U.S. patent number 3,656,564 [Application Number 05/094,909] was granted by the patent office on 1972-04-18 for apparatus for rotary drilling of wells using casing as the drill pipe.
Invention is credited to Cicero C. Brown.
United States Patent |
3,656,564 |
Brown |
April 18, 1972 |
APPARATUS FOR ROTARY DRILLING OF WELLS USING CASING AS THE DRILL
PIPE
Abstract
A drilling system employing casing as drill pipe and a bit
assembly which is bodily insertible and removable through the
casing and releasably attachable thereto for rotation with the
casing.
Inventors: |
Brown; Cicero C. (Houston,
TX) |
Family
ID: |
22247878 |
Appl.
No.: |
05/094,909 |
Filed: |
December 3, 1970 |
Current U.S.
Class: |
175/228; 175/267;
175/261 |
Current CPC
Class: |
E21B
10/66 (20130101); E21B 10/322 (20130101) |
Current International
Class: |
E21B
10/32 (20060101); E21B 10/00 (20060101); E21B
10/66 (20060101); E21B 10/26 (20060101); E21b
009/26 () |
Field of
Search: |
;175/258,259,260,261,228 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leppink; James A.
Parent Case Text
RELATED APPLICATIONS
This application is a continuation-in-part of my co-pending
applications, Ser. No. 778,509, filed Nov. 25, 1968 now U.S. Pat.
No. 3,552,507; Ser. No. 803,911, filed Mar. 3, 1969 now U.S. Pat.
No. 3,552,508; Ser. No. 857,046, filed Sept. 11, 1969 now U.S. Pat.
No. 3,552,509; and Ser. No. 864,747, filed Oct. 8, 1969 now U.S.
Pat. No. 3,552,510.
Claims
What I claim and desire to secure by Letters Patent is:
1. Apparatus for rotary drilling of wells using casing as the drill
pipe, comprising:
a. a bit assembly bodily insertible and removable through the bore
of a string of casing having a landing shoe on its lower end;
b. cooperating means on the bit assembly and said landing shoe for
securing the bit assembly therein in non-rotative relation to the
casing;
c. said bit assembly comprising:
i. a generally tubular body;
ii. radially movable anchor elements mounted on the body for
releasably anchoring the body to said landing shoe;
iii. a sleeve member coaxially disposed in said body for
reciprocation therein between upper and lower positions;
iv. a latching-collar longitudinally slidably mounted about said
sleeve member cooperating with said anchor elements to respectively
release and actuate the same in response to the movements of said
sleeve member between said positions;
v. a main bit carried by the lower end of said body;
vi. a plurality of angularly spaced underreamers mounted on the
body above said bit for radial movement between extended and
retracted positions relative to said body;
vii. connector means pivotally connecting said sleeve member to
said underreamers reciprocable with said sleeve member between said
positions for respectively retracting and extending said
underreamers; and
viii. releasable means initially securing said sleeve member to
said body in said upper position.
2. Apparatus according to claim 1, wherein said bit section
includes lock means carried by said sleeve member operable in
response to movement of said sleeve member to said lower position
to lock said sleeve member to said body in said lower position.
3. Apparatus according to claim 1 wherein said connector means
includes sleeve valve means opening and closing fluid communication
between the interior of said casing and said main bit.
4. Apparatus according to claim 1 including spring means normally
biasing said latching collar toward the position actuating said
anchor elements.
5. Apparatus according to Claim 1 wherein said cooperating means
includes:
a. a tubular landing shoe secured to the lower end of the casing
string;
b. radial slots in the lower end of said shoe spaced to receive the
underreamers when moved to said extended positions.
6. Apparatus according to claim 1 wherein said underreamers
include:
a. arm members pivotally secured to said body;
b. cutter shafts mounted to the outer ends of said arm members;
c. frusto-conical cutters rotatably mounted on said shafts;
d. means for supplying lubricant between the related surfaces of
said shafts and said cutters; and
e. outwardly opening uni-directional seal means between said
surfaces.
7. In a bit assembly according to claim 1, means for securing said
main bit to said body, comprising:
a. a hollow socket member carried by the lower end of said
body;
b. a plurality of angularly spaced cutter-carrying shanks disposed
about said socket member;
c. cooperating dove-tail spline means slidably connecting said
shanks to said socket members; and
d. means for releasably securing said shanks to said socket
member.
