U.S. patent application number 10/558181 was filed with the patent office on 2008-07-03 for method, system, and apparatus of cutting earthen formations and the like.
This patent application is currently assigned to Particle Drilling Technolgies, Inc. Invention is credited to Gordon Allen Tibbitts.
Application Number | 20080156545 10/558181 |
Document ID | / |
Family ID | 33490657 |
Filed Date | 2008-07-03 |
United States Patent
Application |
20080156545 |
Kind Code |
A1 |
Tibbitts; Gordon Allen |
July 3, 2008 |
Method, System, and Apparatus of Cutting Earthen Formations and the
like
Abstract
A cutter element is provided for use on a rotary drill bit of a
drilling string to cut earthen formation and the like. The cutter
element includes a cutting portion formed from cutting material
adapted to cut into the earthen formation, and a substrate
positioned adjacent the cutting portion. The cutting portion and
the substrate form a body having a substantially planar front face,
a longitudinal axis extending centrally through the front face and
the substrate, and a circumferential surface extending inwardly
form the front face and spaced outwardly from the longitudinal
axis. The cutting portion includes a cutting face that provides at
least a portion of the front face. The cutting portion extends
longitudinally inward from the front face to a back surface
engaging or inter-facing the substrate. Thus, a distinct,
longitudinally extending volume of cutting material is provided and
includes a predesignated portion of the circumferential surface
that extends from the cutting face to the back surface, the
circumferential surface portion being predesignated for wearing
contact with the earthen formation.
Inventors: |
Tibbitts; Gordon Allen;
(Murray, UT) |
Correspondence
Address: |
Todd D. Mattingly;BRACEWELL & GIULIANI LLP
P.O. Box 61389
Houston
TX
77208-1389
US
|
Assignee: |
Particle Drilling Technolgies,
Inc
Houston
TX
|
Family ID: |
33490657 |
Appl. No.: |
10/558181 |
Filed: |
May 27, 2004 |
PCT Filed: |
May 27, 2004 |
PCT NO: |
PCT/US04/16987 |
371 Date: |
January 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60473832 |
May 27, 2003 |
|
|
|
Current U.S.
Class: |
175/431 ;
175/434 |
Current CPC
Class: |
E21B 10/573 20130101;
E21B 10/567 20130101 |
Class at
Publication: |
175/431 ;
175/434 |
International
Class: |
E21B 10/36 20060101
E21B010/36 |
Claims
1. A cutter element for use on a rotary drill bit attach to a drill
string to cut earthen formations and the like, said cutter element
comprising: a cutting portion formed from cutting material adapted
to cut the earthen formation; and a substrate positioned adjacent
the cutting portion; wherein the cutting portion and the substrate
form a body having a substantially planar front face, a
longitudinal axis extending centrally through the front face and
the substrate, and a circumferential surface extending inwardly
from the front face and spaced outwardly from the longitudinal
axis; and wherein the cutting portion includes a cutting face
providing at least a portion of the front face, the cutting portion
extending longitudinally inward from the front face to a back
surface engaging the substrate, such that a distinct,
longitudinally extending volume of cutting material is provided and
includes a predesignated portion of the circumferential surface
that extends from the cutting face to the back surface, the
predesignated circumferential surface portion being predesignated
for wearing contact with the earthen formation.
2. The cutter element of claim 1, wherein the back surface deviates
from normal angular relation with the longitudinal axis, such that
the longitudinal distance between the front face and locations on
the back surface varies.
3. The cutter element of claim 2, wherein the front face consists
entirely of the cutting face of the cutting portion.
4. The cutter element of claim 2, wherein the cutting portion is
configured such that at least one longitudinal cross-section of the
cutter element, generally normal to the front face, reveals a
cross-sectional area of the cutting portion with a larger area on
one side of the longitudinal axis than on an opposite side of the
longitudinal axis.
5. The cutter element of claim 2, wherein the cutting portion is
configured such that at least one longitudinal cross-sectional view
of the cutter element, generally normal to the front face, reveals
an exposed circumferential surface of the cutting portion in one
half of the cross-section that is longer than a corresponding
exposed circumferential surface portion of the cutting portion on
an opposite half of the cross-section.
