US 3575245 A
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United States Patent  lnventors Bruce J. Cordary LosAlamitos; Paul J. Arnerich, Fountain Valley, Calif.  AppLNo. 796,778  Filed Feb.5,l969  Patented Apr. 20, 1971 [73} Assignee The Servco Company Long Beach, Calif.
 APPARATUS FOR EXPANDING HOLES '9 Claims, 4 Drawing Figs.
 U.S.Cl 175/268  lnt.Cl ..E21b43/l6  FieldofSearch 175/263, 267,268
[5 6] References Cited UNITED STATES PATENTS 2,754,089 7/l956 Kammerer 175/268 2,799,479 7/1957 Kammerer.... 175/268 2,822,149 2/1958 Kammerer 175/267X 2,922,627 l/1960 Kammerer l75/267X Primary Examiner David H Brown Attorney-Christie, Parker & Hale ABSTRACT: A hole expander for use in conjunction with well bore drill strings which has a tool body defining a cylinder. an axially movable piston disposed in the cylinder, and a skirt portion secured to the piston. A plurality of radially arranged arms have one end secured to the tool body and another end adapted to receive cutting tools such as rotary cone cutters or abrasive cutters that are pivotal about axes transverse to an axis of the cylinder and are movable in an axial direction over a predetermined distance. Sides of the arms adjacent the skirt portion have a configuration to engage the skirt portion. When the piston moves axially in response to pressure being applied to the cylinder, the arms pivot outwardly relative to the axis of the cylinders. An intermediate skirt engaging surface of the sides of the arms is angularly inclined relative to the axis of the cylinder and engages an end ofthe skirt portion. When the arms are farthest removed from the cylinder in an axial direction the intermediate skirt-engaging surfaces of the arms are disposed adjacent the free ends of the skirt portion of the cylinder and bias the skirt portion, together with the piston, in a direction towards the cylinder. When the cylinder is fully extended a skirt-engaging surface of the arms engages a periphery of the skirt and locks the arms in an outwardly projecting position.
PATENTED APRZO [an SHEET 8 BF Q APPARATUS FOR EXPANDING HOLES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to rotary well bore tools and more particularly to rotary well bore tools for enlarging diameters of intennediate portions of the well bore.
2. State of the Prior Art In the drilling of wells such as oil wells, portions of the bore below the surface must often be enlarged for various reasons, such as to enable the packing of the bore with gravel. Frequently the upper portions of the bore are provided with steel casing through which any expanding hole drill apparatus must be lowered. It is therefore necessary to retract the drilling apparatus to a diameter less than the diameter of the upper portion of the well bore or the inner diameter of the well casing. Upon arrival of the hole enlarging apparatus at the desired depth, it is expanded to the desired diameter and the enlarging or underreaming operation can commence.
In the past, underreaming tools of various configurations have been extensively used. All include pivotal arms which are retracted into a tool body while the apparatus is being raised or lowered through the narrow portions of the drill bore and which can be pivoted outwardly relative to an axis of the apparatus. Because of the relatively large forces required to expand the drill arms, hydraulic actuators are usually coupled with the arms by means of linkages. Alternatively, the arms have been provided with inclined surfaces which project into a path of the hydraulic actuator and are engaged by it upon its actuation. This engagement pivotally forces the arms outwardly to the larger diameter.
Upon termination of the drilling operation, the arms must be retracted. To enable the retraction, an axial force must be applied to the piston of the hydraulic actuator to return it to its original position.
In the prior art, the pistons were'returned to their original position in one of two ways. First, the apparatus was provided with helical compression springs which acted against the piston and biased it into an original position against the force to which the hydraulic pressure subjected it. Upon release of the pressure, the spring moved the piston axially into its original position. The second class of underreamers is provided with double-acting pistons which are subjected to a pressure forcing the pistons into their original position upon termination of the drilling operation. This embodiment is frequently employed in conjunction with relatively large size underreamers.
