U.S. patent number 3,589,742 [Application Number 04/851,663] was granted by the patent office on 1971-06-29 for jaw-actuating means for pipe tongs.
This patent grant is currently assigned to Byron Jackson Inc.. Invention is credited to Howard S. Flick.
United States Patent |
3,589,742 |
Flick |
June 29, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
JAW-ACTUATING MEANS FOR PIPE TONGS
Abstract
Jaw-actuating means for pipe tongs in which a roller is
interposed between a pair of relatively movable cam surfaces for
actuating a jaw into gripping engagement with a pipe joint, the
roller being initially resiliently centralized in engagement with
one of the cam surfaces and out of engagement with the other cam
surface, but the roller shifting to engage both cam surfaces upon
actuation towards a pipe-engaging position.
Inventors: |
Flick; Howard S. (Long Beach,
CA) |
Assignee: |
Byron Jackson Inc. (Long Beach,
CA)
|
Family
ID: |
25311335 |
Appl.
No.: |
04/851,663 |
Filed: |
August 20, 1969 |
Current U.S.
Class: |
279/71; 269/235;
81/57.18; 279/114 |
Current CPC
Class: |
E21B
19/164 (20130101); Y10T 279/17717 (20150115); Y10T
279/1926 (20150115) |
Current International
Class: |
E21B
19/16 (20060101); E21B 19/00 (20060101); B23b
031/16 () |
Field of
Search: |
;279/66,1SG,1DA,71,72,1ME,114,115 ;269/235
;81/57.1,57.11,57.18,57.21 ;29/240 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Juhasz; Andrew R.
Assistant Examiner: Coan; James F.
Claims
I claim:
1. In a tong for making up and breaking out pipe joints and the
like: a support structure having an opening for a pipe, a
pipe-gripping assembly including a number of pipe-gripping jaws
movable between retracted positions and positions projecting into
said opening in gripping engagement with said pipe, an angularly
movable member, and jaw-actuating means for moving said jaws to
said positions in gripping engagement with said pipe responsive to
angular movement of said angularly movable member: the improvement
wherein said last mentioned means comprises opposing surfaces on
said jaws and said angularly movable member, rollers interposed
between said surfaces, and resilient means initially holding said
rollers spaced from one of said opposing surfaces, said rollers
engaging said one of said opposing surfaces and rolling between
said opposing surfaces following initial gripping engagement of
said jaws with said pipe, whereby the force for gripping said pipe
between said jaws is a function of the angular relationship between
said opposing surfaces.
2. In a tong as defined in claim 1, said resilient means initially
holding said rollers spaced from the surface on said jaws.
3. In a tong as defined in claim 1, said rollers having shafts
supporting the rollers for rotation, said resilient means initially
acting on said shafts to resiliently hold said shafts against
lateral movement until said rollers roll between said surfaces.
4. In a tong as defined in claim 1, said rollers having shafts
supporting the rollers for rotation, and said resilient means
including bodies of resiliently deformable material engaged with
said shafts for initially resiliently holding said shafts against
lateral movement until said rollers roll between said surfaces.
5. In a tong as defined in claim 1, said rollers having shafts
supporting the rollers for rotation, said resilient means including
shoes engaged with the ends of said shafts, and springs acting on
said shoes to initially resiliently hold said shafts against
lateral movement relative to said shoes until said rollers roll
between said surfaces.
6. In a tong as defined in claim 1, said rollers including shafts
supporting said rollers for rotation, said resilient means
including bodies of resiliently deformable material engaged with
said shafts and initially holding said rollers spaced from the
surfaces on said jaws and against lateral movement of said shafts
until said rollers roll between said surfaces.
7. In a tong as defined in claim 1, said rollers including shafts
supporting said rollers for rotation, said resilient means
including shoes engaged with the ends of said shafts, and springs
acting on said shoes and initially holding said rollers spaced from
the surfaces on said jaws and against lateral movement of said
shafts relative to said shoes until said rollers roll between said
surfaces.
8. In a tong as defined in claim 1, said resilient means including
a member resiliently cooperably engaged with said rollers and
initially holding said rollers spaced from the surface on said jaws
and having detent means resiliently resisting rolling movement of
said rollers between said surfaces following engagement of said
rollers with the surface of said jaws.
