WO1999028589A1

WO1999028589A1 - Continuous self-sharpening cutting assembly for use with drilling systems

Info

Publication number: WO1999028589A1
Application number: PCT/US1998/025446
Authority: WO
Inventors: Robert Paul Radtke
Original assignee: Robert Paul Radtke
Priority date: 1997-12-02
Filing date: 1998-12-01
Publication date: 1999-06-10
Also published as: AU1615499A

Abstract

A continuously self-sharpening cutting assembly (13) for use with a petroleum well or like drilling system is disclosed. The cutting assembly (13) comprises a cutting table (21) preferably made of PDC or TSP diamond material and a supporting stud (22) which can be formed of tungsten carbide. The cutting table (21) and stud (22) are provided with aligned or registered voids or holes (36, 60). In use, the cutting table (21) and stud wear (22) away, but the voids (36, 60) provide a continuously self-sharpening action.

Description

S P E C I F I C A T I O N

TITLE:

"CONTINUOUS SELF-SHARPENING CUTTING ASSEMBLY FOR USE WITH DRILLING SYSTEMS"

Field of the Invention

This invention relates to cutting assemblies used with petroleum or other

earth drilling systems. More particularly, this invention relates to polycrystalline

diamond compact (PDC) and thermally stable polycrystalline diamond (TSP) self-

sharpening cutting assemblies fabricated in the form of a thick- wall hollow

cylinder.

Background of the Invention

Rotary drill bits used in earth drilling are primarily of two major types.

One major type of drill bit is the roller cone bit having three legs depending from

a bit body which support three roller cones carrying steel or tungsten carbide teeth

for cutting rock and other earth formations. Another major type of rotary drill bit

is the fixed cutter diamond drag bit which has fixed teeth of natural and synthetic

industrial diamonds supported on the drill body or on metallic or carbide studs

anchored in the drill body.

There are several types of diamond bits known to the drilling industry. In one type, the diamonds are very small and are randomly distributed in a

supporting matrix. Another type contains diamonds of a larger size positioned in

a predetermined pattern on the surface of a drill bit face. Still another type

involves the use of synthetic diamond insert cutters formed of a polycrystalline

diamond compact supported on a sintered carbide stud. This bit type is variously

called a diamond bit, a PDC diamond bit and a TSP diamond bit, all of which are

fixed cutter drag bits.

Rotary drill bits of the kind to which the invention relates to comprise a

bit body having a shank, adapted for connection to a drill string, and an internal

passage for supplying drilling fluid to the face of the bit. The bit body carries a

plurality of diamond insert cutting assemblies at the surface. Each cutting (or

cutter) assembly comprises a facing table of diamond material, which defines the

front cutting face of the assembly, bonded to a less hard, rigid substrate.

In the manufacturer of earth drilling bits having diamond insert cutters,

the drill bit body is formed in the desired shape, and holes or recesses are

provided into which the diamond insert cutters are pressed. A variety of diamond

insert cutters have been available commercially but all are subject to the problem

of dulling with use due to the wear characteristics of the cutter.

One type of cutting assembly for an earth-boring rotary bit consists of a

substantially planar cutting table bonded or brazed to the supporting surface of a -->-

shaped supporting stud. Each cutting assembly comprises a continuous table of

polycrystalline diamond (PDC) or other abrasive diamond and diamond-like

superhard material, such as thermally stable polycrystalline diamond (TSP),

bonded to a rigid, less hard backing layer, usually tungsten carbide. Such cutting

assemblies are commonly in the form of circular discs, although the prior art

discloses a number of alternative geometries.