SUMMARY OF THE INVENTION The present invention provides apparatus for enlarging subsurface holes, such as well holes. Briefly, it includes a tool body adapted to be secured to a drill string and defining a cylindrical bore having an open end. Another end of the bore is closed and in flow communication with a fluid carrying portion of the drill string. A piston is axially movable in the bore and includes a skirt portion extending past the open end of the bore. Means are provided for communicating an interior space of the cylinder confined by the piston with the exterior of the tool body. A plurality of radially spaced arms are adapted to mount cutting tools adjacent one end of the arms for engaging a portion of the hole to be enlarged. The arms are disposed exteriorly of the bore and are freely movable parallel to an axis of the bore over a predetermined distance. Furthermore, they are pivotal about an axis transverse to the axis of the bore adjacent another end of the arms proximate to the piston. The amrs have a configuration to engage the skirt portion when the piston moves towards the open end of the bore such that the ends of the arms are pivoted outwardly relative to the axis of the bore in opposition to a pivotal force from their weight. When the cutting tools are disengaged from the portion of the hole being enlarged, they engage an end of the skirt remote from the piston and bias the skirt and the piston axially away from the open end of the bore. Stop means limit the outward pivotal movement of the arms.
Preferably, the tool body includes an elongated flange adjacent each side of the arms and a shaft for pivotally and axially movably mounting the anns in a slot of the flanges.
The underreaming apparatus of this invention eliminates the need for a helical compression spring or a double-acting piston to return the piston to its original position. Instead, the piston is biased into its original position by the outwardly extending arms. The arms include first, second and third skirtengaging surfaces which respectively position the arms adjacent the axis of the cylinder when the piston is in its original position; pivot the arms outwardly relative to the axis about the shaft; and position the arms in an extended position so that the ends adapted to receive the cutting tools are remote from the axis of the cylinder. The third surface is in engagement with the skirt portion during the drilling or underreaming operation when an axial force moves the arms to a position closest to the interior space defined by the bore. Upon termination of the underreaming, the apparatus is lifted whereby the arms move axially in an opposing direction away from the interior space under their weight. This axial movement is sufficient to place the free end of the skirt portion adjacent the angularly inclined second skirt-engaging surface of the arms. An axial component force, resulting from the pivotal bias of the arms under their own weight about the shaft securing it to the flanges of the tool body, biases the skirt and the piston ina direction towards their original position until the arms are positioned adjacent the axis of the cylinder.
Although an underreamer constructed according to the present invention can be constructed for underreaming any size hole, it is particularly well adapted for use in conjunction with large diameter drill holes which require large underreamed sections. The relatively heavy arms subject the piston to a large axial force biasing it towards its original position.
The reduction in the number of parts required to construct the underreaming apparatus makes it substantially more economical to manufacture than prior art underreamers. Its simple operating mechanism assures trouble free operation of the apparatus and substantially enhances its service life.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary elevational view, in section, of a hole expanding apparatus constructed in accordance with the present invention and showing arms mounting cutting tools in an expanded operating position in phantom lines;
FIG. 2 is a fragmentary front elevational view, in section, similar to FIG. I wherein the arms are shown in an intermediary position;
FIG. 3 is a fragmentary side elevational view of the apparatus shown in FIG. I; and
FIG. 4 is an illustration like FIG. 1 of a hole expanding apparatus having a modified fluid flow path.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Initially referring to FIG. 1, there is shown a well bore 10 (in phantom lines) and an apparatus l2 for enlarging a portion 14 of the well bore. The apparatus is secured to a drill string (not shown) lowered through an upper portion (not shown) of the bore.
The apparatus I2 is described in conjunction with its application for enlarging or underreaming intermediate portions of a subterranean bore such as an oil well bore. However, it is obvious that this apparatus can be used for cutting and milling tubular conduits, such as oil well casing, by interchanging cutting tools secured to the apparatus. The apparatus of the present invention is therefore not intended to, and is not limited to the underreaming of subterranean drill holes. Rather it is adapted for use in conjunction with all rotatory drilling, boring, cutting, milling, etc. tools which require an apparatus capable of expanding its working surfaces from a lesser to a greater diameter.
The underreaming apparatus I2 includes a tool body 16 adapted to be secured to an upper drill string (not shown). It defines a cylinder 18 having an open end 20, an axially movable piston 22 disposed within the cylinder, and a plurality of pivotally mounted arms 24 and 24. An end 26 of the arms farthest removed from cylinder 18 is adapted to receive a conventional cutting tool which may be a conventional rotary cone cutter 28, a cutter provided with an abrasive surface (not shown) for cutting through tubular conduits, or cutter adapted for other applications. The cutting tools are not further described herein since they do not fonn a part of this invention.