8. In a bit assembly according to claim 7:
a. toothed cutters rotatably supported by the outer ends of said
shanks;
b. a self-contained lubricating system in each of said shanks
operable in response to external fluid pressure to direct lubricant
to the rotary surfaces of their respective cutters.
Description
In the drilling of wells for oil and gas, for example, by the
rotary method, the drilling is conventionally done by the
employment of relatively small diameter string of drill pipe to
which a bit is secured, the entire string being rotated to drill
the bore hole. After a suitable internal has been drilled,
sometimes only a short distance but at other times for the full
depth of the well, casing larger in diameter than the drill pipe
will be run into the bore hole and subsequently cemented to seal
off the formations through which the bore hole extends. This
necessarily involves the series of operations in which the drill
string must be extended as the hole deepens, as by the addition of
sections to the drill pipe, and also the entire drill string must
be withdrawn whenever it becomes necessary to replace the bit and
then re-insert it to resume drilling. Thus making of such so-called
"round trips" are not only time-consuming but also create hazards
of blowouts and other undesirable conditions in the well. After the
appropriate drilling of the hole has been completed, the drill
string must be withdrawn and casing run to the desired depth. This,
too, may present hazards because with the drill string out of the
well, control of the well becomes more difficult.
Heretofore numerous efforts have been made to provide a system
employing the casing itself as the drill pipe in order to overcome
some of the hazards enumerated, as well as time loss. However,
these prior efforts have not proven satisfactory for various
reasons well-known to those skilled in the art.
The present invention, therefore, is directed to an improved
arrangement by which the casing may be employed as the drilling
string and when used in combination with a retractable or removable
bit section will perform all of the functions of drilling and
casing of a well in a sequence of series of operations which
thereby greatly facilitates drilling operations.
In accordance with the present invention a bit assembly is provided
which includes both the primary bit and a plurality of radially
extendible and retractable underreamers, the entire bit assembly
being arranged and constructed to be insertible bodily through the
bore of the casing and moved to the lower end of the casing either
on a wire line tool string or by simply dropping it into the
casing, where, either by gravity alone or supplemented by pumped
fluid pressure, the bit assembly will be forced to the bottom of
the lower end of the casing string, which is provided with a
landing shoe to receive the bit assembly. The bit assembly is
provided with anchor or latch means engageable with appropriate
latch grooves or other anchor-engaging structure in the landing
shoe. The latter, in the illustrative embodiments, includes a
landing shoulder on which the bit assembly is landed and
appropriate spline slots to receive the extended underreamer arms
to lock the bit assembly to the casing against relative rotation
whereby rotation of the casing string will be effective to rotate
the bit for purposes of drilling the well.
The bit assembly also includes connector means pivotally connected
by crank means to the underreamers which will be actuatable from
the upper end of the casing string by a suitable running tool by
mechanical means or by hydrostatic force, as by drilling fluid
circulating through the system, for purpose of extending or
actuating the underreamers so as to enlarge the bore hole drilled
by the pilot bit sufficiently to allow free downward movement of
the casing behind the bit as the hole is being drilled.
Additionally, the bit assembly includes a fluid circulation
passageway controlled by a by-pass valve means which is normally
open to allow by-passing of fluid while the bit section is being
inserted through the casing into the landing shoe or being
withdrawn therefrom but which is closeable in response to the
movement of the connector means to the underreamer-extending
position to direct and confine fluid flow to the bit discharge
passages while drilling. This valve arrangement assures high
velocity wash fluid and minimizes wash fluid requirements.
Novel lock means are provided to lock the underreamers in extended
position contemporaneously with the closing of the by-pass valve
means and additional lock means are provided to actuate and release
the anchor elements employed to anchor the bit assembly to the
landing shoe.
To withdraw the bit assembly a conventional fishing tool or spear
is run into the casing on a wire line and connected to
anchor-releasing elements of the bit assembly, whereby an upward
pull applied to the fishing tool will be effective to retract the
underreamers and release the bit assembly from the landing shoe to
which it has been anchored. The spacing arrangement between the
underreamers and anchor elements is so designed as to assure that
the underreamers are fully retracted before the bit section is
released, thereby avoiding damage to the underreamers which might
otherwise occur if they were not completely retracted when they
pass through the lower end of the landing shoe.
Other and more specific objects and advantages of this invention
will become more readily apparent from the following detailed
description when read in conjunction with the accompanying drawing
which illustrates a useful embodiment and modification thereof in
accordance with the present invention.
