Background of the Invention
1. Field of the Invention
[0001] The present invention relates to the field of earth boring tools and in particular
to rotating bits incorporating diamond elements.
2. Description of the Prior Art
[0002] The use of diamonds in drilling products is well known. More recently synthetic diamonds
both single crystal diamonds (SCD) and polycrystalline diamonds (PCD) have become
commercially available from various sources and have been used in such products, with
recognized advantages. For example, natural diamond bits effect drilling with a plowing
action in comparison to crushing in thecase of a roller cone bit, whereas synthetic
diamonds tend to cut by a shearing action. In the case of rock formations, for example,
it is believed that less energy is required to fail the rock in shear than in compression.
[0003] More recently, a variety of synthetic diamond products has become available commercially
some of which are available as polycrystalline products. Crystalline diamonds preferentially
fractures on (lll), (110) and (100) planes whereas PCD tends to be isotropic and exhibits
this same cleavage but on a microscale and therefore resists catastrophic large scale
cleavage failure. The result is a retained sharpness which appears to resist polishing
and aids in cutting. Such products are described, for example, in U.S. Patents 3,913,280;
3,745,623; 3,816,085; 4,104,344 and 4,224,380.
[0004] In general, the PCD products are fabricated from synthetic and/or appropriately sized
natural diamond crystals under heat and pressure and in the presence of a solvent/catalyst
to form the polycrystalline structure. In one form of product, the polycrystalline
structures includes sintering aid material distributed essentially in the interstices
where adjacent crystals have not bonded together.
[0005] In another form, as described for example in U. S. Patents 3,745,623; 3,816,085;
3,913,280; 4,104,223 and 4,224,380 the resulting diamond sintered product is porous,
porosity being achieved by dissolving out the nondiamond material or at least a portion
thereof, as disclosed for example, in U. S. 3,745,623; 4,104,344 and 4,224,380. For
convenience, such a material may bε described as a porous PCD, as referenced in U.S.
4,224,380.
[0006] Polycrystalline diamonds have been used in drilling products either as individual
compact elements or as relatively thin PCD tables supported on a cemented tungsten
carbide (WC) support backings. In one form, the PCD compact is supported on a cylindrical
slug about 13.3 mm in diameter and about 3 mm long, with a PCD table of about 0.5
to 0.6 mm in cross section on the face of the cutter. In another version, a stud cutter,
the PCD table also is supported by a cylindrical substrate of tungsten carbide of
about 3 mm by 13.3 mm in diameter by 26mm in overall length. These cylindrical PCD
table faced cutters have been used in drilling products intended to be used in soft
to medium-hard formations.
[0007] Individual PCD elements of various geometrical shapes have been used as substitutes
for natural diamonds in certain applications on drilling products. However, certain
problems arose with PCD elements used as individual pieces of a given carat size or
weight. In general, natural diamond, available in a wide variety of shapes and grades,
was placed in predefined locations in a mold, and production of the tool was completed
by various conventional techniques. The result is the formation of a metal carbide
matrix which holds the diamond in place, this matrix sometimes being referred to as
a crown, the latter attached to a steel blank by a metallurgical and mechanical bond
formed during the process of forming the metal matrix. Natural diamond is sufficiently
thermally stable to withstand the heating process in metal matrix formation.
[0008] In this procedure above described, the natural diamond could be either surface-set
in a predetermined orientation, or impregnated, i.e., diamond is distributed throughout
the matrix in grit or fine particle form.
[0009] With early PCD elements, problems arose in the production of drilling products because
PCD elements especially PCD tables on carbide backing tended to be thermally unstable
at the temperature used in the furnacing of the metal matrix bit crown, resulting
in catastrophic failure of the PCD elements if the same procedures as were used with
natural diamonds were used with them. It was believed that the catastrophic failure
was due to thermal stress cracks from the expansion of residual metal or metal alloy
used as the sintering aid in the formation of the PCD element.
[0010] Brazing techniques were used to fix the cylindrical PCD table faced cutter into the
matrix using temperature unstable PCD products. Brazing materials and procedures were
used to assure that temperatures were not reached which would cause catastrophic failure
of the PCD element during the manufacture of the drilling tool. The result was that
sometimes the PCD components separated from the metal matrix, thus adversely affecting
performance of the drilling tool.