6. The cutter element of claim 2, wherein the cutting portion is
configured such that a lateral cross-sectional view of the cutting
element, generally normal to the longitudinal axis, reveals a
larger area of the cutting portion concentrated in one half of the
cross-section adjacent the predesignated circumferential surface
portion than in an opposite half of the cross-section.
7. The cutter element of claim 2, wherein at least one longitudinal
cross-sectional view of the cutting element, generally normal to
the front face, reveals a longitudinally extending area of the
distinct longitudinal volume of cutting material, the area having a
thickness that is reduced as the area extends in the longitudinally
inward direction.
8. The cutter element of claim 1, wherein the volume of cutting
material located in the vicinity of the predesignated
circumferential surface portion substantially larger than the
volume of cutting material located in the vicinity of other
portions of the circumferential surface.
9. The cutter element of claim 1, wherein the substrate form a
portion of the front face.
10. The cutter element of claim 1, wherein a lateral
cross-sectional view through the cutting portion, generally normal
to the longitudinal axis, reveals the substrate forming a portion
of the exposed circumference of the cutter element.
11. The cutter element of claim 10, wherein the cutting portion is
configured such that any lateral cross-sectional view through the
cutting portion, generally normal to the longitudinal axis, reveals
the substrate forming a portion of the exposed circumference of the
cutting element.
12. The cutter element of claim 1, further comprising a bore
extending from a portion of the circumferential surface to a
portion of the cutting face, the cutting portion being situated
therein.
13. The cutter element of claim 1, wherein the cutter portion
includes a reinforcing cutter material providing the distinct
longitudinally extending volume.
14. The cutter element of claim 1, wherein the cutting material is
polycrystalline diamond.
15. The cutter element of claim 1, wherein the cutting portion and
the substrate form a substantially rod shaped body having a
circumferential surface spaced radially from and in generally
parallel relation with the longitudinal axis.
16. A cutter element for use on a rotary drill bit of a drill
string to cut earthen formations and the like, said cutter element
comprising: a cutting portion formed substantially from
polycrystalline diamond material adapted to cut the earthen
formation; and a substrate positioned adjacent the cutting portion;
wherein the cutting portion and the substrate form a substantially
rod shaped body having a substantially planar front face, a
longitudinal axis extending centrally through the front face and
the substrate, and a circumferential surface extending inwardly
from the front face and spaced radially from the longitudinal axis;
and wherein the cutting portion includes a cutting face providing
at least a portion of the front face, the cutting portion extending
longitudinally inward from the front face to a back surface
interfacing the substrate, such that a distinct, longitudinally
extending volume of cutting material is provided and includes a
portion of the circumferential surface that extends from the
cutting face to the back surface, the circumferential surface
portion being predesignated for wearing contact with the earthen
formation; and wherein the cutting portion is configured such that
a lateral cross-sectional view of the cutting element, generally
normal to the longitudinal axis, reveals a larger area of the
cutting portion concentrated in one half of the cross-section
adjacent the predesignated circumferential surface portion than in
an opposite half of the cross-section.
17. The cutter element of claim 16, wherein the cutting portion is
configured such that at least one longitudinal cross-section of the
cutter element, generally normal to the front face, reveals a
cross-sectional area of the cutting portion with a larger area on
one side of the longitudinal axis than on an opposite side of the
longitudinal axis.
18. The cutter element of claim 17, wherein the back surface
deviates from normal angular relation with the longitudinal axis,
such that the longitudinal distance between the front face and
locations on the back surface varies.
19. The cutter element of claim 18, wherein the cutting portion is
configured such that at least one longitudinal cross-sectional view
of the cutter element, generally normal to the front face, reveals
an exposed circumferential surface of the cutting portion on one
side of the longitudinal axis that is longer than a corresponding
exposed circumferential surface portion of the cutting portion on
an opposite side of the longitudinal axis.
20. The cutter element of claim 16, wherein the front face consists
entirely of the cutting face of the cutting portion.
21. The cutter element of claim 16, wherein at least one
longitudinal cross-sectional view of the cutting element, generally
normal to the front face, reveals a longitudinally extending area
of the distinct longitudinal volume of cutting material, the area
having a thickness that is reduced as the area extends in the
longitudinally inward direction.
22. The cutter element of claim 16, wherein the volume of cutting
material located in the vicinity of the predesignated
circumferential surface portion is substantially larger than the
volume of cutting material located in the vicinity of other
portions of the circumferential surface.