In the drawing:
FIG. 1 is a longitudinal, sectional view showing the bit assembly
run on a wire line tool and inserted into the landing shoe
preparatory to anchoring the bit assembly to the landing shoe;
FIG. 2 is a partial view generally similar to FIG. 1 showing an
intermediate stage in the operation of anchoring the bit assembly
to the landing shoe and with the underreamers in their extended
position;
FIG. 3 is a partial view generally similar to FIG. 2 showing the
bit assembly in drilling position with the running tool being
withdrawn from the casing;
FIG. 4 is a view similar to FIG. 3 showing a retrieving tool
inserted in the bit assembly preparatory to withdrawing the latter
from the landing shoe;
FIG. 5 is a view similar to FIG. 4 showing the parts in released
position for withdrawal by the retrieving tool;
FIG. 6 is a cross-sectional view taken on lines 6--6 of FIG. 1;
FIGS. 7 and 8 are cross-sectional views taken on lines 7--7 and
8--8, respectively, of FIG. 2;
FIG. 9 is a cross-sectional view taken on line 9--9 of FIG. 3;
FIGS. 10, 11 and 12 are partial sectional views illustrating
modifications of the pilot bit portion of the bit assembly;
FIG. 13 is a cross-sectional view taken along line 13--13 of FIG.
10;
FIG. 14 is a cross-sectional view taken along line 14--14 of FIG.
12; and
FIG. 15 is a detail of an underreamer cutter seal.
Referring to the drawing, the landing shoe 10 and bit assembly B
comprise the basic drilling structure which is secured to the
casing. Shoe 10 is provided with an internally threaded socket 12
by which it is threadedly secured to the lower end of casing C.
Adjacent its lower end shoe 10 is provided with an internal
shoulder 11 on which the bit assembly will land initially when
lowered through the casing.
Bit assembly B comprises a generally tubular body 16 having a bore
17 and is dimensioned to be freely insertible bodily through the
bore of casing C into the bore of shoe 10. Body 16 is provided
about an intermediate portion thereof with an external shoulder 18
adapted to seat initially on shoulder 11 when the bit assembly is
lowered into the shoe. An annular seal ring 20 is disposed about
the exterior of body 16 above shoulder 18 to seal with the bore
wall of shoe 10.
At a point above seal ring 20, body 16 is enlarged in internal
diameter defining an upwardly facing internal shoulder 19. The
enlarged diameter portion 21 forms a cage which is provided with a
plurality of angularly spaced generally rectangular radial windows
or openings 22 in which are mounted anchor dogs 24 corresponding
generally in shape to openings 22 and adapted when projected
outwardly to be received in an annular anchoring groove 26 formed
in the bore wall of shoe 10. The inner end faces of the anchor dogs
are stepped downwardly to define upwardly facing shoulders 25
intermediate the upper and lower ends of the anchor dogs.
Groove 26 is formed at the upper end of an elongate annular recess
27 into which the anchor dogs are initially projectible before
entering groove 26 as will be described more fully hereinafter. The
anchor dogs are positioned in body 16 so that they will be in
registration with recess 27 and below groove 26 when body 16 is
seated on shoulder 11 (FIG. 1). The upper end of cage 21 is screwed
into a cap ring 28 which overhangs the upper end of the body to
define a downwardly facing annular shoulder 30 spaced from and
opposing shoulder 19.
A setting sleeve 32, having an axial bore 33, is coaxially slidably
disposed in bore 17 and is provided a short distance below its
upper end with an external annular enlargement 31 defining upwardly
facing annular shoulder 34 adapted to abut shoulder 30 in the
running position of the tool (FIG. 1) and a downwardly facing
annular shoulder 35 for purposes to be more fully described
hereinafter.
At a point spaced below enlargement 31 setting sleeve 32 is
provided with a second external enlargement 37 defining upwardly
facing and downwardly facing shoulders 38 and 39, respectively.
A keeper ring or latching collar 36 is slidably mounted about
setting sleeve 32 for longitudinal movement thereon between
enlargements 31 and 37, the ring being shorter in length than the
distance between the enlargements. Keeper ring 36 has a downwardly
and inwardly stepped outer face complementing the stepped inner end
faces of anchor dogs 24 and defining spaced shoulders 40 and 41
successively engageable with the upper inner edges of dogs 24 and
with shoulders 25 on the anchor dogs in the course of projecting
the anchor dogs as seen in FIGS. 1, 2 and 3. Shoulder 41 of the
keeper ring rests on shoulder 38 of enlargement 37 in the running
position of the tool (FIG. 1). A coil spring 42 surrounds sleeve 32
and is mounted in compression between shoulder 30 and the upper end
of keeper ring 36 biasing the latter downwardly. The setting sleeve
is provided wit a downwardly facing internal shoulder 43 which
projects into bore 33 at a point generally opposite enlargement 37
for purposes to be described subsequently.