When a preformed cutting assembly of the kind referred to is mounted on

a drill bit, it is mounted with its front face facing in the direction of movement and

its rear face trailing behind. Thus, during drilling, the diamond cutting edge is

embedded partly into the rock formation being drilled and is advanced through the

rock by bit rotation. Cutting occurs along a cutting edge defined by one side of

the cutting face and part of the peripheral surface of the cutting assembly. As

drilling proceeds, the PDC or TSP assemblies therein gradually wear from the

cutting edge into the assembly to form a wear-flat. However, because the rigid,

less hard backing layers wears away more easily than the PDC or TSP cutting

layer, and therefore does not bear on the formation being cut to the same extent or

with the same pressure as the PDC or TSP table, the two-layer arrangement of the

cutting assembly provides a degree of self-sharpening to the cutting assembly.

Commercially available diamond cutters consisting of PDC or TSP

diamond brazed on a cylindrical stud of tungsten carbide have resulted in dramatic improvements in drilling technology. The bit body may be steel or carbide

matrix. In one type of matrix style body, the TSP diamond material is embedded

in the bit body material formed by a powder metallurgical infiltration process,

whereby tungsten carbide power and the TSP diamond are set in a graphite mold

with a steel shank for attaching the bit body to the drill string. Subsequently, the

powder is infiltrated with a molten copper forming a matrix bit head on a steel

shank with the TSP diamond mechanically and chemically attached. However,

significant problems associated with PDC and TSP cutters remain unresolved.

For example, relatively large diameter cutters must generally be used in soft and

medium formations because small cutters are not very effective when used in

softer formations. Although large cutters may also be used, albeit to a lesser

extent in hard formations, relatively small diameter cutters must generally be used

in hard and very hard formations because smaller arcs of cutting surface are

required for hard formations. However, because small cutters are secured to their

supporting stud on a relatively small surface area, they undergo much higher shear

forces when cutting hard formations and are subject to frequent shear-related

failure. TSP cutters are especially prone to shear-related failure. As a result, TSP

diamond drill bits are used to drill less than 1% of petroleum and geothermal well

footage. PDC cutters fare only a little better, accounting for only about 20% of

the drilling of soft to medium rock drilling. Accordingly, it is an object of this invention to provide cutters that work

well in both hard and soft formations and which are not so susceptible to shearing

failures and dulling.

Another significant contributor to shear failures between the PDC or TSP

and the supporting tungsten carbide stud is heat generation during drilling. It is

well known that the abrasion resistance of the wear- flat rubbing on the formation

generates heat additional to the heat generated by cutting. Because tungsten

carbide has high abrasion resistance, the additional heat generated by abrasion

may be sufficient to cause the thermally activated deterioration of the diamond

table at an increasingly rapid rate. It is generally accepted that a standard cutting

assembly of the kind described, having a tungsten carbide substrate, generally

operates efficiently only until it is about 50% worn. From there on, the cutting

assembly may become thermally unstable and wear extremely rapidly, leading

quickly to failure of the cutter. When a sufficient number of cutting assemblies

have failed in this manner, the bit becomes useless for further drilling. All cutting

assemblies of this type will, in use, eventually become ineffective as a result of

wear, and a bit will have to be taken out of service after an unacceptable amount

of wear has occurred. Often, this point is reached long before half of each circular

disc cutting assembly has worn away.

It is therefore another object of this invention to provide a cutter that has improved wear characteristics in both soft and hard rock formations, increased

attachment strength and resistance to shear- and impact-related failures.

Brief Description of Drawings

FIG. 1 is a perspective view of an earth-boring bit showing continuous

self-sharpening cutting assemblies according to the present invention.

FIG. 2 is a side view of the earth-boring bit of FIG. 1 showing

continuous self-sharpening cutting assemblies according to the present invention.

FIG. 3 is a bottom or end-on view of the earth-boring bit of FIG. 1

showing continuous self-sharpening cutting assemblies according to the present

invention.

FIG. 4a is a sectional view taken normal to the surface of the earth-

boring bit of FIG. 2 substantially in the plane of line 4-4 on FIG. 3 and through

one of the recesses in which the cutting assemblies are positioned and showing the

assembly in elevation with the longitudinal axis of the cutting assembly table

aligned with the longitudinal axis of the cutting assembly stud.

