US 3171502 A
Description (OCR text may contain errors)
March 2, N6 A. w. KAMMERER ExRANsIRLE ROTARY DRILL BITS File'd July 26, 1962 l am.
w w Q w www ad. 122m 1 INVENTOR. QCf/E@ M MMM/weee@ www@ 3,171,502 EXPANSIBLE RTARY BREIL Bild Archer W. Kammerer, Fullerton, Calif., assigner ont onefifth each to .lean K. Lamphere, Fullerton, Carr., and Archer W. Kammerer, Jr., Houston, Tex.
Filed .luly 26, i962, Ser, Noi. 2lZ,69l 7 Claims. (Cl. M5L-267) The present invention relates to rotary drill bits, and more particularly to bits having expandible cutters'for enlarging the diameters of well bores, milling out portions of casing strings in well bores, and the like.
Rotary expansiblc drill bits have been used having cutters expanded outwardly by the hydraulic pressure of fluid pumped down through tubular drilling strings to which the bits are secured. When the drill bit is of small size, the hydraulic area on which the lluid pressure acts may be insuflicient to produce adequate total force for cxpanding the cutters outwardly against the formation to enlarge the diameter of the well bore, or outwardly against a surrounding well casing to sever the same, Even with drill bits of larger size, suli'icient hydraulic pressure for expanding its cutters outwardly may not be present because of inadequacy of the pumps, or in very deep holes because of the very substantial diminution in fluid pressure caused by friction losses in pumping the tluid through comparatively long drilling strings,
An object of the invention is to provide an improved expansible rotary drill bit, in which the hydraulic force available for expanding its cutters is assisted by supplementary means to assure proper and full expansion of the cutters. h
Another object of the invention is to provide an expansible rotary drill bit having cutters expandible :outwardly by a combination of hydraulic and spring forces, in which a spring device can be embodied in the bit capable of exerting a comparatively great force.
A further object of the invention is to provide an expansible rotary drill bit having cutters expandible outward ly by a combination of hydraulic and spring forces, in which assembly of the spring iii the bit under stress, as Well as its disassembly, can be accomplished rapidly and with comparative ease.
An additional object of the invention is to provide improved hydraulically operable, expansible rotary drill bit, in which the hydraulic force for expanding its cutters outwardly is assisted by supplementary means that maintain the cutters expanded upon relieving of the hydraulic force.
Yet a further object of the invention is to provide an expansible rotary drill bit having cutters expanded outwardly by a spring device, in which the cutters can still be shifted to their initial retracted position in the event difficulty is encountered in returning the spring to its initial position within the bit.
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 specification. 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 limiting sense, since the scope of the invention is best dened by the appended claims.
Referring to the drawings:
FIGURE 1 is a longitudinal section through an expansible rotary drill bit, with its cutters occupying a retracted position;
FIG. 2 is a view simliar to FlG. 1, disclosing the cutters in their outwardly expanded position.
United States Patent O ice A rotary expansible drill bit A is disclosed'in the drawings, which is secured to the lower end of a string of drill pipe B extending to the top of a well bore D, by means of which the drill bit is lowered through a string of well casing C to a desired location where the cutters lll of the bit are to be expanded outwardly. The drill bit specifically disciosed has milling type of cutters lll to sever a casing section and mill it away along a desired length. Such cutters are illustrated by way of example only, and it is to be understood that other type of cutters, whether they be drag or roller types, can be used depending upon the operation to be performed in the well bore. The cutters illustrated can, if desired, be used for enlarging the diameter of the well bore D, as well as milling away a section of well casing C therewithin.
The upper portion of the rotary drill bit includes a manrel l1 having an upper pin l2 threadedly connected to the lower end of the string of drill pipe B. This mandrel includes an upper kelly or drill stem member 13 slidably splined to the main body 1d of the bit. The exterior of the lower portion 15 of the kelly is non-circular in Shape, being telescopically received in a companion non-circular socket d6 formed in the main bit body. Specifically, the kelly exterior and the socket may be of hexagonal shape to enable the kelly 13 to be moved longitudinally with respect to the body '14 while being capable of transmitting rotary motion to the body.
