Enhanced diameter clean-out tool and method

Claims

What is claimed is:

1. A downhole cutting tool, comprising:

a body including a slot defined laterally therethrough and further including a longitudinal cavity defined therein in communication with said slot;

two cutting members pivotally mounted in said slot;

movement means, disposed in said cavity so that said movement means is movable between a first position in said cavity and a second position in said cavity, for moving said cutting members to respective extended positions in response to a force acting on said movement means to move said movement means from said first position to said second position; and

said body further including:

first channel means, defined in said body and spaced from said slot, for communicating a liquid from said cavity to an outlet of said first channel means regardless of the position of said movement means between said first and second positions; and

second channel means, defined in said body and spaced from said slot and said first channel means, for communicating a liquid from said cavity to an outlet of said second channel means in response to said movement means moving from said first position to said second position.

2. A tool as defined in claim 1, wherein:

said first channel means includes a longitudinal bore having an end disposed within said body near said first position of said movement means and having another end, defining said outlet of said first channel means, disposed near an end of said body; and

said second channel means includes a longitudinal bore having an end disposed within said body nearer said second position of said movement means than said end of said first channel means and having another end, defining said outlet of said second channel means, disposed near an end of said body.

3. A tool as defined in claim 2, wherein:

said body includes a first end through which said cavity is defined and a second end near which said slot is defined;

said another end of said longitudinal bore of said first channel means opens through said second end of said body; and

said another end of said longitudinal bore of said second channel means opens through said second end of said body.

4. A tool as defined in claim 2, wherein:

said body includes a first end through which said cavity is defined and a second end near which said slot is defined, said second end having a central indentation defined therein;

said another end of said longitudinal bore of said first channel means communicates with said central indentation; and

said another end of said longitudinal bore of said second channel means communicates with said central indentation.

5. A tool as defined in claim 2, wherein:

said body includes a first end through which said cavity is defined and a second end near which said slot is defined;

said tool further comprises cutting means, disposed at said second end of said body, for cutting material within a path having a cross-sectional area substantially the same as the maximum lateral cross-sectional area of said body;

said another end of said longitudinal bore of said first channel means is disposed near said second end of said body so that liquid is communicated through said first channel means to said cutting means; and

said another end of said longitudinal bore of said second channel means is disposed near said second end of said body so that liquid is communicated through said second channel means to said cutting means in response to said movement means moving from said first position to said second position.

6. A tool as defined in claim 1, wherein:

said movement means includes a piston disposed in said cavity in engagement with said cutting members, said piston including:

a diametric surface against which pressurized liquid is caused to act when said cutting members are to be moved to their respective extended positions; and

a longitudinal surface extending from said diametric surface towards said cutting members;

said first channel means includes:

a first circumferential groove defined in said body in communication with said cavity, said first circumferential groove disposed adjacent said diametric surface of said piston but not covered by said longitudinal surface of said piston when said piston is at said first position of said movement means; and

a first passageway defined in said body, said first passageway communicating with said first circumferential groove and extending towards an end of said body; and

said second channel means includes: a second circumferential groove defined in said body in communication with said cavity, said second circumferential groove disposed between said diametric surface of said piston and said cutting members so that said second circumferential groove is covered by said longitudinal surface of said piston when said piston is at said first position of said movement means, but so that said second circumferential groove is at least partially uncovered from said longitudinal surface of said piston when said piston is at said second position of said movement means; and

a second passageway defined in said body, said second passageway communicating with said second circumferential groove and extending towards an end of said body.

7. A tool as defined in claim 6, wherein said piston has a sealing member disposed thereon at a position along said longitudinal surface so that said sealing member does not pass said second circumferential groove in response to movement of said piston between said first and second positions of said movement means.

