Note: Descriptions are shown in the official language in which they were submitted.
10~7164
FIELD OF THE IN ENTION
This invention relates generally to earth boring
apparatus and more particularly to earth boring drills having
rotary cutters for the purpose of accomplishing boring
operations in relatively hard, consolidated earth formations.
This invention also relates to a method of assembling earth
boring drills constructed in accordance with the invention.
BACKGROUND OF THE INVENTION
.
In the drilling of deep wells in earth formations many
different types of earth formations are encountered and boring
or drilling operations in each of these types of formations
require differing boring equipment. For example, in loose or
unconsolidated earth formations such as gravel strata, it is
desirable to utilize integral drill bits having a plurality of
blades for cutting away the formation. Where consolidated, very
hard earth strata is encountered, for example, in deep earth
formations, it is typically desirable to employ drill bits
having a plurality of rotary toothed cutters. The teeth of the
rotary cutters are cooperatively associated so that the earth
formation is cut away as the drill bit is rotatcd at tlle
extremity of the drill pipe extending from the drilling rig to
the formation being drilled. The typical rotary cutter type
drill bit or "rock bit" includes a body portion from which
depend three legs. Spindles or cutter supports extend inwardly
toward the center line of the drill bit from each of these legs.
Rotary cone type cutter elements having cutter teeth formed
thereon are typically rotatably secured to each of the supports
or spindles and are oriented in such manner that the cutter
teeth thereon engage and cut away the earth formation as the bit
structure is rotated by the drill pipe.
)87164
One of the paramount disadvantages of drill bits
having rotary cutters is the inability of the cuttèr bearings to
withstand the severe wear characteristics to which the drill bit
is typically subjected. As drilling operations occur, rock bits
are subjected to severe impacting and vibration as well as other
wear inducing factors that are highly detrimental to the service
life of the rotary cutter bearings and other components of such
drill bits. At times, much of the weight of the drill pipe to
which the rotary drill is connected may be caused to act upon
- 10 the cutter, subjecting the cutters and their bearings to
tremendous mechanical loads. It is therefore desirable that
rotary drill devices be provided which incorporate bearings
having the capability of withstanding extremely high forces,
excessive vibration as well as high temperature operation.
Typically, the drill bodies of rotary cutter devices
take the form of integral cast or forged structures that are
very expensive to manufacture because of the complex
configuration thereof. It is also desirable to provide a rotary
drill bit construction having a body structure of exceptional
strength and durability and yet being of relatively low cost.
Drill bit cost is also adversely affected by the ty~ical
requirement for expensive materials for most of the structural
components of such bits. For example, an expensive bearing
quality material may be required for the drill cutters or the
entire body structure of the bit if any part thereof is to
define a wear resistant bearing surface.
It is also an important feature of the present
invention to provide a novel rotary earth boring bit
construction whereby rotary cutter elements are assembled to
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1~7164
respective spindle and bearing assemblies utilizing controlled
changes in dimension by heating and cooling various ones of the
drill bit components.
It is also a feature of the present invention to
provide a novel rotary earth boring drill construction whereby
mechanical locking means may be provided to insure positive
locking of rotary cutter elements to the spindle bearings and
thereby insure against separation of the cutter elements by
vibration and other operationally induced forces.
Other and further aspects, advantages and features of
the invention will become obvious to one skilled in the art upon
an understanding of the illustrative embodiments about to be
described and various advantages, not referred to herein, will
occur to one skilled in the art upon employment of the invention
in practice.
T~E PRIOR ART
Rotary cutter type roller drills have been
commercially available for an extended period of time as
indicated by Godbold in U.S. patent 1,325,086. In some cases,
the structure of the drill bit body has also been employed to
accomplish bearing capability as taught by U.S. patents
2,620,686 of Peter and 3,361,494 of Galle. Various types of
bearings have also been employed to support roller cutters such
as the complex structures illustrated in U.S. patents 1,839,589,
2,004,012 and 2,126,041 all of Reed. Reed patents 1,839,589 and
2,004,012 and U.S. patent 1,957,532 of Flynn each disclose ear-th
boring drill constructions employing spindle structures that are
secured to the body structure of the bit by mechanical means
such as welding, bolting or the like.