The mandrel 11 has a limited range of longitudinal movement within the body, its downward movement being determined by engagement of the lower end 17 of the kelly with an inwardly directed body shoulder 18, and its upward movement being limited by engagement of an external shoulder or piston portion l@ of the kelly with a cylinder head Ztl secured to the body. The upper end of the head has a flange Z1 engaging a body shoulder 22, the flange being prevented from moving upwardly of the body by split snap retainer rings 23 fitting ina body groove Z4 and overlying the flange 2l,
'The body ld has a plurality of expansible parts mounted on it. These include cutter supporting members 25 pivotally mounted in body slots Z6 on hinge pins 27 suitably secured to the body to prevent'their loss therefrom. Each cutter supporting member 25 depends from its hinge pin 27 and carries a suitable cutter structure 1li, such as a drag or milling cutter, at its lower end, which, as stated above, has the purpose of severing and milling away a section of casing C, enlarging the di-Y ameter of a well bore D, or both.
The cutter supporting members 25 and the cutter structures lll themselves normally occupy a retracted position substantially entirely within the confines of the main body t4 of the bit. These cutter supporting members and the cutter structure are expandible outwardly. In the use of the device illustrated in the drawings, their outward expansion can rst sever the casing C and then mill it away by operating upon the upper-end E of the casing therebelow, or the cutter can act upon the upwardly facing shoulder F which they form in the enlarged well bore D. To accomplish the expansion, each cutter supporting member 25 hasvan inclined expander surface 30 on its inner portion below the hinge pin 27 which tapers in a downward and inward direction. Each expander surface terminates in a lock surface 31 formed on a lock portion 32 of the cutter supporting member. The outward expansion is accomplished by producing relative longitudinal movement between the mandrel 11 and the bit body 14, which will produce relative longitudinal movement between the cutter supporting members 25 and the tubular member 33 of the mandrel. This tubular member includes a lower portion 34 slidable within a guide bushing 35 mounted in a bridge 36 secured to the bodyand extending across the body slots 25. This guide bushing 35 is disposed below the lockportions 32 of the cutter supporting members 25.
Located initially substantially above the guide bushing and below the hinge pins 27 land in .cutter member recesses 37 is a mandrel lock and expander 38which has outer surfaces 39 adapted toV engage the expander surfaces 30 and the lock surfaces 31.V The lock and expander 38 may beformed integral with thev tubular member 33,'the upper end of the latter being vpiloted within a socket 40 formed in the lower portion 15 of the kelly. An enlarged boss 41 on the tubular member engages a downwardly facing shoulder 42' of the kelly, the tubular member 33 being held against this shoulder by a suitable split retainer or .lock ring V43 mounted in an internal groove 44 encompassing the kelly socket 40 and 'engaging the lower end of the tubular member boss 41. Drilling mud or other uid can pass down through the central passagey 45 of the kelly Vor drill -steml and Vinto the central passage 46g extending completely through the tubular member 33. Leakage of fluid around the exterior of the tubular member 33 is prevented'by a suitable side seal ring 47 in the kelly which engages. the exterior of the boss 41. s v Y Y,
Assuming the body 14 of the tool to be elevated relasage 46 through the tubular member 33 ofthe mandrel 11 is of `a restricted diameter, as compared to the pasat an adequate rate through the apparatus will buildup a back pressure of'uid in the passage 45, which pressure Y will be imposed on the fluid inV the cylinder'V space 56,
tively along the tubular mandrel 11, theinclinedexpander p surfaces of the cutter supporting members 25 will be shifted upwardly along the lock and expander portion 38 of the tubular member 33. During such upward shiftward movementof the body 14 with respect to the tubularv mandrel 11 can continue. untilV the cutter structures 10 have. been shifted outwardly to their fullest extent,
as determined by engagement 'of stop shoulders 50 onthe cutter supporting vmembers with companion shouldersk 51 formed in the body on opposite sides of the body slots 26. When such engagement occurs, the lower end 17 of thekelly portion 13 of the tubular 'mandrel will engage the body shoulder 18, and the lock and expander 38 on the tubular member 33 will be disposedfbehind and-in engagementwith the lock portions 32 on the cutter supporting members 25.