8. A tool as defined in claim 6, wherein:

said first channel means further includes a third passageway defined in said body diametrically opposite said first passageway, said third passageway communicating with said first circumferential groove and extending towards an end of said body; and

said second channel means further includes a fourth passageway defined in said body diametrically opposite said second passageway, said fourth passageway communicating with said second circumferential groove and extending towards an end of said body.

9. A tool as defined in claim 1, further comprising:

a second body, including a slot defined laterally therethrough and further including a longitudinal cavity defined therein in communication with said slot of said second body;

two cutting members pivotally mounted in said slot of said second body;

second movement means, disposed in said cavity of said second body so that said second movement means is movable between a first position in said cavity of said second body and a second position in said cavity of said second body, for moving said two cutting members pivotally mounted in said slot of said second body to respective extended positions in response to a force acting on said second movement means to move said second movement means from said first position to said second position of said second movement means;

said second body further including:

third channel means, defined in said second body and spaced from said slot in said second body, for communicating a liquid from said cavity of said second body to an outlet of said third channel means regardless of the position of said second movement means between said first and second positions thereof; and

fourth channel means, defined in said second body and spaced from said slot of said second body and said third channel means, for communicating a liquid from said cavity of said second body to an outlet of said fourth channel means in response to said second movement means moving from said first position to said second position thereof; and

said second body connected to said first-mentioned body so that said outlets of said third and fourth channel means communicate with said cavity of said first-mentioned body.

10. A tool as defined in claim 9, wherein said second body is connected to said first-mentioned body so that said cutting members mounted in said slot of said second body are offset from said cutting members mounted in said slot of said first-mentioned body at an angle for enhancing rotational stability.

11. A tool as defined in claim 10, wherein said angle is about 90.degree..

12. A tool as defined in claim 1, wherein:

said body defines part of an elongated support;

said two cutting members define a first pair of extendible members pivotally connected to said support to move between retracted and extended positions within a first longitudinal plane;

said movement means defines first movement means, disposed in said support, for moving said first pair of extendible members to respective extended positions; and

said tool further comprises:

a second pair of extendible members pivotally connected to said support to move between retracted and extended positions within a second longitudinal plane, said second plane offset at an angle form said first plane so that said first and second pairs of extendible members effect enhanced rotational stabilization; and

second movement means, disposed in said support, for moving said second pair of extendible members to respective extended positions.

13. A tool as defined in claim 12, wherein said angle is about 90.degree..

14. A tool as defined in claim 12, wherein said support includes:

said body characterized as a first cylindrical body, including said slot characterized as a first longitudinal slot defined laterally therethrough and further including said longitudinal cavity characterized as a first longitudinal cavity defined therein between an end of said first cylindrical body and said first longitudinal slot, said first longitudinal slot having said first pair of extendible members mounted therein and said first longitudinal cavity having said first movement means disposed therein;

a second cylindrical body, including a second longitudinal slot defined laterally therethrough and further including a second longitudinal cavity defined therein between an end of said second cylindrical body and said second longitudinal slot, said second longitudinal slot having said second pair of extendible members mounted therein and said second longitudinal cavity having said second movement means disposed therein; and

connector means for connecting said second cylindrical body and said first cylindrical body to establish said angle between said first and second planes.

15. A tool as defined in claim 14, wherein said connector means includes a third cylindrical body, including a first end threadedly connected to said end of said first cylindrical body and further including a second end threadedly connected to another end of said second cylindrical body so that said second cylindrical body is spaced from, but in line with, said first cylindrical body.

16. A downhole cutting tool, comprising:

an elongated support having a continuous fluid communication path defined therein;

a first pair of extendible members pivotally connected to said support to move between retracted and extended positions within a first longitudinal plane;

first movement means, disposed in said support, for moving said first pair of extendible members to respective extended positions, said first movement means including a first piston disposed within said fluid communication path above said first pair of extendible members;

a second pair of extendible members pivotally connected to said support above said first pair of extendible members to move between retracted and extended positions within a second longitudinal plane;

second movement means, disposed in said support, for moving said second pair of extendible members to respective extended positions at a time subsequent to said first movement means moving said first pair of extendible members to their respective extended positions, said second movement means including a second piston disposed within said fluid communication path above said second pair of extendible members, said first and second pistons movable within said fluid communication path independently of each other; and

wherein said second plane is offset at an angle from said first plane so that said first and second pairs of extendible members effect enhanced rotational stabilization in response to said first and second movement means moving said first and second pairs of extendible members to their respective extended positions and maintaining them thereat.