In the presently preferred embodiment, the tool body I6 is defined by a circular end flange 30 which is coaxially secured to the cylinder 18 and projects past a periphery 32 of the cylinder. A face 34 of the end flange opposite face 36 adjacent the cylinder, mounts a tubular member 38 which is provided with a suitable thread engaging portion (not shown) adjacent its end (not shown) remote from the end flange for securing the apparatus 12 to a lower end of a drill string (not shown).
Preferably, a tubular core 40 is secured to face 34 of the end flange and projects through a hole 42 in the flange past side 36 into a space defined by the cylinder 18. An end of the core remote from the end flange includes radial projections 44 and a plurality of relief slots 46 which extend from that end toward the end flange a distance which is slightly greater than the thickness of the piston. The core further includes a recessed hole 48 adjacent the end provided with the radial projections 44 and, disposed in that hole, an axially-movable generally cone-shaped plug 50 provided with seal ring 52 on a cylindrical portion of the plug. An upper end of the plug includes a spearhead 54 connected with a pull cable 56 extending upwardly past the tubular member 38 and the upper drill string (not shown) to the surface of the bore.
The piston 22 disposed within cylinder 18 has a coaxial center bore 58 engaging a periphery of the tubular core 40. A suitable seal ring 60 seals an interior space 62 defined by end flange 30, cylinder I8, and piston 22 from the exterior of the tool body. One or more holes 63 communicate the interior space with the tubular member 38. The cylinder includes a preferably annular protrusion 64 adjacent the center bore 58 to space a face 66 of the piston from face 36 of the end flange 30 when the piston is in an original position adjacent the end flange. A seal ring 68 is disposed about a periphery of the piston adjacent walls of cylinder I8 and further seals the interior space 62 from the exterior of the tool body.
An end of the piston remote from the end flange includes a preferably cylindrical skirt portion 70 which extends from the piston past the open end 20 of the cylinder. A free end 72 of the skirt portion is provided with a taper 74 for purposes to be described hereinafter.
A pair of laterally-spaced elongated flanges 76 are disposed on each side of each arm 24 or 24 and are suitably secured to face 36 of the end flange 30 and the periphery 32 of cylinder 18. The flanges extend from adjacent the end flange past the free end 72 of the skirt and have opposite ends 78 secured to a disc 80 such that the pairs of flanges are substantially rigid. The cylindrical disc suitably connects a tubular protrusion 82 which is coaxial with the disc and an axis of the cylinder. A free end of the protrusion is provided with a threaded end 84 for engaging the apparatus 12 with a lower portion of the drill string (not shown).
Each pair of flanges 76 include a pair of slots 86 which are aligned with each other to slidably receive a shaft 88 secured to ends 90 of the arms 24 or 24'. The anns are thereby pivotal about the axis of the shaft. They can also move in an axial direction parallel to the axis of the cylinder from a lowermost position (shown in FIG. I) which is farthest removed from end flange 30 to an uppermost position (shown in FIG. I in phantom lines) which is proximate to the end flange.
Each arm includes a first skirt-engaging surface 92 immediately adjacent end 90 of the arm on the side of the arm facing towards the skirt portion 70. The first engaging surface is arranged to position an outer side 94 of the arm within an axial projection of end flange 30 to prevent interference between the narrow drill hole 10 and the arms when the apparatus 12 is axially moved through the drill bore. The first engaging surface 92 is substantially parallel to a periphery of the skirt portion 70 when the arm is pivoted about the axis of shaft 88 and positioned within the axial projection of end flange 30.
A second skirt-engaging surface 96 or 96 is joined with the first engaging surface by a preferably arcuate transitional portion 98 and extends from the first surface toward the end 26 of the arm. The second engaging surface is angularly inclined relative to the first surface and projects inwardly towards the axis of the cylinder 18. Immediately adjacent the second engaging surface is a third skirt-engaging surface 100 or 100' which is shorter than either the first or the second engaging surface and which has an angular inclination relative to the first surface which is less than the inclination of the second surface 96 or 96'. The exact angular inclination is a function of both the length and the angular inclination of the second engaging surface 96 or 96 and is such that when the piston, together with skirt portion 70, is axially moved towards disc 80, and the arms have pivoted outwardly relative to the axis of the cylinder, the third skirt-engaging surface 100 or 100' is parallel to the periphery of the cylindrical skirt portion 70 when the piston is adjacent the radial projections 44 of the core 40, as shown in phantom lines in FIG. 1.
