US2764388A

US2764388A - Retractable hard formation drill bit

Info

Publication number: US2764388A
Application number: US268891A
Authority: US
Inventors: John M Camp
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1952-01-29
Filing date: 1952-01-29
Publication date: 1956-09-25
Anticipated expiration: 1973-09-25

Description

Sept. 25, 1956 J. M. CAMP RETRACTABLE HARD FORMATION DRILL BIT 5 Sheets-Sheet 1 Filed Jan. 29, 1952 QfOhfl cam/Q sax/ember Qbboraeg Sept. 25, 1956 J. M. CAMP RETRACTABLE HARD FORMATION DRILL BIT 3 Sheets-Sheet 2 John m. (amp 'lrzvenbor Q5 Z0, CLbuorrzeg Filed Jan. 29, 1952 Sept. 25, 1956 J. M. CAMP RETRACTABLE HARD FORMATION DRILL BIT s sheets-sheet 3 Filed Jan. 29, 1952 A w m 4 m 7/74/ 7 a n M a m m v. :2: k m 4/ & 5

F I G doho. 11 2. Camp Sam a mbgw m Qubornas 2,764,388 Patented Sept. 25, 1956 RETRACTABLE FORMATION DRILL BIT John M. Camp, Tulsa, Okla., assignor to Esso Research and Engineering (Iompany, a corporation of Delaware Application January 29, 1952, Serial No. 268,891

6 Claims. (Cl. 25561) This invention concerns a novel and improved form of retractable drill bit. The drill bit of this invention is adapted to be lowered through a drill stem for expension and clamping in a drill collar at the lower end of the drill string. The drill expands in such a manner as to lock a plurality of cone-type hard formation cutters at the lower termination of the drill collar so as to drill a borehole larger in diameter than the drill string. The bit includes provisions enabling release of the bit at the bottom of the drill collar and permitting the bit to be pulled upwardly through the drill string as, for example, by means of a wire line spearhead retriever.

it has long been appreciated that a desirable form of drill bit for use in oil exploration would be a bit which could be placed in cutting position and could be periodically retracted and returned to the surface of the earth without necessitating removal of the drill string from the borehole. Such a bit is particularly attractive in minimizing the time and expense of pulling a drill string from a well bore and of again running the drill string into the bore hole Whenever necessary to replace or recondition a drill bit. There have been a variety of suggestions as to bits of this general character. However, the problems involved in providing an entirely suitable retractable drill bit are sufiiciently difiicult so that there has been a demand for an improved type of retractable drill bit.

The present invention is concerned with this objective and provides a desirable form of expansible bit overcoming many of the disadvantages of presently known drill bits of this character. For example, as will be brought out, the drill of this invention employs a drill collar which is free of internal slots or grooves which would be subject to disabling plugging by drill cuttings, sediment, etc. Again, for example, provision is made to transfer torsion from the drill stem to the cutters without necessitating use of a slotted drill collar or the like, imposing undesired stress limitations. These and other advantages of the novel drill bit herein disclosed may be appreciated from the following description.

The retractable drill bit of this invention utilizes a tubular drill collar in which a cylindrical mandrel element is slidably maintained. A number of longitudinal slots or grooves are cut in the mandrel element corresponding in number to the cone cutters to be employed. A sliding support member for each of the cone cutters is arranged for longitudinal movement in the grooves of the mandrel within the limits of the drill collar. The cone cutter support members are slidably fastened to the mandrel element. A suitable arrangement of latching dogs and mating shoulders on the diiferent elements described is employed to control positioning of cone cutters for both retraction of the cutters into the drill collar and for expansion of the cone cutters through the lower end of the drill collar. In the expanded position, a tapered portion of the mandrel element acts with a tapered section of the drill collar to form a wedge-shaped aperture in which the cone cutters can be wedged in order to transmit torque directly from the drill collar to the cone cutters for drilling purposes.