17. A tool as defined in claim 16, wherein said angle is about 90.degree..

18. A tool as defined in claim 16, wherein said support includes:

a first cylindrical body, including a first longitudinal slot defined laterally therethrough and further including a first longitudinal cavity defined therein between an end of said first body and said first slot, said first slot having said first pair of extendible members mounted therein and said first cavity having said first movement means disposed therein;

a second cylindrical body, including a second longitudinal slot defined laterally therethrough and further including a second longitudinal cavity defined therein between an end of said second body and said second slot, said second slot having said second pair of extendible members mounted therein and said second cavity having said second movement means disposed therein; and

connector means for connecting said second body and said first body to establish said angle between said first and second planes.

19. A tool as defined in claim 18, wherein said connector means includes a third cylindrical body, including a first end threadedly connected to said end of said first body and further including a second end threadedly connected to another end of said second body so that said second body is spaced from, but in line with, said first body.

20. A method of cutting material located within a borehole having a tubing disposed therein, said method comprising the steps of:

lowering a clean-out tool into the tubing, which clean-out tool includes: a first pair of members movable below the tubing to an extended position in response to a pressurized fluid, and a second pair of members movable below the tubing to an extended position in response to a pressurized fluid;

rotating and lowering the clean-out tool through the lower end of the tubing and into the borehole;

applying a pressurized fluid to the clean-out tool so that the first pair of members is moved to its extended position when the first pair of members is lowered below the tubing and into the borehole;

transmitting, to the surface from which the borehole and tubing extend, a signal indicating the first pair of members has moved to its extended position within the borehole below the tubing;

maintaining rotating and lowering the clean-out tool in the borehole through and after said step of transmitting and cutting the material with the extended first pair of members;

maintaining applying a pressurized fluid to the clean-out tool so that the second pair of members is moved to its extended position when the second pair of members is lowered below the tubing and into the borehole;

transmitting to the surface a signal indicating the second pair of members has moved to its extended position within the borehole below the tubing; and

maintaining the first and second pairs of members in their respective extended positions simultaneously, and concurrently continuing rotating and lowering the clean-out tool against the material in the borehole, and stabilizing the rotating clean-out tool with the extended second pair of members and cutting the material in the borehole with the extended first pair of members.

21. A method as defined in claim 20, wherein:

the first-mentioned step of transmitting includes opening a first longitudinal channel, defined through a lower portion of the clean-out tool, to the pressurized fluid; and

the second-mentioned step of transmitting includes opening a second longitudinal channel, defined through an upper portion of the clean-out tool, to the pressurized fluid.

22. A method as defined in claim 21, wherein the step of lowering a clean-out tool into the tubing includes:

rotating the clean-out tool within an upper portion of the tubing having a first diameter;

applying a pressurized fluid to the clean-out tool so that the first and second pairs of members are extended substantially to the first diameter within the upper portion of the tubing;

lowering the clean-out tool through a constriction in the tubing so that the first and second pairs of members engage the constriction and are moved back to a second diameter smaller than the first diameter;

rotating the clean-out tool within a lower portion of the tubing below the constriction, which lower portion has a diameter substantially equal to the second diameter; and

applying a pressurized fluid to the clean-out tool so that the first and second pairs of members are extended substantially to the diameter of the lower portion of the tubing within the lower portion of the tubing.