[0011] With the advent of thermally stable PCD elements, typically porous PCD material,
it was believed that such elements could be surface-set into the metal matrix much
in the same fashion as natural diamonds, thus simplifying the manufacturing process
of the drill tool, and providing better performance due to the fact that PCD elements
were believed to have advantages of less tendency to polish, and lack of inherently
weak cleavage planes as compared to natural diamond.
[0012] Significantly, the current literature relating to porous PCD compacts suggests that
the element be surface-set. The porous PCD compacts, and those said to be temperature
stable up to about 1200°C are available in a variety of shapes, e.g., cylindrical
and triangular. The triangular material typically is about 0.3 carats in weight, measures
4mm on a side and is about 2.6mm thick. It is suggested by the prior art that the
triangular porous PCD compact be surface-set on the face with a minimal point exposure,
i.e., less than 0.5mm above the adjacent metal matrix face for rock drills. Larger
one per carat synthetic triangular diamonds have also become available, measuring
6 mm on a side and 3.7 mm thick, but no recommendation has been made as to the degree
of exposure for such a diamond. In the case of abrasive rock, it is suggested by the
prior art that the triangular element be set completely below the metal matrix. For
soft nonabrasive rock, it is suggested by the prior art that the triangular element
be set in a radial orientation with the base at about the level of the metal matrix.
The degree of exposure recommended thus depended on the type of rock formation to
be cut.
[0013] The difficulties with such placements are several. The difficulties may be understood
by considering the dynamics of the drilling operation. In the usual drilling operation,
be it mining, coring, or oil well drilling, a fluid such as water, air or drilling
mud is pumped through the center of the tool, radially outwardly across the tool face,
radially around the outer surface (gage) and then back up the bore. The drilling fluid
clears the tool face of cuttings and to some extent cools the cutter face. Where there
is insufficient clearance between the formation cut and the bit body, the cuttings
may not be cleared from the face, especially where the formation is soft or brittle.
Thus, if the clearance between the cutting surface-formation interface and the tool
body face is relatively small and if no provision is made for chip clearance, there
may be bit clearing problems.
[0014] Other factors to be considered are the weight on the drill bit, normally the weight
of the drill string and principally the weight of the drill collar, and the effect
of th
4 fluid which tends to lift the bit off the bottom. It has been reported, for example,
that the pressure beneath a diamond bit may be as much as 1000 psi greater than the
pressure above the bit, resulting in a hydraulic lift, and in some cases the hydraulic
lift force exceeds 50% of the applied load while drilling.
[0015] One surprising observation made in drill bits having surface-set thermally stable
PCD elements is that even after sufficient exposure of the cutting face has been achieved,
Dy running the bit in the hole and after a fracion of the surface of the metal matrix
was abraded away, the rate of penetration often decreases. Examination of the bit
indicates unexpected polishing of the PCD elements. Usually ROP can be increased by
adding weight to the drill string or replacing the bit. Adding weight to the drill
string is generally objectionable because it increases stress and wear on the drill
rig. Further, tripping or replacing the bit is expensive since the economics of drilling
in normal cases are expressed in cost per foot of penetration. The cost calculation
takes into account the bit cost plus the rig cost including trip time and drilling
time divided by the footage drilled.
[0016] Clearly, it is desirable to provide a drilling tool having thermally stable PCD elements
and which can be manufactured at reasonable costs and which will perform well in terms
of length of bit life and rate of penetration.
[0017] It is also desirable to provide a drilling tool having thermally stable PCD elements
so located and positioned in the face of the tool as to provide cutting without a
long run-in period, and one which provides a sufficient clearance between the cutting
elements and the formation for effective flow of drilling fluid and for clearance
of cuttings.
[0018] Run-in in diamond bits is required to break off the tip or point of the triangular
cutter before efficient cutting can begin. The amount of tip loss is approximately
equal to the total exposure of natural diamonds. Therefore, an extremely large initial
exposure is required for synthetic diamonds as compared to natural diamonds. Therefore,
to accommodate expected wearing during drilling, to allow for tip removal during run-in,
and to provide flow clearance necessary, substantial initial clearance is needed.
