, which again must be
 constructed section by section. As is thus obvious, this process, known as
 a "trip" of the drill string, requires considerable time, effort and
 expense. Accordingly, it is always desirable to employ drill bits which
 will drill faster and longer and which are usable over a wider range of
 formation hardness.
 The length of time that a drill bit may be employed before it must be
 changed depends upon its rate of penetration ("ROP"), as well as its
 durability or ability to maintain an acceptable ROP. The form and
 positioning of the cutter elements (both steel teeth and TCI inserts) upon
 the cone cutters greatly impact bit durability and ROP and thus are
 critical to the success of a particular bit design.
 Bit durability is, in part, measured by a bit's ability to "hold gage",
 meaning its ability to maintain a full gage borehole diameter over the
 entire length of the borehole. To assist in maintaining the gage of a
 borehole, conventional rolling cone bits typically employ a heel row of
 hard metal inserts on the heel surface of the rolling cone cutters. The
 heel surface is a generally frustoconical surface and is configured and
 positioned so as to generally align with and ream the sidewall of the
 borehole as the bit rotates. The inserts in the heel surface contact the
 borehole wall with a sliding motion and thus generally may be described as
 scraping or reaming the borehole sidewall.
 In addition to the heel row inserts, conventional bits typically include a
 primary "gage" row of cutter elements mounted adjacent to the heel surface
 but oriented and sized so as to cut the corner as well as the bottom of
 the borehole. Conventional bits can also contain a secondary gage trimming
 row or a nestled gage row with lesser extension to assist in trimming the
 bore hole wall. Conventional bits also include a number of additional rows
 of cutter elements that are located on the cones in rows disposed radially
 inward from the gage row. These cutter elements are sized and configured
 for cutting the bottom of the borehole and are typically described as
 primary "inner row" cutter elements. Together, the primary gage and
 primary inner row cutter elements of the bit form the "primary rows."
 Primary row cutter elements are the cutter elements that project the most
 outwardly from the body of the rolling cone for cutting the bore hole
 bottom.
 A review of post run bit performance data from 1991 through 1995 indicated
 that most aggressive roller cone cutting structures from both milled tooth
 and tungsten carbide insert bits were sub-optimal at addressing very soft
 rock formations (i.e. less than 2000 psi unconfined rock compressive
 strength). Ultra-soft to soft formations typically consist of clays,
 claystones, very soft shales, occasionally limy marls, and dispersed or
 unconsolidated sands, typically exhibit plastic behavior. Very soft or
 weak clays/shales vary in their mechanical response from more competent
 (harder) shales, under the same compression loads, as applied in rotary
 rock bit drilling. Soft shales respond plastically, or simply deform under
 the applied load, as opposed to a brittle failure or rupture (crack)
 formed in more competent rocks to create the cutting or chip. In these
 very soft/plastic formation applications, we cannot rely on conventional
 brittle rock failure modes, where cracks propagate from the loaded tooth
 penetration crater to the adjacent tooth craters, to create a chip or
 cutting. For this reason, the cutting structure arrangement must
 mechanically gouge away a large percentage of the hole bottom in order to
 drill efficiently. In these types of formations, maximum mechanical
 efficiency is accomplished by maximizing the bottom hole coverage of the
 inserts contacting the hole bottom per revolution so as to maximize the
 gouging and scraping action.
 SUMMARY OF THE INVENTION
 The present invention provides maximum scraping action and allows greater
 flexibility in the number of cutter elements used on a drill bit.
 According to the present invention, at least one cutter element on a bit
 is provided with a non-positive draft. The term "draft" is used to refer
 to the relationship between the extending portion of the cutter element
 and envelope defined by the cutter element base. More particularly, the
 term "non-positive draft" is used to refer to cutter elements in which the
 extending portion of the cutting element extends out to or beyond the
 envelope of the base portion. According to the present invention, the
 non-positive draft can take the form of either a zero or a negative draft.
 The concepts of the present invention can be used in cutter elements that
 have non-circular or non-cylindrical bases and can be used in tungsten
 carbide inserts, in tungsten carbide inserts coated with superabrasive,
 and in steel teeth.