23. A downhole cutting tool, comprising:

an elongated support;

a first pair of extendible members pivotally connected to said support to move between retracted and extended positions within a first longitudinal plane;

first movement means, disposed in said support, for moving said first pair of extendible members to respective extended positions;

a second pair of extendible members pivotally connected to said support to move between retracted and extended positions within a second longitudinal plane, said second plane offset at an angle from said first plane so that said first and second pairs of extendible members effect enhanced rotational stabilization;

second movement means, disposed in said support, for moving said second pair of extendible members to respective extended positions; and

wherein said support includes:

a first cylindrical body, including a first longitudinal slot defined laterally therethrough and further including a first longitudinal cavity defined therein between an end of said first body and said first slot, said first slot having said first pair of extendible members mounted therein and said first cavity having said first movement means disposed therein;

a second cylindrical body, including a second longitudinal slot defined laterally therethrough and further including a second longitudinal cavity defined therein between an end of said second body and said second slot, said second slot having said second pair of extendible members mounted therein and said second cavity having said second movement means disposed therein; and

connector means for connecting said second body and said first body to establish said angle between said first and second planes.

24. A tool as defined in claim 23, wherein said connector means includes a third cylindrical body, including a first end threadedly connected to said end of said first body and further including a second end threadedly connected to another end of said second body so that said second body is spaced from, but in line with, said first body.

BACKGROUND OF THE INVENTION

This invention relates generally to downhole cutting tools and cleaning methods and more particularly, but not by way of limitation, to clean-out tools having enhanced stability and including longitudinal fluid channels defined therethrough and used a method for removing material from a tubular string and/or a borehole.

Casing fixed downhole in a well bore sometimes needs to be cleaned of cement, sand, shale, mud and other types of deposits as is known in the oil and gas industry. This requires a type of tool which can be lowered through a relatively narrow diameter tubing string to clean the tubing string and which can be lowered for subsequent use to clean below the lower end of the tubing string in the relatively wider diameter casing. This type of tool will be referred to herein as an enhanced diameter clean-out tool, or simply a clean-out tool. An early form of such a clean-out tool which has been in commercial use is disclosed in my U.S. patent application Ser. No. 888,418, filed July 23, 1986, now abandoned.

Other types of tools have been disclosed to include blades which are to be retracted within the support portion of the tool so that the blades and the tool can pass through tubing string having an inner diameter smaller than the maximum diameter of the blades when they are extended. Once having passed through the tubing string, the blades can be extended outwardly to cut out a diameter up to substantially the inner diameter of the casing or other borehole surface within which the tool is used.

It is my understanding that some tools which have been proposed or used have utilized springs to extend or retract the blades or have otherwise been mechanically operated to achieve the movement of the blades between their extended and retracted positions. Pistons moved by pressurized fluid have also been used to extend the blades. Some of these tools also have had jet ports through which fluid can be ejected to assist in cutting the material and in subsequently flushing the cut material out of the well. Others use ports which are opened to pressure-affecting fluid flow in response to the blades being extended.

Larger diameter tools of a generally similar type have been used in the cutting and parting of casing strings but these have not been of a type that can be passed through smaller diameter tubulars.

I am also aware of a pipe or casing cutter which cuts pipe or casing at its outer point and not along its side edges. A specific type of cutter of which I am aware is a Bowen internal pressure pipe cutter having a plurality of knives each separately pivotally connected within a body in which a piston is also disposed. The piston is used to drive the blades outwardly to apply pressure by which a pipe is cut.

A formation notching apparatus including two sets of cutting elements is disclosed in U.S. Pat. No. 3,050,122.

Although there are various types of downhole cutting devices, there has existed the need for an improved clean-out tool which has enhanced stability so that it can be used effectively, without substantial vibrations being created, on what is known as a coil tubing motor. An example of one such motor is known as a SLIMDRIL motor marketed by SlimDril, Inc. of Houston, Tex. There has also existed the need for an improved clean-out tool which provides significant liquid flow longitudinally through it for washing out, or otherwise lubricating, cuttings but which also generates through such liquid flow signals indicating when the extendible elements of the tool have opened.