[0019] Still another advantage is the provision of a drilling tool in which thermally stable
PCD elements of a defined predetermined geometry are so positioned and supported in
a metal matrix as to be effectively locked into the matrix in order to provide reasonably
long life of the tooling by preventing loss of PCD elements other than by normal wear.
[0020] It is also desirable to provide a drilling tool having thermally stable PCD elements
so affixed in the tool that it is usable in specific formations without the necessity
of significantly increased drill string weight, bit torque, or significant increases
in drilling fluid flow or pressure, and which will drill at a higher ROP_than conventional
fits under the same drilling conditions.
Brief Summary of the Invention
[0021] The present invention is an improvement in a rotating bit having a bit face wherein
the improvement comprises a plurality of teeth disposed on the bit and wherein each
tooth includes a diamond cutting element. The diamond cutting element is particularly
characterized by having the shape of a segment of a cylinder. The segment includes
at least one planar surface and the planar surface forms, at least in part, a leading
surface of the tooth.
[0022] More specifically, the cylindrical segment is a split half cylinder or a split quarter
cylinder. The diamond cutting element is characterized by having a longitudinal axis
lying along the length of the cylinder and wherein the cylindrical shape is a half
cylinder shape, the planar surface is a planar surface lying along a diameter of the
cylindrical shape. In the case where the cylindrical segment is a quarter segment
of a full cylinder,-the quarter segment includes an apical edge which lies along the
longitudinal axis of the cylinder. In each case, the apical edge of the quarter cylinder
and the planar surface of the half cylinder diamond cutting element serves as an exposed
leading surface of the tooth and is disposed adjacent to a fluid channel thereby forming
in whole or in part one edge or wall of the fluid channel. As a result of these improvements
a cutting tooth is provided using cylindrical elements characterized by improved cutting
efficiency, cleaning and cooling efficiency, and less tendency to dull or polish than
is the case with prior art fully cylindrical elements used in rotating bits.
[0023] The present invention and its various embodiments are better understood by first
considering the following drawings wherein like elements are referenced by like numerals.
Brief Description of the Drawings
[0024]
Figure 1 is a cross-sectional view of a tooth incorporating a cylindrical diamond
segment according to the present invention.
Figure 2 is a plan view of three teeth of the type show! in Figure 1.
Figure 3 is a cross-sectional view through a rotating bit showing the area of a gage-to-shoulder
transition incorporating the teeth of Figure 1.
Figure 4 is a plan view in reduced scale showing a coring bit incorporating the teeth
of Figures 1 and 2.
Figure 5 is a half profile view of the coring bit of Figure 4.
Figure 6 is a plan view of the gage-to-shoulder transition of the coring bit in Figure
4 in conformity with the teaching of Figure 3.
Figure 7 is a cross-sectional view in enlarged scale of a tooth incorporating a second
embodiment of the present invention.
Figure 8 is a plan view of three teeth devised according to the second embodiment
shown in Figure 7.
[0025] The present invention and its various embodiments may be better understood by viewing
the above figures in light of the following detailed description.
Detailed Description of the Preferred Embodiments
[0026] The present invention is an improvement in a tooth design used in rotating bits,
particularly rotary bits, wherein the tooth includes a diamond cutting element and
in particular a diamond cutting element derived from cylindrical polycrystalline synthetic
diamond (PCD). Such full cylindrical elements are generally commercially available
but not in segment form. Such synthetic diamond is formed in the shape of a full circular
cylinder having one planar end perpendicular to the longitudinal axis of the cylindrical
shape and an opposing domed end, generally formed in the shape of a circular cone.
Such elements are typically available in a variety of sizes with the above described
shape.
[0027] According to the present invention, the full cylindrical diamond element is segmented
to form a cylindrical segment wherein the segment is then axially disposed within
a bit tooth. Such segmented or split cylindrical elements thus provide a cutting element
with improved cutting efficiency with less use o diamond material and less tendency
to dull or polish. The present invention and its various embodiments may be better
understood by now turning to Figure 1.