While the invention is susceptible to various modifications and alternative
 forms, specific embodiments thereof are shown by way of example in the
 drawings and are described in detail below. It should be understood,
 however, that the drawings and detailed description thereof are not
 intended to limit the invention to the particular form disclosed, but on
 the contrary, the intention is to cover all modifications, equivalents and
 alternatives falling within the spirit and scope of the present invention
 as defined by the appended claims.
 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring first to FIG. 1, an earth-boring bit 10 made in accordance with
 the present invention includes a central axis 11 and a bit body 12 having
 a threaded section 13 on its upper end for securing the bit to the drill
 string (not shown). Bit 10 has a predetermined gage diameter as defined by
 three rolling cone cutters 14, 15, 16, which are rotatably mounted on
 bearing shafts that depend from the bit body 12. Bit body 12 is composed
 of three sections or legs 19 (two shown in FIG. 1) that are welded
 together to form bit body 12. Bit 10 further includes a plurality of
 nozzles 18 that are provided for directing drilling fluid toward the
 bottom of the borehole and around cutters 14-16. Bit 10 further includes
 lubricant reservoirs 17 that supply lubricant to the bearings of each of
 the cutters.
 Referring now to FIG. 2, in conjunction with FIG. 1, each cutter 14-16 is
 rotatably mounted on a pin or journal 20, with an axis of rotation 22
 orientated generally downwardly and inwardly toward the center of the bit.
 Drilling fluid is pumped from the surface through fluid passage 24 where
 it is circulated through an internal passageway (not shown) to nozzles 18
 (FIG. 1). Each cutter 14-16 is typically secured on pin 20 by ball
 bearings 26. In the embodiment shown, radial and axial thrust are absorbed
 by roller bearings 28, 30, thrust washer 31 and thrust plug 32; however,
 the invention is not limited to use in a roller bearing bit, but may
 equally be applied in a friction bearing bit. In such instances, the cones
 14, 15, 16 would be mounted on pins 20 without roller bearings 28, 30. In
 both roller bearing and friction bearing bits, lubricant may be supplied
 from reservoir 17 to the bearings by apparatus that is omitted from the
 figures for clarity. The lubricant is sealed and drilling fluid excluded
 by means of an annular seal 34. The borehole created by bit 10 includes
 sidewall 5, corner portion 6 and bottom 7, best shown in FIG. 2. Referring
 still to FIGS. 1 and 2, each cutter 14-16 includes a backface 40 and nose
 portion 42 spaced apart from backface 40. Cutters 14-16 further include a
 frustoconical surface 44 that is adapted to retain cutter elements that
 scrape or ream the sidewalls of the borehole as cutters 14-16 rotate about
 the borehole bottom. Frustoconical surface 44 will be referred to herein
 as the "heel" surface of cutters 14-16, it being understood, however, that
 the same surface may be sometimes referred to by others in the art as the
 "gage" surface of a rolling cone cutter.
 Extending between heel surface 44 and nose 42 is a generally conical
 surface 46 adapted for supporting cutter elements that gouge or crush the
 borehole bottom 7 as the cone cutters rotate about the borehole. Conical
 surface 46 typically includes a plurality of generally frustoconical
 segments 48 generally referred to as "lands" which are employed to support
 and secure the cutter elements as described in more detail below. Grooves
 49 are formed in cone surface 46 between adjacent lands 48. Frustoconical
 heel surface 44 and conical surface 46 converge in a circumferential edge
 or shoulder 50. Although referred to herein as an "edge" or "shoulder," it
 should be understood that shoulder 50 may be contoured, such as by a
 radius, to various degrees such that shoulder 50 will define a contoured
 zone of convergence between frustoconical heel surface 44 and the conical
 surface 46.
