U.S. patent number 3,692,126 [Application Number 05/110,870] was granted by the patent office on 1972-09-19 for retractable drill bit apparatus.
Invention is credited to Frank C. Rushing, Albert B. Simon.
United States Patent |
3,692,126 |
Rushing , et al. |
September 19, 1972 |
RETRACTABLE DRILL BIT APPARATUS
Abstract
Apparatus including a retractable annular drill bit formed by
tightly interfitting groups of bi-directionally tapered sectors
normally clamped in the lower end of a drill sub by an axially
movable inner clamping sleeve. The sleeve is actuable by hammer
blows from a releasable cable-operated elevator and hammer tool to
effect expansion and contraction of such sector groups sequentially
into and sequentially out of the drill sub interior for insertion
and removal via the interior of the drill string to which the drill
sub is attached. Axially movable flexible translational support
stem assemblies for the bit sector groups, in affiliation with a
system of radially fixed stop shoulders, cooperate with axial
movement of the clamping sleeve to enable it to effect such sector
group expansion and contraction. A separately removable core barrel
accepts the core sample made by the bit.
Inventors: |
Rushing; Frank C. (Ellicott
City, MD), Simon; Albert B. (Ellicott City, MD) |
Family
ID: |
22335357 |
Appl.
No.: |
05/110,870 |
Filed: |
January 29, 1971 |
Current U.S.
Class: |
175/259;
175/246 |
Current CPC
Class: |
E21B
10/66 (20130101) |
Current International
Class: |
E21B
10/00 (20060101); E21B 10/66 (20060101); E21b
009/26 () |
Field of
Search: |
;175/246,249,257-261 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Brown; David H.
Claims
We claim:
1. A retractable bit assembly comprising,
a tubular drill sub for mounting on the lower end of a drill
string,
an annular drill bit assembly at the bottom of said drill sub
formed by tightly interfitting groups of bi-directionally tapered
sectors having upper shank portions forming a divided mounting boss
extending upwardly into the lower end of said drill sub,
a clamping sleeve disposed in said drill sub in extension into said
mounting boss in tight slidable fit therewith,
flexible translational support stem assemblies attached to the bit
sector groups and extending upward therefrom around said clamping
sleeve, and
radially fixed stop shoulder means affiliated with said drill sub,
said clamping sleeve, and said support stem assemblies, cooperable
with axial movement of said clamping sleeve to effect sequential
contraction and expansion of said bit sector groups to and from
said annular bit assembly.
2. The retractable bit assembly of claim 1, including in
combination therewith, a core barrel removably affiliated therewith
to receive a formation core bored by said annular drill bit
assembly.
3. A retractable drill bit assembly comprising,
a tubular drill sub for mounting on the lower end of a drill
string,
said drill sub having a downwardly flaring tapered annular shoulder
at its lowermost end and an inwardly projecting annular stop
shoulder disposed above such lowermost end;
plural tightly interfitting groups of drill bit sectors forming a
continuous divided annular array in assembled position on the
lowermost end of said drill sub,
each of said drill bit sectors having an outer segmented annular
shoulder in engagement with respective portions of said downwardly
flaring tapered annular stop shoulder at the lowermost end of said
drill sub,
the bit sectors of the several groups being tapered lengthwise and
widthwise to permit sequential expansion and contraction of such
groups to and from said annular array by simultaneous axialwise and
radialwise movement thereof, and
each of said bit sectors having corresponding bi-directionally
tapered shank portions extending vertically upward which form a
continuous divided mounting boss configuration coaxial with said
annular array;
a clamping sleeve disposed in said drill sub in tight-fitting
disposition within said divided mounting boss thereby forced
outwardly against an inner cylindrical wall of said drill sub
disposed beneath its aforesaid inwardly projecting annular stop
shoulder,
said clamping sleeve having a thick-walled upper end that affords
an elongated annular clearance space therebelow between its outer
cylindrical surface and the inner cylindrical surface of said drill
sub,
said thick-walled upper end of said clamping sleeve being adapted
to receive a cable-operated releasable elevator-and-hammer tool for
imparting suspension forces and bi-directional vertical percussive
blows to such upper end, and
said clamping sleeve having a plurality of combined longitudinal
stop and circumferential spacer tabs extending radially outward
therefrom near the bottom of said sleeve in abutting engagement
with the aforesaid annular stop shoulder within said drill sub;
a plurality of vertically extending translational supports stems
disposed in the aforesaid annular clearance space in
circumferentially spaced-apart array between the aforesaid
longitudinal stop and circumferential spacer tabs on said clamping
sleeve,
said translational support stems being connected at their lower
ends to respective shank portions of said bit sectors and being
relatively rigid longitudinally for delivery of longitudinal thrust
and pull forced to such bit sectors during their assembly and
disassembly to and from the aforesaid annular array, while also
being flexural to permit radial movement of such bit sectors during
such assembly and disassembly,
said translational support stems consisting of stem groups, equal
in number to the number of bit sector groups,
the stems of each group being equal and interconnected at their
upper ends by a respective lift ring in close sliding fit with the
outer surface of said clamping sleeve,
the stems of the several stem groups being of sufficiently
different length to permit sequential radial contraction of the bit
sector groups from the aforesaid annular array to different
vertical positions by progressive upward movement of said
longitudinal stop and circumferential spacer tabs sequentially into
displacing abutment with the several lift rings;
and a plurality of vertically extending longitudinally rigid stop
means attached at their upper ends to the several lift rings,
respectively, and in abutment at their lower ends with the
aforesaid annular stop shoulder in said drill sub.