At a short distance below enlargement 37, sleeve 32 is provided
with a plurality of radial windows or openings 44 in which are
mounted lock dogs 45 which at a certain stage of operation of the
tool, as will be described hereinafter, are adapted to be projected
into an annular lock recess 46 provided in the wall of bore 17.
A lock sleeve 47 having an axial bore 48 is coaxially slidably
disposed in bore 33 of the setting sleeve and is provided at an
intermediate point with an external upwardly facing annular
shoulder 49 adapted to abut shoulder 43 during retraction of the
tool (FIG. 5). Lock sleeve 47 is provided with an external annular
lock recess 50 adjacent its lower end spaced to be in registration
with lock dogs 45 in the running position (FIG. 1) so as to allow
lock dogs 45 to be in retracted position during running of the
tool. Bore 48 of the lock sleeve is provided with an annular recess
48a intermediate its ends which is adapted for engagement by a
retrieving tool as will appear subsequently.
The lower end of body 16 carries a downwardly facing internally
threaded tubular socket 50a adapted to receive the externally
threaded shank 51 of a bit 52 which constitutes the primary or
pilot bit and may be of any conventional design for drilling a bore
hole to any desired nominal diameter determined by the dimensions
of the bit. Between shoulder 18 and socket 50a, body 16 is provided
with a plurality of longitudinally extending radially opening slots
53 in which are mounted underreamers 54 of any suitable and known
design mounted to arms 55. The latter are pivotally mounted on
pivot pins 56 which extend transversely of the respective slots for
enabling the underreamers to be angularly moved so as to be
radially projected and retracted with respect to the slots 53. A
tubular nozzle 57, having a bore 58 is secured to the lower end of
lock sleeve 32 by means of an annular piston head 58a having a
sliding sealed fit in bore 17. Nozzle 57 projects downwardly
centrally of the tool. The lower end of nozzle 57 is provided with
lateral ports 59 to define a sleeve valve which extends through a
coaxial bore 60 in socket 50a fitted with an O-ring seal 61
arranged to control fluid flow from nozzle 57, when nozzle 57 is
moved axially relative to socket 50a, as will be described
subsequently.
Each of the underreamer arms 55 is fixedly connected to an
angularly extending crank arm 62 having its free end secured to a
crosshead pin 63 mounted in a crosshead groove 64 formed in the
exterior of nozzle 57 at a point below piston 58a. With this
arrangement it will be seen that the movement of nozzle 57
downwardly will act through crank arms 62 to rotate the
underreamers outwardly and upwardly while reverse movement of the
nozzle will act to retract the underreamers. The same movement of
nozzle 57 will simultaneously function to open the valve means
formed by sleeve valve ports 59 and the upper end of socket 50a.
The intermediate portion of the latter is conically tapered to form
sloping walls 61b which are provided with a plurality of jet
nozzles 61a positioned to direct a spray of high pressure wash
fluid against the underreamer cutters when the latter are in
extended position (FIG. 2) to clean the surfaces of the cutters.
The lower end of landing shoe 10 is provided with downwardly
tapering spline slots 11a shaped to cooperate with arms 55 to limit
the outward movement of the underreamers to the extent desired and
to form a rotary drive connection between the shoe and the
underreamers.
The device is designed to be run on a suitable running tool,
designated generally by the letter R, which may, in turn, be run on
a conventional sand or wire string, or on a string of tubing P. As
illustrated tool R includes a tubular body 70 connectible at one
end to the running string and having its other end abutting the
upper end of lock sleeve 47. A collet ring 71 is slidably mounted
about body 70 and is split to provide a plurality of spring collet
fingers 72 terminating in enlarged heads 73 which initially are
adapted to be latched in an annular recess 74 provided in the bore
of setting sleeve 32 adjacent its upper end and to be held therein
by the upper end of lock sleeve 47. A spacer ring 75 surrounds
fingers 72 and extends between collet ring 71 and the upper end of
setting sleeve 32. A keeper collar 76 surrounds the abutting end
portion of spacer ring 75 and setting sleeve 32 and is pinned to
spacer ring 75 by means of a shear pin 77. In this position the
lower end of collar 76 bears against the upper end of cap 28 (FIG.
