Note: Descriptions are shown in the official language in which they were submitted.
` ~
METHOD OF MANUFACTURING
LARGE DIAMETER OIL WELL DRILLING BIT
& LARGE DIAMF.TER OIL W:ELL_DRILLING BIT
BACXGROUND OF THE INVENTION
The present invention generally involves oil well
drilling bits, and more particularly discloses the large diameter
drilling bits commonly termed, "top hole" bits used to drill the
very first section of borehole beginning at the ground surface,
and are also used for drilling casing openings. The -top hole bi-ts
10 generally range in size from about 18 inches up to about 28 inches
and are very cumbersome and heavy. Generally, top hole bits
comprise either four-cutter bits commonly called, "cross cutter"
bits, or else they comprise tri-cone rolling cutter bits such as
that disclosed herein. The general method of manufacturing large
15 tri-cone rolling cutter bits is in the segmen-ted arc construction
method. This method utilizes three 120-clegree arcuate lug sec-
tions, each comprising one-third of the drill bit body and an in-
dividual leg portion with a bearing journal thereon. These three
arcuate sections are usually forged and then machined to form the
20 bearing surfaces on the bearing journals and the mating surfaces
~`
along each edge where the three sections are welded together.
Prior to joining the three arcuate sections to form a cylindrical
body, the cutter assembly with bearlngs and retention means must
first be mounted on the inwardly projecting bearing journals be-
cause of the impossibility of so mounting the cutters after thethree arcuate sections have been welded together.
After the bearing assemblies and cutters are mounted
on the machined bearing journals, the three lugs are then placed
in a welding jig and welded to each other to form the cylindrical
bit body. After this welding has occurred a tapered thread is
machined on the upper end of the bit, which tapered threaded end
is commonly referred to as the "pin" end, and the bit is ready
for use. The difficulties with this assembly method in manufac-
turing tophole or large diameter bits is that because of the size
of these bits, minor variations and tolerances in alignments of
the three lug sections results in substantial final errors in the
bit specifications and dimensions. The forged lug sections of
the prior art bits are relatively rouyh and inaccurate and the
machining of the mating surfaces likewise is c~lfficult to control
to close tolerances. When the three lug sections are eventually
welded together to form a single cylindrical structure wit.h cut-
ter assemblies already permanently motmtecl thereon, most often
the results are that the cutters are not only non-concentric about
the rotational axis of the bit, but the cutters also extend dif-
ferent distances downward from the pin end of the bit. Thus,one cutter may extend further downward than the other two and may
provide almost all of the cutting action on the borehole bottom
until that cutter is worn substantially to match the shorter two
cutters. This tends to cause premature failure of either the
3~ bearings or the cutter shell on that one cutting assembly, which
in turn will result in early failure of the bit. Likewise, ra-
dial placement of the lucJs is diffic~lt to control and ma~ resultin the drill bit cutting under gage, which is undesirable because
of the borehole being smaller than necessary and smaller than
specified. Also, if one cutter extends radiall~ further outwar~
than either one or both o~ tl~e other cutters, a resulting effect
could be " tracking" of the cutting teeth on the cutters and even-
tual gyratiOIl or orbiting action of the bit about the rotational
a~is thereby s~stantially eliminating the cutting efficienc~ of
the bit.
l'he present invention elimina-tes these disadvantages
found in the big diameter or top hole bits by providing a struc-
ture that is much more easily assembled and in whicn tolerances
can be closely controlled during assembly of the bit. Further
disclosure is made of a method of assembli:ng the bit to provide
extremely close tolerances in the radial and axial directions of
the cutter assemblies. Also disclosed is 2 method of varying the
offset of the cutter axes by relatively simple and inexpensive
means during construction of the bit. The invention is achieved
by utilizing a cast bit body which is formed in a single section
and which has three platform areas formed tnereon for receiving
three independent cutter assemblies which are then welded to the
cast iron body. Each cutter assembly has a countersunk alignment
point which is engaged by the hydraulic or mechanical alignment
tool which forms a part of this invention. The alignment tool
fixes the cutter assemblies in place on the cast metal body where-
upon they are welded in place to form a highly accurate, closetolerance, large diameter tri-cone drilling bit.
