US2754090A

US2754090A - Stage expansible rotary drill bits

Info

Publication number: US2754090A
Application number: US393724A
Authority: US
Inventors: Archer W Kammerer
Original assignee: Rotary Oil Tool Co
Current assignee: Rotary Oil Tool Co
Priority date: 1953-11-23
Filing date: 1953-11-23
Publication date: 1956-07-10
Anticipated expiration: 1973-07-10

Description

July 10, 1956 A, w. KAMMERER 2,754,090

STAGE EXPANSIBLE ROTARY DRILL BITS Filed NOV. 25, 1953 2 Sheets-Sheet l MAN.

JNVENToR. 22 Aem/se /l/ KAM/veeel?,

r rice/YE Y.

July 10, 1956 A. W KAMMERER 2,754,090

STAGE EXPANSIBLEI ROTARY DRILL BITS Filed NOV. 23, 1953 2 Sheets-Sheet 2 J4 INVENTOR.

.4T Tae/Vey.

Aem-.15e W HAM/145252,

2,754,090 STAGE EXPANSIBLE RGTARY DRILL BITS Archer W. Kammerer, Fullerton, Calif., assignor, by

direct and mesne assignments, to Rotary Oil Tool Company, Huntington Park, Calif., a corporation of California Application November23, 1953, Serial No. 393,724 11 Claims. (Cl. 255-76) The present invention relates to drill bits, and more particularly to bits of the expansible type wihch are capable of drilling or enlarging a bore hole below a string of casing to a larger diameter than the inside diameter of the casing string. y

An object of the present invention is to provide an improved expansible rotary drill bit which is capable of greatly increasing the diameter of the bore hole in stages, particularly in relatively hard formations.

Another object of the invention is to provide an expansible rotary drill bit embodying a tandem arrangement of sets of cutters for increasing the diameter of the bore hole in stages, in which the sets of cutters are locked initially in retracted position and are selectively released for outward expansion to increase the bore hole diameter, the upper set of cutters increasing the diameter of the hole to a greater extent than the lower set of cutters.

A further object of the invention is to provide an expansible rotary drill bit embodying a tandem arrangement of sets of cutters for increasing the diameter of the bore hole in stages, each set of cutters being locked positively in an expanded position to prevent inadvertent retraction of the cutters. In a more limited sense, the lower set of cutters can be locked in its expanded position before the upper set of cutters and, for that matter, before outward expansion of the upper set of cutters has commenced.

Yet another object of the invention is to provide an expansible rotary drill bit in which lower and upper sets of cutters can be locked positively in their outward expanded position by a simple device, which is common to both sets of cutters, the cutters being easily released from their outwardly expanded positions to enable their retraction and removal of the drill bit to the top of the bore hole.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of a form in which it may be embodied. This form is shown in the drawings accompanying and forming part of the present specilication. It 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 description is not to be taken in a limitingsense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a longitudinal section through an expansible rotary drill bit disposed in a well bore, with the cutter members held in their retracted position, the section being taken generally along the line 1 1 on Fig. 4;

Fig. 2 is a view similar to Fig. 1, in which the lower set of cutters has been released and expanded to its maximum hole enlarging diameter;

Fig. 3 is a view similar to Figs. 1 and 2, in which the upper set of cutters has also been expanded outwardly ,to its maximum hole enlarging diameter;

Patented July 10, 1956 Fig. 4 is a cross-section, on an enlarged scale, taken along the line 4 4 on Fig. 1;

Fig. 5 is a cross-section, on an enlarged scale, taken along the line 5 5 on Fig. 3;

Fig. 6 is a cross-section, on an enlarged scale, taken along the line 6 6 on Fig. 3.