 In the embodiment of the invention shown in FIGS. 1 and 2, each cutter
 14-16 includes a plurality of wear resistant inserts 60, 70, 80 that
 include generally cylindrical base portions that are secured by
 interference fit into mating sockets drilled into the lands of the cone
 cutter, and cutting portions connected to the base portions having cutting
 surfaces that extend from cone surfaces 44, 46 for cutting formation
 material. The present invention will be understood with reference to one
 such cutter 14, cones 15, 16 being similarly, although not necessarily
 identically, configured.
 Cone cutter 14 includes a plurality of heel row inserts 60 that are secured
 in a circumferential row 60a in the frustoconical heel surface 44. Cutter
 14 further includes a circumferential row 70a of nestled gage inserts 70
 secured to cutter 14 in locations along or near the circumferential
 shoulder 50 to cut the borehole wall. Cutter 14 further includes a
 plurality of primary bottom hole cutting inserts 80, 81, 82, 83 secured to
 cone surface 46 and arranged in spaced-apart inner rows 80a, 81a, 82a,
 83a, respectively. Relieved areas or lands 78 (best shown in FIG. 1) are
 formed about nestled gage cutter elements 70 to assist in mounting inserts
 70. As understood by those skilled in this art, heel inserts 60 generally
 function to scrape or ream the borehole sidewall 5 to maintain the
 borehole at full gage and prevent erosion and abrasion of heel surface 44.
 Cutter elements 81, 82 and 83 of inner rows 81a, 82a, 83a are employed
 primarily to gouge and remove formation material from the borehole bottom
 7. Inner rows 80a, 81a, 82a, 83a are arranged and spaced on cutter 14 so
 as not to interfere with the inner rows on each of the other cone cutters
 15, 16.
 It is common for some of the cutter elements to be arranged on conical
 surface 46 so as to "intermesh" with each other. More specifically,
 performance expectations require that the cone bodies be as large as
 possible within the borehole diameter so as to allow use of the maximum
 possible bearing size and to provide adequate recess depth for cutter
 elements. To achieve maximum cone cutter diameter and still have
 acceptable insert protrusion, some of the rows of cutter elements are
 arranged to pass between the rows of cutter elements on adjacent cones as
 the bit rotates. In some cases, certain rows of cutter elements extend so
 far that clearance areas corresponding to these rows are provided on
 adjacent cones so as to allow the primary cutter elements on adjacent
 cutters to intermesh farther. The term "intermesh" as used herein is
 defined to mean overlap of any part of at least one primary cutter element
 on one cone cutter with the envelope defined by the maximum extension of
 the cutter elements on an adjacent cutter.
 Referring now to the particular construction of cutter elements, a prior
 art chisel insert 90 is shown in FIGS. 3A-D and a prior art conical insert
 92 is shown in FIGS. 4A-C. As shown in these figures, the entire cutting
 portion of the insert is contained within the envelope of the cylindrical
 base portion. This is because the conventional way of manufacturing these
 inserts is by a punch and die method, which requires positive draft at the
 cutting portion so as to allow the die halves to separate after pressing
 operations. This restriction in manufacturing process imposes limitations
 on the geometry of the cutting portion of the insert. These limitations in
 turn prevent the optimization of this geometry for maximizing the bottom
 hole coverage and scraping action needed to increase rate of penetration
 in soft formations. Typical positive draft angles utilized in the
 manufacturing of these inserts are not less than 10 degrees as measured
 per side, as shown in FIGS. 3B and 4B.
 The drawings show bases that are generally cylindrical, with some being of
 circular cross-section and some being non-circular (e.g. oval or
 elliptical). However, the bases may be of any convenient cross-sectional
 shape and need not be cylindrical. While the following discussion and
 corresponding Figures relate to cutter inserts having cylindrical bases,
 it will be understood that the principles of the present invention can be
 applied with equal advantage to cutter inserts having non-cylindrical
 bases. In cutter elements having non-circular or cylindrical bases,
 "positive draft" refers to instances where the entire cutting portion of
 the insert is contained within the envelope defined by projecting the
 shape of the base portion along the longitudinal axis of the cutter
 element. As used herein, the term "longitudinal axis" refers to the
 longitudinal axis of the base portion.