Thus, according to the present invention, there is
provided an oil well drilling bit for drilling large diameter
boreholes which comprises an integrally formed cast metal body
member having a pin end, a central bore passage, and a plurality
of equispaced platform arms formed thereon. The platform arms
-3 ~
s
each have two different planes of machined alignment surfaces
thereon in abutting relationship. A lug assembly is welded
to each of the platform arms and has a lug member at one end and
an inwardly projecting bearing ~ournal at its opposite end
and further has a frustoconical cutter rotatably mounted on the
bearing journal by bearing means. The body member and the lug
members form one of at least two drill bits of significantly
different diameters.
In a further embodiment, the invention contemplates
an oil well tricone rolling cutter drilling bit for drilling
top hole and large diameter boreholes and comprises an
integrally formed cast metal body member having a pin end,
a central bore passage, and three equispaced platform arms
formed thereon. The platform arms each have a plurality of
alignment surface means comprising two different planes for a
lug assembly in abutting relationship while permitting verti-
cal, horizonta:L, and skew adjustment during assembly and
adapted to support a lug assemhly of a size selected from
at least two different sizes. A lug assembly of a size
selected from at least two different sizes are welded to each
of the platform arms and has a lug member with a ley section
at its attachment end and a bearing journal extending
radially inwardly at its opposite end. The journal is
adapted to support a cutter of a size selected from at
least two different sizes, and the lug assembly further has
a frustoconical cutter of a size selected from at leas-t two
different sizes rotatably mounted on the bearing journal by
bearing means. The b~dy member and the lug member form
one of at least two differently sized drilling bits of
significantly different diameters.
~ 3a ~
. . .
The invention also encompasses the novel method of
manufacturing a plurality of sizes of oil well drilling bits and
comprises forming an integral body member having a tapered end
and a plurality of outwardly extending platform arms thereon,
with each of the arms having a plurality of surfaces adapted to
receive and support a cutter-supporting lug member in abutting
relation thereto and permitting adjustable movement of such lug
member in a vertical or horizontal direction during assembly.
Lug members are formed in a plurality of sizes operable to fit
each of the platform arms, with each lug member having an attach-
ment end and, at the opposite end, an inwardly projecting bearing
journal. Rotatable cutter members are formed in a plurality of
sizes and are constructed so that each size lug member fits two
different sizes of the cutter members. A lug member of predeter-
mined size is se:Lected for installation on each of the platformarms, and a cutter member is selected from the different sizes
which fit the selected lug member. The selected cutter members
are rotatably mounted on respective ones of the lug members with
bearing means therebetween, prior to securing the lug members on
the body member. Each of the selected lug members, with cutter
members mounted thereon, is placed in operative engagement with
at least two of the surfaces on respective ones of the platform
arms. Each selected lug member is adjusted to a preselected
position while maintaining operative contact with the platform
arm surfaces. The lug members are clamped in the preselected
position, and are welded to the platform arms while being main-
tained in the preselected position.
BRIEF DESCRIPTION OF THE DRAWINGS
. . . _
Figure 1 is a side elevational view of the present
invention showing the bit body and a typical cutter assembly in
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cross-sectional view Figure 2 is an axlal view of the cast
metal body of the bit prior to the cutter assemblies being joined
thereto. Figure 3 is a partial schematic drawiny taken in a
radially outward direction of one cutter assembly illustrating
its mounting on the cast bi-t body. Figure 4 is a block diagram
illustrating the interchangeability of parts throughout the bit
and the assembly method for obtaining four different bit sizes.