In its general aspects, the invention contemplates a drill bit that is capable of being lowered through a well casing and enlarging a well bore below the casing shoe to a substantial extent. The drill bit is comparatively compact, despite the fact that it embodies a tandem arrangement of sets of outwardly expansible cutters. Both sets of cutters are positively held initially in retracted position, the lower set rst being released and expanded outwardly to its maximum position, where it is locked positively in such outward position. Thereafter, the second or upper set of cutters is released and expanded outwardly to its maximum hole enlarging diameter, which is greater than the diameter of the hole that can be drilled by the lower set of cutters. The upper set is then positively locked in its outwardly expanded position without disturbing the locked relationship of the lower set of cutters in their maximum expanded position. A single device is used for locking all sets of cutters in their outward expanded position.

As disclosed in the drawings, it is desired to drill or enlarge a well bore A below a string of well casing B to a diameter substantially greater than the inside diameter of the casing and of the casing shoe C forming the terminal end of the string of casing. A single rotary expansible drill bit is provided for this purpose. This drill bit includes an elongate main body 10 carrying upper and lower sets of

cutter devices

11, 12 which are capable of operating upon the wall of the well bore A. The lower end of the body 10 may be formed as a pilot bit 13, serving to center the tool in the well bore, or for drilling the central portion of the hole in the absence of a pre-existing hole below the casing shoe C.

The upper and lower sets of

cutter devices

11, 12 are essentially duplicates of one another, so that a specilic description of one set, such as the lower set 12, will suice for both sets. It is sufficient to state at this time that the lower set of cutter devices 12 is adapted to enlarge the diameter of the bore hole to a certain intermediate extent, the cutters 14 of this set forming and acting upon a transverse formation shoulder D produced by the cutters in the well bore. The cutters 15 of the upper set of devices 11 are expandible outwardly to a greater extent than the lower cutters 14 to enlarge the well bore to a still greater diameter, these cutters 15 producing and operating upon a transverse formation shoulder E outside the path D traced by the lower set of cutters.

Circumferentially spaced cutter supporting members 16 may be disposed equi-angularly around the main body 10 of the tool, these cutter supporting members being located within transverse slots 17 in the body. Each cutter supporting member 16 is pivotally mounted on a pivot or hinge pin 18 extending therethrough and suitably secured, as by welding, to the body. Depending from each pin 18 is a leg portion 19 of the cutter supporting member having a downward and inwardly inclined bearing pin 20 at its lower end rotatably receiving a roller side cutter 14, which is appropriately mounted on the pin 2t) through the agency of roller bearing elements 21 and ball bearing elements 22 capable of being interposed between the bearing supporting pin and cutter in any known and suitable manner.

Upwardly from the pin 18, each cutter supporting member 16 is constituted by an ann 23 against which one end of a compression expander spring 24 bears, the spring being received within a body socket 25 with its outer portion bearing upon the body 10. It

Jce

is evident that each compression spring 24, which is arranged with its axis transversely of the bit, tends to force the cutter supporting arm 23 inwardly to urge the depending 'leg '19', :and the roller cutter 14 .mounted vthereon, in an outward direction. Thespring 2o, when permitted to expand the cutter 14 in outward direction, can only do so to the extent determined by engagement of a stop shoulder 26 .on the cutter supporting member above the hinge pin with the upper end 27 -of the body slot l. Thus when :the stop shoulders 26 on the cutter supporting members 16 engage fthe upper en `s of the slots i7, 'the cutters 14 will have been `expanded outwardly to their maximum hole enlarging-diameter.

iheupperset of cutter supporting members ien, `cutters It, springs V24er, and the like, vare essentially the same as the lower set. However, it -is desired to have the uppe set of cutters F15 expand outwardly Yto a greater maximum diameter than @the 'lower set. The arms 23a may disposed above the hinge Apins 1Sa-ot the upper of devices to essentially lthe same extent as the `lower set oi arms 23. However, ftor the same angular motion of the upper cutter supporting members i661', the upper cutters l may be moved outwardly lto agreater extent by making the depending leg portions i9a of the cutter supporting members longer, so that the cutters l5 extend downwardly from the hinge kpins 18a to a greater extent. When the uppe-r Astop `shoulders 26a engage the upper ends 27a of the upper slots 17a, the cutters le? will be in their maximum outward expanded position, in order to enlarge the diameter of the well bore to a greater extent than the enlarged well bore diameter produced by the lower set ofl cutters 14, when 'the latter have been expadded outwardly to their maximum extent. lt is preferable that the upper 4set of cutters 1S have their inner tooth portions overlap the path Ytraced by the lower set of cutters 'il-l to a slight extent to insure the removal or the yformation'material and the enlargement of the well bore diameter to the desired maximum extent.