Relative longitudinal movement between the tubular mandrel 11 and the body 14 ofthe tool is accomplished hydraulically. The enlarged piston portion 19 on the drill stem 13 isreceived within acounterbore 52l formed on an intermediate portion 53 of the Vbody of the tool.` This intermediate portion actually constitutes a cylinder having aV cylindrical wall y54 Yextending from a 'lower shoulderrSS defining the bottom ofthe counterbore to the cylinder head 20. Y
A confined cylinder space56 isrformed between -the piston portion 19 of the kelly, the periphery of the kelly 13 above the piston, and the cylinderv 53. Asuitable packing or side seal ring 57 may vbe disposed inthe piston 19 which is adapted to slidably seal against the cylindrical wall 54 of theV cylinder. Fluid isthereby preventedifrom'passing in a downward direction between the piston 19 and the cylinder 53. Fluid is4 also prevented from passing in Van upwardI direction from -the annular cylinder space 56 by .an .inner side'seal ring Y59 carried in the cylinder head 20 and slidably and sealingly engaging the periphery of the kelly 13 `above the piston 19, and also byran outer side seal ring 58 disposed in the head'20 and sealingly engaging the cylinder wall 54;
Fluid under pressure in the string of drillpipe B and in the tubular mandrel passage 45 can be `fed into the cylinder space 56 through one or rmore side ports 60 establishing, communication betweenthe central pasv sage through the kelly and the cylinder space. Such tiuid under pressure is developed in the specific tooldisclosed in the drawings by virtuelof .the faetthatthepasacting Vupon vthe cylinder head 20 to urge the body 14 of the tool in an upward direction with respect to the tubular mandrel '11, to secure `'outwardexpansionrof the cutter supporting members 25 and,y cutter structures 10 Yto their fullestextent, as above described.
The upward movement of the body 1401:'v the .tool with respectto the tubular mandrel 11 is assisted, Vin the appa 1 ratus illustrated in the drawings, by a spring 7i) .which adds its force to the hydraulic force acting upwardly on the cylinder head 20'. vAs shown, the body 14 includes a spring housing portion 71l extending upwardly from the cylinder 53, which isV spaced from the kelly 13 to provide an annular spring chamber 72 in which a helical compression spring 70` is disposed; The lower end of the spring bears againstfa thrust ring or flange 73fwhich is prevented from moving downwardly by resting upon an'inherently contractable split retainer ring 74 disposed ina peripheral groove y75 in the. kelly and extending outwardly therefrom. The upper end of the spring 70 bears against'a spring seat 76 which is prevented from moving upwardly ofthe housing byvengaging a split retainer ring f77 ,disposed in an'internal groove 78 in the housing. -In order to prevent entry of drilling mud, .or other well bore fluid and substances, into the spring housing 71, a guide 79 is releasably inserted in the upper end of the housing, being retained in position by a split expansible spring-like ring 80 disposedin a groove 81 in the guide and received within an internal groove 82 in the upper end ofthe housing.
The` spring is constantly exerting a force on the housing '71 and body 14 of the tool tending to elevate the latter along the mandrel 11' in order to effect outward expansion of thecutter supporting members 25 and cutters 10. Such upward movement can occur since an adequate space Y 83 is provided initiallybetween the cylinder head 20 and v stantial, thereby'allowing theuseof. aspring '70 having a largeinitjial vcompressive force. When disposed in its s initial position, the spring, for'example, may exert a force of 'about '1,500 pounds tending to elevate the body 14 along the mandrel 11 of the tool. This force will supplement the force of thelhydraulic pressure acting upon the pressure effective area of the .cylinder head 20 and tending to elevate the body of the tool along vthe mandrel, andgthereby effect outward expansionofthe cutters 10.
In the operation of the apparatus A, it is run in the well casing, the cutterl supporting members25 and cutters 10 occupying their initial retracted position, vdespite the tendency of the spring 70to expand the latter. The outer sides of the cutter supporting members 25' willmerely slide, along theV inner Wall of the casing C. When the desired location in the well casing is reached at which the casing severing action or hole'enlarging operation Vis to commence,.the drill string B and the rotaryv drill bit A Vare turnedat the. desired rate of speed and the pumps at the top of the vwell bore started to pump yfluid at a suicient rate through the drill pipe and into the mandrel passages 45, `46, building up a back pressure inthe kelly passage 45 and of the fluid in the ports 60 and cylinderA space 56,1which lpressure acts upon the cylinder head 20 to urge the body 14, the cutter supporting members 25,
and the cutter structures l@ in an upward direction with respect to the mandrel 11. Such upward movement is assisted by the force exerted by the spring 70, which spring force can, as in the example given above, be quite considerable. During upward movement of the body 14 relative to the mandrel 11, the expander surfaces 3h are brought to bear against the lock and expander portion 3S of the mandrel, the cutter structures 1l) being urged in an outward direction against the wall of the well casing C, and gradually milling it away. During this operation, the apparatus A is retained in substantially the same longitudinal position in the well casing. As the casing is cut away, the hydraulic force and the spring force acting upon the body 14 raises the latter and the cutter supporting members Z5 and cutter structures 11D to a further extent until the cutters have completely severed the casing C. Continued rotation of the drill pipe B and the pumping of fluid through the drill bit will cause the cutters 1h to cut away additional casing and dig into the formation, the spring force and hydraulic force combining to expand the cutters outwardly, until the cutters 1li have been expanded outwardly to their fullest extent, as determined by engagement of the stop shoulders Si?, 51 with one another and the lower end 17 of the kelly portion of the mandrel with the body shoulder 18. With the parts in this position, the lock portion 32 of each cutter supporting member 25 will bear against the lock and expander portion 38 of the tubular member 33 to preclude inadvertent partial retraction of the cutter structures 1li from their fully expanded position.