The appended drawings illustrate a preferred embodiment of the drill bit of this invention illustrating as Well a number of desirable features which may be included in the apparatus. It should be observed that for simplicity the drawings have been prepared to illustrate a retractable hard formation drill bit having two cone cutters. In actuality it is preferred to employ three cone cutters but the principles of operation can better be understood by considering a drill bit employing two cone cutters.

Figure 1 of the drawings illustrates the drill of this invention in elevational cross-sectional detail, showing the drill bit in an extended and locked drilling position in the drill collar;

Figure 2 is a right side view of the drill bit, showing the drill collar in cross section;

Figure 3 is a cross-sectional elevational view of the lower portion of the drill bit in retracted position;

Figure 4 is a cross-section view of the apparatus of Figure 2 along the line IV-IV;

Figure 5 is a cross-section of Figure 1 along the line V-V;

Figure 6 is a detailed cross-sectional elevational view of a preferred arrangement of the upper portion of the drill;

Figure 7 is a view of a suitable fishing tool for use with the drill bit illlustrated, permitting the bit to be lowered into position and permitting recovery of the drill bit, and;

Figure 8 is a fragmentary view corresponding to a portion of Figure 2 in which the two circumferential grooves or recesses have been replaced by a single circumferential recess.

Referring now to Figure 1, a drill collar is designated by the numeral 1 which is of novel design to cooperate with the drill bit illustrated. Drill collar 1 may be fixed to a conventional casing or drill string by means of suitable threaded couplings. The drill collar will have substantially the same internal diameter as the drill stem with which the drill is to be operated. Preferably, however, the external diameter of the drill collar 1 is somewhat enlarged so as to provide a thicker walled drill collar. member of substantial wall thickness to provide the necessary strength required to drive the drill bit fixed within this drill collar. The lower and inner termination of the drill collar is provided with an outwardly and downwardly opening enlargement. This serves to provide a downwardly and outwardly open taper 3 against which the drill cutters may be wedged as will be described. Two circumferential grooves or

recesses

4 and 5 are machined in the drill collar to accommodate latching dogs positioned on the drill bit. As described therefore, the drill collar simply comprises a tubular member having

circumferential grooves

4 and 5 and provided with an outwardly flared opening 3. The drill collar is notable for the absence of any longitudinal slots or grooves and by its simplicity of construction.

Fitting within the drill collar 1 is a retractable drill bit essentially comprising three elements. An inner mandrel '8 constitutes the central portion of the drill bit having a diameter somewhat less than the internal diameter of the drill collar. The mandrel 8 is provided with two diametrically opposed longitudinal grooves or slots extending substantially the length of the mandrel. These grooves are best shown in Figures 2 and 4 and are identified by numerals 1 1 and '12. Fitting within the grooves 11 and 12 are the two remaining principal elements of the drill bit consisting of

slidable sections

13 and 14. As will be described, each of the slidable sec- The drill collar simply comprises a tubular 3

tions

16 and 14 is free to slide upwardly or downwardly with respect to mandrel 8 in the groove or slot provided to the extent permitted by the latching dogs and mating shoulders provided on sliding sections 13 and 1'4 and mandrel 8.

Each of the sliding sections l '3 and 14 serves as a supporting and guiding member for the cone cutters ill) which are suspended from them and will hereinafter be identified .as cone cutter guide members. The cone cutters of conventional design may be suspended from the guide members by the straps or suspension arms 15. A pivot pin 16 passing through the lower termination of each suspension arm and passing through each cone cutter 10 serves to permit pivotal movement of the cone cutters within the drill collar. Downward movement of each guide member '13 or :14, with respect to the drill collar is limited by latching dogs 6 which are pivotally fixed to each sliding element and are arranged to bear against the upward facing bearing surface of the annular groove 5 machined in the drill collar. Each of the latching dogs 6 is urged outwardly into latching position by means of leaf springs 7. The latching dogs 6 are provided with inward extensions, shaped to mate with a

recess

20 or 21 cut in the slotted portions of mandrel 8. The extensions of the latching dogs may thus fit within the

recesses

20 and 21 when the dogs are forced into these recesses, permitting the latching dogs to lie flush with the periphery of the mandrel.