[0028] Figure 1 is a cross-sectional view of a first embodimen of the present invention
showing a tooth, generally denoted by reference numeral 10, incorporating a diamond
cutting element, generally denoted by reference numeral 12. Element 12 is axiall disposed
within the tungsten-carbide matrix material 14 of the rotating bit. In other words,
longitudinal axis 16 of element 1 is orientedT to be approximately perpendicular to
bit surface 18 at the location of tooth 10. Bit surface 18 may be bit face of crown
of a rotating bit or may be the superior surface of a raised land or pad disposed
upon a bit crown. In either case, bit surface 18 is taken in the present description
as the basal surface upon which tooth 10 is disposed.
[0029] As better seen in Figure 2, element 12 is approximately a quarter section or 90 degrees
of the full cylindrical shape of the PCD element normally available. Element 12 is
cut using a conventional laser cutter. For example, deep cuts are made every 90 degrees
parallel to the longitudinal axis 16 of a full cylindrical diamond element. Although
the laser could be used t completely cut through the diamond element, it has been
found possible that with deep scoring, the diamond can then be fractured with propagation
of the fracture lying approximately along the continuation of the plane of the laser
cut. For example, the laser may cut a millimeter or less into and along the length
of the full cylindrical diamond element. A diametrically opposed cut of equal depth
is also provided on the cylinder. Thereafter, the cylinder may be split in half and
then later quartered on another laser cut by fracturing the diamond element using
an impulsive force and chisel.
[0030] Diamond element 12 is disposed within tooth 10 as isshown in Figure 2 so that the
apical edge 20 of diamond 12 formed by the cleavage planes or laser cuts which have
formed radial surfaces 22, is oriented in the leading or forward direction of tooth
10 as defined by the rotation of the bit upon which tooth 10 is disposed.
[0031] Turning again to Figure 1, it can be seen that a portion of element 12 is fully exposed
above bit surface 18 and in particular, that apical edge 20 forms the foremost portion
of diamond element 12 as the tooth moves forwardly in the plane of the figure. Surfaces
22 define a dihedral angle and the tangential direction of movement of tooth 10 during
normal cutting operation is generally along the direction of the bisector of the dihedral
angle. In the illustrated embodiment a channel 24 is defined immediately in front
of apical edge 20 to serve as a waterway or collector as appropriate. Thus, leading
surfaces 22 and edge 20 can be placed virtually in channel 24 or immediately next
thereto, forming as shown in Figure 1, one wall of channel 24 or a portion thereof,
whereby hydraulic fluid supplied to and flowing through channel 24 during normal drilling
operations will serve to cool and clean the cutting face of tooth 10 and in particular
the leading edge and surfaces of diamond element 12.
[0032] Further, in the illustrated embodiment, tooth 10 is shown as having a trailing support
26 of matrix material integrally formed with matrix material 14 of the bit and extending
above bit surface 18 to the trailing surface of diamond element 12. The slope of trailing
support 26 is chosen so as to substantially match the slope of the top conical surface
28 of element 12 with the opposing end of element 12, which is a right circular plane,
being embedded within matrix material 14. However, it must be understood that the
exact shape and placement of trailing support 26 can be varied without departing from
the spirit and scope of the present invention. For example, with larger diameter elements
12, cut from large diameter synthetic cylinders, no trailing support 26 may be provided
at all and element 12 may be totally free standing above bit surface 18 like an embedded
stud. In the cases of thinner cylindrical elements 12, trailing support 26 may be
even more substantial than that shown in-Figure 1 and may assume a slope different
from surface 28 of element 12 to thereby provide additional matrix reinforcing material
behind and on top of conical surface 28 and leading surfaces 22.
[0033] Figure 2 illustrates in plan view the tooth of Figure 1 in a double row or triad
configuration. In other words, a first row of teeth including teeth 10a and 10b is
succeeded by a trailing tooth or second row of teeth including tooth 10c, wherein
tooth 10c is placed halfway between the spacing of teeth 10a and 10b. Therefore, it
can be appreciated that as the teeth 10a-c move forward during cutting of a rock formation,
the diamond cutting elements incorporated within each of the teeth effectively overlap
and provide a uniform annular swath cut into the rock formation as the bit rotates.