After the cutters 14, l5 have been expanded outward ly, they are locked or held in their maximum outward expanded position to prevent their inadvertent retraction to even a partial extent, which might result in the production of an undergauged hole. The outward loching of .cutters is accomplished by a mandrel 3% telescoped within the body l0. This mandrel includes an upper Kelly or drill stem member 31 which has alower portion `provided with an external non-circular shape 32, such as a hexagonal shape, received within a companion non-circular or .hexagonal socket 33 in the body le. The upper end of vthis Kelly portion of the mandrel is provided with a pin 3d threadedinto a sub 35 threadedly secured to the lower end of a string of drill pipe F extending to the top of the well bore. The mandrel 3b also includes a tubular member 36 extending .through the Kelly portion 3l, with a shoulder 37 on .the tubular member engaging ya 4companion shoulder 33 on the Kelly. The tubular .member 36 and Kelly 31 may be secured together, as by .threading a nut 39 on the .upper threaded -end d@ of the .tubular member, whichengages an upper shoulder il in the Kelly adjacent its pin 34.

The mandrel .39 is insertable .in the body lil of the tool, Kwith the tubular member 36 extending downwardly through the region of the upper setof cutters l5 and rntothe region of the lower set of cutters 14, the lower end of `the tubular member 'being movable longitudinally through a lower .bearing guide 42 forming part of the body and extending transversely -thereacross The mandrel Btl lcan partake 'of longitudinal movement with respect to the body lil, its downward movement being limited by engagement of the lower end 43 of the Kelly with a guide washer dit resting upon `a Vbody shoulder 45. Upward movement of the mandrel 30 audits removal from the body is prevented by an external shoulder or tl'ange 46 provided on the Kelly above its hexagonal portion 32 received within a counterbore 47 in the body 16 above its hexagonal socket 33 and engageable with a retainer ring 4S encompassing the Kelly and suitably secured to the body, as by use of welding material 49.

The mandrel 30 has several purposes. It Serves as the instrumentality for connecting the drill bit to the string of drill pipe F. It also functions to transfer the rotation of the drill pipe F to the main body 1) of the tool through the Kelly portion 3l and the companion hexagonal or non-circular socket 33 in the body. Initially, the mandrel Sil occupies an upward position within the body lll, but upon outward expansion of each set of cutters lll, l5 to their maximum extent, the mandrel can be lowered with respect to the body, to lock the cutters in their outward expanded position. Thus, the lower portion oi the tubular member 36 has a lock ring Sti initially disposed within recesses 51 in the cutter supporting members lo of the lower set above inwardly directed locking lugs 52 provided on the cutter supporting members. These Vlugs 'initially extend :inwardly under the lower lock ring Sil. Similarly, the mandrel 3i) is `provided 'with an upper lock ring 53 received initially Vwithin recesses 54 in the upper cutter supporting members 16a located above inwardly extending lock lugs 55 on the upper supporting members, the locking lugs extending under the upper lock ring 53.