SUMMARY OF THE INVENTION

The present invention meets the aforementioned needs by providing a downhole enhanced diameter clean-out tool which includes channels through which cutting-lubricating liquid flows to provide signals indicating when extendible elements of the tool have opened. In one embodiment the tool has two sets of extendible elements angularly offset relative to each other to provide enhanced stability when the tool is rotated.

One embodiment of the downhole enhanced diameter clean-out tool of the present invention comprises: a body including a slot defined laterally therethrough and further including a longitudinal cavity defined therein in communication with the slot; two cutting members pivotally mounted in the slot; movement means, disposed in the cavity so that the movement means is movable between a first position in the cavity and a second position in the cavity, for moving the cutting members to respective extended positions in response to a force acting on the movement means to move the movement means from the first position to the second position; and the body further including: first channel means, defined in the body and spaced from the slot, for communicating a liquid from the cavity to an outlet of the first channel means regardless of the position of the movement means between the first and second positions; and second channel means, defined in the body and spaced from the slot and the first channel means, for communicating a liquid from the cavity to an outlet of the second channel means in response to the movement means moving from the first position to the second position.

Another embodiment of the downhole enhanced diameter clean-out tool of the present invention comprises: an elongated support; a first pair of extendible members pivotally connected to the support to move between retracted and extended positions within a first longitudinal plane; first movement means, disposed in the support, for moving the first pair of extendible members to respective extended positions; a second pair of extendible members pivotally connected to the support to move between retracted and extended positions within a second longitudinal plane, the second plane offset at an angle from the first plane so that the first and second pairs of extendible members effect enhanced rotational stabilization when the support is rotated; and second movement means, disposed in the support, for moving the second pair of extendible members to respective extended positions.

The present invention also encompasses a method of cutting material, such as cement, located within a borehole, such as a cased well bore, having tubing located in the borehole. This method comprises the steps of: lowering a clean-out tool into the tubing, which clean-out tool includes a first pair of members movable below the tubing to an extended position in response to a pressurized fluid, and a second pair of members movable below the tubing to an extended position in response to a pressurized fluid; rotating and lowering the clean-out tool through the lower end of the tubing and into the borehole; applying a pressurized fluid to the clean-out tool so that the first pair of members is moved to its extended position when the first pair of members is lowered below the tubing and into the borehole; transmitting, to the surface from which the borehole and tubing extend, a signal indicating the first pair of members has moved to its extended position within the borehole below the tubing; maintaining rotating and lowering the clean-out tool in the borehole through and after the step of transmitting and cutting the material with the extended first pair of members; maintaining applying a pressurized fluid to the clean-out tool so that the second pair of members is moved to its extended position when the second pair of members is lowered below the tubing and into the borehole; transmitting to the surface a signal indicating the second pair of members has moved to its extended position within the borehole below the tubing; and maintaining the first and second pairs of members in their respective extended positions simultaneously, and concurrently continuing rotating and lowering the clean-out tool against the material in the borehole and stabilizing the rotating clean-out tool with the extended second pair of members and cutting the material in the borehole with the extended first pair of members.

Therefore, from the foregoing, it is a general object of the present invention to provide a novel and improved downhole enhanced diameter clean-out tool and method. Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art when the following description of the preferred embodiments is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic illustration of a preferred embodiment of the clean-out tool of the present invention located within a tubing string disposed within a cased well bore, which tool is shown as having fluid pressure applied thereto so that extendible members are partially extended to clean the inside of the tubing string.

FIG. 1B is a schematic illustration showing the preferred embodiment of the tool from FIG. 1A in a lower position so that a set of extendible members (specifically, cutting members) of the tool are opened below the tubing string.