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SUMMARY OF TH~ I~VENTION
In one aspect the lnvention claimed hcreill ~CI. t.lills
to a method of manufacturing a rotary earth boring drill includ-
ing assembling a drill cutter, spindle and bearing means to
establish a non-rotatable retained relation between the bearing
means and the cutter. The method includes providing a spindle
defining a bearing surface having inner and outer extremities
and providing a bearing means having a tapered cutter engaging
surface formed thereon which causes one extremity of the bearing
means to be larger than the other extremity thereof. The
bearing means is placed in rotatable assembly about the bearing
surface of the spindle with the other extemity thereof directed
toward the inner extremity of the spindle. The method further
includes providing a rotary drill cutter having a cavity formed
therein to receive the bearing means, the deepest portioll of
the cavity defining the inner extremity of the cavity and the
mouth of the cavity defining the outer extremity of the cavity.
The cavity is defined at least in part by an internally tapered
bearing engaging surface, the inner extremity of the bearing
engaging surface of the cavity being of larger dimension than
the outer extremity thereof. The bearing means and spindle are
cooled as assembled to reduce the outside dimension of the
bearing means and the drill cutter is heated to increase the
inside dimension of the cavity. The assembled and cooled
bearing means and spindle is inserted into the cavity of the
heated drill cutter, and the drill cutter, the bearing means and
the spindle are allowed to return to normal temperature and di-
mension to cause a tight retention fit to develop ietween the
bearing means and the drill cutter. Thus a structural interlocking
relation is developed between the drill cutter and the bearing
means when the one extremity of the bearing means is received
at the inner extremity of the bearing engaging surface of the
cutter.
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In another aspect of the invention claimed herein
there is provided a rotary earth boring drill for conl~ectioll to
the clrill pipe of drilling apparatus. The drill includes drill
body means defining a plurality of depending cutter support legs
and a splndle element extends from each of the cutter support
legs and defines a generally cylindrical bearing surface.
Bearing means are disposed in rotatable relation with the spindle
element, the bearing means having inner and outer extremities.
There is provided a cutter element having a cavity formed therein,
the deepest part of the cavity defining the inner extremity of
the cavity and the mouth of the cavity defining the outer
extremity of the cavity, the cavity receiving the bearing means
therein. Means mechanically interlock the cutter element and
the bearing means which means comprises a tapered cutter engaging
surface formed on the bearing means causing the outer extremity
of the bearing means to be larger than the inner extremity
thereof and an internally tapered bearing engaging surface
being formed within the cutter element and defining at least
a part of the cavity and causing the bearing engaging surface
at the inner extremity of the cavity to be of larger dimension
than the outer extremity thereof. The outer extremity of the
bearing means is received at the inner extremity of the bearing
engaging surface of the cutter element.
10~64
More particularly, rotary e<~rth bc-rillg ~Iri ] 1 I i t
structures having rotary cutter elements are provided in
accordance with the present invention having cutter elements
that are uniquely connectable to the body structure of the bit
and which function efficiently to withstand the detrimental
effects of excessive loads and vibration during drilling
operations. Depending leg structures of the drill body may be
formed to define spindle bores tllat receive a b~arilly s~)indle
which may be secured to the depending leg structures by a simple
welding operation. The spindle structure may be composed of
metal having unique bearing capability and a cylindrical bearing
surface may be formed on the spindle in conventional manner.
The bearing surface may be specifically treated such as by
chrome plating, if desired to provide additional resistance to
wear under exceptionally heavy loads. Prior to assembly of
the spindle structure to the drill body by welding or any other
suitable form of connection, a bearing element will be assembled
to the spindle and the spindle and bearing assembly will be
assembled to a rotary cutter.
The rotary cutter will be of generally cone like
configuration having a plurality of external teeth formed thereon
for cutting engagement with the earth formation to be drilled.