FIG. 4b is a sectional view similar to FIG. 4a taken normal to the surface

of the earth-boring bit of FIG.2 through one of the recesses in which the cutting

assemblies are positioned and showing the assembly in elevation with the

longitudinal axis of the cutting assembly table aligned with the inclined

longitudinal axis of the cutting assembly stud. FIG. 4c is a sectional view similar to FIG. 4a taken normal to the surface

of the earth-boring bit of FIG. 2 through one of the recesses in which the cutting

assemblies are positioned but showing the assembly in elevation with the

longitudinal axis of the cutting assembly table not aligned with the longitudinal

axis of the cutting assembly stud.

FIGS. 5a, 5c, 5e and 5g are fragmentary, perspective section views

showing the progressive wear of continuous self-sharpening cutting assemblies

according to the present invention.

FIGS. 5b, 5d, 5f and 5h are fragmentary, front views corresponding to

FIGS. 5a through 5d and showing the progressive wear of continuous self-

sharpening cutting assemblies according to the present invention.

FIG. 6 is a front-face view of an oblong cutting assembly according to

the present invention.

FIG. 7 is an enlarged cross-sectional view through the center of a

continuous self-sharpening cutting assembly according to the present invention.

FIG. 8 is an enlarged cross-sectional view through the center of a

continuous self-sharpening cutting assembly according to the present invention

showing a non-tapered cutting table plug. FIG. 9 is an enlarged cross-sectional view through the center of a

continuous self-sharpening cutting assembly according to the present invention

showing a tapered cutting table plug.

FIG. 10 is an enlarged cross-sectional view through the center of a

continuous self-sharpening cutting assembly according to the present invention

showing another configuration of a tapered cutting table plug.

Detailed Description of the Invention

The drill bit showing in FIGS. 1, 2 and 3 and described below is

primarily a rotary bit of the type having fixed diamond surfaced cutting

assemblies or inserts. Many of the bit features described relate to the construction

of a diamond-containing bit of a type already known. However, these features are

used in the bit in which the improved diamond cutter assembly of this invention is

used. It will be appreciated that the drawings illustrate only one example of the

many possible variations of the type of bit and cutter assembly to which the

invention is applicable; many other geometries are possible.

The drill bit 10 comprises a tubular body 11 which is adapted to be

connected, as by a threaded connection (not shown), to a drill collar (not shown)

in a conventional drill string. The surface of the drill bit 10 is provided with a

plurality of sockets 12 or recesses spaced there around in a preselected pattern.

One such recess 12 is shown in FIG. 4a. As will be seen from the bottom plan view in FIG. 3, the sockets or recesses 12, and the cutting assemblies 13 which are

positioned therein may be arranged in substantially a circular pattern. However,

the invention is adaptable for use in a wide variety of drill bit geometries and,

thus, in now way is limited to use in the illustrated bit. In FIGs. 4a, 4b and 4c, the

sockets or recesses 12 are shown in more detail with various cutting assemblies 13

being illustrated. In operation, the drill bit is rotated by a drill string (not shown).

The diamond surfaced cutting assemblies 13 cut into the rock or other earth

formations as the bit is rotated in the direction R (FIG. 3) and the rock particles

and other debris are continuously flushed by drilling fluid (e.g., drilling mud)

which flows through the drill string and the interior passage of the drill bit and is

ejected through nozzle passages (not shown).

The relative size of the rigid supporting studs of the cutting assemblies

13 and the diameter of the bit recesses 12 are selected so that the cutting

assemblies 13 will have a tight interference fit in the recesses 12. The recesses are

oriented so that when the cutting assemblies are properly positioned therein the

diamond faced cutters 14 will be positioned with the cutting surfaces 15 facing the

direction of rotation of the drill bit. Without departing from the invention, cutter

angular position relative to the centerline of the bit body and the circular path R

described by the vector of each cutter may be varied according to the application

of the drill bit. A plurality of such cutter assemblies 13 are mounted in the body 1 1 of a

rotary drill bit 10 of the kind first referred to. The bit body 1 1 is formed over the

surface thereof with a plurality of cylindrical sockets 12 of circular cross-section

and received in each socket 12 is the substrate or stud 17 of a cutter assembly 13.