The lower portion of guide member 18 has cutaway inner portion so as to provide a shoulder 23 positioned some distance below latching dog 6. The lower termination of slot 11 of mandrel 8 is built out somewl'xat so as to provide .a shoulder 24 adjacent the lower portion of the mandrel. As will be described, shoulder 2'4 is adapted to meet shoulder 23 so as to limit downward movement of guide member 11 3 with respect to the mandrel 8. Guide member 14- is similarly provided with a shoulder 25, which, however is positioned at a diii-ere-nt distance below latching dog 6 fixed to guide member. Again, shoulder 25 is adapted to bear on a shoulder 26 provided in the slot 12 of the mandrel 8.

The lowermost portion of each guide slot 11 and 12 of the mandrel is cut away more deeply to form a bed in the slot which is tapered inwardly. When the drill is in the position shown in Figure 1, the tapered shanks of cone cutters '10 tit against the taper of the slots referred to. The wedge shaped shank of the cone cutters there- -fore wedges tightly between the drill collar 1 and the mandrel 8 when weight is placed on the cone cutters.

In order to maintain the mandrel in a locked downward position to maintain the cone .cutters in the positions illustrated in Figure l1 when weight is applied to them, latching dogs 30 are provided at the upper end of the mandrel 8. These latching dogs are pivoted in slots of the mandrel and are normally urged outwardly by leaf springs 31 as better shown in Figure 6. The latching dogs will thus be forced into the circumferential recess 4 of the drill collar when registered therewith so as to bear against the downward facing bearing surface in groove 4 and thus lock the mandrel 8 against upward movement with respect to drill collar 1. It is apparent that when the mandrel has been forced downwardly suificiently far to permit the latching dogs Bil to spring outwardly into the latching position illustrated, the drill cutters 11d will be locked into the expanded position shown in Figures 1 and 2 so as to permit drilling.

The inner portions of the latching dogs '30 are provided with recess-es 36 which may close over the spearhead 37 ot,a retrieving tool when the latching dogs 30 are forced inwardly.

With this description of the general arrangement of the elements of the retractable drill bit illustrated, the operation of this drill bit may now be understood. Assuming that the drill bit is in the extended drilling position illustrated in Figure 1, operation of the elements 4 will be described as the drill bit is forced into retracted position for removal from the drill string.

In order to retract the drill bit of Figure 1, a retrieving tool having a suitable spearhead 37 is lowered into the drill string by means of a wire line or cable. As will be brought out in connection with Figure 7 of the drawings, the retrieving tool in addition to the spearhead 37 must have tapered surfaces of a nature to force the latching dogs 30 inwardly over the spearhead to permit the latches 34) to pass upwardly into the drill string while preventing release of the spearhead from the recesses 36 provided in the latching dogs. When the latches have been forced to this position, spearhead 37 may be pulled upwardly through the drill collar and drill string together with the drill b it when retracted,

In a first step of the retraction operation, mandrel 8 will be pulled upwardly while guide members 13 and id remain in a fixed position with respect to the chili collar. Thus on retraction of latching dogs 3d the mandrel is free to slide upwardly. However, upward movement of the guide members 13 and 14- supporting the cone .cutters is impossible during this step of the operation. This is true for the reason that latching dogs 6 associated with each guide member are essentially wedged in the circumferential recess 5 of the drill collar so as to prevent upward movement of each guide member until latching dogs 6 may be forced into retracted position.