Each of the cutter elements is also formed to define an internal
cavity of particular size and configuration for receiving the
bearing and spindle assembly. The cavity is defined in part by
a tapered internal surface that cooperates with a tapered exter-
nal surface defined by a sleeve bearing that causes a mechani-
cally interlocked relationship to develop between the cutter
element and the bearing. The particular taper of the internally
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)t37~64
tapered surface of the cutter an(l externally ta~ere(l suLIa~e
of the bearing is correlated with the coefficient of expansion
of the particular materials from which the cutter and bearing
are composed. The method of assembling the cutter to the
spindle and bearing assembly comprises heating the cutter element
to a particular temperature, for example 225 C and at the same
time cooling the bearing and spindle assembly to a low tempera-
ture, for example -75 C or -175 C. After this has been done,
the cooled cutter and spindle assembly is inserted into the
cavity of the cutter, bringing the tapered surfaces of the
cutter and bearing into intimate engagement. After the heated
and cooled parts reach normal temperature, for example 25 C,
external expansion of the bearing element and internal contrac-
tion of the internally tapered surface of the cutter will
develop a tightly seized relationship between the bearing and
cutter. Thus, the cutter, which may be composed of metal having
exceptional abrasion resistance, may be provided with a bearing
composed of material having exceptional bearing capability.
To further er.hance the wear resisting characteristics of the
rotary cutter, spindle and bearing assembly the spindle may
be provided with a lubrication system, enabling the bearings
of each of the cutters to be lubricated as desired.
A simple and low cost drill body structure may be
developed in accordance with the present invention by providing
a plurality of body segments that may be assembled in any suit-
able manner. Each of these body segments may be composed of
low cost forgings or castings of a material havillg sufficient
strength for adequately resisting the forces to which the body
structure will be subjected during drilling operations and yet
being of relatively low material cost. The simple structure
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of each of the body segments enables the body segments to be
developed by forging or casting at relatively low cost. Addi-
tionally, each of the body segments may be of generally identical
configuration, thereby simplifying the pattern or mold costs
that are required for production of the body structure. For
example, the body structure may be composed of three segments
that may be placed in intimate assembly. The segments may be
joined by welding to form an integral drill body structure.
BRIEF DESCRIPTION OF TIIE DRAWINGS
In order that the manner in which the above recited
advantages and features of the invention are attained as well
as others, which will become apparent, can be understood in
detail, more particular description of the inventioll, briefly
summarized above, may be had by reference to the specific
embodiments thereof that are illustrated in the appended drawings,
which drawings form a part of this specification. It is to be
understood however that the appended drawings illustrate only
typical embodiments of the invention and are therefore not to
be considered limiting of its scope, for the invention may
admit to other equally effective embodiments.
In the drawings:
Figure 1 is a pictorial representation of a rotary
cutter type drill bit constructed in accordance with the present
invention.
Figure 2 is a fragmentary sectional view of the
drill bit structure of Fig. 1 illustrating one of the leg
structures of the drill body and showing the assembled relation-
ship between the leg, a rotary cutter element and a bearing
and spindle assembly.
C
~ 37164
Figure 3 is an exp]oded view of a drill cutter and
a bearing and spindle assembly with part thereof being shown
in section.
Figure 4 is a fragmentary sectional view of a drill
bit structure representing a modified embodiment of the present
invention.
Figure 5 is a sectional view taken along line 5 -
5 of Fig. 4.
Figures 6, 7 and 8 each depict one of the three body
segments of a drill body each having one of the three rotary
cutting elements rotatably secured thereto in accordance with
the teachings of the present invention.
Figure 9 is a transverse sectional view of a drill
body structure formed by three connected body sections and
showing the body sections to be welded together to form an
integral drill body structure, appearing with Figure 5.