 Referring now to FIGS. 5A-C, the chisel insert 100 of the present invention
 having an expanded geometry provides for increased mechanical
 scraping/shearing action by providing increased crest length beyond that
 formed on prior art inserts manufactured using conventional manufacturing
 techniques. Insert 100 includes base 102 and cutting portion 104. The
 insert axis is shown as "a." Further optimization of mechanical
 scraping/shearing action can be achieved with additional expansion of
 cutting portion geometry as shown in FIGS. 6A-D. As shown in FIGS. 6A-D,
 insert 110 has a non-circular base 112 and cutting portion 114 which
 includes expanded crest 116. Using the terminology employed with
 conventional manufacturing means, this novel insert has a negative draft
 114, on the cutting portion which extends beyond the envelope "e" of the
 cylindrical base portion. It is preferably made by the manufacturing
 techniques described below.
 Conventional roller cone drill bits generate an uncut area on the bore hole
 bottom known in the art as uncut bottom as shown in FIG. 3E. In FIG. 3E,
 the cutter elements from all rolling cone cutters are depicted in rotated
 profile, that is, with the cutting profiles of the cutter elements shown
 as they would appear if rotated into a single plane. The uncut bottom is
 the area on the bore hole bottom that is not contacted by the crests of
 the primary row cutter elements. If this uncut area is allowed to build
 up, it forms a ridge. In some drilling applications this ridge is never
 realized, because the formation material is easily fractured and the ridge
 tends to break off. In very soft rock formations that are not easily
 fractured, however, the formation yields plastically and the ridge builds
 up. This ridge build-up is detrimental to the cutter elements and slows
 the drill bit's rate of penetration. Ridges of rock left untouched by
 conventional cutting structure arrangements are reduced or eliminated by
 the use of the present invention as illustrated in FIG. 6E. FIG. 6E shows
 the reduction in uncut bottom or increased bottom hole coverage provided
 by the expanded crest geometry of the cutter elements of the present
 invention.
 To obtain the same degree of bottom hole coverage shown in FIG. 6E using
 conventional cutter elements, the diameter of the base portion of the
 cutter elements would typically be increased to achieve the corresponding
 increase in crest width. This increase in insert diameter would have the
 result of reduced clearance between inserts in the same row, as well as
 decreased insert-to-insert clearances between adjacent cones. To achieve
 adequate clearances in these areas would require severe compromise in
 insert count and placement. These compromises are avoided through the use
 of the present invention.
 This invention is particularly suited for cutter elements used in the
 primary rows where, in soft formations, maximum shearing and scraping
 action of the rock is the preferred method of cutting. Cutter elements
 with elongated crests are used in these formations to provide shearing
 capability. The crest width of these cutter elements inserts influences
 the aggressiveness of the cutting action relative to the formation. Thus,
 the function of expanded crest widths on an insert made in accordance with
 the principles of the present invention can increase the volume of
 shearing/scraping performed by the cutter element relative to a
 conventional prior art chisel insert.
 Hard formations can also be addressed by this invention. Increased cutter
 volume can be attained by expanding the insert extension beyond the base
 while maintaining effective clearances between cutter elements in adjacent
 positions in the same row and between elements in adjacent rows (both on
 the same cone and in different cones). With an expanded insert extension
 and a reduced base diameter, insert quantities can be increased, thereby
 providing greater cutter density with additional strikes to the formation.
 The increase in cutter density also provides additional wear time for the
 insert, thereby extending bit life.
 Depending on the shape and/or orientation of the cutter element, bottom
 hole coverage can be maximized to reduce or eliminate the amount of uncut
 hole bottom. If the cutter elements are positioned to maximize bottom hole
 coverage, the number of bit revolutions necessary to gouge and scrape the
 entire hole bottom can be reduced 40-60% from a typical conventional
 3-cone tungsten carbide insert (TCI) rock bit.