Consequently on upward movement of the spearhead, mandrel 8 will 'be pulled upwardly until recess 21%. provided in the mandrel registers with latching dog 6 that is pivotally fixed to guide member 14. Shoulder 26 provided on mandrel 8 is positioned to contact shoulder 25 of guide member 14 when recess 1 registers with latching dog "6. Consequently when the mandrel has been pulled upwardly to this position, shoulder 26 hearing against shoulder 25 will force guide member M to move upwardly through the drill collar with the mandrel "8. This upward movement of guide member 14 will force the latching dog 6 associated therewith into the recess 21 into the position particularly illustrated in Figure 3. The cone cutter it supported by guide member 14 will be free to swing inwardly into the drill collar for upward movement therethrough, again as illustrated in Figure 3.

It will be observed that during this phase of the operation, that is when the first guide member and first cone cutter are pulled upwardly into the drill collar, the second cone cutter and the guide member associated therewith are still maintained in a locked position. Thus the latching dog 6 that is associated with guide member 13 is wedged in annular groove 5 of the drill collar, preventing movement of guide member 13 with respect to the drill collar until the recess 20 in mandrel 8 registers with this latching dog. When the mandrel 8 carrying the first guide member 14 is pulled upwardly sufficiently for recess 2 to register with latching dog 6 of guide member 13, shoulder 24 of the mandrel will bear against shoulder 23 of guide member 13. Consequently in the course of upward movement of mandrel 8, when this occurs, guide member 13 will be pulled upwardly through the drill string. Latching dog 6 mounted on guide member 13 will be forced into the recess 20 as illustrated in Figure 3. The cone cutter 10 supported from guide member 13 may then swing inwardly into the drill collar at a position below the first cone cutter. The entire apparatus may then be pulled upwardly through the drill string with all elements thereof in the retracted position shown in Figure 3.

The manner in which the retractable drill can be lowcred through the drill string to assume drilling position will now be described. It is assumed that the elements of the retractable drill are placed in the arrangement shown in Figure 3; in addition latching dogs 30 are closed over the spearhead of a lowering tool and are held in this position by the inner surface of the drill string and drill collar. The drill is lowered through the drill string into the drill collar without change in the relative position of the elements until the latching dog 6 that is associated with guide member 13 reaches the lower annular groove or recess 5 provided in the drill collar. When this occurs, latching dog 6 expands outwardly so as to prevent further downward movement of guide member 13. Mandrel 8 will continue to move downwardly together with the second guide member 14. When lowered sufliciently, the latching dog 6 that is associated with guide member 14 will similarly expand to latching position in the annular groove 5 of the drill collar to prevent further downward movement of guide member 14. At this instant in the operational sequence, the two cone cutters associated with the

guide members

13 and 14 will be at the proper horizontal position with respect to drill collar 1. However, the cone cutters will be hanging loosely within the lower portion of the drill collar. Mandrel 8 is, therefore, forced downwardly, sliding with respect to guide

members

13 and 14, until the tapered surfaces provided on the lower termination of the mandrel wedge the cone cutter supports against the drill collar. This occurs when the mandrel 8 has been lowered to the position shown in Figure 1 at which position upper latching dogs are enabled to extend into latching position in the upper circumferential groove 4 provided in the drill collar. Extension of these upper latching dogs serves to lock the entire drill in the position shown in Figure l and also serves to release spearhead 37 permitting removal of the lowering tool.

On then lowering the drill string sufiiciently to cause the cone cutters to contact the bottom of the borehole, the cone cutters will further be wedged between the mandrel 8 and the drill collar 1 to permit drilling.

While not essential, as shown in Figure 5, an extension or lug 38 may be positioned in the upper circumferential groove 4 of the drill collar 1. This lug will limit rotational movement of the latches 30 with respect to the drill collar. This serves to prevent rotation of all of the drill elements with respect to the drill collar 1. This will prevent any rotational slipping prior to the time the cone cutter supports are firmly wedged between the mandrel and the collar as described. It should be observed, however, that substantially no rotational torque is transmitted through lug 38 during normal drilling operations since the torque is transmitted directly through the drill collar to the wedged cone cutters.