Figure 5 is a schematic axial view of the bit body illustrating
the sweeping pattern of the nozzle system located thereon. Figure
6 is a schematic side view of the bit showing one cutter arm in
place. Figure 7 is a close-up, broken-out view showing the align-
ment method for assembling the bi-t. Figure 8 is a schematic view
of the alignment system for assembling the cutter assemblies on
the bit body.
DESCRIPTION OF ~HE PREFERRED EM3ODIMENTS
_, .
Referring now to the figures, and more particularly
to Figure l, a tri-cone, rolling cutter drill bit according to
the present invention is partially disclosed in cross-sectional
view in Figure 1. Figure 1 illustrates the body and a typical
lug assembly attached to the body. In normal procedure a tri-cone
bit, according to this invention, would comprise a body and three
of the leg assemblies as shown attached to the body in relatively
equidistant relationship around the body; i.e., at approximately
120-degree intervals. In Figure 1, the tri-cone drill bit 10
comprises a single, integrally formed, steel body 11 having a
central bore area 12 and a tapered pin section 13. Cen-tral bore
12 communicates through pin area 13 via pin bore 14. Three outwardly
extending platforms 15 (only one shown) are integrally formed on
body member 11 during the fabrication of the body member. Plat-
form 15 generally comprises a relatively flat, upward-facing, moun-
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ting surface ~6 and a relatively flat, vertical, shoulder ~but-
ment 17 joined with surface 16 to form an L-shaped mountiny plat-
form for the lug assembly 18.
In one partlcular embodiment of the present invention,
the body member 11 was formed in a single operation by means of
casting from suitable steel alloy. By utilizing selective cast-
ing techniques and e~tremely accurate casting, body member 11 can
be obtained having a close-tolerance tapered section 13 and being
close to tolerance on surfaces 16 and 17 of arm 15. In this par-
ticular embodiment, tapered pin 13 was accurate enough to providealignment of the body member for final machining of surfaces 16
and 17 prior to attachment of lug assembly 18 thereto. The ma-
chining of surfaces 16 and 17, because of the accuracy of the cas~
ting techniques, generally nèeds only a minor bit of machine work
to smooth up the area for abutment of leg assembly 18~ Alterna-,
tive to machining surfaces 16 and 17 off of the alignment with
unflnished tapered pin 13 is to machine the final threaded por-
tion on the external surface of pin 13, (which threaded surface
is utilized to interconnect the drill bit with the drill string),
and then threading the tapered end 13 into a female threaded
alignment jig before machining surfaces 16 and 17.
The lug assembly 18 comprises, a unitary lug member
19 which in this embodiment was formed in a forging operation.
Lug 19 comprises leg section 20 having a L-shaped end with hori
25 zontal surface 21 and vertical surface 22. Surfaces 21 and 22
preferably are machined on leg section 20 to match surfaces 16
and 17 and provide proper alignment of leg assembly 18 on member
11~ At the upper end of lug member 19 (as shown in Figure 1),
a compound bearing journal 23 is formed on the lug member during
the forging operation and ls final-machined to provide roller bear-
o~;
ing surfaces 24 and 25. ~lso a ball bearing race 26 is formed
on journal 23 as well. as a thrust bearing recess 27. Alternative-
ly, roller bearlng races 24 and 25 could be replaced with fric-
tion bear;.ng surfaces should the bit manufacturer wish to utilize
5 sleeve-type frlction bearings in place of the roller bearings as
disclosed herein.
A plurality oE roller bearings 28 are located in
roller bearing recess 24 to substantially encircle bearing jour-
nal 2 3 and provide rotatable contact with the cutter mounted there-
10 on. Likewise, a set of smaller roller bearings 29 are locatedi.n roller bearing recess 25. A plurality of ball bearings 30 are
located in ball bearing race 26 to encircle bearing journal 23.
A small, flat, circular thrust disc 31 is located in thrust re-
cess area 27. Thrust disc 31 may be comprised of any suitable
15 bearing material such as copper, steel or any of the softer metals
such as lead, s ilver, indium; or may be formed of any combinatlon
of these elements. Roller bearings 28 and 29 and ball bearings
30 are preferably formed of a hard, tough metal alloy such as steel,
which i.s suitable for receiving high loads without galling or
20 spalling. Such alloys are well known in the art and not disclosed
herein.