23. The cutter element of claim 16, wherein the substrate provides
a portion of the front face.
24. The cutter element of claim 16, wherein the cutting portion is
configured such that any lateral cross-sectional view through the
cutting portion, generally normal to the longitudinal axis, reveals
the substrate forming a portion of the exposed circumference of the
cutter element.
25. A method of drilling a borehole, comprising the steps of:
providing a drill bit having a plurality of cutting elements
thereon, the cutting elements having, a cutting portion formed
substantially from polycrystalline diamond material adapted to cut
the earthen formation; and a substrate positioned adjacent the
cutting portion; wherein the cutting portion and the substrate form
a substantially rod shaped body having a substantially planar front
face, a longitudinal axis extending centrally through the front
face and the substrate, and a circumferential surface extending
inwardly from the front face and spaced radially from the
longitudinal axis; wherein the cutting portion includes a cutting
face providing at least a portion of the front face, the cutting
portion extending longitudinally inward from the front face to a
back surface interfacing the substrate, such that a distinct,
longitudinally extending volume of cutting material is provided and
includes a portion of the circumferential surface that extends from
the cutting face to the back surface, the circumferential surface
portion being predesignated for wearing contact with the earthen
formation; and wherein the cutting portion is configured such that
a lateral cross-sectional view of the cutting element, generally
normal to the longitudinal axis, reveals a larger area of the
cutting portion concentrated in one half of the cross-section
adjacent the predesignated circumferential surface portion than in
an opposite half of the cross-section; mounting the bit on the end
of a drill string; directing the drill bit at a position such that
the cutting elements engage the earthen formation at an angle,
whereby the predesignated circumferential surface portion is in
contact with the earthen formation; and operating the drill string
such that the drill bit and the cutting elements cut into the
earthen formation, thereby creating a wear flat along the
predesignated circumferential surface portion.
Description
[0001] The present application claims the benefit of the filing
date of U.S. Provisional Application Ser. No. 60/473,832, filed May
27, 2003 (pending) (hereby incorporated by reference for all
purposes and made a part of the present disclosure).
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to methods, systems, and/or
apparatus for cutting earthen formations that may be above ground
or subterranean, and, more particularly, but not by way of
limitation, to methods of and apparatus for cutting earthen
formations for various applications such as oil, gas, and
geothermal production, in addition to excavations including
tunnels, pipe chases, foundation piers, building stone, quarried
rock, etc.
[0004] 2. Description of the Related Art
[0005] The prior art is replete with designs for cutting elements
or cutters secured on a drill bit and utilized in the drilling of
well bores or the cutting of formations for the construction of
tunnels and other subterranean earthen excavations. One type of
conventional cutter is a polycrystalline diamond cutter (PDCs) that
is axisymmetric and includes a diamond table attached to a
substrate, usually tungsten carbide. Such a cutter is described in
U.S. Pat. Nos. 4,552,232, 4,981,183, and 5,119,511, which are
hereby incorporated by reference for all purposes and made a part
of the present disclosure.
[0006] The life of the cutter is controlled largely by wear or
fracture. Fracture is typically a result of a combination of
applied cutting loads and stresses associated with the cutter
geometry and stresses residual to the high pressure/high
temperature manufacturing process. Wear is a function of diamond
feed stock size, integrated metallurgy, and "sintering" conditions.
Wear is also a function of the volume of the diamond available at
the cutting interface between the cutter and the rock
formation.
[0007] FIG. 1 illustrates a prior art cutting element or cutter 110
engaging an earthen formation 112. The cutter 110 has a front or
cutting face 120 and circumferential all-around wall or surface 118
extending longitudinally inwardly therefrom. The conventional
cutter 110 includes a cutting surface or table 122 and a substrate
124 positioned adjacent thereto. The cutting table 122 has a front
planar surface that provides the cutting face 120 and a back face
110a positioned adjacent a forward planar face of the substrate
124. The back face 110a is planar, in parallel relation with the
cutting face 120, and thus, generally normal to the longitudinal
axis, L.