Figure 10 is a partial sectional view of a drill
body and cutter representing an alternative embodiment utilizing
segmented bearings.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
With reference now to the drawings and first to
Fig. 1, a rotary cutter type drill bit shown ~enerally at 10
in quarter section which is also typically referred to in the
industry as a "rock bit". The rotary bit structure 10 generally
comprises a body structure 12 having a threaded upper extremity
14 for attachment of the drill bit to the lower section of a
string of drill pipe, not shown. The body structure 12 also
includes a plurality of depending cutter support legs 16 each
supporting a rotary cutting element such as shown at 18 and 20
each having a plurality of teeth 22 formed thereon to provide
for optimum engagement between the teeth of each of the cutter
elements and the formation being drilled. Each of the cutter
--- 1087~64
elements of the bit structure will be of slightly different con-
figuration, whereby the teeth of each cutter will cooperate with
the teeth of the other cutters to provide for efficient cu-tter
engagement with the formation as the rock bit is rotated relative
thereto.
Referring IIOW to Fig. 2, the rotary cutter 20 and
its support structure is illustrated in greater detail. The
depending leg 16 of the drill bit body structure may be formed
to define a generally planar bearing face 24 against which the
cutter element 20 bears as it rotates relative to the body
structure of the bit. An annular groove 26 may also be defined
in the bearing face portion of each depending leg 16 and a suit-
able sealing element, such as an O-ring 28, for example, may be
located within the annular groove 26 to prevent ingress of
drilling mud into the support bearing of the cutter and cutter
support assembly. The depending leg structure 16 may also be
formed to define a bore 30 having its axis oriented in such
manner as to intersect the center-line axis of the drill bit.
If the drill bit incorporates rotary cutter elements for example,
the center-line axis of each of the bores 30 will be oriented
to intersect the vertical center line of the drill body at a
point, unless it is desirable to orient the rotary axis of each
of the rotary cutters in some other desirable manner.
A cutter support spindle 32 may be provided which
includes a reduced diameter portion 34 adapted to be received
within the bore 30. The reduced diameter portion 34 of the
spindle may be inserted into the bore 30 to such extent that
an annular shoulder 36 of the spindle engages the bearing face
surface 24, thus controlling the position of the spindle rela-
tive to the depending leg structure 16 of the drill body. Thespindle may also be formed to define an inclined end surface
38 that may be oriented in surface alignment with the outer
surface 40 of the depending leg 16. Connection between the
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1~537164
spindle and the depending leg 16 may be positively established
by welding as shown at 42.
Prior to assembly of the spindle structure 32 to the
depending legs 16 of the body structure of the bit, it will
be desirable to form an assembly between the rotary cutter ele-
ments 20 and the respective bearings and spindles thereof.
This may be conveniently accomplished in the manner identified
particularly in conjunction with Figs. 2 and 3. To establish
a rotatable relationship between the rotary cutter element 20
and the spindle 32, the spindle may be formed to define a cylin-
drical bearing surface 44 about which may be received a bearing
element 46. The bearing surface 44 may be such as to provide
for efficient smooth rotation of the bearing 46 relative to
the spindle. For example, the bearing surface 44 may be chrome
plated if desired and may be ground to an extremely smooth
finish. If the metal from which the spindle 32 is formed is
of extremely good bearing quality, the bearing surface 44 may
simply be surface ground to an efficient finish for good bearing
capability. The spindle structure may also be formed to define
an enlarged head portion 48 defining an annular shoulder 50
that cooperates with the bearing 46 to retain the bearing in
proper operative position relative to the bearing surface 44.
It is desirable that each of the rotary cutter
elements of the drill bit have a positively retained and non-
rotatable relationship with the exterior surface of the bearing
element 46. This feature may be conveniently accomplished in
the manner illustrated in the exploded view of Fig. 3. As
shown at the lower portion of Fig. 3, the bearing element 46
is shown to be provided with a generally cylindrical internal
bearing surface 52 that is positioned in intimate bearing
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engagement with cylindrical surEace 44 of spindle 32 upon
assembly. The bearing 46 is also formed to define an external
cutter engaging surface 54 that is tapered as shown at 55 with
respect to the cylindrical surface 52 such that the bearing
structure 46 is provided with a large extremity directed toward
the cutter element and a small extremity directed toward the
planar surface 24 of depending leg 16. The taper of surface 54
may, for example, be in the order of .002 inches throughout the
length of the bearing element 46, which may be in the order oE
2 inches. Conversely, the cutter element 20 may be formed to
define an internal cavity 56 which is of a configuration to
receive the head portion 48 of the spindle and the bearing 46
in close relationship therein. The cavity 56 may be defined in
part by a tapered surface 58 that is of larger dimension at the
inner extremity thereof than at the outer extremity as shown
at 59. Throughout the extremity of the tapered surface 58 the
degree of taper may be in the order of .002 inches for example.