Downweight in a proper amount can now be imposed von the string of drill pipe B, which downweight is transmitted through the kelly 13 to the body shoulder 18, and from the body to the stop shoulders Si), 51 directly to the cutter supporting members 25 and the cutter structures 10, urging the cutter structures against the upwardly facing severed end E of the well casing and against the upwardly facing formation shoulder F. The imposition of a proper downweight or drilling weight on the apparatus and its rotation at a proper speed will cause the cutters to act upon the severed end E of the casing and the 'shoulder F to mill the casing away, and also to drill away the formation shoulder. During such milling and drilling actions, drilling fluid is being pumped down through the drill pipe in the apparatus, discharging from the latter and carrying the casing cuttings and formation cuttings upwardly around the tool A and the drill pipe B to the top of the hole.
After the desired length of casing C and hole D have been cut and drilled away, the tool can be withdrawn from the well bore. Pumping of fluid can cease and the drill pipe B and the drill bit A elevated in the well bore D. The spring 70 will retain the body 14 upwardly along the mandrel 11, so as to maintain the cutters in their outward expanded position, until the cutter supporting arms engage the downwardly facing shoulder H provided by the upper severed end of the casing C, which will tend to prevent further upward movement of the tool. Accordingly, the taking of a suicient upward strain on the drill pipe B and mandrel 11 will cause the mandrel to move upwardly within the body 14 against the force of the spring 7tl, compressing the latter and elevating the lock portion 38 of the mandrel above the lock and expander surfaces 31, of the tool, allowing the cutter supporting members 25 and cutters 10 to shift inwardly entirely within the contines of the body 14 and the casing C. The tool, with the cutters in retracted position, can now be elevated through the casing to the top of the well bore, the cutter supporting members 25 merely sliding along the inner wall of the well casing C.
In the absence of the spring 70, in the event the cutter members 25 were elevated from the upwardly facing casing end E and the shoulder F, and the pump pressure ceased, the body 14 of the tool would tend to drop downwardly along the mandrel 11 and the cutters 10 could then shift to a retracted position. However, with the spring 7i) constantly exerting a force holding the body 14 in its upward position with respect to the mandrel 11, the relieving of the hydraulic pressure will not result in the cutters 1d shifting to a retracted position. Instead, they will remain in their outwardly expanded position, such as disclosed in FIG. 2.
In relatively small size tools, the effective area of the cylinder head 2t), as compared to the hydraulic pressure available for action upon such head, may be insufficient to insure the exertion of suiiicient outward force of the cutters 1lb against the casing C to sever the latter upon rotation of the drill pipe B and the drill bit A, or to enlarge the diameter of the well bore D by bearing against the wall of the formation. Such ineffective huid pressure may not only be due to the relatively small annular area of the cylinder head, but to the unavailability of adequate pumps at the top of the well bore capable of supplying sufficient pressure. Even where large capacity and relatively high pressure pumps are available, the use of the drill bit A at the lower end of a very long string of drill pipe B is associated with very substantial losses in iluid pressure due to the frictional resistance of the fluid owing through the pipe itself. In all of such instances where hydraulic force may be inadequate, the presence of the comparatively strong compression spring 71B acting between the mandrel 11 and body 14 of the tool will insure tne supplementing of the hydraulic force, and the presence of an adequate total force effecting full outward expansion of the cutters 19 for the purpose of fully severing the well casing C, or enlarging the well bore D to its fullest extent, or both, the body 14 being elevated along the mandrel 11 to its fullest extent at which the lock portion E8 will hold the cutter supporting members 2S and cutters 1t? in their outward expanded position.