After the lower Aset of cutters i4 has been expanded outwardly by the Ysprings 24 to their maximum extent, determined by engagement of the supporting member stop shoulders 26 with the companion body stop shoulders 27, the `lower cutters are Vresting upon an annular formation shoulder' D. The drill pipe F may then be lowered, to lower the mandrel 3i) and shift the lower lock ring Eid `within and behind the lower lugs 52. Accordingly, any reactive force of the formation on the lower cutters le cannot shift them inwardly, since such action is resisted by the engagement of the lugs 52 with the lock ring 5t?. Similarly, after the upper set of cutters l5 has been expanded outwardly to their maximum extent, determined by engagement of the upper stop shoulders 26a ou the supporting .members 16a with the body stop s'houl ders 27a, the mandrel 3i) is lowered with respect to the body it) to shift the lock ring 53 behind the lugs 5S of the upper cutter supporting members, to prevent the upper cutters 15 from being shifted inadvertently toward a retracted position. lt is preferred that the upper locifL ring "53 be disposed initially above the upper supporting member lugs .55 to a substantially greater extent than the lower lock ring 50 Vwith respect to the lower supporting member lugs 52, inorder that the lower cutters iid can be locked outwardly lin .their maximum .expanded position before the upper cutters 15 are locked outwardly in their maximum expanded position, or, for that matter, even before the upper cutters are expanded outwardly from their initial retracted position.

The lower set of cutters 14 is held initially in retracted position by a latching device, which is hydraulically releasable. Thus, the lower cutter supporting members lo may be provided with hooks 60 received within holes 61 in a latch plate 62 extending across a central passage 63 through the tubular member 36 and immediately below the latter. Theupper set of cutters 15 is also held initially in a retracted position by securing hooks 64 to the upper cutter supporting members 16a, which are received within holes 65 in a latch plate 66 secured to the tubular member 36 in any suitable manner. The lower latch plate 62 is removed hydraulically from the hooks oil, to allow the lower cutters 14 to be released. The securing vof `the latch plate 66 tothe mandrel 30 .provides a mechanical release of the plate 66 .from 'the upper set of hooks 5d through downward movement of the tubular member 36 with respect to such hooks. Such downward movement of the mandrel member 36 .also locates the lower lock ring 53 behind the lower stop lugs 52. it is preferred that the lower lock ring 50 Ybe placed in its locking position behind the lower lugs S2 before the upper latch plate 66 is released from the hooks 64. For that reason, the depending portions 67 of the hooks 64 are made suiciently long, so that the lower ring 50 is behind the lugs 52 before the plate 66 is moved downwardly off the upper hook elements 64.

In the operation of the apparatus disclosed, the mandrel 30 is initially disposed in its upper position within the body 19, to place the lock rings 50, 53 above their respective companion lock lugs 52, 55 on the

cutter supporting members

16, 16a. The upper latch plate 66 is connected to the upper hooks 64, to hold the upper set of cutters 15 in retracted position, whereas the lower latch plate 62 is connected to the lower hooks 60 to hold the lower set of cutter supporting members 16 and the lower cutters 14 in retracted position.

The rotary drill bit is secured to the drill pipe F and is lowered through the well casing B and into the bore hole A below the casing shoe C. When the position in the bore hole is reached at which the hole enlarging operation is to commence, the drill pipe F is rotated and Huid under pressure pumped down the drill pipe to ilow through the tubular member passage 63 and impinge upon the lower latch plate 62. The force of the stream of fluid issuing from the tubular member will remove the plate 62 from the hooks 60, which then allows the expanding springs 24 to shift the arms 23 of the lower cutter supporting members 16 inwardly and urge the cutters 14 outwardly against the wall of the well bore A. The drill pipe F is rotated without attempting to impose down weight on the tool until the cutters 14 have been expanded outwardly to their maximum extent, determined by engagement of the lower stop shoulders 26 with the companion body stop shoulders 27. At this time, the lower cutters 14 will have produced the transverse formation shoulder D in the wall of the well bore which is capable of supporting the body 1i) of the tool.