9. In a tong as defined in claim 1, said rollers having shafts
supporting the rollers for rotation, said resilient means having
detent means engaged with the ends of said shafts and resiliently
resisting rolling movement of said rollers between said surfaces
following engagement of said rollers with the surface on said
jaws.
10. In a tong as defined in claim 1, said rollers having shafts
supporting the rollers for rotation, said resilient means
comprising bodies of resilient material engaged with the ends of
said shafts and having a depression in which the ends of said
shafts are initially disposed for resiliently resisting rolling
movement of said rollers between said surfaces following engagement
of said rollers with the surfaces on said jaws.
11. In a tong as defined in claim 1, said rollers having shafts
supporting the rollers for rotation, said resilient means including
shoes, means mounting said shoes for movement relative to said
jaws, springs biasing said shoes into engagement with the ends of
said shafts, and said shoes having depressions in which the ends of
said shafts are initially disposed for resisting rolling movement
of said rollers between said surfaces following engagement of said
rollers with the surfaces on said jaws.
12. In a tong for making up and breaking out pipe joints and the
like: a support structure having an opening for a pipe, an outer
ring revolvably supported by said support structure, an inner ring
revolvably supported by said outer ring, a plurality of radially
shiftable jaws carried by said inner ring for gripping a pipe
disposed in said opening, and means for shifting said jaws radially
between pipe-gripping and retracted positions, rollers carried by
said jaws, oppositely sloped cam surfaces on said outer ring
engaged with said rollers for moving said jaws towards said
pipe-gripping positions upon rotation of said outer ring in either
direction relative to said inner ring, and means for retracting
said jaws upon movement of said outer ring in the other direction,
the improvement comprising surfaces on said jaws engageable by said
rollers following initial engagement of said jaws with said pipe,
and resilient means for holding said rollers spaced from said
surfaces on said jaws, said resilient means being deformable to
allow rolling movement of said rollers between said cam surfaces
and said surfaces on said jaws following initial engagement of said
jaws with said pipe.
13. In a tong as defined in claim 12, said resilient means
comprising bodies of resiliently deformable material, said rollers
having shafts engaged by said bodies.
14. In a tong as defined in claim 13, said bodies of resiliently
deformable material being composed by polyurethane.
15. In a tong as defined in claim 12, said rollers having shafts,
shoes slidably supported by said jaws and engaged with said shafts,
and said resilient means comprises springs acting on said
shoes.
16. In a tong assembly as defined in claim 12, said rollers having
shafts having end portions projecting from said rollers, said jaws
having slots into which said ends of said rollers extend, and said
resilient means being disposed in said slots and acting on the ends
of said shafts.
Description
BACKGROUND OF THE INVENTION
In the making-up and breaking-out of well pipe or rod joints, such
as the threaded joints of drill pipe, tubing, casing, or sucker
rods, all referred to herein for simplicity as joints or pipe
joints, it has been the practice, in many cases, to employ a power
tong for turning one pipe or joint part, while the other joint part
or pipe is held against rotation by a backup tong. Various jaw
devices and jaw-actuating means have been utilized, both for
actuating the jaws of the power tong and the backup tong. The jaws
are initially or normally retracted to allow movement of a joint
part into or through the tong, but when the joint part is to be
gripped, the jaws are actuated toward one another.
A common mode of effecting closure of the jaws on a pipe is the use
of an angularly movable member, a cam, and a cam follower,
interposed between the jaws and the angularly movable member to
move the jaws radially inward or toward one another to grip the
pipe or joint part between the jaws, the radial component of force
on the jaws being a function of the cam angle. In order to drive
the pipe joint in opposite directions, the power tong must either
be rolled over, or it must have oppositely extended cam surfaces
which are effective to close the jaws upon angular movement of the
angularly movable member in either direction. Rolling the power
tong over may be objectionable and in some instances is impossible,
if, for example, the tong is circumferentially continuous and is
disposed about the pipe.