[0008] As shown in FIG. 1, the cutter 110 may be inclined with a
negative back rake angle, .theta., to the direction of travel 114
in the rock formation 112. In order to keep the cutter 110 buried
at a constant depth 116 in the cut, a normal load, N, is applied to
the cutter 110 (often referred to as the weight on bit (WOB)). A
load, L, is also applied in the direction of the cut, forcing the
cutter 110 to abrade the rock formation 112 and displace rock
fragments 112a. This load, L, is a result of the torque applied to
a rotating bit and transferred to the cutter 110 secured
therein.
[0009] In general, only a portion of the cutter 110 actually
contacts the rock formation 112. This includes a portion 126 of the
cutting face 120 and a portion of the circumferential surface 118.
As this contact area increases to cause diamond abrasion (i.e.,
wearing contact), it is referred to as the wear flat. FIGS. 2A-2D
illustrate the process of wearing as applied to a conventional
cutter 210 contracting a rock formation. FIG. 2A illustrates a
substantially uniform and unworn cutter 210. FIG. 2A illustrates
the formation of a wear flat 228 on the cutter 210 after operation
in the formation. The wear flat 228 is, however, confined to the
cutting surface or diamond surface 222 of the cutter 210. After
continued use, the wear flat 228 is worn further, as shown in FIG.
2C. At this point, the wear flat 228 extends from the cutting table
222 and into the substrate 224, thereby exposing the material of
the substrate 224. In the side view of FIG. 2D, the wear flat 228
is shown extending well into the substrate. Such exposed substrates
have high rates of failure and therefore may lead to the
progressive failure of the entire drill bit. Bit failures cost time
and money through reduced performance and additional trip time.
SUMMARY OF THE INVENTION
[0010] In one aspect of the present invention, a cutter element is
provided for use on a rotary drill bit of a drilling string to cut
earthen formations and the like. The cutter element includes a
cutting portion formed from cutting material (e.g., polycrystalline
diamond) adapted to cut into the earthen formation, and a substrate
positioned adjacent the cutting portion. The cutting portion and
the substrate form a body (e.g., substantially rod shaped) having a
substantially planar front face, a longitudinal axis extending
centrally through the front face and the substrate, and a
circumferential surface extending inwardly from the front face and
spaced outwardly from the longitudinal axis. The cutting portion
includes a cutting face that provides at least a portion of the
front face. The cutting portion extends longitudinally inward from
the front face to a back surface engaging or interfacing the
substrate. Thus, a distinct, longitudinally extending volume of
cutting material is provided and includes a predesignated portion
of the circumferential surface that extends from the cutting face
to the back surface, the circumferential surface portion being
predesignated for wearing contact with the earthen formation.
[0011] In a method according to the invention, operation of a drill
bit having such a cutting elements generates a wear flat along the
predesignated portion of the circumferential surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] For a more complete understanding of the present invention,
and for further objects and advantages thereof, reference is made
to the following description taken in conjunction with the
accompanying drawings in which
[0013] FIG. 1 (Prior Art) is a side view of a prior art cutter
engaging a rock formation;
[0014] FIG. 2 (Prior Art) is an illustration of the progressive
wear of the prior art cutter of FIG. 1;
[0015] FIGS. 3A-3C are illustrations of one embodiment according to
the present invention;
[0016] FIG. 3D is an illustration of the cutter of FIG. 3A-3C
engaging a rock formation;
[0017] FIG. 4 is an illustration of an alternate embodiment of the
cutter of the present invention;
[0018] FIG. 5 is an illustration of an alternate embodiment of the
cutter of the present invention;
[0019] FIG. 6 is an illustration of alternate embodiment of the
cutter of the present invention;
[0020] FIG. 7 is an illustration of an alternate embodiment of the
cutter of the present invention;
[0021] FIG. 8 is an illustration of an alternate embodiment of the
cutter of the present invention;
[0022] FIG. 9 is an illustration of a worn cutter of one of the
embodiments of the present invention; and
[0023] FIG. 10 is an illustration of a worn cutter of one of the
embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0024] FIGS. 3A, 3B, and 3C provide front, longitudinal (vertical)
cross-sectional, and bottom views, respectively of a cutting
element or cutter 310 according to the present invention. The
longitudinal axis ZZ may be described as dividing the cross-section
into two halves.