 Cutter Element Shapes
 There are numerous variations within this invention for the configuration
 of the cutting portion of the insert that extend beyond the envelope of
 the base portion. The geometry of the cutting element can be sculptured or
 non-sculptured. As used herein, the terms "contoured," "sculpted" and
 "sculptured" refer to cutting surfaces that can be described as
 continuously curved surfaces wherein relatively small radii (typically
 less than 0.080 inches) are not used to break sharp edges or round-off
 transitions between adjacent distinct surfaces as is typical with many
 conventionally-designed cutter elements. The cutting portion of the
 cutting element can extend up to and beyond the envelope of its base
 anywhere along the perimeter of the base portion and any multitude of
 times. The preferred manufacturing techniques described below allow for
 new insert shapes that extend up to and beyond the "envelope" of the base
 portion of the insert thereby opening the door for countless new
 geometries. Several embodiments of the invention as applied to insert type
 cutter elements are illustrated in FIGS. 5 through 18. Like the
 embodiments shown in FIGS. 5A-C, 6A-D, these embodiments incorporate the
 principles of the present invention. For each embodiment in FIGS. 7
 through 18, the comments in Table I set out the mechanical advantages that
 are believed to result from the specific features of that embodiment.
 TABLE I
 FIG.
 Number Insert Description Comment
 FIG. 7A-C Offset crest chisel with Optimize aggressive scraping
 negative draft. action in specific applications.
 FIG. 8A-C Offset crest chisel with The reinforcement rib provides
 negative draft and increased support to improve
 reinforcement rib. durability when drilling through
 hard stringers.
 FIG. 9A-C Offset conical with Optimize scraping action in non-
 negative draft. plastic formations.
 FIG. 10A-C Biased negative draft Optimize scraping action where
 chisel. insert-to-insert clearances between
 cones is constrained.
 FIG. 11A-C Partial biased negative Optimize scraping action where
 draft chisel. insert to insert clearances between
 cones is constrained.
 FIG. 12A-C Arc crest chisel with Structural support for insert crest/
 zero draft. corners and improved scraping
 action.
 FIG. 13A-C Arc crest chisel with Structural support for insert crest/
 negative draft. corners and optimized scraping
 action.
 FIG. 14A-C Spline crest chisel with Structural support for insert crest/
 zero draft. corners and improved scraping
 action.
 FIG. 15A-C Spline crest chisel with Structural support for insert crest/
 negative draft. corners and optimized scraping
 action.
 FIG. 16A-C Partial negative draft Insert chisel crest corner
 chisel. protection for tougher applications.
 FIG. 17A-C Offset crest chisel with Aggressive positive rake for
 negative draft on maximum formation removal.
 leading flank.
 FIG. 18A-C Slant crest chisel with Increased unit load upon entering
 negative draft. the formation to maximize
 penetration.
 Cutter Element Placement
 Further optimization of the cutter elements of the present invention can be
 achieved by their orientation and placement within the cone bodies. This
 will further maximize the desired level of scraping action for increased
 mechanical efficiency.
 Referring to FIG. 28, novel inserts 110 are shown placed in a conventional
 orientation in a row 110a with the axis of each insert being coplanar with
 the cone axis. Another arrangement is shown in FIG. 29, in which each
 insert 110 is oriented in the cone body such that the axis "a" of the
 cylindrical portion of the insert is offset a distance "D" with respect of
 the cone axis. This further gives the designer flexibility to optimize the
 scraping action with regards to the specific formation and application.
 FIGS. 30 and 30A show another orientation wherein the crest 116 of the
 insert 110 is rotated about the insert axis "a" such that an angle .alpha.
 is formed with respect to the projection of the cone axis. It will be
 understood that in certain applications, it may be advantageous to rotate
 one or more inserts in the opposite direction such as by an amount
 .alpha.'. FIG. 31 shows another embodiment wherein the insert 110 is both
 offset a distance "D" and rotated about its axis "a." Any of the inserts
 shown in FIGS. 5-8 may be employed in the arrangements or orientations
 shown in FIGS. 28-31. The cutter elements 110 can be mechanically or
 metallurgically secured in the cone by various methods, such as,
 interference fit, brazing, welding, molding, casting, or chemical bonding.