1). Cooperating shoulders 78 and 79 are provided on spacer ring 75
and collar 76 to retain the collar on the ring when shear pin 77
has been broken (FIG. 2) and the running tool is being withdrawn
(FIG. 3). Setting sleeve 32 has an expansible split latch ring 80
mounted in the bore thereof just below recess 74 and lock sleeve 47
is provided with a matching latch recess 81 in its exterior
adjacent its upper end to enable securing lock sleeve 47 to setting
sleeve 32 upon relative downward movement of the lock sleeve as
will be described subsequently.
In operation, the bit section secured to running tool R will be
inserted into the upper end of casing C and will be lowered through
the bore of the casing until the bit section is brought to a stop
by the engagement of shoulder 18 on shoulder 11 in the landing
shoe. At this stage, as the bit section is lowered into place,
sleeve valve 59 will be above seal 61 in the bit socket, permitting
free by-passing of well bore fluids through the bore of bit section
which might otherwise hinder the movement of the bit section
through the casing. The parts of the bit section will be positioned
as illustrated in FIG. 1 in which the setting sleeve is held in its
retracted position by collet fingers 73 and shear pin 77. Anchor
dogs 24 will thus be free to retract, whereby to allow the free
movement of the bit section through the casing and into landing
shoe 10. At the same time, lock dogs 45 will be in their retracted
positions, as seen in FIG. 1.
WIth the bit section thus in place in the landing shoe, downward
jarring force is applied through the running string to break shear
pin 77. Thereupon the downward force will be transmitted to setting
sleeve 32, as well as to lock sleeve 47. The resulting downward
movement of both sleeves will move latches 45 into recess 46 and
latch ring 80 into recess 81, while shoulder 35 will contact the
upper edge of keeper ring 36 to drive anchor dogs 24 into recess
27.
The downward movement of the setting sleeve will also be
transmitted via nozzle 57 through the crosshead pins 63 and crank
arms 62 to underreamer arms 55 to swing the underreamers outwardly
toward their extended positions (FIG. 2).
Now, running tool R may be pulled upwardly while casing C is
rotated and lowered to align slots 11a in the casing shoe with the
underreamer arms to receive the latter and form therewith a rotary
drive connection between casing C and the bit section (FIG. 3).
This additional downward movement of the casing relative to the bit
section will bring anchor recess 26 in registration with anchor
dogs 24 which will then be projected outwardly into the recess by
the pressure of spring 42 acting on keeper ring 36. As a result the
bit section will now be effectively locked to the landing shoe in
position to be rotated by rotation of the casing string.
The downward movement of nozzle 57 in effecting extension of the
underreamers will move ports 59 of the sleeve valve below seal 61
and thereby direct wash fluid into the bit passages as well as to
jets 61a.
With anchor dogs 24 locked into groove 27 and setting sleeve 32 and
lock sleeve 47 in their respective locked positions as seen in FIG.
3, running tool R will be freed for withdrawal from its connection
to the bit section and retrieval from the well.
The underreamers illustrated in FIGS. 1 to 5 employ a novel form of
lubricant seal which has proven very useful in this portion of the
bit structure heretofore described. As illustrated, each
underreamer arm 55 carries a cylindrical shaft 85 on which the
cutter 54 is rotably mounted by means of a central hub 86. A
plurality of roller bearings 87 are appropriately arranged between
hub 86 and shaft 85. A body of lubricant is introduced to the
bearings through a duct 88 extending through the shaft. An
outwardly opening one-way, lip-type seal 89 is mounted about shaft
85 between the inner end of hub 86 and the inner face of arm 55. As
best seen in FIG. 15, seal 89 is mounted in a metal cup 90 which is
dimensioned to provide a small amount of clearance about shaft 85
sufficient to allow the escape of lubricant expanding due to heat
generated in the operation without causing destruction or blowout
of the cutter seals which is a common occurrence in more
conventional cutter designs.