The cutter assembly 13 is usually shrink-fitted or brazed into it socket 12. The

general construction of such drill bits is well known and will not therefore be

described in further detail.

The preferred embodiment of the proper invention comprises a diamond

cutting assembly adaptable for use in a rotating drag bit. Indicated generally in

FIGS. 1, 2 and 3 and more significantly in other Figures is a cutter assembly 13

constructed in accordance with the present invention. The cutter assembly 13

includes a PDC or TSP cutting table 21, in the form of a short hollow cylinder,

preferably with a circular or ovoid shape, bonded or brazed to a supporting steel

or tungsten carbide cutting stud 22, also in the form of a relieved or partially-

hollow cylinder. The cutter assembly 13 can be formed by a variety of methods,

such as conventional hotpress techniques or by infiltration techniques separately

from the bit body or may be formed simultaneously through infiltration

techniques with the bit body. The techniques for forming the cutter assembly are

known in the art.

As shown in greater detail in FIGS. 5a and 5b, each cutting assembly 13 comprises a cutting table 21 mounted on a carrier in the form of a stud 22 which is

located in a socket 12 (FIGS. 4) in the bit body 11. Each cutting assembly 13 is in

the form of a relieved or partially hollow circular or ovoid cylinder (or other

cross-section) comprising a facing table 21 of, for example, PDC or TSP diamond

bonded or brazed to a suitably oriented surface on the stud 22. Other super hard

materials such as diamond film or cubic boron nitride can be used.

As suggested in Figures 5-10, a cutting table 21 is generally defined by

four surfaces, a front surface 31, a rear surface 32, an outer surface 33 and an

inner surface 34. The intersection of the front and outer surfaces 31 and 33

defines a cutting edge 35. As can be seen in FIGS. 7-10, the preferred

embodiment of the cutting table 21 comprises a closed-loop or cylinder

configuration such as a ring or ovoid having a predetermined thickness or depth.

The cutting table 21 is also defined in terms of an inner diameter IB and an outer

diameter OB. Although the illustrated embodiment shows a cutting table 21 in

the shape of a ring defining a symmetrically centered void 36; a cutting table 21 in

accordance with the present invention can have many alternate geometries

defining a cutting table and a void. For example, and without intending to limit

the invention, the cutting table may be oval or triangular or chisel-shaped in cross-

section. Likewise, the cutting table void may, for example, be oval or any other

shape. The void may also be disposed asymmetrically in the cutting table (i.e., extending close to the outer edge of the table) without departing from the

invention. In other words, the cutting table geometry may be altered to suit

particular drilling requirements. Where the configuration is that of a generally

circular diameter ring, the inner diameter ID and outer diameter OD will be

substantially constant irrespective of measurement location. However, where the

configuration is ovoid, for example, the inner and outer diameters will naturally

vary as a function of measurement location. As noted, the cutting table may be

sized and configured in any manner which provides an appropriate closed-loop or

void-defining geometry. As used herein, the term "substantially planar" includes

and encompasses not only a perfectly flat surface or table but also concave,

convex, ridged, waved or other surfaces or tables which define a two-dimensional

cutting surface surmounted by a cutting edge.

In accordance with the preferred embodiment, the stud of the cutting

assembly generally comprises a partially hollow cylinder of circular ovoid cross-

section of substantially the same configuration as the cutting table 21. That is, the

cutting table 21 and stud 22 have substantially the same inner and outer diameter

measurements with respect to each other, and the cutting table and stud voids are

in registry with one another as shown in the drawings. The stud 22 is generally

defined by a bit end 41, an attachment end 42 and an outer surface 43.