Such tongs, moreover, are preferably adaptable to use on joints
over a wide range of diameters with a minimum of interchangeability
of parts, such as die holders or jaws. However, when the angularly
movable member has oppositely inclined cam surfaces to provide for
jaw closure in both directions of angular movement of the member, a
problem is encountered respecting the size of the tong assembly, on
the one hand, or, on the other hand, the permissible range of sizes
of joints which can be effectively gripped by the jaws without
modification of the jaws. The cam surfaces are generally on the
angularly movable member and are long arcs, the slope of which
governs the radial force applied to the jaw and thus the
effectiveness of the gripping of the pipe by the jaws. Within a
given tong size, if the cam slope is such as to enable a wide range
of jaw movement, for use in gripping a wide range of joint
diameters, the slope is so steep that insufficient radial force can
be applied to the joint to effectively grip the same. This is a
problem which can be obviated by reducing the slope of the cam
surface, but, then, the range of jaw movement is inherently
reduced.
SUMMARY OF THE INVENTION
The present invention provides jaw-actuating means for tongs of the
general type referred to above, wherein the jaws are actuatable to
grip a wide range of joint diameters, without requiring
modification of the jaws, responsive to angular movement of the
angularly movable member in either direction, and wherein a second
cam surface cooperates with the follower to increase or intensify
the radial component of force on the jaws after the jaws initially
engage the pipe.
More particularly, the present invention involves the use of a
roller follower carried by a jaw and engageable with the cam
surface, the follower being rotatable on an axle which is
resiliently centralized, so that during initial movement of the jaw
the roller revolves about its axis and moves the jaw toward the
joint part, but following the engagement of the jaw with the pipe,
the roller is shifted to also engage another surface on the jaw and
opposed to the cam surface on the angularly movable member.
Thereafter, the roller will roll along both of these surfaces, so
that the radial component of force produced by the cam surface is
increased as a function of the angular relationship of the two
opposing surfaces engaged by the roller, and the axle of the roller
is shifted from its initial position.
An object of the invention, then, is to provide a tong which is
operable to grip pipe or points over a wide range of sizes or
diameters, while providing intensified radial forces on the jaws to
effectively grip the pipe and prevent slipping of the jaws with
respect to the pipe.
This invention possesses many other advantages, and has other
purposes which may be made more clearly apparent from a
consideration of forms in which it may be embodied. These forms are
shown in the drawings accompanying and forming part of the present
specification. They will now be described in detail, for the
purpose of illustrating the general principles of the invention;
but it is to be understood that such detailed descriptions are not
to be taken in a limiting sense, since the scope of the invention
is best defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view illustrating a tong assembly
incorporating the invention;
FIG. 2 is an enlarged top plan of the tong head with parts broken
away;
FIG. 3 is an enlarged vertical section as taken on the line 3-3 of
FIG. 2;
FIG. 4 is a horizontal section on a reduced scale as taken on the
line 4-4 of FIG. 3;
FIG. 5 is a fragmentary view in vertical section, as taken on line
5-5 of FIG. 3, through one of the pipe-gripping jaws;
FIG. 6 is a horizontal section, as taken on the line 6-6 of FIG. 5,
showing one of the jaws in the fully retracted position;
FIG. 7 is a view corresponding to FIG. 6, but showing the jaw
actuated into initial gripping engagement with the pipe;
FIG. 8 is a view corresponding to FIGS. 6 and 7, but showing the
jaw actuated into tight gripping engagement with the pipe;
FIG. 9 is a fragmentary vertical section as taken on the line 9-9
of FIG. 4, showing the reverse stop mechanism;
FIG. 10 is a fragmentary vertical section as taken on the line
10-10 of FIG. 9;
FIG. 11 is a plan view of a modified jaw mechanism with the jaw in
a fully retracted position;
FIG. 12 is a detailed view in vertical section, as taken on the
line 12-12 of FIG. 11;
FIG. 13 is a view corresponding to FIG. 11, but showing the jaw
actuated into initial gripping engagement with the pipe; and
FIG. 14 is a view corresponding to FIGS. 11 and 13, but showing the
jaw further actuated into tight gripping engagement with the
pipe.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As seen in the drawings, a power tong assembly T has a tong head H
adapted to be disposed about a length of pipe P. The tong assembly
T includes at least one motor M for operating the tong head under
the control of a control mechanism C, so that the tong head will
grip the pipe P and rotate the same in either direction, depending
upon whether it is desired to makeup or breakout a joint J which
connects a lower length of pipe P1 to the length of pipe P, all as
is well known in the art.
The details of the tong assembly in general are not germane to the
present invention, which involves the mode of actuation of the
pipe-gripping mechanism included within the tong head H.