 The inserts described in the FIGS. 5 and 7-18 and orientations 28-31 are
 shown with a cylindrical base portion for interference fit into a matching
 socket. It will be understood negative draft does not require that the
 base portion be cylindrical, but does require that the cutting portion of
 the insert extend up to or beyond the noncylindrical envelope defined by
 the base portion, as shown in FIGS. 6A-D.
 Insert Material Types
 An insert of the present invention can be made of tungsten carbide and in
 addition can be partially or fully coated with a "superabrasive" (i.e., a
 material having a hardness of at least 2,700 Knoop kg/mm.sup.2) such as
 PCD, PCBN, etc.
 Insert Manufacturing Techniques
 Conventional rolling cone bit inserts are manufactured by press and die
 operations. As shown in FIG. 19, the top and bottom dies 8, 3 are pressed
 axially with respect to the longitudinal axis "a" of insert 1, to form an
 insert 1 with a cylindrical base 9 and an extending portion 2, contained
 within the envelope of the cylindrical base. Positive draft must be
 provided so as to keep extending portion 2 within the constraints of the
 cylindrical base. Draft refers to the taper given to internal sides of a
 closed-die to facilitate its removal from the die cavity. To complete the
 conventional insert 1, a centerless grind operation is performed on the
 base portion 9 to provide specified cylindrical geometry and surface
 finish. In centerless grinding the insert 1 is supported on a work rest
 and fed between the grinding wheel and a rubber bonded abrasive regulating
 wheel. Guides on either side of the wheels direct the work to and from the
 wheels in a straight line.
 When inserts have extending geometries that extend out to and beyond the
 envelope of the cylindrical base as contemplated by the present invention,
 conventional manufacturing techniques such as axial insert pressing and
 centerless grinding cannot be used. Techniques have been and are being
 developed to provide the ability to create the novel inserts of the
 present invention such as those shown in FIGS. 5-18. For example, instead
 of pressing each insert along the longitudinal axis of its base "a," the
 inserts of the present invention (such as insert 110 of FIGS. 6A-D) can be
 pressed normal to that axis, as shown in FIG. 20, thus creating sides
 instead of a top and bottom. The present insert 110 can also be
 manufactured by injection molding, multi-axis CNC milling machine, wire
 EDM, casting, stereolithography or other free-forming methods.
 The insert base portion 112 can be finished by using other grinding methods
 (post grinder, in-feed centerless grinder) or by single point machining
 (turning).
 Other Applications for Invention
 Application of this invention is not restricted to use on the rolling cones
 of insert bits. The cutter elements can be used on the primary rows of big
 hole cutters and the bottom hole cutting elements of hammer bits. Further,
 the advantages of this invention are not limited to inserts or compacts,
 but can be equally applied to teeth of a steel tooth bit.
 Steel tooth bits typically have teeth that are milled, cast or otherwise
 integrally formed from the base material or parent metal of the cone.
 FIGS. 21A-B depict a portion of a rolling cone cutter of a steel tooth
 bit. Specifically, FIGS. 21A-B depict a row 120 a having steel teeth 120.
 The other inner rows of steel teeth of this cone cutter are not shown in
 these figures. The profile of steel tooth 120 is best shown in FIG. 32.
 Tooth 120 is depicted in FIGS. 21A-B without hard facing, a hard, durable
 metal coating that is applied to the parent metal of tooth 120 to increase
 its durability. The hard facing 120h and parent metal 120p of tooth 120
 are shown in FIG. 32. As shown, the parent metal of conventional tooth 120
 includes crest 122 having crest length (CL) and a root 124 with a root
 length (RL) that is greater than (CL).
 FIGS. 22A-B disclose a row 126 a of steel teeth 126 of a prior art cone
 cutter. FIG. 34 discloses a profile view of tooth 126. As shown, tooth 126
 includes a crest 128 having recess 130 and root 132. As with tooth 120,
 tooth 126 includes a root 132 having root length (RL) greater than the
 crest length (CL) of crest 128. The crest 128 having recess 130 is
 referred to herein as a radiused crest steel tooth.