[0025] The cutter 310 has a front or cutting face 320 outlined by a
circumference or peripheral edge 320a (which may be a chamfered,
beveled, or straight edge), and the longitudinal axis, ZZ,
extending from the center of the cutting face 320 and generally
normal thereto. The cutter 310 includes a substantially forward
cutting portion 322 that is preferably comprised of polycrystalline
diamond material and thus, referred to as a diamond table. In other
embodiments, the material for the cutting portion may be tungsten
carbide, cubic boron nitride, or other commonly used materials. The
cutter 310 further includes a substantially rearward portion
provided by a substrate 324. The substrate 324 is preferably formed
from tungsten carbide material, and, in other applications, other
carbide materials having suitable thermal expansion properties
relative to the that of the cutting material.
[0026] Referring to the cross-sectional view of FIG. 3B, the lower
half of the cutter 310 includes substantially more area of the
cutting portion 322 than the upper half. As shown therein, the back
surface 320A of the cutting portion 322 that interfaces the
substrate 324 is non-planar, in contrast to the substantially
planar surface of the cutting face 320. The inward back surface
320A is also oriented at an angle other than normal in respect to
the longitudinal axis, ZZ. Accordingly, the cutting material 322
extends longitudinally inward more so at different radii locations
(and in certain sectors) than in others. In other word, the
longitudinal distance, e.g., distances 320B, 320C, between the
front face 320 and the back face 320A vary. For example, an exposed
surface 350 shown in FIG. 3B extends from the cutting face 320
longitudinally inward through a distance or depth significantly
greater than at the longitudinal axis, L, or at the opposite top
edge 370. The cutter 310 is said to have a greater or
longitudinally extended volume of cutting material 310 adjacent a
predesignated exposed or surface portion (e.g., surface portion
350) that extends inwardly from the cutting or front face 320. In
FIGS. 3B and 3C, this "longitudinally extended volume of cutting
material" is denoted by reference 350'.
[0027] FIG. 3D illustrates engagement of the cutter 310 with the
rock formation 312, thereby providing a depth of cut 316 into the
formation 312. The engagement is provided as a result of an axial
load N and a tangential load L applied through the cutter 310. The
cutter 310 has the diamond table 322 extended opposite the cutter
face 320 in the area of the wear flat 328, (i.e., corresponding to
350 of FIGS. 3B, 3C). At wear flat 328, the cutter 310 is subjected
to both abrasive wear through contact under load to the rock 312 as
well as heat generated to the cutter 310 from the energy exerted in
the cutting process. By longitudinally extending the diamond table
322, more diamond volume is available to be worn during the
drilling process, thereby confining or containing the wear flat or
wear scar to the cutter material portion of the cutter 310. Such a
longitudinally extended volume of diamond 350 life and subsequently
better bit performance.
[0028] A variety of options, shown as FIGS. 3E-EH, accomplish
extension of the diamond table 322 in the vicinity of the expected
wear flat 328 to increase the amount of diamond available to be
abraded as the cutter wears. Full face and partial diamond face
geometries may be utilized for the cutter. In each of these
vertical cross sections, of FIGS. 3E-3G, the longitudinally
extended volume of cutting material is provided in the lower half
of the cutter 310 and in adjacent a surface portion 350 expected or
designated to correspond with the expected wear flat 328. In FIG.
3H, the longitudinally extended diamond volume 350' is provided
above, as well as below the longitudinally axis, ZZ.
[0029] FIG. 4 illustrates alternative embodiments of a cutter 410
according to the invention. FIGS. 4A, 4B, and 4C provide front,
vertical cross sectional, and bottom views, respectively, of a
second embodiment of the present invention. FIGS. 4G-4I provide yet
further variations of this alternative embodiment. In these
Figures, like elements are indicated using like reference numerals.
Furthermore, in each further variation, the cutter 410 employs a
diamond table 422 and a reinforcing structure 460 positioned
adjacent the table 422.
[0030] Referring to FIGS. 4A-4C, the cutter 410 of this embodiment
utilizes a reinforcing structure 460 integral to the diamond table
422. The reinforcing structure 460 also provides a longitudinally
extended diamond table to increase the volume of diamond available
for wear (i.e., longitudinally extend diamond volume 450'). This
feature will allow key areas of the diamond to be in a higher
compressive stress state which is favorable to the reduction of
fracture in the cutter. As shown in these additional Figures, there
are a variety of geometrical shapes that may be utilized to form
this embodiment of the cutter. Moreover, the reinforcing structure
may be provided by a variety of cutting material, including
polycrystalline diamond.