,
Each of the three lug members 19 are preferably lo-
cated on platorms 15 of body member 11 and attached thereto
by welding as shown in Figure 1 at 32. Welding is performed
25 along a weld groove 33, which is formed along the outer edge of
leg section 20 around surfaces 21 and 22. The particular weld
configuration may be seen more clearly in Figure 3 where like
numbers represent identical elements.
.. .. .. .. . .... ...... .... . . ........ .. .. .. . .. . . . .
s
Each lug member 19 also has rotatably mounted thereon
a generally frusto-conical cutter 34 having a plurality of cut-
ting elements or teeth 35 protruding outwardly therefrom. In this
particular embodiment the cutter 34 ls formed by casting of a
high-strength, tough, steel alloy and the teeth 35 are integrally
formed thereon. These teeth are generally wide and flat and
represent a general chisel shape. Alternatively, the cutters
may be formed by forging a frusto-conical cutter blank of suffi-
cient size to include the integral teeth. After the forging opera-
tion material is machined away to leave the protruding chisel-shaped
teeth.
The embodiment shown in Figure 1, as mentioned previ-
ously, is a tri-cone bit, although only a single lug assembly
is shown for simplification reasons. The illustration in Figure
1 does show the tooth profile of all three cutters of the bit
super-imposed upon the single cutter 34. The illustration of
cutter 34 is that of the number two cutter on the bit. The teeth
of the number one cutter are shown at 36, and the teeth of the
numb~r three cutter are shown at 37. Thusl while it was not neces-
sary to show all three of the lug assemblies 18 in order to fullydisclose the tri cone bit since each of the cutters 34 have a dif-
ferent tooth arrangement to allow for better bottomhole coverage
and better intermesh of the teeth without interference betweer.
adjacent teeth, the profiles of the three cutters are combined
to illustrate the total bottomhole tooth coverage. Figure 7 bet-
ter illustrates the individual cutter profiles showing the indi-
vidual spacing relationships of the teeth for each cutter.
One particular feature of the present invention is
illustrated in Figure 1 by the lines drawn in phantom thereon.
In the lug member 19, an alternate surface 38 is shown drawn in
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)s
phantom. Likewise, in cutter 34, an alternate ~aye surface 39
is shown in pllantom. These alternate surfaces will be explained
in more detail with reference to the description relating to
Figure 4~ ~
S In addition to the attacllment of lug assembly 18 to
body member 11 on platform 15, the body member has additional
elements as disclosed in Figure 1. A plurality of fluid jetting
nozzles are located in sufficiently sized openings formed through
the central upper porti.on 40 of body member 11 communicating with
central bore 12. ~he nozzles comprise a single center nozzle 41,
a plurality of intermediate nozzles 42, and a plurality of outer
nozzles 43. The angular orientation o~ the intermediate nozzles
42 is shown in relation to a vertical axis Vl drawn ~rough the
center of the nozzle 42. One nozzle in this embodiment was placed
at an angle of five degrees, the second intermediate nozzle was
angled at fifteen degrees, and the thlrd intermediate nozzle was
angled at twenty-five degrees from axis Vl. Likewise, the angu-
lar displacement of the outer nozzles,43 can be shown with res-
pect to a vertical axis V2 drawn through the center of outer noz-
zle 43. In this particular ernbodiment, nozzles 43 are angled at
25 degrees from axi.s V2.