More particularly, the tong head subassembly comprises a housing or
case 1 having an upper case section 2 and a lower case section 3
interconnected by a suitable number of peripheral fasteners 4. A
driven gear 5 extends into the case 1 and is in mesh with a ring
gear 6 which constitutes an outer rotary ring and which is
supported for rotation in the case 1 by upper bearings 7 and lower
bearings 8. An inner ring assembly includes upper and lower plates
9 and 10 joined together, as seen in FIG. 9, by a suitable number
of fasteners 11. The inner ring plates 9 and 10 define a central
pipe opening 12 therethrough. The upper plate 9 of the inner ring
assembly includes an outer marginal flange 13 which is slideably
disposed on the annular body 14 of the outer ring or ring gear 6,
whereby the inner ring is supported on the outer ring for relative
rotation during the operation of the pipe-gripping means,
hereinafter to be described.
The pipe-gripping means, in the tong head now being described,
comprises a pair of radially shiftably disposed jaws 15, 15 which
are reciprocably disposed in windows 16 defined by the inner ring
plates 9 and 10. A typical jaw 15 is best illustrated in FIG. 4, 5
and 6 as comprising a body 17 having a die carrier 18 supported
thereon by means of a spherical joint at 19 and retainer pins 20
which are threaded into the die carrier 18 and have their upper
ends 21 and their lower ends 22, respectively, loosely disposed in
openings 23 and 24 in the jaw body 17, whereby the die carrier 18
is free to partake of limited universal movement. The die carrier
18 included dovetailed slots 25 adapted to receive two tong dies 26
provided for the purpose of gripping the pipe P to rotate the same
upon actuation of the jaws into gripping engagement with the pipe
P.
The jaws are normally spring biased to retracted positions within
the windows 16. Accordingly, each jaw body 17 is provided with
outstanding ears 27 on opposite sides thereof engaged by U-shaped
connectors 28. The ends 29 of the connectors 28 are turned back and
are provided with spring seats 30 on which seat coiled compression
springs 31. These coiled compression springs 31 extend into
spring-seating bores 32 in the respective inner ring plates 9 and
10. Thus, the springs 31 normally act to move the jaws outwardly to
their retracted positions.
The outer ring or ring gear 6, as best seen in FIG. 4, has a cam
surface generally indicated at 33 thereon engageable with cam
followers or rollers 34 carried by the jaw body 17, whereby upon
relative rotation of the outer ring or ring gear 6 and the inner
ring assembly 9 and 10, the jaws 15 will be actuated inwardly to
projected or pipe-gripping positions.
More particularly, the cam surface 33 is a compound cam surface
which is symmetrical and includes opposite cam portions 33a adapted
to engage the rollers 34 upon rotation of the outer ring or ring
gear 6 in a clockwise direction to make up pipe joints, and the cam
surface 33 also includes opposing cam portions 33b adapted to
engage the rollers 34 when the outer ring or ring gear 6 is rotated
in a counterclockwise direction to break out joints of pipe.
Intermediate the cam surface portions 33a and 33b are central
depressions 33c in which the rollers 34 are disposed when the jaws
15 are fully retracted, as seen in FIG. 4.
In order to resist initial rotation of the inner, jaw-carrying ring
assembly with the outer ring 6, so that the cam surfaces and
rollers may effect actuation of the jaws 15 from the retracted
positions to the pipe-engaging positions, a brake band 35 having
friction facing material 36 thereon is disposed within the case
section 2 and is adapted to engage an annular surface 37 on a
flange 38 of the inner ring plate 9. Referring to FIG. 2, it will
be noted that the brake band 35 is suitably anchored by an anchor
lug 39 which is welded or otherwise secured to the band 35 and has
a vertical slot 40 adapted to receive a lug 41 provided within the
outer case section 2. The brake band 35 has end ears 42 through
which a brake adjuster screw 43 extends. A coiled spring 44 is
disposed about the screw 43 and acts on one of the ears 42 and on
the head of the adjuster screw 43 to supply a spring force tending
to normally hold the brake band in frictional engagement with the
annular face 37 of the inner ring assembly. Accordingly, initial
rotation of the inner ring assembly is prevented so that angular
movement of the outer ring or ring gear 6 relative to the inner
ring assembly will cause the rollers 34 to engage either the cam
faces 33a or the cam faces 33b depending upon the direction of
rotation of the outer ring 6, whereby to cam the jaws 15 toward
pipe-gripping positions.