After the formation shoulder D has been produced, the rotation of the drill pipe F can continue, to rotate the body and the cutters 14 around the axis of the apparatus and of the well bore. Down weight is now imposed upon the drill pipe F, to shift the mandrel 30 downwardly within the body and to locate the lower lock ring 56 behind the lugs 52 of the lower supporting members 16, thereby positively locking the lower supporting members and the lower cutters 14 in their maximum outward expanded position (Fig. 2.) Such location of the lower ring 50 behind the lower lugs 52, at least to a partial extent, occurs before the downward movement of the tubular member 36 with respect to the body 10 will shift the latch plate 66 off the upper set of hooks 64. Downward movement of the dr' pipe and the mandrel with respect to the body to a slightly greater extent will now shift the upper plate 66 from the upper hooks 64, and this action will occur before the upper lock ring 53 engages the upper set of lugs 55, which are still projecting inwardly below the upper lock ring.

The removal of the upper latch plate 66 from the hooks 64 then allows the upper set of springs 24a to expand, urging the upper cutter arms 23a inwardly and the depending leg portions 19a and upper set of cutters 15 in an outward direction against the wall of the well bore. Rotation of the drill pipe F continues, the springs 24a expanding the upper cutters voutwardly until they are shifted to their maximum outward extent, determined by engagement of the upper stop shoulders 26a with the companion body shoulders 27a. When in this position, the upper cutters 15 have enlarged the diameter of the well bore to a greater extent than the lower set of cutters 14 and are bearing upon a formation shoulder E outside of the annular path of the lower formation shoulder D produced by the lower set of cutters 14.

When the upper set of cutters 15 has been expanded outwardly to the maximum extent, downward movement of the drill pipe F with respect to the body 10 to a still further extent will now dispose the upper lock ring 53 behind the upper set of lugs 55, to positively hold the upper set of cutters 15 in their maximum outwardly expanded position. During such additional downward movement, the lower lock ring 50 merely moves downwardly to a further extent behind the lower lugs 52, but always remains in substantial bearing engagement therewith. The mandrel 30 is movable downwardly within the body 10 to the extent determined by engagement of the lower end 43 of the Kelly or drill stem member 31 with the washer 44.

Rotation of the drill pipe F can continue to rotate the body 10 of the tool while down weight is being imposed upon the

cutters

14, 15, the lower set 14 of cutters operating on the inner formation shoulder D and moving downwardly progressively to enlarge the well bore to an intermediate diameter, whereas the upper set of cutters 15 is operating on the outer formation shoulder E at the same time, to enlarge the diameter of the well bore to a still greater extent. Drilling proceeds until the well bore has been enlarged to the desired depth, whereupon the tool can be retrieved from the hole. At first, the drill pipe F and the mandrel 30 attached thereto are moved upwardly, which elevates the tubular member 36 within the body 10 and moves the upper and lower lock rings 53, 5t) above their respective companion stop lugs S5, 52, so as to remove the restraint to retraction of the sets of

cutters

14, 15. The cutters will remain in their outward expanded positions until the drill bit has been elevated into a smaller diameter well bore above the region where the hole enlarging operation occurred, or until the

cutter supporting members

16a, 16 engage the casing shoe C. Such engagement will shift the upper legs 19a and the upper set of cutters 15 inwardly to a retracted position, the wall of the casing B thereafter holding the parts in such retracted position. As elevation of the tool continues, the lower set of legs 19 will engage the casing shoe C, the casing shoe also shifting the lower legs 19 and lower cutters 14 inwardly to their retracted position, where they will remain by virtue of the holding action of the inner wall of the casing B upon the lower set of depending legs. The drill pipe F can be raised, to elevate the expansible rotary drill bit in the well casing to the top of the hole, where the tool can be removed from the latter.

It is, accordingly, apparent that a rotary expansible drill bit has been provided with which the hole enlarging operation takes place in stages. The cutters are held initially in their retracted position, the upper and lower sets of cutters being released whenever their outward expansion is to occur. When they have been expanded outwardly to their fullest extents, then the cutters are locked in such outward expanded position. More specically, the lower set of cutters 14 is released for outward expansion and is locked in its maximum outward expanded position before the upper set of cutters 15 is released for expansion outwardly to enlarge the hole to a greater maximum extent than is produced by the lower set of cutters, whereupon the upper set of cutters is also locked outwardly in its maximum expanded position. A single instrumentality is availed of for locking both sets of

cutters

14, 15 outwardly, this instrumentality being elevated when the bit is to be retrieved from the well bore, to unlock the cutters and enable them to be shifted to their retracted positions.