Joined to the third engaging surface I00 or 100 is an inner side 102 of the arm which defines the outline of the arm intennediate the end of the third surface and the end 26 of the arm 24 or 24'. This inner side has a configuration to position the cutting tool 28 adjacent the tubular protrusion 82, as shown in FIG. I.
The arms 24 and 24' further include stop pins 104 which preferably protrude from each face 106 of the arms and engage suitable cutouts 108 in flanges 76 for limiting the pivotal movement of the arms about shaft 88 in a direction away from the axis of the cylinder 18.
Turning now to the operation of the underreaming apparatus I2, it is first secured to a drill string (not shown) and lowered into a drill hole 10. After it has reached the depth where the diameter of the hole is to be enlarged, the downward movement of the apparatus is halted. The drill string is filled with fluid drilling mud which enters the tubular member 38 and, through holes 63 in the end flange 30, the interior space 62 of the tool body 12. Thereafter the drill string and the apparatus 12 are rotated by a suitable rotatory table (not shown) on the surface of the well bore 10. The piston 22 is disposed in its original position, the shafts 88 of the arms are disposed at the lowermost position farthest removed from end flange 30, and the arms, by virtue of their weight, are pivoted inwardly to a position where ends 26 are closest adjacent the axis of the cylinder 18.
The drilling mud is pressurized through the drill string to actuate the piston 22 and move it axially away from end flange 30. When the end 72 of the skirt portion 70 arrives at the transitional portion 98 intermediate the first and second skirtengaging surfaces 92 and 96 or 96', respectively, the arms are pivoted outwardly away from the axis of the cylinder. The free end of the skirt and particularly the taper 74 of the free end, slides along the second engaging surface 96 or 96. This imparts a pivotal force onto the arms which opposes the pivotal force imparted upon them by their weight. The movement of the anns continues until the periphery of the skirt portion 70 is disposed adjacent the third engaging surface 100 or 100', as shown in phantom lines in FIG. I.
Simultaneously with the pivotal movement of the arms, the cutting tools 28 disposed adjacent ends 26 of the arms. begin to engage the formation and commence their underreaming action. To effectively drill and expand the hole, weight is applied to the drill string from the surface to impart an axial force onto the cutting tools. This axial force is transmitted to the cutting tool through flanges 78 and shaft 88. It causes the arms 24 and 24' and the shaft 88 to move relative to the flanges 76 within the confines of slot 86 until the shafts are in their uppermost position adjacent the ends of the slots proximate the end flange 30.
The downward movement of the piston 22 continues and the skirt portion 70 is given a length such that when the shafts 86 are disposed proximate to the end flange, the third engaging surface 11M or K00 is disposed on the periphery of the skirt portion. Additionally, the cutouts 108 of the flanges are arranged to engage the stop pins and prevent a further pivotal, outward movement of the arms when surface 100 or 166' abuts skirt portion 70. [n this position, the arms extend outwardly a maximum distance.
The radial projections 44 on the tubular core 40 are arranged to engage the piston 22 when the free end 72 of the skirt portion 70 is disposed just beyond the end of the third engaging surface we or 100' and the arms are proximate to the end flange 30. The relief slots 46 in the tubular core now permit unrestricted circulation of drilling mud from the interior space 62 to the exterior of the tool body 16. Pressure in the interior space 62 is thereby relieved. No additional axial forces are imparted upon the piston which remains in the position adjacent the radial projections during the drilling or underreaming operation.
The resulting pressure drop in the interior space 62 as well as in the drill string is sensed at the surface. It simultaneously communicates to the operator that the piston has reached its lowermost position and that, by necessity, the arms are fully extended. Moreover, as long as the drilling operation continues and no pressure builds up in the interior space and the drill string the operator knows that the arms are in a locked position and prevented from collapsing inwardly. The operator is assured that the hole is underreamed to the desired diameter.