Although not shown in the drawings, the attachment end of 42 of the stud 22 may have the geometry of a plug dimensioned to partially or completely

fill the void of the cutting table. Notwithstanding the dimensions of the plug, if

any, the outer diameter of the stud 22 and the inner diameter of the bit recesses 12

are sized so that the cutting assembly 13 will have a tight interference fit in the

recesses 12. The recesses 12 are oriented so that when the cutting assemblies are

properly positioned therein, the diamond cutting tables will be positioned with the

cutting surfaces facing the direction of rotation R of the drill bit (FIG. 3). While

the use of recesses 12 or sockets providing an interference fit is preferred, the

cutting assemblies 13 can be used in any type of recess or socket which will hold

them securely in place.

In an alternative embodiment, instead of the cutting assembly being a

two part assembly (i.e., a cutting table and a stud), it may comprise a unitary

cutting assembly of PDC or TSP material. Likewise, without departing from the

concept of the present invention, the bit can be manufactured or fabricated such

that the cutting assemblies do not require separate attachment but, rather, are an

integral part of the bit as manufactured or fabricated.

The stud 22 of the cutting assembly is formed of a hard metal such as

cemented tungsten carbide or similar material having high hardness and abrasion-

resistance. Where it is desired to reduce the abrasion resistance of the stud 22,

tungsten or molybdenum metal or some other softer refractory material may be used or included with the tungsten carbide. The attachment end of the stud may

be inclined relative to the longitudinal axis of the stud. In one embodiment (see

FIG. 4b) of this invention, the rear surface 32 of the cutting table 21 is flat and

brazed or otherwise bonded to the inclined plane attachment surface of the carbide

stud 22, as in the conventional STRATAPAX type cutters. The supporting stud

may be beveled at the bottom, have edge-tapered surfaces, a top tapered surface

and an angularly oriented supporting surface.

In other embodiments (see FIGS. 8, 9, and 10), the rear surface 32 of the

cutting table is not planar as in FIG. 7 but, rather, contains a plug 50 designed to

mate with a correspondingly dimensioned cavity 51 in the inclined plane

attachment surface of the carbide stud such that after accounting for braze or bond

material, the plug and cavity provide an interference fit. In the preferred

embodiment of the plug configuration, the plug 50 is a continuous part of the

cutting table and the entire configuration is composed of the same material (e.g.,

PDC, TSP). As should be evident, the void 36 or central bore of the cutting table

extends through the plug 50. Where, for example, the shape of the plug 50 is

generally circular or ovoid, the outer diameter of the plug must be greater than the

inner diameter of the front surface of the cutting table and smaller than the outer

diameter of front surface. The plug 50 and corresponding cavity 51 may be of any

desired configuration. For example, the side surface(s) of the plug may be perpendicular to the rear surface of the cutting table, as in FIG. 9, or may be

tapered, as in FIGS. 8 and 10.

Like the planar embodiment, the plug embodiment is brazed or otherwise

bonded to the cutting stud. However, where the cutting table and stud materials

have different expansion and contraction coefficients, for example, where the

cutting table is TSP diamond and the stud is tungsten carbide, the tungsten carbide

cavity will actually shrink-fit to the diamond plug to provide a compression braze

joint. Moreover, because the plug 50 is essentially inserted into and brazed to the

stud 22, it can be seen that greater shear forces will be required to separate the

plug 50 from the stud 22 to which it is brazed than will be required to separate the

planar, non-plug from its stud, all other factors being equal. That is especially

true where the differing coefficients of expansion of the cavity and plug materials

create a compression braze joint.

According to the preferred embodiment, the cutting assembly 13

comprises a configuration which provides an arcuate cutting table 21 or surface

for cutting hard formations and has a cutting stud 22 of substantially the same or

larger radius which provides a bonding or brazing area for securing the cutting

table 21 to the stud 22. Likewise, while the specific composition and

configuration of the cutting assembly, cutting table and cutting stud is determined

by the type of drilling desired and the particular characteristics of the earth formation being drilled, all embodiments coming within the spirit of the present

invention are deemed within its scope.