The inventor claims:

l. A rotary well drilling bit, including a main body, upper and lower cutter means mounted on said body, means engaging said lower cutter means for expanding said lower cutter means laterally outward to drill a hole of a predetermined diameter, means engaging said upper cutter means for expanding said upper cutter means laterally outward to a position wherein said upper cutter means drills a hole of a greater predetermined diameter than said lower cutter means, a mandrel slidably splined `to saidbody, said mandrel 'having a connection for securing said mandreldirectly to a drill string, whereby torque is transmitted from the drill string to said mandrel and from said mandrel to said body, said mandrel having upper and lower lock means thereon engageable with said upper and lower cutter means, respectively, for preventing .inward movement of said upper and lower cutter means from their respective outwardly expanded positions,.said upper and lower lock means being spaced from each other such that 'longitudinal movement of said mandrel in one longitudinal direction relative to said body engages said lower lock means with said lower cutter means to loc'lt said 4lower cutter means outwardly prior to engagementof said upper lock means with said upper cutter means to lock said upper cutter means outwardly.

2. A rotary drill bit, including a main body, lower cutter means mounted on said body and expandible ylaterally outward of said body to drill a hole of a predetermined diameter, Vupper cutter means mounted on said body and expandible .laterally outward of said body to drill a hole of a greater predetermined diameter than said lower cutter means, means engageable with said upper andlower cutter means Sfor so expanding said upper and lower cutter means and to locl; said upper and lower cutter means in their respective expanded positions, said expanding and locking means comprising `a mandrel slidably splined to said body, said mandrel having a connection for securing said .mandrel directly to `a drill string, whereby torque is transmitted from the drill string to said mandrel and from said mandrel to said body, said mandrel having upper and lower lo means thereon engageable with'said upper and 'lower cutter means, respectively, for preventing inward movement of said upper and lower cutter means from their respective outwardly expanded positions, said upper md lower lock means being spaced from each other such that longitudinal movement of said mandrel in one-longitudinal direction relative to said body enga-ges said lower locl; means with said lower cutter means to loclt said lower cutter eans outwardly prior to engagement of said upper lock means with said upper cutter means to lock said Vupper cutter means outwardly.

v3. A rotary well drilling bit, including a main body, upper and lower cutter means mounted on said body, means engaging said lower cutter means for expanding said lower cutter means laterally outward to drill a hole of a predetermined diameter, means engaging said upper cutter lmeans for expanding said upper cutter means laterally outward to a position wherein said upper cutter means drills a hole of a greater predetermined diameter than said lower cutter means, a mandrel siidably splincd to lsaid body and adapted to be connected directly to a drill string, said mandrel having upper and lower loci; means thereon engageable with said upper and lower cutter means,.respeetively, for preventing inward movement of said upper and lower cutter means from their respective outwardly expanded positions, said upper and lower lock'meansibeing spaced from cach other such that longitudinal movement of said mandrel in one longitudinal direction relative to said body engages said lower locit means with .said lower cutter means to lock said lower cutter means outwardlyprior to engagement of said upper lock means with said upper cutter means to loci(` said upper cutter means outwardly, releasable latch means engaging said lower cutter means to hold said lower cutter means outwardly in retracted position on said body, and releasable latch means engaging said upper cutter means to 'hold said upper cutter means initially in retracted position on said body.