4. The retractable drill bit assembly of claim 1, wherein,
said clamping sleeve is adapted for releasable connection with said
elevator-and-hammer tool by inclusion of an upwardly flaring
annular groove in its inner surface near its upper end, and
said elevator-and-hammer tool comprises pivotal latching fingers
for end engagement with said annular groove,
a lower abutment member for engagement with the upper end of said
clamping sleeve,
a vertical guide member attached to said flange and having an upper
abutment member disposed above said lower abutment member,
a weight member vertically movable on said guide member to strike
hammer blows on such upper and lower abutment members selectively,
and
cable means for effecting raising and lowering of said tool and
vertical actuation of said weight member.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to core drilling apparatus, and more
particularly to such apparatus as includes a retractable core bit
capable of being removed and inserted via the interior of a drill
string to avoid withdrawal of such string from the drilled hole for
replacement of drilled bits.
2. Description of the Prior Art
The following U.S. patents were received as a result of a
preliminary search: U.S. Pat. Nos. 3,437,159; 2,982,366; 2,979,144;
2,842,343; 2,764,388; 2,345,699; and 2,068,704.
Each of the above prior art patents discloses some form of
retractable bit assembly having a circular array of cutter elements
at the ends of flexible arms that permit their being displaced
radially inward for transport via the interior of a drill string,
and radially outward to a working position on a drill sub or collar
at the bottom of such drill string. In all of these assemblies, the
cutter elements are expanded radially outward toward their working
positions on the drill sub or collar by the spreading action of an
end tapered member actuated downwardly by gravity under control of
a lowering cable and tool which may include an auxiliary weight to
assist such gravity actuation.
A number of the assemblies in their collapsed state, store the
several retractable cutter elements at an equal number of different
vertical locations to and from which the elements are moved
sequentially during contracting and expanding the bit. In the
remaining assemblies, all of the cutter elements are expanded and
contracted simultaneously. The foregoing sequential-actuation
arrangements are characterized by a high degree of complexity
involving a system of spring biased dogs, slots, longitudinal guide
grooves, annular dog-accommodating grooves, conns, etc.; and the
foregoing simultaneous-actuation arrangements sacrifice cutter
surface area in order to enable sufficient contraction of the total
cutter element array to pass simultaneously into the drill sub.