The spring 7 il is readily assembled in the tool and disassembled therefrom, being insertable in place through the upper end of the housing portion '71 against the lower thrust ring or ange 73. Through use of a suitable spring compression tool, the spring seat 76 is placed on top of the spring and forced toward the thrust ring or flange 73 to compress the later, whereupon the retaining ring 77 is inserted in place, overlying the upper spring seat 76 and snapped Iinto its groove 78. The annular guide '79 can then be mounted in place. The spring will shift the body 14 upwardly along the mandrel 11 to expand the cutters. To prevent such expansion and to start the tool in the casing C, a holding screw may he threaded in a hole 91 in 'the body, the screw overlying the guide 79 and Ithereby preventing the spring 70 from expanding. Following inserting of the cut-ters 10 and supporting members 25 in the casing C, the screw 9) may be removed and the tool A lowered `in the casing.`
When disassembly is desired, the annular guide 70 is easily removed in an upward direction from the upper end of the housing 71, land a suitable tool provided for shifting the spring seat 76 downwardly to a slight extent to relieve the annular ring 77 of the spring force, allowing the latter to be retracted from its groove 78 and removed from the housing, whereupon the spring force can be gradually released and the spring 70 also removed from the housing.
Assurance is had that the cutters 1l) can 'be shifted to a retracted position from their fully expanded position, despite the fact that it might not be possible, due to foreign substances in the spring chamber 72, for example, to recompress the spring 76 back to its initial position after it has expanded and shifted `the body 14 upwardly along the mandrel 11 to its fullest extent, such as disclosed in FlG. 2. To accomplish this purpose, the lower side 92 of the groove 75 containing the split retainer ring '74 against which the thrust ring 73 'bears can be tapered in an upward and inward direction, engaging the lower end of the retainer ring. This ring 74 inherently tends to remain -in an inward posi-tion and is vof such dimensions as to resist its outward expansionv from 'the groove '75. The exertion-of a suiiicient vupward force on the mand-rel 11 of the tool will cause they ananas-a Y ing torque is transmitted'from said mandrel to said body; said body having a housing portion spaced laterally from said mandrehspring means in said housing portion actingupon said mandrel and housing portion for'elevat'- Y ing said body and cutter means with respect .to said mandrel to hold said cutter means Vlaterally outward; and means releasably securing said spring means Yto said mandrel and .being releasable in response to a predetermined portions 32 Vof lthe cutter supporting arms25,'allowing y effect shifting of the retainer ring 74 from the groove 7 5.Y
If, for example, the maximum force exerted by thel spring is about 1,500 pounds, the upwardiforce on the mandrel 11 required'to shift the ring 74 Afrom itsY groove 75 may beV of the order of about 5,000 pounds," thereby assuring that the retainer ring will normally remain wi-thin the groove and serves as an abutment for the thrust ring or flange 73. which retraction of the cutters cannot take place as a result of inability to recompress the spring'7ii, that the taking of a sucient upward pull on Vthe mandrel 11 will expand the retainer ring 74 from its groove 75 and thereby `release the mandrel from the thrust ring 73, allowing the mandrel to move upwardly within theV body V14 .to a position allowing full retraction of the cutters 10,.
f1. In a rotary well drillingbit: a main body; cutter f means mounted on said body for expansion laterally outward of said body; a mandrell connectible to aV drill string and slidably splined to said body, whereby drilling torque is transmitted from said mandrel to said body;
It is only under emergency ',cponditions,V in
mandrel; said mandrel having a iluid passage communito said mandrel to cause said expander means to expand said cutter means laterally outward. V Y
2. In a rotary well drilling bit: a main body; cutter meansmounted on said body for expansion laterally outward of said body; a mandrel connectible to a drill vstring and slidably splined'to said body, whereby drilling torque is transmitted from said mandrel to said body; coengageable expander means on said mandrel and cutterVV means; said body havinga cylinder portion above said expander means slidably and sealingly engaging said mandrel; said mandrel having. a iiuid passage communieating with the drill string and cylinder portion to 'feed iuid under pressure to said cylinder portion to elevate said body and cutter means with respect to said mandrel to cause said expander means to expand said cutter means laterally outward; said body having |a housiugport-ion above said cylinder portion in spaced relation to said mandrel; and spring means in said housing portion acting upon said mandrel and 'housing portion for elevating said body and cutter means with respect Ito said mann and lslidably splined to said body, whereby drilling torque drel to Acause said expander means to expand said cutter f means laterally outward. n
3. In a rotaryV well drilling bit: a main body; cutter means mounted on said body `for expansion laterally out-'kV force. imposed thereon. by said mandrel to enable said mandrel to move upwardly with respect to said body and cutter means and allow said cutter lmeans to move laterally inwardly to retracted position.