4. A rotary well drilling bit, including a main body, upper .and lower cutter means mounted on said body, means engaging said lower cutter means for expanding said lower cutter means laterally' outward to drill a hole of a predetermined diameter, means engaging said upper cutter means for expanding said upper cutter means latorallyV outward to a position wherein said upper cutter means drills a hole of a greater vpredetermined diameter than .said lower 'cutter means, a mandrel slidably splined to 'said body and adapted tozbe connected directly to a drill string, saidniandrel having upper and lower lock means thereon engagea'ble with 4said upper and lower cutter means, respectively, for preventing inward movement of said upper and lower cutter means from their respective outwardly expanded positions, said upper and lower locl; means `being spaced from eachother such that longitudinal movement of said mandrel in one longitudinal direction relative to said body engages said lower lock means with said lower cutter Vmeans vto lock said lower cutter means outwardly prior to engagement of said upper lock means with said upper cutter means Vto lock said upper cutter means outwardly, releasable latch vmeans engaging said lower cutter means to hold said lower cutter means outwardly in retracted position on said body, and releasable latch means engaging said upper cutter means to hold said upper cutter means vinitially in retracted position on said body and releasable Vin response to longitudinal movement of said mandrel when shifting said 'lower lock means into locking engagement with'said lower cutter means.

5. A rotary drill bit, including a main body, lower cutter means Amo-unted on said body and expandible laterally outward of said body to drill a hole of a predetermined diameter, upper cutter means mounted on said body and expandible laterally outward of said 'body to drill a hole of a greater predetermined diameter than said lower cutter means, means engageable with said upper and lower cutter means for so expanding said upper and lower cutter means and to lock said upper and lower cutter means in their respective expanded positions, said expanding and locking means comprising a mandrel slidably splined to said body and adapted to be connected directly to a drill string, said mandrel having upper and lower lock means thereon engageable with said upper and lower cutter means, respectively, for preventing inward movement of said upper and lower cutter means from their respective outwardly expanded positions, said upper and lower lock means being spaced from each other such that longitudinal movement .of said rmandrel in one longitudinal direction relative to said body engages said lower lock means with said lower cutter means to lock said lower cutter means outwardly prior to `engagement of said upper lock means with said upper cutter means to lock said upper cutter means outwardly, releasable latch means engaging said lower cutter means to hold said `lower cutter means initially in retracted position on said body, and releasable atch means engaging said upper cutter means to hold said upper cutter means initially in retracted position on said body.

6. A rotary drill bit, including a main body, lower cutter means mounted on said body and expandible laterally outward of said body to drill a hole of a predetermined diameter, upper .cutter means mounted on said body and expandible laterally outward of said body to drill a hole of a greater predetermined diameter than said lower cutter means, means engageable with said upper and lower cutter means for so expanding said upper and lower cutter means and to lock said upper and lower cutter means in their respective expanded positions, said expanding and locking means comprising a mandrel slidably splined to said body and adapted to 'be connected directly to a drill string, vsaid mandrel having upper and lower lock means thereon engageable with said upper and lower cutter means, respectively, for preventing inward movement of said upper and lower cutter means from `their respective outwardly expanded positions, said upper and lower lock means being spaced from each other such that longitudinal movement `of said mandrel in one longitudinal direction relative to saidbody engages said lower lock means with said lower cutter means to lock said lower cutter means outwardly prior to engagement of said upper lock means with said upper cutter means to lock said upper cutter means outwardly, releasablelatch means engaging said lower cutter means to hold said lower cutter means initially in retracted position on said body, and releasable latch means engaging said upper cutter means to hold said upper cutter means initially in retracted position on said body and releasable in response to longitudinal movement of said mandrel when shifting said lower lock means into locking engagement with said lower cutter means.

7. A rotary drill bit, including a main body, lower cutter means mounted on said body and expandible laterally outward of said body to drill a hole of a predetermined diameter, upper cutter means mounted on said body and expandible laterally outward of said body to drill a hole of a greater predetermined diameter than said lower cutter means, means engageable with said upper and lower cutter means for so expanding said upper and lower cutter means and for simultaneously holding said upper and lower cutter means in their respective expanded positions, said expanding means comprising instrumentalities movable downwardly relative to said body into a position holding said lower cutter means in its fully expanded position relative to said body prior to full expansion of said upper cutter means with respect to said body.