Drilling mud continues to be pumped down through the drill string, the interior space 62, past the relief slots 46, and into the space exterior of the tool body to facilitate the drilling operations and remove loosened formation to the surface. The drilling mud rises in the annular space intermediate the drill string and the well bore or a casing (not shown) disposed therein. Upon termination of the drilling operation, the drill string, together with the apparatus 112, is lifted off the bottom of the underreamed hole to disengage the cutting tools 28 therefrom. The weight of the arms 24 and 24' and the cutting tools now axially moves the arms and the shafts 88 relative to the flanges 76 in slots 86 until the arms are at the lowermost position. The length of this movement, and therefore of slot 86, is sufficient to disengage the third engaging surface 100 or 1160 from the periphery of the skirt portion 70 and engage the taper M of the free end 72 of the skirt with the second engaging surface 96 or 96. The weight of the arms 24 or 24', together with the cutters, pivotally biases the arms about the axes of shafts 86. An axial component force acting in a direction towards the end flange 30 is thereby imparted on the taper 74 of the skirt portion. This axial force moves the piston axially towards the end flange until the first engaging surface 92 engages the periphery of the skirt portion. In that position, the arms are fully retracted to within the axial projection of the end flange and the apparatus can be axially moved through the well bore 10 to the surface. After the drilling operation is terminated, the cable 56 is pulled to remove plug 50 from the recessed hole 46 in the tubular core 40. The drill mud in the drill string is thereby drained, and the interior space 62 is communicated with the exterior of the tool body 16 such that no resistance force is exerted upon the piston during its axial movement towards the end flange.
If the diameter of the enlarged portion 14 of the drill bore W is substantially greater than the diameter of drill hole 10, the arms 24 and 24' are pivoted outwardly different amounts such that some of the cutting tools 28 cut a diameter which is greater than the diameter cut by the other cutting tools. in an apparatus having, say, six cutting tools 28 and arms 24 and 24, three of them 24 are provided with a second skirtengaging surface 96' which is substantially longer than that of the other three. Their engaging surfaces are therefore substantially closer to the axis of the cylinder when they are in a collapsed position. Upon actuation of the piston 22, the arms 24' provided with the longer second skirt-engaging surface 96' pivot outwardly a substantially greater amount than the other arms 24. The length and angular inclination of the engaging surfaces are arranged such that when all arms are in a fully extended position, the cutting tools make annular cuts into the formation which have successively greater diameters to cover the full width of the underreamed bore with a cutting tool. The operation of the apparatus remains identical to that described above.
FIG. 4 illustrates a hole opening apparatus adapted for use in conjunction with drilling operations requiring reverse circulation of the drilling mud. in reverse circulation, where the drilling mud is brought down from the surface to the drill tool through a first annular space intermediate a first outer drill string 121 and a second inner string 122 and is returned to the surface through the second inner drill string, the tubular core 40 disposed in the end flange is left open. The exterior of the tool body is in flow communication with the interior of the inner string through the tubular core 40. The relief slots 46 in the tubular core are omitted such that no fluid communication between the interior space 62-and the exterior of the tool body is possible adjacent the center bore 58 of the piston. The first outer drill string, however, fluidly communicates with the interior space 62 through holes 63.
Included are a plurality of holes 123 extending radially through walls of cylinder 18 and positioned so that the interior space 62 communicates with the exterior of the tool body when the piston is adjacent the radial projections 44 on tubular core 40. The holes are connected with suitable conduits 124 (hidden by flange 76) disposed substantially parallel to the flanges 76 which terminate adjacent the circular disc 80. Drilling mud pumped down through the annular space between the outer and inner drill strings is then discharged adjacent the bottom of the enlarged portion 14 being drilled and returns to the surface through the hole 42 in the tubular core 40 and the inner drill string 122. The operation of the apparatus, namely the pivotal and axial movements of the arms, the axial movement of the cylinder and the axial return of the cylinder to its original position by the weight of the arms, remains identical to the above described operation.
1. Apparatus for enlarging the diameter of subsurface holes comprising:
a tool body adapted to be secured to a drill string;
walls defining a bore in the tool body having an open end and another end in flow communication with a fluid carrying portion of the drill string;
a piston axially movable in the bore and provided with a skirt portion;
means for limiting the axial movement of the piston in the bore;
a plurality of radially spaced arms adapted to mount cutting tools adjacent one end of the arms for engaging a portion of the hole to be enlarged and disposed exteriorly of the bore, means for mounting the arms for free movement parallel to an axis of the bore over a predetermined distance, and pivotable about axes transverse to the axis of the bore adjacent another end of the arms proximate to the piston, means on the arms for engaging the skirt portion when the piston moves towards the open end of the bore for pivoting the ends of the arms outwardly relative to the axis of the bore in opposition to a pivotal force from the weight of the arms and for biasing the skirt and the piston axially away from the open end of the bore when the cutting tools are disengaged from a portion of the subsurface hole; and
stop means for limiting the outward pivotal movement of the arms.