The internal dimension of the cavity 56 defined particularly by
tapered surface 58 may be correlated with the dimension of the
external surface 54 of the bearing such that an extremely
tight fit will be developed between surfaces 54 and 58 when the
cutter and bearing are in assembly. Moreover, the enlarged inner
extremity of the bearing 46 and the cavity 56 will allow the
cutter element to be firmly mechanically interlocked ~ith the
bearing element 46, thereby preventing not only rotation between
the cutter and the bearing but also preventing separation of
the cutter from the bearing.
To accomplish assembly of the cutter elements to
the respective bearing and spindle assemblies, the cutter
elements may be heated for the purpose of increasing the inter-
nal dimension established by the tapered surface 58, while at
37~64
the same time the bearing and spindle assembly may be cooled
for the purpose of reducing the external dimension of the
bearing. For example, a rotary cutter element having a cavity
dimension of 1.504 inches at a normal temperature of 25 C
(72 F) when heated to a temperature of 225 C was determined
to have increased in internal dimension to 1.5076 inches. At
the same time, reducing the temperature of the bearing and
spindle assembly from a normal temperautre of 25 C t72 F) to
-75 C (-100 F) resulted in a dimensional decrease of the exter-
nal surface of the bearing from 1.503 inches to 1.5022 inches.
With the drill cutter thus heated and the bearing and spindle
assembly cooled, it is possible to readily force the bearing
into properly seated relationship within the cavity 56 of the
cutter. It should be borne in mind that the heated, cooled
and normal temperature relationships set forth hereinabove,
together with the particular dimensions identified at these
temperatures, is not intended to be in any way limiting as far
as this invention is concerned. It is considered obvious that
other temperature ranges and dimensions may be utilized for
the various parts, depending upon the particular coefficientof expansion of the materials involved, without departing from
the spirit or scope of this invention.
In the event the drill bit might be subjected to
extremely heavy loads or excessive vibration, it may ~e desir-
able to provide means other than the mechanical expansion and
contraction of parts to retain the cutters in assembly with
the bearing structures. If this is desired, the cutters may
be formed to define an internal groove 60 that may be positioned
in registry with an annular groove 62 formed in the outer
periphery of the bearing 46 when the bearing is properly
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positioned within the cavity 56. In this case, a retainer ring
64 shown in Fig. 2 may be located within the groove 62 of the
bearing prior to assembly of the bearing and cutter. The re-
tainer ring 64 may be a split ring capa~le of being su~stan-
tially fully received within the annular groove 62 of the bear-
ing, thereby enabling the retainer ring to be forced into the
cavity 56 of the cutter along with the bearing during assembly.
As the annular groove 62 of the bearing moves into registry
with the groove 60 of the cutter, the retainer ring, which may
be formed of spring material, will expand so as to become par-
tially received within both of the grooves 60 and 62. After
the retainer ring has become so positioned, the cutter element
will separate from the bearing 46 only upon the development
of forces that are sufficiently great to shear the retainer
ring 64.
It may also be desirable to provide the drill cutter
assembly with means for providing periodic lubrication of the
cutter bearing. This may be conveniently accomplished by
forming the spindle structure 32 shown in Fig. 2 with a lubri-
cant passage 66, the outer extremity of which may be internallythreaded as shown at 68. An externally threaded lubricant fitting
such as a conventional Zerk fitting 70 may be extended through
a recess 72 and may be received within the internally threaded
portion 68 of the lubricant passage. The recess 72 allows the
fitting 70 to be recessed sufficiently to prevent the fitting
from being damaged or worn as drilling operations are conducted.