After the pipe has been gripped by the jaws, then the brake means,
described above, will slip to allow rotation of the inner ring
assembly along with the driven outer ring or ring gear 6, whereby
to impart corresponding rotation to the pipe P.
When, following rotation of the pipe P in one direction, it is
desired to release the jaws from gripping engagement with the pipe,
the outer ring or ring gear 6 is rotated in the opposite direction,
until the cam rollers 34 are disposed in the depressions 33c
Reverse stop means are provided to limit such rotation of the outer
ring relative to the inner ring, so that the jaws 15 will not be
reversely actuated to reengage the pipe P. This reverse stop means
is best illustrated in FIGS. 4, 9 and 10, as comprising a traveling
stop pin 50 which is carried by and extends downwardly beneath the
outer ring or ring gear 6. The stop pin 50 is adapted to abut with
either a makeup reverse stop 51 or a breakout reverse stop 52 which
are respectively reciprocably disposed in chambers 53 and 54 formed
in the plate 10 of the inner ring assembly 9, 10. A spring 55 is
disposed behind the inner end of the makeup reverse stop 51 and a
similar spring 56 is disposed behind the inner end of the breakout
reverse stop 52, so as to normally bias these stops outwardly into
the path of the traveling stop 50. An actuator ring 57 is provided,
having an inner peripheral flange 58 which is supported on a
retainer ring 59, the ring 59 being carried by a downwardly
extended annular flange 60 on the inner ring assembly plate 10.
This actuator ring 57 has a cam surface 61 thereon which engages an
actuator pin 62 projecting downwardly from the reverse stop 51 and
another actuator pin 63 which projects downwardly from the reverse
stop 52. The cam surface 61 includes a section 64 having a
depression 65 which will hold the actuator ring 57 against
inadvertent movement and which will hold either of the reverse
stops 51 or 52 retracted. In FIG. 4 the actuator pin 63 is shown as
engaged in the depression 65. When it is desired to allow the
reverse stop 52 to be projected and the reverse stop 51 retracted,
the actuator ring 57 is rotated in a clockwise direction, releasing
the reverse stop 52; then the cam surface 61 will cause progressive
retraction of the reverse stop 51. When either of the stops 51 or
52 is in the projected position, reverse rotation of the outer ring
or ring gear 6 relative to the inner ring assembly is limited to a
position at which the rollers 34 are in the depressions 33c of the
outer ring cam surface 33, and thereafter the outer ring 6 and the
inner ring assembly will rotate as a unit with the jaws fully
retracted.
The details of the tong assembly, as thus far described, are not
germane to the present invention except that the assembly functions
to effect movement of the pipe-gripping jaws 15 between the
retracted positions and the pipe-gripping positions in response to
angular movement of the outer ring in either direction. SInce the
cam surface 33 of the outer ring 6 is a compound cam surface,
operable upon angular movement of the outer ring in either
direction, the effective range of the operability of this type of
tong has heretofore been limited, unless the jaws were modified by
the provision of adapters or die carriers to cooperate with
different sizes of pipe. The problem experienced by this type of
tong involves the necessity that the cam surfaces of the outer ring
not only provide for the gross movement of the pipe-gripping jaws,
regardless of the size of pipe to be gripped, but also the same cam
surfaces operate to cause gripping engagement of the dies with the
pipe. Under these circumstances, the gripping effectiveness may be
insufficient to provide the desired or necessary radial component
of force tending to grip the pipe with the jaws. The present
invention is more particularly concerned with the structure whereby
the radial force tending to cause the gripping of the pipe by the
jaws is enhanced or intensified.
Referring to FIGS. 5 through 8, the radial force intensifier is
more particularly illustrated in one embodiment of The invention.