2. Apparatus according to claim 1 including a member secured to the tool body and projecting through an axial center bore in the piston to a region in fluid communication with the exterior of the body, a fluid passage in the end of the member projecting through the piston; the member having a sufficient length that the bore in the tool body fluidly communicates with the exterior of the body when the arms are fully pivoted outwardly.
3. Apparatus according to claim I wherein the tool body includes a flange adjacent each side of each arm, each pair of flanges adjacent each arm having aligned slots engaging shaft means secured to each arm such that the arms are pivotal about axes of said shaft means and are movable in a direction parallel to the axis of the bore within the confines of the slot.
4. Apparatus according to claim 3 including at least two pluralities of arms, ends of each plurality of arms projecting outwardly from the axis of the hole a distance different from the other pluralities of arms when the arms are fully pivoted outwardly.
5. Apparatus for enlarging the diameter of subsurface holes comprising:
a tool body adapted to be secured to a drill string and including hydraulic actuating means having an axially extending skirt portion;
a plurality of radially arranged arms disposed adjacent the skirt portion and adapted to mount cutting tools adjacent an end of the arms remote from the actuating means;
means for mounting the arms for pivotal movement about axes substantially transverse to an axis of the skirt portion, and for movement parallel to the axis of the skirt portion over a predetermined distance;
a first skirt engaging surface on each arm for positioning the end of the arm adjacent the axis of the skirt portion;
a second surface on each arm for engaging a free end of the skirt portion and pivoting the end of the arm in a direction away from the axis of the tool body in response to actuation of the actuating means;
a third skirt engaging portion for positioning the ends of the arms remote from said axis;
the predetermined distance being sufficient that the second skirt engaging portion is disposed adjacent the free end of the skirt portion after the hydraulic means have been actuated and the arms are at one end of their axial movement;
means for securing the arms to the tool body such that they are pivotable and axially movable over the predetermined distance;
stop means for limiting the pivotal movement of the arms in a direction away from the axis of the skirt portion; and
means for limiting the axial movement of the skirt portion in response to actuation of the actuating means.
6. Apparatus according to claim 5 wherein the means for mounting the arms includes laterally spaced flanges secured to the tool body adjacent sides of the arms and shafts connected with the flanges.
7. Apparatus according to claim 6 wherein the body defines a cylinder and the actuating means include a piston disposed in the cylinder and secured to the skirt portion, the cylinder being in flow communication with a fluid carrying portion of the drill string and provided with an opening adjacent the piston to fluidly communicate an interior space of the cylinder with the exterior of the tool body when the free end of the skirt portion is adjacent the third engaging surface and the arms moved axially over the predetermined distance in a direction opposite to a direction the piston moves when pressure is applied to the interior space.
8. Apparatus for enlarging the diameter of sub-surface holes, the apparatus comprising:
a. a tool body having:
i. an end flange adapted to secure one end of the tool body to a drill string;
ii. a cylinder having an axis, the cylinder being adapted to be in fluid communication with a fluid carrying rtion of the drill string and having one end secure to the flange and another end open; and
iii. a plurality of pairs of laterally spaced elongated flanges adjacent a periphery of the cylinder extending axially away from the end flange;
b. an axially movable piston disposed in the cylinder and including a skirt portion projecting past the open end;
c. an arm disposed intermediate a pair of flanges having a free end adapted to mount a cutting tool and another end adjacent the open end ofthe cylinder pivotally and axially movably secured to the flanges, the axial movement being limited to a predetermined amount, the arms having a first, second and third skirt-engaging portion progressively engageable by the skirt portion when the piston moves away from the end flange in response to a fluid pressure being applied to the cylinder such that the arm is pivoted outwardly in response to such movements of the skirt portion while a free end of the skirt portion is in engagement with the second surface;
d. means for relieving the pressure in the cylinder in response to a free end of the skirt ponion being positioned adjacent the third engaging surface of the arm and the arm is axially farthest removed from the end flange; t
e. stop means for limiting the pivotal movement of the arm in a direction away from an axis of the cylinder;
f. means for pivotally and axially movably securing the other end of the arm to the flanges; and
g. means connected with ends of the flanges remote from the end flange for connecting another end of the tool body to a drill string.
9. Apparatus according to claim 8 wherein the means for securing comprises a shaft disposed intermediate each pair of flanges and the arm disposed between such flanges, and a slot in each flange, the shaft being axially movable in the slot to pivotally and axially movably secure the arm to the pair of flanges.