SUMMARY OF THE INVENTION
The present invention:
In providing a core bit formed as a complete annulus of
interfitting sectors, enables mutual support of the bit sectors
circumferentially, rather than relying on special grooved
configurations in the drill sub as heretofore, and affords
opportunity for a greater cutting area of the bit;
In providing an arrangement whereby the sectors making up such
complete interfitting annular bit are raised and lowered in two or
more groups, the vertical space occupied by the bit apparatus when
in its fully retracted state is minimized;
In providing an arrangement wherein the bit sectors are tapered
both lengthwise as well as widthwise to enable those of a first
group to slide between those of a second group while moving
longitudinally, enables the two groups to be actuated positively
with percussive blows to and from their expanded interfitting
working positions in the bit annulus;
In providing a releasable cable-operated tool for effecting the
hammer-blow assembly and disassembly of the retractable bit, the
positive actuation is afforded by cable manipulation from the top
of the bore hole;
By provision of an inner clamping sleeve on which the bit sector
groups are slidably mounted during transport while retracted, and
which tightly clamps them in position when expanded in working
position, a core barrel for receipt of the core sample bored by the
bit is enabled to be raised and lowered through the drill stem
without disturbing the bit, in contrast to certain of the prior art
arrangements where the core barrel serves such functions and the
bit is retracted and expanded each time the core barrel is raised
and lowered; and
By provision of a relatively simple arrangement of flexible support
stem assemblies for the bit sector groups, in affiliation with a
system of radially fixed stop shoulders, cooperation with the
clamping sleeve is afforded whereby the sequential expansion and
contraction of such sector groups into and out of the drill sub by
the hammer blow actuation is afforded in a positive manner, rather
than in a negative manner of certain of the prior art arrangements
where reliance is placed on spring-biased dogs dropping into
openings, which may be subject to plugging with drill cuttings, to
accomplish sequential bit sector positioning.
Other features and advantages of the present invention will become
apparent from the following detailed description when taken in
connection with accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an elevation view, partly in outline and partly in
section, showing an exemplified embodiment of the retractable core
drill bit apparatus of the present invention, including a
cable-operated elevator-and-hammer tool, in place in a drill pipe
sub;
FIG. 2 is a perspective view in outline, showing the retractable
core drill bit and elevator-and-hammer tool of FIG. 1 as they
appear when the bit is contracted and removed from the interior of
the drill pipe;
FIGS. 3 and 4 are segmental section views of a portion of the
retractable core drill bit of FIG. 1, showing relationships between
a bit sector and a stop shoulder in the drill sub during different
stages of assembly of the bit;
FIG. 5 is a segmental view of an alternate configuration of the
drill sub shoulder shown in FIGS. 3 and 4;
FIG. 6 is an elevation view, in cross section, showing the
retractable core drill bit apparatus of FIG. 1 as assembled on the
drill pipe sub, but with the elevator-and-hammer tool of FIG. 1
withdrawn, and showing one suitable arrangement for location of a
core barrel atop the clamping sleeve of such apparatus;
FIG. 7 is a bottom view in outline, showing an exemplification of
the annular core drill bit of the present invention as composed of
two interfitting groups of bit sectors;
FIG. 8 is a vertical elevation view, partly in outline and partly
in section, showing an alternate construction of the
elevator-and-hammer tool of the present invention, which enables
automatic release of such tool upon completion of bit assembly;
FIG. 9 is a section view taken along the line IX--IX in FIG. 8;
and,
FIG. 10 is an elevation view, partly in outline and partly in
section, showing an alternate arrangement and construction of the
core drill bit for accommodating the core barrel within the
clamping sleeve of the bit apparatus, rather than atop such sleeve
as in FIG. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring particularly to FIGS. 1, 6 and 7 in the drawings, in its
assembled state, the exemplified core drill bit 12 of the present
invention is in the form of a ring composed of two interleaved
groups U and L of tightly interfitting bi-directionally tapered bit
sectors 14 having mutually aligned upwardly contracting segmented
annular shoulders 15 at their upper and outer portions which are
tightly squeezed by the lower end of a central clamping sleeve 18
against a correspondingly tapered downwardly flaring annular
shoulder 16 of a cylindrical drill sub 17. Upwardly extending
bi-directionally tapered shank portions 20 of each of the bit
sectors 14 collectively form a continuous segmented tightly fitting
hollow cylindrical integral portion of the annular ring array 12 of
bit sectors 14, which portion is also tightly clamped radially
between the outer surface of the central clamping sleeve 18 and the
inner cylindrical surface of the drill sub 17.
The inner and outer cylindrical surfaces, as well as the bottom
annular surface of the drill bit 12 is studded with the usual
cutting elements 22, such as diamonds, so that as such bit is
rotated by the drill sub 17 via the drill pipe (not shown), a
cylindrical core (not shown) is bored in the subsurface formation
and travels upwardly through the center of such bit into the
interior of the clamping sleeve 18 to be received and retained by a
core barrel 24, either located with its receiving end atop such
clamping sleeve 18 as shown in FIG. 6, or disposed within such
sleeve 18 with its receiving end immediately atop the annular bit
12. The inner diameter of the annular bit 12, will be, as shown, of
such size as to assure that the core diameter is accommodated by
the interior of the clamping sleeve 18 and/or the core barrel 24,
in the two cases.