Figure 4, which shows in plan view a coring bit incorporating the teeth of Figures
1 and 2 illustrates the disposition of such a double row of configured teeth, collectively
denoted by reference numeral 32, on pad 30.
[0034] Bit 34 also includes an inner gage 44 wherein the inner and outer gage are connected
by waterways 31. Each pad 30 begins at or near inner gage 44 and is disposed across
the bit face in a generally radial direction as seen in Figure 4 and splits into two
pads which then extend to outer gage 36. The bifurcated pads are separated by a collector
33 which communicates with a gage collector 35 or junk slot 37 as may be appropriate.
Clearly, other types of coring bits and petroleum bits could have been illustrated
to show the use of the teeth of Figures 1-3 other than the particular bit illustrated
in Figure 4. Therefore, the invention is not to be limited to any particular bit style
or in fact, even to rotating bits.
[0035] Turning now to Figure 3, a cross-sectional view of the shoulder-to-gage transition
utilizing the teeth of Figures 1 and 2 is illustrated. The bit, generally denoted
by reference numeral 34, is characterized by having a vertical cylindrical section
or gage 36 which serves to define and maintain the diameter of the bore drilled by
bit 34. Below gage 36, bit 34 will slope inwardly along a designed curve toward the
center of the bit. In the example of coring bit of Figure 4, a half profile is shown
in Figure 5 and is a simple elliptical cross section characterized by an outer shoulder
38, nose 40 and inner shoulder 42. Inner diameter of the core is then defined by inner
gage 44. Turning again to Figure 3, outer gage 36 is shown as incorporating a half
cylindrical segment 46, which is surface set and embedded into gage 36 so that the
rounded cylindrical surface 48 is exposed above bit surface 50 of gage 36 with the
flat longitudinal face 52 of the half cylindrical segment embedded within matrix material
54 of bit 34. Half cylindrical diamond crystalline element 46 is more clearly depicted
in cross-sectional view in Figure 4 on gage 36.
[0036] Moving from gage 36 to outer shoulder 38, teeth 32 as shown in Figure 4 include quarter
cylindrical segments, shown in rear view in Figure 3 as exemplified by diamond elements
56 and 58. Each element 56 is disposed within bit 34 so as to extend therefrom in
a perpendicular direction as defined by the normal to bit surface at each point where
such element is located.
[0037] In the preferred embodiment each element 56 and 58 is exposed by a uniform amount,
namely, 2.7 mm (0.105") above the bit face. Element 56 which is the diamond element
closest to gage 36 is placed upon shoulder 38 at such a position next to the beginning
of gage 36 so that its outermost radially extending point, namely, apex 60, extends
radially from the longitudinal axis of rotation of bit 34 by an amount equal to the
radial distance from the longitudinal axis of bit 34 by the gage diamonds, in particular
diamond 46. For example, in the preferred embodiment, gage diamond 46 extends above
bit surface 50 by 0.64 mm (0.025"). While element 56 extends above bit face 50 by
2.7 mm (0.105") it is placed as the first tooth on the bit face at such a distance
from the gage 36 that the radially outermost exposed portion of diamond element 56
will equal the radial distance of the gage diamonds 46 from the axis of rotatior of
bit 34.
[0038] Thus, as illustrated in Figure 6, which shows a plan view of the gage of the bit
of Figure 4, a double row of gage diamonds 46a is disposed at and slightly below gage
level 62 on < type I gage column corresponding to a type I pad 30 shown in plai view
in Figure 4. Gage diamonds 46b are thus placed adjacent to a pad of type II and gage
diamonds 46c placed on a gage section correspondingg to a type III pad. Gage diamonds
46a-c thus form a staggered pattern as best illustrated in Figure 6 which effectively
presents a high cutting element density as the bit rotates. Above gage diamonds 46a-46b
are conventional natural diamonds surface set in broaches, namely, kickers which are
typical of the order of 6 per carat in size. Whereas the double row of diamonds within
one gage section are offset from each other by approximately half a unit spacing,
a unit spacing being defined as the length of a gage diamond 46, the adjacent row
of teeth on the next adjacent gage section begins at a quarter spacing displaced from
the corresponding row of gage diamonds on the adjacent pad. In other words, while
type I pad corresponds to gage diamonds 46a having two rows with each row offset by
half a space between each other, pad II corresponds to gage diamonds 46b which are
similarly offset with respect to each other and are spaced down the gage one quarter
of a spacing as compared to gage diamonds 46a on pad type I.