In this form the cam roller 34 is rotatably mounted upon a shaft
70, the opposite ends of which extend through enlarged openings 71
in the jaw body 17. The roller 34 in each jaw is disposed in a
laterally opening slop 72 which terminates in a face 73 opposed to
the cam surface 33 of the outer ring 6. Means are provided for
resiliently holding the rollers 34 in engagement with the cam
surface 33 but spaced from the opposing jaw surfaces 73, as seen in
FIGS. 5 and 6. In the embodiment now being described, a pair of
shoes 74 is provided. The shoes 74 are reciprocable in upper and
lower grooves 75 in the jaw body 17. A suitable number of coiled
compression springs 76 is interposed between the inner wall of the
grooves 75 and the shoes 74 so as to normally bias the shoes 74
outwardly into engagement with the roller shaft ends. Each shoe 74
is indented or provided with opposing angular faces 77 converging
to form a detent 77a (FIG. 8) which engages with one of the shaft
ends, so that the shaft ends will normally be centralized with
respect to the shoes 74 and the rollers 34 will normally be spaced
from the jaw faces 73. However, the rollers 34 may shift withing
the shoe slots 75 and ride up the inclined surfaces in either
direction. Accordingly, the springs 76 essentially function to
centralize the rollers 34 with respect to the shoes 74 under normal
circumstances.
However, when the outer ring 6 is rotated relative to the inner
jaw-carrying ring assembly, say in a direction to make up pipe, the
jaws 15 will first be actuated inwardly by the action of the cam
surfaces 33a on the radius of the respective rollers 34, until the
dies 26 contact the pipe P, as seen in FIG. 7, at which time the
rollers 34 will be interengaged between the cam surface 33a and the
surface 73 of the jaw body 17 across the diameter of the rollers
34. At this point, the force tending to cause the jaws 15 to grip
the pipe becomes a function of the relationship between the slope
of the cam surface 33a and the opposing jaw surface 73. This jaw
surface 73 is herein illustrated as being on a plane normal to the
radial direction of the travel of the jaws 15, but since the force
acting to cam the jaws inwardly is a function of the relationship
of the cam surfaces 33a and the jaw surface 73, it will be
appreciated that the surface 73 may itself be disposed on an angle
or on an arc to cause the desired radial component of force with
the selected slope of the cam surface 33a or 33b, as the case may
be.
In this connection, it will be noted in FIG. 8 that following
initail engagement of the die 26 with the pipe, and responsive to
continued angular movement of the outer ring 6, the rollers 34 roll
between the cam surface 33a or 33b, depending upon the direction of
the rotation of the outer ring 6. The rollers 34 effectively shift
within the slots 75, and the shaft 70 will ride up one of the
angular shoe faces 77. Under some circumstances of maximum die
penetration into the pipe P, the shafts 70 may abut with the side
of the shoe slot 75, at which point further penetration of the dies
into the pipe P will be limited. When the outer ring 6 is reversely
rotated to retract the jaws, the springs 76, acting on the shoes
74, will again center the rollers 34 with respect to the inclined
surfaces 77 of the shoes 74.
Referring to FIGS. 11 through 14, a modified construction is
illustrated, wherein, in lieu of the shoes 74 and the springs 76
for centralizing the rollers 34 in the slots 75, a body 174 of
resilient deformable material is disposed in each slot 75, so as to
be engaged with an end of the respective roller shafts 70. The
resilient deformable material may be polyurethane or other suitable
material having opposed inclined surfaces 177 forming a detent
177a, whereby to centralize the roller shafts 70 when the jaws 15
are retracted and until sufficient force is applied to effect
coengagement of the rollers 34 between the cam surfaces 33a or 33b,
as the case may be, and the jaw surface 73, as seen in FIG. 13.
Thereafter, further angular movement of the outer ring 6 will
effect transverse displacement of the rollers 34 and resilient
deformation of the pads or bodies 174, as seen in FIG. 14.
While two illustrative embodiments have been shown, it will be
understood that the essence of the invention is the provision of
the resilient means such as the shoes 74 and the springs 76 or the
deformable resilient bodies 174 to normally maintain the rollers 34
spaced from the jaw surface 73, but to allow coengagement of the
rollers 34 with the jaw surface 73 upon initial gripping engagement
of the jaws 15 in a radial pipe; whereupon, the forces acting on
the jaws 15 in a radial pipe-gripping direction become a function,
not of the radii of the rollers 34 and the slope of the cam surface
33a or 33b, but, instead, the radial gripping force is a function
of the relationship between the slope of the cam surfaces 33a and
33b and the jaw surfaces 73. Initially, the rollers 34 act only on
their radii, but following shifting of the rollers 34 into
engagement with the jaw surfaces, the rollers act substantially
across their diameters.
* * * * *