P~eferring now to Figure 2, a top view looking down
the central rotational axis is ill,ustra-ted showing the body mem-
ber 11 prior to assembly of the lug assemblies 18. In Figure 2
the cen-ter nozzle 41, the intermediate nozzles 42 and the outer
nozzles 43 are shown in relationship to each other. The outer
nozzles 43 are located in recessed areas or valleys 44 formed
in body member 11. The angular placement of the intermediate
nozzles 42 is i.ndicated by the phantom lines extending downward
3~ therefrom which illustrate the location of the nozzle bodies
.
i. -8-
)S
inside their openin~s which h~ve been cast or machined into body
member 11. Nozzles 41, 42 and 43 may be retained in me~ber 11
by any of se~eral alternate methods such as threading, press-fitting,
welding and retention by snap rings.
Figure 5 is a schematic diagram showing a top axial
view of body member 11 after the h~draulic nozzle system has been
installed but prior to attachment of the lug assemblies 18. The
schematic diagram of Figure 5 illustrates the spiral or sweep
pattern of the nozzles as installed. The seven nozzles thus
arranged allow the cleaning of different sections of the bit and
the borehole, starting with the center nozzle and moving radially
outward towards the outer nozzles, which are directed to the gage
area being cut in the borehole.
Referring now to Figure 3, a radial view of one lug
member 19 is disclosed welded in place on body member 11. The
cutter 34 has been omitted in order to better illustrate the
method of welding the member l9 to member 11. In this embodiment
a weld channel has been formed by beveling the outer edges of
the lower end 20 of lug member 19 so that weldment may be formed
between leg section 20 and pla-tform 16 and 17. The weldment i5
illustrated in Figure 3 at 32.
Referring now to Figure 7, the three typical cutters
utilized on the bit of this embodiment have been cross-sectioned
and laid out in a profile to illustrate intermesh of the teeth
amongst the set of three cutters for one bit. Likewise, Figure
7 illustrates the placement of the fluidic nozzles with respect
to the cutters to show the flow of drilling fluid therebetween.
It should be noted that because of the three-dimensional aspect
of the cutter placement, the three-dimensional cutter profile in-
dicated in Figure 7 must involve splitting one of the cutters in
half to more realistically de~ine the -three-dimensional relation
ship in a two-dimensional, planar drawiIIg. From Figure 7 it can
be seen that the nozzle system is primarily directed to the in-ter-
mesh areas between the cutters to better sweep cut-tings Erom the
borehole face as they are broken out. It is preferred that no
nozzle be directed against a cutter shell because of the inherent
problems arising from fluid erosion when the nozzles are directed
against the cutter bodies.
Figures 6 and 8 illustrate in schematic diagram the
system for assembling the lug assemblies on the body member. The
system primarily consists of a relatively large, flat base plate
45, having three interspaced sliding aligriment arms 46 located
thereon, which alignment arms are arranged to be brought into
contact with the radially outward portion of leg section 20.
The alignment arms 46 are spaced at intervals of 120 degrees
around plate 45 from each other when ~he embodiment of the inven-
tion is that of a trl-cone bit. Base plate 45 has a tapered open-
20 ing 47 for receiving tapered pin section 13 of body member 11.
Pin opening 47 may be either internally threaded to match the ex-,
ternal threaded portion of pin 13 or may be smooth-walled to re-
ceive either the threaded pin end 13 or could be used to receive
pin end 13 prior to the threads having been machined thereon.
In either instance, opening 47 preferably is dimensioned to snugly
fit pin end 13 and secure body member 11 in a rigid, stationary
position to accurately locate lug assemblies 18 thereon. The align-
ment arms ~6 are relatively rigid and preferably allowed movement
only in a radially outward and inward direction. Movement of arms
46 can be controlled by means well known in the art such as elec-
trical, hydraulic, mechanical or pneumatic.