When necessary to withdraw the bit section from the casing in order
to replace or repair the pilot bit, underreamers or any other part
of the bit section, a fishing tool, designated generally by the
letter T, of the form illustrated and described in my co-pending
application, Ser. No. 869,562, filed Oct. 27, 1969, or of any other
generally conventional form, the details of which do not form a
part of this invention, will be run into the casing bore on a wire
line, or tubing string if desired, and will be latched into groove
48a of lock sleeve 47, as seen in FIGS. 4 and 5. On application of
upward pull to the fishing string, the lock sleeve will be drawn
upwardly bringing shoulders 49 and 43 in abutment (FIG. 5) and
placing lock recess 50 in registration with lock dogs 45, freeing
the latter from recess 46. This same upward movement, now
transmitted through abutting shoulders 37 and 46 will raise setting
sleeve 32 a distance to raise keeper ring 36 sufficiently to
release anchor dogs 24 which will thus be free to retract from
anchor groove 26. Additionally, the upward movement of the setting
sleeve will be transmitted to nozzle 57 which will, in turn, raise
sleeve valve 59 above seal 61 opening the by-pass valve to allow
fluid to dump back into the well as the bit section is raised.
Further the upward movement of nozzle 57 will rotate the
underreamers back to their retracted position inside slots 53. The
parts will now be in the same positions as when running into the
casing (FIG. 1) and the entire bit section may now be withdrawn
through the casing.
When drilling is to be resumed, the bit section, with the parts in
the original retracted positions, will be returned through the bore
of the casing to its lodgment in shoe 10, the bit section anchored
and the underreamers extended as described, and drilling will be
resumed.
FIGS. 10 to 14 illustrate several modifications of the bit section,
particularly in the mounting of the pilot bit to the bit body and
in the lubricating systems for the pilot bits and underreamers.
In FIGS. 10 and 13 socket 50a is replaced by an annular plug 150
having a bore 151 closed at its lower end by a wall 152. Three
rotary cones 153 are releasably secured about plug 150 at
120.degree. intervals by means of dovetail shanks 154 which are
arranged to slide into longitudinally extending dovetail slots 155
formed in the exterior of plug 150 and are secured thereto by means
of screws 156. Jets 157 mounted in end wall 152 are arranged to
direct mud flush from nozzle 57 on cones 153.
Cutters 153 are mounted for rotation about shafts 158 integral with
shanks 154. Anti-friction bearings 159 are provided between the
cutters and the shafts and are lubricated through a duct 160
communicating with a lubricant reservoir 161 formed in shank 154
and closed by a sliding seal piston 162 which is exposed to the
pressure of the mud flush in the bore of plug 150 by means of a
duct 163 leading from bore 151 to the interior of reservoir outside
piston 162.
When nozzle 57 is moved downwardly to close sleeve valve 159, fluid
pressure from nozzle 57 will be directed through duct 163 against
piston 162 thereby maintaining pressure on lubricant in reservoir
161 sufficient to continuously force lubricant to the bearing
surfaces. A portion of the fluid will also be discharged through
jets 157 against the cutting faces of cutters 153.
The lubricant system in the underreamers is also modified in that
duct 88 is fed from a reservoir 188 fitted with a sliding seal
piston 189 which is exposed to fluid pressure exteriorly of the bit
section which produces a differential pressure across piston 189
sufficient to feed lubricant slowly from reservoir 188 to the
bearing surfaces of the underreamer.
FIG. 11 modifies the structure of FIG. 10 in that shank 254 which
carries the cutters 253 is made integral with hollow plug 250
carried by the lower end of body 16. Lubricant reservoir 261 is
formed in shank 254 and communicates with duct 260 leading to the
cutter bearings. A differential area piston is mounted in reservoir
261 having its larger diameter section 262 disposed in reservoir
261 and its smaller diameter section 263 exposed to the fluid
pressure in the bore of plug 250.
The lubricating system in the underreamers of this modification is
the same as that in the modification illustrated in FIGS. 10 and
13.
FIGS. 12 and 14 illustrate a further modification of the cutter
mountings of the pilot bit. In this instance the cutters are
carried on shanks 354 which carry transverse dove-tail splines 355
which are received in complementary dove-tail grooves 356 which
extend transversely of a plug 350 otherwise similar to plug 150 of
FIGS. 10 and 13. The shanks are secured to the plugs by means of
screws 357. The lubricating system in this modification is
identical with that shown in FIGS. 10 and 13, as is the lubricating
system for the underreamers.
It will be understood that various changes and modifications may be
made in the details of the illustrative embodiments within the
scope of the appended claims but without departing from the spirit
of the invention.
* * * * *