The core barrel may take the usual form as including, FIG. 6, an
outer shell 26 rotatable in unison with the drill sub 17 and an
inner shell 28 suitably mounted by bearing means (not shown) to
remain non-rotationally disposed within such outer shell, with a
fingered core-catcher 30 disposed at its lower core-accepting end.
By use of the usual cable-operated core elevator (not shown) the
core barrel 24 may be raised and lowered into and out of the drill
pipe or casing string (not shown) for recovering the core, without
disturbing the drill bit 12 at the bottom of drill sub 17.
The usual chip release grooves (not shown) may be provided the bit
sectors 14 to permit the cuttings to pass radially outward to the
bit exterior for removal, as by liquid or pneumatic flushing, and
the usual liquid circulation passages (not shown) also may be
provided such bit sectors for communication to the inner regions of
such chip release grooves.
In retraction of the bit 12 from its working position at the bottom
of the drill sub 17 as shown in FIGS. 1, 6, 7, and 10, after cable
removal of the core barrel 24, FIGS. 6 and 10, an
elevator-and-hammer tool 32, FIG. 1, is lowered by a cable 33
downwardly through the drill pipe or casing (not shown) and into
the drill sub 17, while they remain stationary in the formation
hole made by the core bit 12. A lower latching end of the tool 32
enters the upper end of the clamping sleeve 18 until its downward
movement is arrested by engagement of a stop flange 34 atop such
latching end with the top of the clamping sleeve, whereupon,
continued lowering of the cable 33 permits a pair of vertical
compression springs 36 reacting against the bottom of flange 34 to
lower a pair of latch-retraction arms 38 away from the under side
of a pair of pivotally mounted latching fingers 40 while
simultaneously lowering a pair of latch-effectuation arms 42 into
actuating contact with the upper side of such fingers 40 to cause
same to flare outwardly into nested disposition at their upper ends
in a tapered annular groove 44 in the inner wall of the clamping
sleeve 18 near its upper end. The upper end of the groove 44 forms
an annular shoulder 46 for abutting engagement by the upper ends of
latching fingers 40. Relatively strong pins 48 pivotally connect
the lower ends of latching fingers 40 to the flange 34 via parallel
plates 50 and 51 attached to and depending therefrom. In an actual
construction, duplicate latching fingers 40, retraction arms 38,
effectuation arms 42, springs 36, and plates 50 and 51 are arranged
in extension at right angles to those shown in FIG. 1.
Once having thus introduced the lower latching end of the
elevator-and-hammer tool 32 to the upper end of the clamping sleeve
18, the cable 33 is allowed to remain relaxed, while a pair of
hammer-blow-actuation cables 53 are periodically lifted from atop
the drill or casing string (not shown) to intermittently raise an
annular weight member 54, weighing about 5 pounds in one particular
actual construction, a considerable distance, about 2 feet in such
construction, to cause such member 54 to repeatedly strike the
under-side of an annular flange 56 at the upper end of a hollow rod
58 attached to and extending centrally upward from the flange 34;
cable 33 extending downwardly through such hollow rod 58, and
weight member 54 encircling it for slidable guidance.
It should be understood that between each successive raising of the
weight member 54 into striking engagement with the stop flange 56,
there will be a corresponding lowering, but at a slower rate aimed
at preventing any significant downward blows of such member 54
against the top of the flange 34 at this time.
The foregoing upward blows dealt repeatedly against the under
surface of the stop flange 56, are transmitted to the clamping
sleeve 18 via the hollow rod 58, flange 34, depending plates 50 and
51, pins 48, the latching fingers 40, and the annular shoulder 46
which becomes repeatedly engaged by the upper ends of such
fingers.
Such repeated upward blows thus transmitted to the clamping sleeve
18, forces such sleeve upwardly from its clamping position within
the bit sectors 14 and their shanks 20 to a raised position where
its lower end is disposed at the dot-and-dash line 62 in FIG. 1,
whereupon a plurality of circumferentially spaced-apart outwardly
projecting rectangular stop tabs 64, FIGS. 1 and 2, comes into
abutment with the under side of a lift ring 66 encircling such
sleeve 18, from which depend a plurality of circumferentially
spaced-apart flexible stems 67 extending downwardly into attachment
with inner recessed regions of the shanks 20 of bit sectors 14
forming the upper group U of the assembled bit 12.