 FIG. 36 shows a profile view of another prior art tooth 140 similar to
 teeth 120, 126 previously described. Tooth 140 includes crest 142, sides
 144 and root 146. The corners of the tooth 140 at the intersection of
 sides 144 and crest 142 have an inverted radius at 148.
 On conventional steel tooth bits, the width of the cutting portion of the
 parent metal of the tooth is smaller than the width of its base. More
 specifically, the crest length (CL) is less than the root length (RL) of
 the tooth for a conventional steel tooth as best shown in FIGS. 32, 34 and
 36. By contrast, in this invention, the width of the cutting portion of
 the tooth can be larger than the base, before hardfacing is applied, as
 shown in FIGS. 33, 35 and 37. Although the steel tooth does not have a
 cylindrical base portion with a cutting portion extending beyond this base
 portion, the cutting portion does have a substantially wider crest length
 than the root length of conventional bits. This wider crest length, and
 the increased bottom hole coverage it provides, maximizes the scraping and
 shearing action on the formation, thus significantly improving the
 penetration rate of the bit. Several variations of steel teeth designed
 according to the principles of the present invention are described below
 and illustrated in FIGS. 23 through 27. For each embodiment in FIGS. 23
 through 27, the comments in Table II describe the mechanical advantages
 that are believed to result from the specific features of that embodiment.
 TABLE II
 FIG. 23A-B Negative draft steel Increased mechanical scraping/
 tooth. shearing action due to increased
 crest length beyond prior art steel
 teeth.
 FIG. 24A-B Negative draft steel Similar to FIG. 21, but employing
 tooth with radiused the benefits of the radiused or
 crest. rounded corners to enhance the
 retention of hardfacing onto the
 tooth (as described in Smith
 International patent 5,152,194).
 FIG. 25A-B Biased negative draft Optimize scraping action where
 steel tooth. tooth-to-tooth clearances between
 cones is constrained.
 FIG. 26A-B Partial negative draft Tooth crest corner protection for
 steel tooth. tougher applications.
 FIG. 27A-B Offset crest steel Optimize aggressive scraping
 tooth with negative action in specific applications.
 draft.
 In the more detailed description that follows, the steel teeth of the
 invention will be described and depicted without hardfacing, it being
 understood that hardfacing could, and in many applications would, be
 applied over the parent metal of the tooth.
 One embodiment of the present invention employed in a steel tooth bit is
 shown in FIGS. 23A, 23B and 33. The rolling cone cutter includes a row
 200a of steel teeth 200. As best shown in FIG. 33, tooth 200 includes a
 crest 202 and root 204. Crest length (CL) of crest 202 is greater than
 root length (RL) of root portion 204.
 Another embodiment of the present invention is shown in FIGS. 24A, 24B and
 35. As shown, the rolling cone cutter includes a row 206a of radiused
 crest steel teeth 206. As best shown in the profile view of FIG. 35, tooth
 206 includes crest 208 and root portion 210. Crest 208 includes a recess
 212. Tooth 206 is formed such that crest length (CL) is greater than root
 length (RL) in accordance with the principles of the present invention.
 Another embodiment of the present invention is shown in FIG. 37. FIG. 37 is
 a profile view of a steel tooth similar to that shown in FIGS. 33 and 35.
 In the embodiment shown in FIG. 37, tooth 220 includes crest 222 and root
 224. The crest length (CL) of crest 222 is greater than root length (RL)
 of root 224. The corners of tooth 220 formed at the intersection of crest
 222 and sides 226 includes a portion 228 having an inverted radius. In
 this embodiment, the crest length is measured between the points of
 intersection formed by extensions of the crest 222 and sides 226 as shown
 in FIG. 37. Similarly, the root length is measured between the
 intersections of the extensions of sides 226 and cone surface 230.