--10--
Figure 6 is a schematic illustration of a portion of
Figure 8 broken out and enlarged to better illustrate the align-
ment technique for aligning lug member 19 on platform 15. The
end of each alignment arm ~6 is formed with a particular geomet-
ric configuration such as a right circular cone 47 e~tending ra-
dially inward towards the lug member 19. Likewise, a complemen-
tary indentation ~8 is formed in lug member 19 to receive the geo-
metric end 47 of arm 46. When such configuration as a conical
end 47 and a conical indentation 48 are used, it can be seen that
movement radially inward by arm 46 when it contacts the indenta-
tion 48 will locate member 19 in an identical position each andevery time. Should a misalignment occur, the force of arm 46 mov-
ing inward into opening 48 will move member l9 until the geomet-
ric end 47 is completely embedded in socket 48, thereby providing
proper alignment. ~t that time should there be spacing between
lug member l9 and platform 15, a requisite number of metal shim
plates 49 may be inserted prior to ~elding of lug member l9 on
platform 150 It should be noted that although Figure 8 illustrates
a single lug member being attached to the body member, all three
such members may be attached simultaneously for optimum alignment
of the lug assemblies. It should also be pointed Ollt that the
three lug assemblies 18 are completely assembled, including all
bearings, seals and cutters, prior to attachment to body member
ll because of the impossibility of attaching the cutters after
the lugs l9 have been welded to the bodyO The lug assemblies 18
have been simpli~ied in Figure 8 to more cl~arly illustrate the
method o assembly, but in the preferred embodiment, the three
lug assemblies 18 in complete assembly form are attached to body
member 11 simultaneously by the use of welding techniques in con~
junction with alignment system 45.
Figure 4 illustrates a schematic block diagram show-
ing the versatility of the present invention in forming different
. . .
sizes of bits using interchangeability of various components~
~or instance in ~his particular embodiment, a single body casting
ll can be utilized in forming four different diameter bits. This
body casting can be used in a 20-inch bit, 22-inch bit, 24~inch
bit and 26-inch bit. In order to manufacture these four sizes
of bits, two different lug members 19 are utilized -- l9a and l9b.
Lug member l9a is utilized to form a 20-inch bit and a 22-inch
bit. These two bits utilize -the same body casting and the same
lug, but use different size cutters 34a and 34aa. Likewise, the
two larger bits r the 24-inch diameter and the 26-inch diameter,
each use the same body casting ll and the same lug l9b, but like-
wise use two different cutters 34b and 34bb. Thus, the manufac-
ture of four different size bits ranging from 20-inch diameter
to 26-inch diameter requires only a single type body member, two
different types of lugs and four different size cutters.
In addition to this tremendous fle~ibility and effi-
ciency in assembly, further optimum savings can be obtained by
utilizing~lug members 19a and l9b, which are substantially iden-
tical except in on]y a small particular area. For instance, re-
ferring back to Figure 1, the lug member l9a of Figure 4 can beseen in Figure l is defined by the phantom line 38. The larger
lug member 19~ is defined by the outer line of member 19 rather
than the phantom line 38. Similarly, optimum efficiency in manu-
facture of cutters 34 can be achieved by casting the individual
cutters and utilizing casting shells that are identical in many
respects.` The smaller cutters 34a and 34aa are defined by the
phantom lines 39 whereas the larger cutters 34b and 34bb are de-
fined by the outer lines along the gage surface rather than thephantom lines 39. Thus, by merely changing the gage portion of
the cutters at 39 and by changing the radial outward shoulder areas
at 38 of the lugs and also by the use of a single body member 11,
S
four different 5ize bits can ~e manufactured basically using sub-
stantially the same amount of tooling and casting equipment as
would normally be required in a single diameter bit.
With the great advancements in casting techniques re-
cognized today, such as the investment casting and centrifugal
casting methods, the cutters 34 having the integrally formed teeth
provide a cutter of identical quality to the conventional method
of machining the cutters. Because of the accuracy of modern cast-
in~ techniques, the cutter dimensions and the teeth configurati~ns
are acceptable in the casting and need no machining except in the
minor bearing areas internally in the cutter. Preferably, the
lug members 19 are forged and machined in the bearing areas be
cause of the strength requirements and the simplicity in forging
this relatively uncomplicated shape. The body members 11 prefer-
ably are cast in a single operation to form a single, integral
body section which ls relatively inexpensive to cast and in which
the final casting has substantially all of the external dimensions
within acceptable tolerances. l'he only remaining machining is
the shoulder areas lS and in some cases the nozzle bores for the
20 fluidic nozzles 41, 42 and 43. In addition the threaded pin end
13 is machined after the casting. The casting of body member 11
utilizing the known casting techniques is accurAte enough that
the alignment system 45 can be utilized with the cast pin end 13
even prior to machining of the pin threads thereon.