[0039] Turning now to Figure 7, a second embodiment of the present invention is illustrated
wherein a tooth, generally denoted by reference numeral 66, incorporates a half cylindrical
segment diamond element 68 extending from and embedded in matrix material 14 in much
the same manner as illustrated in connection with the first embodiment of Figures
1 and 2. As better seen in plan view of Figure 8, PCD element 68 is- characterized
by a half cylindrical surface 70 and a planar leading surface 72, which is formed
as described above by cleaving a full cylinder along the diameter.
[0040] Turning again to Figure 7, diamond element 68 also includes a conical or domed upper
surface 74 forming the apical point 76 of element 68. A trailing support 78 of integrally
formed matrix material is smoothly fared from surface 74 to bit face 18 to provide
tangential reinforcement and support for diamond element 68 against the cutting forces
to which element 68 is subjected. As better seen in plan view in Figure 8, trailing
supports 78 are tapered to a point 80 on bit face 18 thereby forming a teardrop shaped
plan outline for tooth 66.
[0041] As shown in Figure 7, diamond element 68 is placed immediately adjacent to and forms
one side of a channel 80 formed into matrix material 14 which channel 80 serves as
a conventional waterway or collector as may be appropriate with the same advantages-as
described in connection with the first embodiment of Figure 1.
[0042] As described in connection with Figure 2, the second embodiment of Figure 8 similarly
consists of two rows of teeth 66a and 66b followed by a second row represented by
tooth 66c. Tooth 66c is located halfway between the spacing between tooth 66a and
66b as defined with respect to the direction of tangential movement during normal
drilling operations. The double row of teeth are disposed on a petroleum or coring
bit in the same manner as illustrated in connection with the first embodiment of the
invention in Figure 4. Teeth 66 are thus disposed within matrix material 14 and used
on a bit in the same
[0043] manner as are teeth 10 of Figures 1 and 2. However, teeth 66 as shown in Figure 8,
clearly provide a broader cutting surface and a diamond element 68 containing twice
the diamond material and structural bulk as compared to diamond elements 12 of the
first embodiment. Therefore, in those applications where a larger cutting bite is
required or where greater structural strength is needed in the diamond element, the
half cylindrical split elements 68 of the second embodiment may be more advantageously
used than the quarter split diamond elements of the first embodiment.
[0044] Many alterations and modifications may be made to the present invention without departing
from its spirit and scope. For example, although the split cylindrical segment has
been shown as perpendicularly embedded into the matrix material, it is clearly contemplated
that it may be either forwardly or rearwardly raked if required by design objectives.
Therefore, the illustrated embodiment must be understood as presented only as an example
of the invention and should not be taken as limiting the invention as set forth in
the following claim.
1. In a rotating bit having a bit face, an improvement comprising:
a plurality of teeth disposed on said bit wherein each said tooth includes a diamond
cutting element having a longitudinal axis, said diamond cutting element being characterized
in shape as a segment of a cylinder including at least one planar surface, said planar
surface forming at least in part a leading surface of said tooth.
2. The improvement of Claim 1 wherein said cylindrical shape of said diamond cutting
element is a circular cylinder.
3. The improvement of Claim 1 wherein said segment of said cylindrical shape is a
half cylinder shape, said planar surface being a planar surface lying along a diameter
of said cylindrical shape.
4. The improvement of Claim 3 wherein said planar surface is oriented and exposed
to form said leading surface of said tooth.
5. The improvement of Claim 1 wherein said segment of said cylindrical shape of said
diamond cutting element is characterized by an apical edge defining a dihedral angle
of less than 180 degrees.
6. The improvement of Claim 5 wherein said segment of cylindrically shaped diamond
cutting element is a quarter segment of a full cylinder and wherein said apical edge
lies along said longitudinal axis.