The space between the spindle and bearing assembly and the
internal wall surfaces of the cavity 56 effectively define a
reservoir 74 that receives a quantity of lubricant. As drilling
operations occur, lubricant will be transferred to tlle bearin~
surfaces 44 and 52.
-14-
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--`` 10~37164
Figs. 4 and 5 are representative of a urther
embodiment of the present invention, whereby the depending leg
structure of the drill body may take similar form as illustrated
in F:igs. 1 and 2, with the exception that an annular seal groove
76 may be provided for containing a sealing element 78 such
as an O-ring. The annular groove 76 will be of larger dimension
as compared to the annular groove 26 in Fig. 2. A spindle
element 80 may be provided that is retained in connection with
the depending leg structure 16 in the same manner as discussed
above in connection with Fig. 2. The spindle 80 111.1~' b c ~oL-mc-l
to define a bearing surface 82 of cylindrical configuration,
which bearing surface may be located between an enlarged head
portion 84 and an intermediate flange portion 86. In this case,
a bearing structure may be provided in the form of a pair of
semi-cylindrical bearing segments 88 each having an exterior
locking groove 90 formed therein. The cutter element 20 will
be of substantially identical configuration as compared to the
cutter shown in Fig. 2 with an annular internal groove 60 formed
therein for registry with the grooves 90 of the bearings seg-
ments 88. As shown in section in Fig. 5, the cutter element
20 will be formed to define a tangential retainer insertion
passage 92 that is oriented in substantially tangential rela-
tionship with the registry grooves 60 ancl 90. ~n e1()~ ted
retainer element 94 may be inserted through the passage 92 into
the annular retainer chamber defined cooperatively by grooves
60 and 90. The retainer element 94 is flexible and capable
of following the annular retainer chamber as it is forced
through the passage 92. The retainer element 94 may be com-
posed of a flexible metal material or, in the alternative, it
may be formed of any other suitable metallic or non-mctallic
material without departing from the spirit and scope of the
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present invention. Afterinsertic)n of tl-e retainer element
the passage 92 may be closed, such as by hardenable plastic
material.
As a further alternative, bearing segments may be
employed such as shown at 88 in Fig. 5 and a retainer ring
element such as the retainer ring shown at 64 in Fig. 2 may
be placed in assembly within the annular groove portion 90.
After this has been done, the cooled bearing and spindle assem-
bly may then be further assembled to a heated cutter element
in the manner discussed above in COIllleCtiOIl Wi ~h l~`.i g~ . ~ a~
3.
It is also considered desirable to provide a drill
body structure that is of low cost nature without any sacrifice
from the standpoint of strength and durability. This feature
may be conveniently accomplished in the manner illus~ra-ted
in Figs. 6 through 8 which show a plurality of body segments
that may be connected in assembly by welding to form the body
structure of a rotary cutter type drill bit. Figs. 6 - 8 each
show drill segments 96, 98 and 100 that are of substan-tially
identical configuration. In fact, each of the drill body
segments shown in Figs. 6, 7 and 8 may be identical and may
be formed by casting or forging as desired. Since the casting
or forging design of each of the body segments is oE simL~le
configuration, the casting or forging costs will be quite low
and yet the body structure that is developed will be of sub-
stantial strength and durability when the body sections are
assembled. As further shown in Figs. 6 - 8, each of the body
sections may be provided with cutter elements 102, 104 and 106
that are of cooperating configuration, allowing the development
of a rock bit structure having optimum boring capability upon
welded assembly of the body segments 96, 98 and 100. The cutter
elements may be rotatably connected to the body structure or
to the body segments as the case may be in the same manner dis-
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- 10~371~4
cussed above in connection with Figs. 2 - 5. Further, if desired,
the cutter elements may be assembled to the body segment struc-
tures prior to welded connection of the body segments, thus
simplifying the assembly procedure for the cutter elements and
further enhancing the low cost nature of the drill bit structure.
The upper threaded extremity of the drill bit body may be formed
by machining after the body segments have been joined.