Continued delivery of upwardly delivered percussive forces to the
clamping sleeve 18, will be experienced by its stop tabs 64, the
lifting ring 66, stems 67, shanks 20 and bit sectors 14 of group U.
Due to the bi-directional taper of the bit sectors 14, and the
slope of tapered shoulder 16 at the bottom of drill sub 17, such
forces will cause progressive inward and upward dislodgement of
such sectors of group U from their tight-fitting positions between
those of group L, as such dislodgement permits of continued
progressive upward movement of the clamping sleeve 17 while tabs 14
carry the contracted array of bit sectors 14 of group U along with
it via ring 66 and the stems 67. Once such bit sectors of group U
are thus percussively broken free of the annular assembled
formation between the group L bit sectors, continued percussion
blows may not be necessary and a steady pull on the cables 53 while
the weight member 54 is held against stop flange 56 may
suffice.
As the lifting ring 66 is carried upwardly by the stop tabs 64 on
the clamping sleeve, which results in raising of the radially
contracted array of group U bit sectors, such ring 66 comes into
contact with a lift ring 70 for the bit sector group L which is
relatively easily radially contracted and carried upwardly through
the interior of the drill sub 17 in disposition beneath contracted
bit sector group U, via respective support stems 71 extending
downwardly from such ring 70, through accommodating openings in the
lift ring 66, to the shanks 20 of the bit sectors of such upper
group. In the case of both groups, their radially inward contracted
positions can be maintained by an inward flexural bias imparted to
the stems 67 and 71, although, even if outwardly biased, or without
any significant bending bias, they will remain compacted by the
inner cylindrical surface of the drill sub 17 and the interior of
the drill or casing string (not shown) enroute to the surface for
removal of the collapsed bit for inspection and/or replacement of
the dulled bit.
During run-in of a replacement bit, a collapsed bit assemblage as
shown in FIG. 2, with the upper group of bit sectors U contracted
inwardly between the support stems 71 for the lower group of bit
sectors L which are also contracted inwardly and disposed beneath
sectors U, is introduced into the top of the drill or casing string
(not shown) and lowered via the cables 53 and the
elevator-and-hammer tool 32, which is held suspended via the weight
member 54 in supporting engagement with the stop flange 56 (FIGS. 1
and 2) and which in turn supports the collapsed bit assemblage by
way of the hollow rod 58, the flange 34, plates 50 and 51, the pins
48, the latching fingers 40, and the tapered annular shoulder 46 in
the clamping sleeve 18 of such collapsed bit assemblage.
During such lowering of the tool 32 and depending collapsed bit
assemblage, the rings 66 and 70 will be maintained adjacent to the
stop tabs 64 on the clamping sleeve, as shown in FIG. 2, by virtue
of a friction fit between such rings and sleeve, while the width of
such tabs 64 maintains circumferentially spaced-apart alignment
between the stems 67 and the stems 71, hence between the upper bit
sectors U and the lower bit sectors L. Simultaneously, cable 33 is
played out, but maintained slack.
Continued lowering in suspension by cables 53 ultimately results in
outwardly projecting stop tabs 75 near the lower ends of the stems
71 and/or non-bending divided portions thereof, FIGS. 1 and 2, come
into abutting engagement with an annular stop shoulder 77
projecting inwardly from the inner wall of the drill sub 17 near
its bottom open end; the lower bit sectors U, including their upper
shank portions 20, having first moved down past such shoulder in
their inwardly cocked attitude, as indicated in FIGS. 3 and 4.