7. The improvement of Claim 6 wherein said diamond cutting element is disposed within
each tooth so that each apical edge provides the leading portion of said diamond cutting
element.
8. 'The improvement of Claim 7 wherein the tangential direction of movement of said
tooth lies approximately along the bisector of said dihedral angle defining said apical
edge.
9. The improvement of Claim 1 wherein said tooth further includes a trailing support
disposed behind said diamond cutting element is contiguous thereto and is substantially
congruous with a trailing surface of said diamond cutting element, said trailing support
tapering from said trailing surface of said diamond cutting element to said bit face.
10. The improvement of Claim 1 wherein said diamond cutting element forms one wall
of an adjacent fluid channel defined into said bit face in front of said tooth.
11. The improvement of Claim 1 wherein said bit includes a gage and a sloping shoulder,
said teeth being disposed on said shoulder near said gage and extending above said
bit face by a first predetermined distance, said gage including cutting elements disposed
above said bit face of said gage by a second predetermined distance and said bit further
being characterized by a longitudinal axis of rotation, the radial distance from ssaid
longitudinal axis of rotation of said cutting elements disposed and extending above
said gage being approximately equal to the radial distance from said longitudinal
axis of rotation of an uppermost one of said diamond cutting elements disposed on
said shoulder, said uppermost diamond cutting element on said shoulder being positioned
on said shoulder next to said gage at a location such that said radial distances from
said longitudinal axis of rotation of said cutting elements on said gage and of said
uppermost diamond cutting element are set approximately equal.
12. In a rotating bit having a bit face and a plurality of teeth disposed thereon,
an improvement comprising a cylindrically shaped polycrystalline diamond element incorporated
within each said tooth, said diamond cutting element characterized by a shape assumed
in the form of a segment of a cylinder and further characterized by having one end
of said cylindrical shape formed into a conical segment, said segment of said cylindrical
shape of said diamond cutting element providing at least one planar surface, said
planar surface of said diamond cutting element oriented within said tooth to provide
at least in part a leading surface of said tooth as defined by the direction of movement
of said tooth during normal cutting operation when said bit rotates, whereby said
cylindrically shaped diamond cutting element provides improved cutting efficiency
and bit lifetime.
13. The improvement of Claim 12 wherein said segment of said cylindrically shaped
diamond cutting element is a half cylindrical segment, thereby defining a planar leading
surface lying along a diameter of said cylindrical shape.
14. The improvement of Claim 12 wheren said segment of said cylindrically shaped diamond
cutting element is a quarter segment, thereby defining an apical edge and two leading
surfaces forming a dihedral angle behind said edge, said dihedral angle being approximately
90 degrees.
15. The improvement of Claim 14 wherein said cylindrically shaped diamond cutting
element is characterized by a longitudinal axis lying along said apical edge and wherein
said diamond cutting element is oriented with respect to said bit face so that said
longitudinal axis is approximately perpendicular thereto.
16. The improvement of Claim 15 wherein a channel is defined into said bit face immediately
in front of said diamond cutting element and wherein said apical edge is disposed
on and serves at least as part of an adjacent wall of said fluid channel.
17. The improvement of Claim 16, further including a trailing support integrally formed
with said bit face and extending in a tapered fashion from said bit face to a trailing
surface of said diamond cutting element.
18. The improvement of Claim 17 wherein an end of said diamond cutting element exposed
above said bit face is formed in the shape of a segment of a cone, the slope of said
cone shaped segment approximately matching the slope of said trailing support.
19. The improvement of Claim 12 wherein a plurality of rows of said teeth are disposed
on said bit and wherein said rows are paired to form a first and second related row,
the distance of spacing between teeth within said first and second row being substantially
constant, said teeth of said second row being disposed behind said teeth of said first
row as defined by tangential motion of said teeth during rotation of said bit during
normal cutting operations, said teeth of said second row being readily disposed halfway
between said teeth of said first row, whereby said teeth of said first and second
rows cut a uniform annular swath as said bit rotates of a higher effective tooth density
than achievable by tooth density within said first or second row alone, said teeth
of said second row following behind said teeth of said first row in the gaps between
and behind said teeth of said first row.