FIG. 1C is a schematic illustration showing the preferred embodiment of the tool from FIG. 1A in a still lower position so that both the set of cutting members and an upper set of the extendible members, used primarily for stabilization but also possibly providing some cutting, are opened below the tubing string.

FIG. 2 is an elevational view of the tool schematically shown in FIGS. 1A-1C.

FIG. 3 is a top view of the tool as taken along line 3--3 shown in FIG. 2 but without the illustrated connected conveyancing structure.

FIG. 4 is a sectional elevational view, taken along line 4--4 shown in FIG. 3, wherein the sets of extendible elements are in retracted positions.

FIG. 5 is a sectional elevational view as illustrated in FIG. 4, but showing, the sets of extendible elements in extended positions.

FIG. 6 is a sectional view taken along line 6--6 shown in FIG. 2.

FIG. 7 is a sectional view taken along line 7--7 shown in FIG. 2.

FIG. 8 is a sectional elevational view taken along line 8--8 shown in FIG. 7.

FIG. 9 is a sectional elevational view as shown in FIG. 8 but showing passageways converging to a central indentation in the bottom of the tool.

FIG. 10 is a schematic illustration of casing in which are disposed two tubing strings of different diameters (but both smaller than the diameter of the casing) connected in line; this illustrates another structure in which the present invention is contemplated to have utility.

FIG. 11A schematically shows a portion of another embodiment of the clean-out tool of the present invention under pressure and positioned in the larger diameter tubing string of the structure represented in FIG. 10.

FIG. 11B schematically shows the portion of the tool depicted in FIG. 11A after it has been lowered into the smaller diameter tubing string of the structure represented in FIG. 10.

FIG. 11C schematically shows the same portion of the tool depicted in FIGS. 11A and 11B but now lowered below the connected tubing strings and into the casing of the structure represented in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A-1C illustrate three stages of usage of the present invention within a downhole environment. This environment includes a well bore 2 having a cased or uncased borehole. As illustrated, the well bore 2 is cased with suitable casing 4 (e.g., 7-inch casing).

Disposed within the well bore 2 is a tubing string 6 of a suitable type as known to the art (e.g., 41/2-inch tubing). As illustrated, the tubing string 6 is centered coaxially within the casing 4; however, the present invention is also useful where a tubing string is off-centered.

Lowered into the tubing string 6 is a downhole enhanced diameter clean-out tool 8 schematically shown in FIGS. 1A-1C but more particularly described hereinbelow and embodying a preferred embodiment of the apparatus of the present invention. The tool 8 is moved into and out of the tubing string 6 and the well bore 2 on suitable conveyancing means 10 of a type as known to the art. One example of such a conveyancing means is a coil tubing motor apparatus of a type as known to the art for rotating and lowering (and subsequently raising) the tool 8. An example of a coil tubing motor apparatus is one including a SLIMDRIL motor of SlimDril, Inc. of Houston, Tex. Another example of a conveyancing means is a tubing string of smaller diameter than the tubing string 6.

The downhole tool 8 is used to cut material 12 located in the borehole and/or the tubing string 6. An example of such material is cement which has been pumped into the well bore for a known purpose and which has set up (hardened).

FIG. 1A illustrates the tool 8 at an initial stage of cutting. This cutting occurs within the tubing string 6 and is done with cutting elements 14 located on the bottom end (as oriented in FIG. 1A) of the tool 8. The cutting elements 14 have an overall width substantially equal to the width of the main body of the tool 8; therefore, the cutting elements 14 cut material within a path which is in line with the tool 8 and which has a cross-sectional area substantially the same as the maximum cross-sectional area of the main body of the tool 8. Cutting is also done in part by extendible members 16, 18 which are partially extended by fluid pressure exerted down through the conveyancing means 10 to the tool 8 in a manner known to the art. The members 16, 18 are only partially extended because they are limited by the inner diameter of the tubing string 6 which is not to be cut by the tool 8. Prior to application of fluid pressure, the members 16, 18 are fully retracted to the position illustrated in FIG. 4.