[0031] Referring to FIGS. 5A-5C, another embodiment of the cutter
of the present invention is illustrated. The cutter 510 differs in
that a geometrical shape of diamond 522 is confined within the
frontal area of the cutter 510 and supported partially therearound
by the adjacent substrate 524. If the diamond material is located
at an angle to the centerline of the cutter 510, the extend of
diamond material in contact with the formation during operation is
extended, again creating more diamond material volume available for
wear.
[0032] By configuring the geometric shape over most of the surface
area with the substrate 524, the diamond is stressed favorably to
better resist fracture. The stresses to which the diamond is
subjected are created as part of the fabrication process. The
entire cutter 510, including diamond and substrate, are elevated to
extreme temperature and pressure (sintering) to allow diamond to
diamond grain growth. On cooling and reduction of pressure, the
substrate has a tendency to shrink at a faster rate than the
diamond because the coefficient of thermal expansion is higher in
the substrate than in the diamond. The end result is that the
diamond table 522 is compressionally stressed, whereas the
substrate 524 near the diamond table 524 holds more tension. In
this concept, the additional stresses created through the cutting
process are mostly directed to the diamond portion 522 of the
cutter 510 already, which is in a more favorable stress state than
the cutter substrate 524.
[0033] Referring now to FIG. 6, another embodiment of the present
invention is illustrated. This cutter is related to the cutter of
FIG. 5 in that not only is the majority of the diamond surface area
in contact with the substrate but the diamond is completely
surrounded by the substrate for a significant portion of the
diamond volume. By surrounding the geometrical shape contained in
the substrate, the favorable stresses in the diamond are further
enhanced, as well has having some substrate support to the rear of
the cutting portion of the diamond, which in most cases is an
enhancement to the stress state of the diamond near the wear flat
and substrate boundary of the cutter.
[0034] It should be noted that the above lateral cross-sectional
views, in many embodiments, is substantially similar along the
longitudinal length of the cutter portion. In each such view, the
area of cutting portion in one half of the cross-section is larger
than in the opposite half.
[0035] Referring to FIG. 7, an alternate embodiment of the cutter
of the present invention is shown. The cutter 710 of this
embodiment is similar to that of FIG. 6 in that the cutter 710 has
a geometric shape which allows a different improved stress state
for the diamond in addition to providing a more rigid structure
relative to the highest applied loads. As shown in the lateral
cross-sectional view of FIG. 7A, the cutting portion 722 occupies
only a portion of the cutter 710. In this particular embodiment,
the cutting portion 722 is substantially bounded by the substrate
724. It should be noted that any such cross-sectional view along
the longitudinal length of the cutting portion 722 reveals the
substrate 724 occupying a portion of the cross-sectional are and
specifically, the circumference 718. In respect to the embodiment
of FIG. 7C, the area occupied by the cutting portion 722 is reduced
as the longitudinal position approaches the back surface 760.
[0036] Referring to FIG. 8, yet another alternate cutter is
illustrated. This cutter 810 is different from the previously
described embodiments in that the substrate 824 is oriented with a
rake angle opposite of the previous embodiments. The cutter 810 is
also different because the diamond cutting portion 822 incorporated
into the substrate 824 rather than a face of the substrate 824.
This concept provides a cutter having either planar or non-planar
diamond elements by altering the geometry of the diamond portion of
the cutter assembly.
[0037] FIGS. 9 and 10 illustrate the wearing process applied to
some of the embodiments of the cutters 910, 1010 of the present
invention. The cutters 910, 1010 illustrated have a wear flat 928,
1028 that has been worn down by cutting into a rock formation. The
wear flat 928, 1028, although worn, maintains its integrity because
the wear flat 928, 1028 maintains mostly a diamond surface for the
life of the cutter 910, 1010. Because the geometry and/or placement
of the diamond has been modified, the substrate 924, 1024 does not
become part of or integral to the wear flat 928, 1028 when the
cutter 910, 1010 is eroded from cutting the rock formation.
[0038] It is thus believed that the operation and construction of
the present invention will be apparent from the foregoing
description. While the drill bit and drilling system shown and
described have been characterized as being preferred it will be
obvious that various changes and modifications may be made therein
without departing from the spirit and scope of the invention.
* * * * *