As shown in Figs. 6 - 9, each of the body segments
may be provided with internal passage surfaces 108, 110 and 112
respectively that cooperate to define a flow passage 114 when
the segments are welded in assembly. Each of these body seg-
ments may further be formed to define segment abutment surfaces
that are oriented at an angular relationship of 120. When
the body segments are assembled, the abutment surfaces will
be in engagement, thus orienting the rotary cutter elements in
proper relationship for optimum cutting capability. E~ch of
the body segments may also be formed to cooperatively define
weld grooves such as shown at 116, 118 and 120 so that simple
linear welds 122, 124 and 126 may be formed to retain the body
segments in assembly to define an integral drill body.
Referring now to Fig. 10 there is shown an alter-
native embodiment of this invention wherein segmented bearings
are employed. Each of the legs 130 of the body of the bit will
be constructed essentially as shown in Figs. 4 and 6 - 9 with
a bore 132 being formed to receive the connecting portion 134
of the spindle 136. The spindle will be formed to define an
enlarged diameter bearing engaging surface 138 and a head por-
tion 140 that defines an annular stop shoulder 142. The seal
groove 144 in this case will be of slightly larger diameter as
compared to seal groove 76 of Fig. 4 and the sealing element 146
will be of correspondingly larger dimension.
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~` 10t371~i4
The cutter element 148 will be formed internally
in such manner as to receive the spindle with circular bearing
surface 150 engaging the planar end surface 152 of the spindle.
The cutter element is also formed internally to receive bearing
segments 154 that may be of semi-circular configuration or, in
the alternative, may be of other partially circular configuration.
The cutter element also defines an internal cavity 156 that is
formed to allow insertion of the bearing segments after the
spindle and cutter have been brought into assen~ly. Il'his feature
allows the cutter, bearing segments and spindle to be secured
in interlocked assembly without requiring a retainer ring such
as shown at 90 in Fig. 4. ~-
To assemble the cutter element to the spindle,
the spindle and cutter will be placed in angulated relation with
the spindle within the cutter and with one bearing segment
positioned within the bearing insertion chamber of the cutter.
Another of the bearing segments will than be inserted into its
proper position relative to the cutter. Upon movement of the
cutter element and spindle to the coaxial relationship thereof
the bearing segment retained within the bearing insertion
chamber will be shifted to its proper bearing relationship with
the spindle. The bearing segments will then be enc~psulated
and the cutter element will be rotatably secured to the spindle.
In view of the foregoing it is clearly apparent
that the present invention provides a rotary drill bit construc-
tion having a body structure of exceptional strength and
durability and yet being of low cost. The drill body segments,
being low cost forged or cast metal structures, may be connected
in assembly by simple and efficient low cost welding procedures
to define an integral body structure of exceptional strength and
durability. The invention also provides for optimum utilization
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10~37164
of materials for the various components of the drill bit
construction to insure optimum drilling capability and excep-
tional service life. Low cost, high strength materials may
be utilized for the spindle and bearing structures and the
cutter elements may be formed of optimum materials for insuring
extended service life. Further, the spindle may be secured
by simple welding procedures to the drill body legs or segmen~s
thereby further simplifying the construction of the drill bit.
Also, the rotary cutter devices may be assembled to body seg-
ments prior to formation of the integral body to further sim-
plify the assembly procedure and pipe threads may be machined
after the body structure has been assembled. The present inven-
tion also promotes utilization of lubrication systems that allow
the drill bit structure to be periodically lubricated to fur-
ther enhance the service life of the bit structure. It is
apparent therefore, that the present invention is one well
adapted to attain all of the objects and features hereinabove
set forth, together with other advantages which will become
obvious and inherent from the description of the apparatus
itself. It will be understood that certain combinations and
subcombinations are of utility and may be employed without
reference to other features and subcombinations. As many
possible embodiments may be made of this invention without
departing from the spirit or scope thereof, it is to be under-
stood that all matters herein set forth or shown in the accom-
panying drawings are to be interpreted as illustrative and not
in a limiting sense.
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