In the preferred embodiment of this invention, the stud 22 is hollow,

being provided with a longitudinally extending recess 60 which may, but need not

terminate at the bit end of the stud 22. The recess 60 of the stud 22, as well as the

void 36 of the cutting table, may be filled with an abrasive material if desired in

order to, for example, extend the range of formation hardness that can be drilled

without alternating types of cutters. For example, when the cutting table void 36

and/or stud recesses are packed with an engineered material and a soft, less

abrasive rock formation is being drilled, the material packed in the void may wear

at a rate essentially equal to that of the more abrasion resistant diamond material.

However, when drilling a harder, more abrasive rock formation, the material may

wear at a substantially greater than the diamond material and ensure self-

sharpening of the cutting assembly. Thus, this cutter type may be better suited to

drilling more effectively through formations of varying softness and hardness and

at a substantially greater overall rate of penetration than a cutting assembly

without the material packed in the void.

The preferred embodiment of the supporting stud 22 for the preferred

cutting table is typically between about 3 mm and about 40 mm in diameter and

between about 5 mm and about 50 mm long along the axial dimension. As noted, the face of the stud 22 may be inclined relative to the longitudinal axis of the stud

(FIG. 4b). Where inclined, the angle of inclination of the face relative to the

longitudinal axis may be up to about 30 degrees. The cutting table 21 is bonded

on the inclined attachment surface, preferably by brazing or the like.

The cutting table 21 of the preferred embodiment has a thickness of

between about 1 mm and about 15 mm. Likewise, the cutting table 21 has an inner

diameter of between about 2 mm and 20 mm and an outer diameter of between

about 3 mm and 40 mm. The void or hole in the cutting table can vary in size and

shape, and a plurality of spaced-apart voids or holes can be provided. The

currently preferred hole is about 3.8 mm in diameter and is centered about 3.8 mm

from the periphery or edge of the cutting table. The voids or holes may improve

or increase cooling at the cutting edge of the cutting table, and may relieve

stresses in the cutting table, thus contributing longer life and a faster overall drill

bit rate of penetration. The improved cutting assemblies, tables and studs of this

invention may be constructed in the desired shape originally or may be cut to

shape from a larger assembly.

According to a preferred embodiment of the present invention, the stud

22 of the cutting assembly is formed of a hard metal such as cemented tungsten

carbide or similar material having high hardness and abrasion-resistance. The

cutting table 21 is formed of PDC or TSP diamond. As stated before, upon installation of the cutting assembly by interference fit in the bit recess 12, one of

the cutting table surfaces, the front surface, will define a gage surface, and the

cutting table outer surface, in conjunction with the stud outer surface, will define a

heel surface. The gage and heel surfaces, converge at a right angle to define a

circumferentially oriented cutting edge for engagement with the sidewall or

bottom surface of the borehole.

Efficient cutting by the cutting table requires maintenance of a sharp

cutting edge. In accordance with the present invention, the differential rates of

wear of the cutting table 21 and the stud 22 results in a self-sharpening cutting

assembly that is capable of maintaining a sharp cutting edge over the drilling life

of earth-boring bit. Generally, the cutting table may be formed of a different

grade or composition of hard metal than the stud. According to a preferred

embodiment, the cutting table is formed of a PDC or TSP material having a

greater wear-resistance than the material of the cutter stud, which is usually

tungsten carbide, so that a self-sharpening wear can be maintained at the

intersection of gage and heel surfaces.

In operation, the drill bit is rotated by a drill string. The cutting

assembly 13 cuts into the rock or other earth formations as the bit is rotated, the

rock particles and other debris being continuously flushed by, for example,

drilling mud, which flows through the drill string and the drill bit and subsequently ejected. As the cutting assembly 13 abrades and cuts the drilled

formation, the cutting table 21 begins to wear away, thus forming a single wear-

flat at the cutting edge. The wear-flat is, however, self-sharpening due to the

different hardness of the table and stud materials, as discussed above and as can

be envisioned by sequential reference to FIGS. 5a-5h. Due to the disk shape of

the cutting table, the width of the wear-flat (i.e., the distance between the points

on the circumference of the table connected by the wear-flat) increases in size as

the table wears away. That causes the cutter to become progressively more dull.