Following such abutment of stop tabs 75 of stems 71 with the drill
sub shoulder 77, the lower bit sectors L, their stems 71, and their
ring 70 are thereby arrested against further downward movement, and
continued lowering of the clamping sleeve 18 (which at this and
subsequent stages can be assured by alternate gentle raises and
rapid drops of the cables 53 to cause the weight member 54 to
deliver downward hammer blows to the flange 34 and thereby the top
of sleeve 18) results in sliding movement of such sleeve through
the ring 70 while the upper bit sectors U, accommodated by
longitudinal tapers of both bit sector groups, are carried by
friction drag of the ring 70 on sleeve 18, past the drill sub
shoulder 77 and between the lower bit sectors L which thereby
become displaced radially outward toward their ultimated desired
seated position against the tapered shoulder 16 on the drill sub
bottom. During the final stages of such wedging movement of the
upper bit sectors U between the lower bit sectors L, as such
wedging action becomes tighter, stop tabs 80 on or near the lower
ends of stems 67 and/or non-bending divided portions thereof will
have come into abutment with the drill sub shoulder 77, and
continued downwardly hammered movement of the clamping sleeve 18
forces such sleeve downwardly through both rings 70 and 66, (now
spaced apart vertically as shown in FIG. 1) and through the
edge-abutting shank portions 20 of the bit sectors 14 until the
stop tabs 64 on such sleeve also reaches the drill sub shoulder 77,
whereupon the assembly of the bit 12 is thus completed.
At this time, manipulation of the cables 53 are terminated, and a
pull is exerted on the cable 33, FIGS. 1 and 2, to raise the
latch-effectuation arms 42 and the latch-retraction arms 38, via a
common support member 82 to which such cable is anchored, against
the bias force of the springs 36 to cause the latching fingers 40
to swing inwardly about pins 48, free of the groove 44 and support
shoulder 46 in the clamping sleeve 18. By sustaining such pull on
the cable 33 the latching fingers are maintained inwardly retracted
and the elevator-and-hammer tool 32 is lifted out of the clamping
sleeve 18 and raised to the surface via the interior of the drill
sub 17 and the drill pipe or casing (not shown) from which such sub
depends, thereby enabling introduction of the core barrel 24 and
rotation of the assembled core bit 12 in a manner previously
described.
In behalf of assuring that the elevator-and-hammer tool assembly 32
is not withdrawn prior to complete assembly of the drill bit 12
onto the drill sub 17, such tool may take an alternate form, as
shown in FIGS. 8 and 9, for example, constructed, in conjunction
with slight modification of the clamping sleeve 18, to enable the
tool to be raised only after such complete assembly.
In accord with such exemplification as shown in FIGS. 8 and 9,
parts which correspond functionally to those in tool 32 in FIG. 1,
are given the same reference numerals. The automatic release
function is provided by a pair of retractable release arms 84
pivotally connected by pins 86 to the bottom of the common support
member 82 for the latch-retraction arms 38 and latch-effectuation
arms 42. During run-in of the tools for pick-up of the bit
assembly, the arms 84 are ineffectuated by contracting same
downwardly to end-abutting positions indicated by dot-dash outlines
88 in FIG. 9 in which they are held by over-center tension springs
90, to enable such tool to function as previously described in
connection with bit assembly pick-up. When used during lowering of
the retracted bit assembly down through the drill string, however,
the arms 84 are aligned horizontally and held therein against a
horizontal shoulder 92 near the bottom of support member 82 by the
same springs 90, the ends of such release arms 84 projecting into
longitudinal slots 94 in the clamping sleeve 18. The release arms
84 are so arranged that when in their horizontal positions, their
projecting ends extending through the grooves 94 lie in the path of
relative vertical travel between the ring 70 for stems 71 of the
lower bit sectors L and the clamping sleeve 18, and function to
lift the support member 82, during the final stages of bit
assembly, sufficiently to cause its latch-retraction arms 38 to
disengage the latching fingers 40 from the clamping sleeve 18 to
free the tool 32, which only then can be raised via the cables 53
(FIG. 1) the weight member 54, the flange atop hollow rod member
58, flange 34, and plates 50 and 51. Sufficient vertical clearance
is provided at the top of grooves 94 to permit raising of the tool
32 clear of the support shoulder 46 in clamping sleeve 18, before
the automatic release arms 84 strike the upper ends of such grooves
and become deflected downwardly and tend to permit re-expansion of
the latching fingers 40, which may be rounded at their outer
projecting edge to permit sliding travel along the inner wall of
the drill pipe, or arranged to have such travel limited. Otherwise,
the cable 33 of FIGS. 1 and 2, could be provided, if necessary, to
suspend the tool 32 and hold fingers 40 retracted as previously
described in connection with FIG. 1, once such automatic release
has been realized during an initial stage of raising of the tool by
the cables 53 as described above.
* * * * *