As the conveyancing means 10 rotates and lowers the tool 8, cutting continues as just described until the lower set of extendible members 16 (comprising two pieces 16a, 16b in the depicted preferred embodiments and shaped as shown in FIGS. 4 and 5) is moved below the bottom of the tubing string 6. This position is illustrated in FIG. 1B. At this point of the operation, the fluid (e.g., hydraulic) pressure exerted through the tubing string 6 opens farther the cutting members 16, which thereafter cut a wider (i.e., enhanced diameter) path radially beyond what the bottom cutting elements 14 cut. As subsequently described, a signal is generated for communication to the surface at this time so that accurate positioning of the tool 8 can be known (i.e., by indicating that the lower members 16 are just below the tubing string 6, which has a length which is known). Such signal also indicates the opening or extension and the degree of opening or extension of the set of members 16.

Continued rotation and lowering of the tool 8 ultimately moves the upper set of members 18, functioning primarily as stabilizers but also being of a cutting construction (and shaped) the same as the members 16 so that the members 18 are sometimes referred to herein as an upper set of cutting members, below the bottom of the tubing string 6 and into open or extended positions in response to the fluid pressure within the tubing string 6. This position is illustrated in FIG. 1C. Another signal is generated at this time to mark the position of the tool 8 and the opening (and degree thereof) of the stabilizer members 18 (which are illustrated as including two pieces 18a, 18b). Use of the stabilizers in this exemplary environment, wherein the tool 8 is driven by a coil tubing motor, is important to enhance the stability of the tool 8 during rotation within the wider region below the tubing string 6, which enhanced stability reduces vibrations or "chattering" arising from the tool being rotated within a cut region having a significantly wider diameter than the diameter of the main support body of the tool 8.

With reference to FIGS. 2-9, preferred embodiments of the downhole cutting tool 8 will be more particularly described. The tool 8 includes an elongated support 20 comprising a cylindrical body 22, a cylindrical body 24, and connector means 26 for connecting the two bodies 22, 24 to establish an angle between the set of cutting members 16 associated with the body 22 and the set of cutting members 18 associated with the body 24. The cylindrical body 22 provides support for a lower subassembly 28, and the cylindrical body 24 provides support for an upper subassembly 30. In the preferred embodiment of FIG. 2 the two subassemblies are connected through an adapter defined by the connector means 26.

The connector means 26, or adapter, of the preferred embodiments of FIGS. 2-9 has a cylindrical shape defined by an annular wall 32 (FIGS. 4 and 5). A threaded inner surface 34 defines a coupling receptacle for threadedly engaging with a mating portion of the cylindrical body 24. A threaded outer surface 36 is part of a protuberant portion of the adapter 26 for engaging with a mating portion of the cylindrical body 22. The adapter 26 is used in the preferred embodiments to establish a predetermined angle by which a longitudinal plane in which the stabilizing cutting members 18 are retained is circumferentially offset from a longitudinal plane in which the cutting members 16 are retained. This offset is obtained by appropriately machining an upper radial surface 38 against which a surface of the body 24 abuts when the body 24 is connected to the adapter 26. That is, by machining the surface 38, one can control the degree to which the cylindrical body 24 can be screwed into the adapter 26 thereby defining the relationship between a longitudinal plane of the cutting members 18 and the body of the adapter 26 and thus the relationship to the lower cylindrical body 22. This angular offset is important to provide for the enhanced rotational stability. In the illustrated preferred embodiments the angle is about 90.degree. (as illustrated, a longitudinal plane for the members 16 could include the sheet containing FIG. 4 and a longitudinal plane for the members 18 would include one perpendicular to the sheet containing FIG. 4). Of course, this relative positioning could be obtained by other suitable means. As is apparent from the drawings, the cylindrical body of the adapter 26 spaces or separates the two bodies 22, 24 from e