 Referring to FIGS. 25A-B, another embodiment of the present invention is
 applied to a steel tooth bit. As shown, the steel tooth cone cutter
 includes a row 240a of steel teeth 240. Each tooth 240 includes a crest
 242 and a root portion 243. Crest 242 intersects sides 244, 246 in angles
 .theta..sub.1 and .theta..sub.2, respectively. As shown, .theta..sub.1 is
 an angle greater than 90.degree., while .theta..sub.2 is an angle less
 than 90.degree.. The crest length (CL) of crest 242 is greater than the
 root length (RL) of root 243. Although in this particular embodiment,
 .theta..sub.1 is greater than .theta..sub.2, the invention is not limited
 to this or any other relationship for .theta..sub.1 and .theta..sub.2.
 Likewise, the crest can take various forms such as a rounded crest or
 non-linear crest, but the intent is that the overall linearly-measured
 width of the crest exceeds that of the root.
 Another embodiment of the invention is shown in FIGS. 26A-B, and FIG. 38.
 As shown, a steel tooth cone cutter includes a row 250a of steel teeth
 250. Each tooth 250 includes a crest 252, root portion 254, a pair of
 upper sides 258 and a pair of lower sides 259. The intersection of each
 upper side 258 and lower side 259 forms a central portion having an
 expanded length EL that is greater than root length (RL) and, in this
 embodiment, greater than crest length (CL). The root length (RL) is
 measured from the intersections of the extensions of lower sides 259 and
 cone surface 260.
 FIG. 27A and 27B shown an embodiment similar to that depicted in FIGS. 23A,
 23B; however, the embodiment shown in FIGS. 27A, 27B is formed such that
 crest 202 is offset a distance D from a line that is parallel to crest 202
 and that passes through the axis 300 of the cone. Crest orientations
 similar to TCI FIGS. 30 and 31 can also be applied to steel tooth designs.
 Bit Design Intent
 Depending on the bit design objectives, the amount of uncut bottom can be
 reduced or eliminated. Currently, most bits are designed with cutter
 intermesh between the rolling cones, which can invoke limitations on the
 wider crest of the cutter elements. Hence, designing bits without
 intermesh can allow greater latitude in crest width.
 Additionally, these cutter elements can be used in all types of rolling
 cone bits having one, two or more rolling cones.
 The increased bottom hole coverage attainable with the present invention
 permits the use of fewer rows of cutter elements on the cone cutters of
 the bit. Having fewer rows of cutter elements, as compared to conventional
 prior art bits, increases the unit loading per cutter element thus
 increasing rate of penetration. For example, in one conventional 3-cone
 TCI roller cone bit, a total of nine rows of primary cutter elements were
 dispersed among the three cones employed to cut the bottom hole as shown
 in rotated profile in FIG. 3E, there being three rows, specifically Rows
 7, 8 and 9, aligned in the same rotated profile position. Using the
 expanded crest geometry of the present invention, and as shown in rotated
 profile FIG. 39, the bottom hole coverage can be attained using only a
 total of 8 rows of cutter elements on this 3-cone bit. Thus, the present
 invention allows TCI bits to be designed with 8 or fewer rows, in contrast
 to conventional prior art TCI bits, which typically have 9 or more rows.
 Similarly, prior art steel tooth bits such as that shown in rotated profile
 in FIG. 41 typically included a total of seven rows of cutter elements for
 bottom hole coverage. Use of the present invention, as shown in FIG. 40,
 permits bottom hole coverage to be attained using only six rows of cutter
 elements made in accordance with the present invention. Thus, the present
 invention allows steel tooth bits to be designed with 6 or fewer rows, in
 contrast to conventional prior art steel tooth bits, which typically have
 7 or more rows.
 While various preferred embodiments of the invention have been shown and
 described, modifications thereof can be made by one skilled in the art
 without departing from the spirit and teachings of the invention. The
 embodiments described herein are exemplary only, and are not limiting. For
 example, the present invention includes cutter elements having shapes
 other than the shapes shown and described herein. Many variations and
 modifications of the invention and apparatus disclosed herein are possible
 and are within the scope of the invention. Accordingly, the scope of
 protection is not limited by the description set out above, but is only
 limited by the claims that follow, that scope including all equivalents of
 the subject matter of the claims.