Correspondingly, the thickness of the table, as measured from the wear-flat to the

nearest point on the inner diameter of the table, decreases. Eventually, continued

drilling causes the entire thickness of the table to be worn through to the inner

diameter of the table, thus exposing the central void 36, whether filled with an

engineered material or not, to the formation (FIGS. 5g-5h). At that point, the

single, uninterrupted wear-flat experiences a discontinuity at about its mid-point

resulting in the emergence of two distinct cutting edges or wear flats of roughly

equal length, each less than one-half the width of the prior, uninterrupted wear-

flat. As should be evident, each of the two smaller wear-flats is itself self-

sharpening due to the differential harness of the table and stud materials. Thus,

unlike the devices of the prior art, which continue to dull as the wear- flat width

increases, the cutting assembly of the present invention is continuously self- sharpening (CSS) and the drilling life of the cutting assembly is thereby

substantially extended. By continuous self-sharpening is meant a process

whereby a single cutting edge transforms through routine cutting use into two

separate cutting edges having smaller individual and combined surface areas than

the single cutting edge prior to transformation and wherein each of the two cutting

edges is itself self-sharpening.

As drilling continues and more of the cutting assembly is worn away, the

distance between the wear-flats increases due to the circumferential inner diameter

of the table and stud. As a result of the two self-sharpening cutting edges

separated by a void or softer engineered void filler material, a rock ridge in the

formation being cut is created. It has been shown that drag bits which form rock

ridges on the bottom hole surface minimize cutter side forces which cause

destructive "bit whirl." Of course, an off-set trailing CSS cutter may be used for

drilling operations where rock ridges are not wanted or required.

While the invention has been described in conjunction with specific

embodiments thereof, it is evident that alternatives, modifications and variations

will be apparent to those skilled in the art in light of the foregoing description.

Accordingly, it is intended to embrace all such alternatives, modifications and

variations as fall within the spirit and broad scope of the invention.

Claims

1. A continuously self-sharpening cutting assembly for use with

drilling systems comprising, in combination, a cutting table which, in its original

configuration, surrounds and defines a void therein, and a stud mounting the

cutting table.

2. A cutting assembly according to Claim 1 wherein said stud,

in its original configuration, surrounds and defines a void, the stud void being in

underlying registry with the cutting table void.

3. A cutting assembly according to Claim 1 wherein said

cutting table is made of a relatively hard material and said stud is made of a

relatively less hard material so as to render the cutting table self-sharpening.

4. A cutting assembly according to Claim 1 wherein said

cutting table includes a polycrystalline diamond compact material.

5. A cutting assembly according to Claim 1 wherein said

cutting table includes a thermally stable polycrystalline diamond material.

6. A cutting assembly according to Claim 1 wherein said stud

includes a sintered carbide material

7. A cutting assembly according to Claim 1 wherein said stud

includes a tungsten carbide material.

8. A cutting assembly according to Claim 1 wherein said

cutting table is brazed to said stud.

9. A cutting assembly according to Claim 1 wherein said

cutting table includes a plug and said stud includes a recess adapted to receive the

cutting table plug with an interference fit.

10. A continuously self-sharpening cutting assembly for use with

well drilling systems comprising, in combination, a polycrystalline diamond

cutting table defining, in its original configuration, a void of predetermined shape,

and an underlying carbide stud, the stud defining, in its original configuration, a

void of predetermined shape, the cutting table and stud being brazed to each other

and the voids being in registry with each other.

11. A cutting assembly according to Claim 10 wherein said

cutting table includes an axially extending plug and said stud defines an axially

extending recess adapted to receive the cutting table plug with an interference fit.

12. A cutting assembly according to Claim 10 where at least one

of said voids is filled with an abrasive material.