4. In a rotary well drilling bit: a main body; cutter means mounted on said body for expansion laterally outwart of .said body; means forV expanding andholding said cutter means laterally outward, said expanding and holding means comprising. a mandrel connectible vto'vaidrill string and slidably splined tofsaid body, whereby drilling torque is transmitted'fr'onr said mandrel to said body; said body having a housing portion spaced-laterally from said mandrel; a thrust-member surroundingY said mandrel; means releasable in response to a predetermined force imposed thereon by said mandrel releasably securing said thrust member to said mandrel; al seat member secured to said `housing portion; and a helical Vcompressionfspning in Vsaid housing portion-bearing against said members 'to elevate said body and cutter means with respect to said mandrel to hold said cutter means laterally outward; release of said 'releasable means enabling said mandrel to move upwardly with Vrespect to said'body and cutter means and allowsaid cutter means to move inwardly to retracted position.
5. In :a rotary well drilling bit:V a malin body member; cutter means mounted on. said body member for expansion laterally outward of said body member; means for expanding and holding said cutter means laterally outward, said rexpandingand holding means comprising a mandrel vmember `conne'ct-ible to la d-rill string vand slidably splined to said body member, whereby drilling'torqueis transmitted from said mandrel member tosaid body member; said body member having a housing portion spa-ced laterally from said mandrel member; spring means in sa-id housing portion acting upon-said mandrel member and housing portion for elevating said :body member and cutter means with respect to said mandrelmember to hold said cutter means laterally outward; and means releasably securing said spring means to one of `said members and being reg lea-sable in Vresponse to a predetermined force imposed thereon by-said mandrel member to enable said mandrel member to move -upwardly with respect to said body mem- Vber land cutter means andV allow said 'cutter means to Imove laterally'inwardlyV to retracted position.
16. In a rotary well drilling bit: a main body; cutter means mounted on said body for expansion laterally outward of said body; afmandrel connectible to a drill string is transmitted from said mandrel to said body; Coengageable `expander means on/said mandrel and cutter means;
saidV body having a ycylinder portion above said expander.
means slida'bly and sealingly engaging said mandrel; said mandrel having a iiuid passage communicating with the drill string and cylinder portion to feed iluid under pressure toy said cylinderportion to elevate said body and cutter means with respect to Isaid mandrel to cause said expander means to expand said cutter means laterallyoutward; said body having a housing portion above said cylinder portion inspaced relation to said mandrel; a thrust member surrounding said mandrel; means releasable in response to a predetermined force imposed thereon by said mandrelreleasably securing said thrust member .to said mandrel; a seat membersecured to said housing portion; and a helical compression spring in'said housing portion bearing against saidmembers to elevate said body and cuttermeansjwith respect to said mandrel'tocause said expander means to expand said cuttermeans laterally outward.
7. In a rotary Well drilling bit: a main body; cutter means mounted on `said tbody `for expansion laterally out- Ward of said body; ya mandrel member connectible to a drill string land slidably splined to said body, whereby drilling torque is transmitted from said mandrel member to said body; coengageable expander means on said mandrel member and cutter means; said body having a cylinder portion above said expander means slidably and sealingly engaging said mandrel member; said mandrel member having la Huid passage communicating with the drill string `and cylinder' portion to feed fluid under pressure to said cylinder portion to elevate said body and cutter means with respect to said mandrel member to cause said expander means to expand said cutter means laterally outward; said Ibody having a housing member above said cylinder portion in spaced relation to said mandrel member; spring means in said housing member acting upon said mandrel member and housing member for elevating said body and cutter means with respect to said mandrel member to hold sa-id ycutter means laterally outward; and means releasably securing said spring means to one of said members and being rele-asable in response t0 a predetermined force imposed thereon by said mandrel member.
References Cited in the le of this patent UNITED STATES PATENTS 2,122,332 Wurzinger June 28, 1938 2,500,125 Huber Mar. 7, 1950 2,710,172 Kammerer June 7, 1955 2,719,700 Kammerer Oct. 4, 1955 2,755,071 Kammerer July 17, 1956 2,754,088 Kammerer July 10, 1956 2,799,477 Kammerer July 16, 1957 2,922,627 Kammerer Jan. 26, 1960