8. A rotary drill bit, including a main body, lower cutter means mounted on said body and expandible laterally outward of said body to drill a hole of a predetermined diameter, upper cutter means mounted on said body and expandible laterally outward of said body to drill a hole of a greater predetermined diameter than said lower cutter means, means engageable with said upper and lower cutter means for so expanding said upper and lower cutter means and for simultaneously holding said upper and lower cutter means in their respective expanded positions, said expanding and holding means comprising instrumentalities movable downwardly relative to said body to at least partially expand said lower cutter means outwardly of said body prior to expansion of said upper cutter means outwardly of said body.

9. A rotary well drilling bit, including a main body, upper and lower cutter means mounted on said body, means engaging said lower cutter means for expanding said lower cutter means laterally outward to drill a hole of a predetermined diameter, means engaging said upper cutter means for expanding said upper cutter means means drills a hole of than said lower cutter means, a mandrel slidably splined to said body and adapted to be connected directly to a drill string, said mandrel having upper and lower lock means thereon engageable with said upper and lower cutter means, respectively, for preventing inward movement of said upper and lower cutter means from their respective outwardly expanded positions, said upper and lower lock means being spaced from each other such that longitudinal movement of said mandrel in one longitudinal direction relative to said body engages said lower lock means with said lower cutter means to lock said lower cutter means outwardly prior to engagement of said upper lock means with said upper cutter means to lock said upper cutter means outwardly, hydraulically releasable latch means engaging said lower cutter means to hold said lower cutter means initially in retracted position on said body, said hydraulically releasable latch means being released by tluid pumped down through said mandrel, and mechanically releasable latch means on said mandrel engaging said upper cutter means to hold said upper cutter means initially in retracted position on said body, said mechanically releasable latch means being released by said mandrel in moving said lower lock means into locking engagement with said lower cutter means.

l0. A rotary well drilling bit, including a main body, upper and lower cutter means mounted on said body, means engaging said lower cutter means for expanding said lower cutter means laterally outward to drill a hole of a predetermined diameter, means engaging said upper cutter means for expanding said upper cutter means laterally outward to a position wherein said upper cutter means drills a hole of a greater predetermined diameter than said lower cutter means, a mandrel slidably splined to said body, said mandrel having a connection for securing said mandrel directly to a drill string, whereby torque is transmitted from the drill string to said mandrel and from said mandrel to said body, said mandrel having upper and lower lock means thereon engageable with said upper and lower cutter means, respectively, for preventing inward movement of said upper and lower cutter means from their respective outwardly expanded positions, said upper and lower lock means being spaced from each other such that downward movement of said mandrel relative to said body engages said lower lock means with said lower cutter means to lock said lower lock means outwardly prior to engagement of said upper lock means with said upper cutter means to lock said upper lock means outwardly.

11. A rotary drill bit, including a main body, lower cutter means mounted on said body and expandible laterally outward of said body to drill a hole of a predetermined diameter, upper cutter means mounted on said body and expandible laterally outward of said body to drill a hole of a greater predetermined diameter than said lower cutter means, means engageable with said upper and lower cutter means for so expanding said upper and lower cutter means and to lock said upper and lower cutter means in their respective expanded positions, said expanding and locking means comprising a mandrel slidably splined to said body, said mandrel having a connection for securing said mandrel directly to a drill string, whereby torque is transmitted from the drill string to said mandrel and from said mandrel to said body, said mandrel having upper and lower lock means thereon engageable with said upper and lower cutter means, respectively, for preventing inward movement of said upper and lower cutter means from their respective outwardly expanded positions, said upper and lower lock means being spaced from each other such that downward movement of said mandrel relative to said body engages said lower lock means with said lower cutter means to lock said lower cutter means outwardly prior to engagement of said upper lock means with said upper cutter means to lock said upper cutter means outwardly.

References Cited in the le of this patent UNITED STATES PATENTS