SU~ARY OF TEIE INVENTION
The present invention is directed to a multi-cutter,
rolling cone drill bit for use in large diameter boreholes, particu-
larly the initial borehole at the top of the drilling operation.
mhese bits are generally of the three-cone configuration and are
termed, "top hole" bits. The present invention discloses a top
hole bit of extremely accurate external dimensions and a method
of manufactu~ing this bit utili~ing fle~ibility in part selection
and interchangeability of parts to provide various sizes of bits
from con~on components. The present invention utilizes an in-te-
gral cast body rather than the three arcuate segments of the prior
art bits. The invention utilizes two sets of forged lugs to pro-
vide four sizes of bits.
Likewise, this invention utilizes cast metal cutters10 rather than machined cutters with four different cutters for the
four bit sizes. The two smaller size cutters differ only in the
small gage area along the large part of the cone. Also, the two
larger diameter bits utilize two different cutter configurations
which differ from each other only in the small area added along
the gage of the cutter. In addition to these features, the pre-
sent invention discloses a spiral sweep nozzle arrangement uti-
lizing seven nozzles in a fluidic system which is particularly
advantageous in cleaning the entire bottom of the borehole as itis being drilled.
Furthermore, an additional feature and advantage of
this invention i5 the ease and accuracy of the as~embly method.
The body member is securely attached in a base plate or table to
which are slidably attached three alignment armC having geomet-
rical alignment ends for matching engagement in the lug assemblies.
It should be noted here that in addition to providing close align-
ment of the lug assemblies, an easy method of introducing skewed
axes into these bits reveals itself with the present alignment
system. For instance, if a particular skew dimension in the jour-
nal axis is desired, the correlative amount of offset in the align-
ment indentation 48 can be introduced into each of the lugs such
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.. .. . . . . ....
S
that the alignment arm ~6 properly positions each luy to obtain
the desired a~is skew. Thus, the bi-t axis s]~ew can-be controlled
very closely by simply relocating the aliynment indentations 48
in each of the lugs. Likewise, proper axial alignment, i.e., height
of the cutters above the body men~er, is easily obtained by the
alignment system 46 in conjunction wi-th -thin metal shims ~g.
In addition to this extremely close control over the
height measurements of the three cutter cones, which height con-
trol allows a proper weight and wear distribution on each of the
three cones, the radial measurements of the three cutters can be
held to close tolerances by the same shi~ning methods along sur-
face 17. Thus, the cutters, b~ proper shimming on surfaces 16
and 17, will end up properly balanced with respect to load and
each sharing proportionately in the cutting of the gage diameter.
This greatly reduces rapid wear and failure of the cutter assem-
blies and provides proper gage cutting action. Thus, it can be
seen that the present invention involves large bits and their meth-
od of manufacture, which bits offer advanced techniques for ease
of assembly and for close control of critical tolerances.
Although certain preferre~ embodiments of the inven-
tion have been herein descrihed in order to provide an understand-
ing of the general principles of the invention, it will be appre-
ciated that various changes and innovations can be effected in
the described large diameter, tri-cone drilling bit without de-
parting from these principles. For example, it is obvious that
one could alter the number of lug assemblies provided in the bit
to include more than the three assemblies illustrated. Also, rath-
er than utilizing cut-ters which are formed by casting, one could
utilize machined cutters instead. The invention, therefore, is
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declared to cover all chan~es and modifications of a specific ex-
ample herein disclosed for purposes of illustration which do not
constitute departures from the spirit and scope of the inventi.on.
: -16-