A central channel 39 is provided in the center of mandrel 8 associated with ports 40 adjacent the cone cutters. Drilling mud may be forced through the drill string and through these ports to lubricate the cutters and flush the cuttings out of the bottom of the hole during drilling.

As formerly indicated, while the invention has been described with reference to a drill bit employing two cone cutters, it is particularly contemplated that the drill bit should employ three cone cutters. Employing the principles described, this is readily achieved by positioning three equally spaced longitudinal grooves in mandrel 8 in place of the two described. An additional recess is placed on mandrel 8 corresponding to

recesses

20 and 21 of Figure 1. This additional recess will again be at a different level from

recesses

20 and 21. Consequently these provisions will enable a third drill cone to be suspended below the other two in the same manner described. As a practical observation it may be noted that drill cones of larger sizes may be employed when three rather than two cone cutters are used. This is possible by virtue of the fact that the conical shape of these cutters acting with the 120 spacing around the mandrel permits utilization of somewhat larger cone cutters. It should be observed that if desired, latches 30 may be fixed to mandrel 8 in such a manner as to register with the same circumferential recess that receives the latching dogs 6, thus requiring only one circumferential recess instead of two, provided that the single recess presents both an upward facing facing bearing surface 34 and the upward facing bearing surface 35.

The apparatus heretofore described is preferably provided with additional apparatus features. These are illustrated in Figure 6. Figure 6 illustrates a preferred embodiment of the drill bit showing only the portion of the drill bit above the latching dogs 6. In all other respects the drill bit will have the construction which has been described. As illustrated in Figure 6, the mandrel 8 is provided with a separate section maintained in telescopic sliding relation with the upward termination of mandrel 8 which is cut to have a reduced external diameter. Sliding movement of the upper portion 50 with respect to the lower portion 8 is then possible. One or more pins 51 fastened in the tubular member 50 extend into slots 52 positioned in the upper portion of mandrel 8. Slots 52 have sufficient longitudinal length, extending upwardly and downwardly, to permit limited movement of element 50 with respect to mandrel 8. A rubber sleeve 53 is positioned on a shoulder of mandrel 8 just below the lower termination of element 50. This rubber sleeve 53 preferably has an upward and outwardly opening taper at its upper portion to accommodate the downward and inward tapering termination of member 50. Thus when member 50 is forced downwardly, so as to slide with respect to mandrel 8, the tapered termination of member 50 will force the rubber sleeve 53 firmly against drill collar 1. This serves to provide a circumferential seal between the drilling apparatus and the drill collar. The purpose is to prevent by-passing of drilling fluid between the drill collar and the drill bit. All drilling fluid is thus forced downwardly through channel 39 of the mandrel to be supplied to the cone cutters.

Another preferred feature illustrated in Figure 6 concerns the arrangement of latching dogs 30. As shown in Figure 6, the inner portion of each latching dog 30 is provided with teeth to mate with teeth positioned on the upper termination of mandrel 8. This wicker arrangement, identified by numeral 54, provides an important function. As a practical detail of construction it is undesirable to require that the drill bit be machined with such accuracy that latch 30 will just reach operational position when cone cutters 10 are forced into the tightest locked position on lowering of mandrel 8. The wicker referred to serves to eliminate necessity for construction of this precision. Thus the latch 30 in the embodiment of Figure 6 is pivotally supported on element 50 which in turn fits on mandrel 8, so that the latch 30 will normally extend somewhat above the recess 4 in which it is intended to seat when the drill bit has been lowered to drilling position. Consequently, on applying downward force on the spearhead employed to position the drill bit in the drill collar, element 50 may be forced downwardly suiiiciently to cause the latch 30 to move the remaining distance necessary to seat in the annular groove 4. This will serve to forcibly extend the packing element or rubber sleeve 53 into sealing position. Once the latches 30 have been forced downwardly so as to enter the groove 4, as illustrated in Figure 6, then the teeth of wicker 54- will serve to lock the mandrel in the indicated position when the insertion force applied by the spearhead is removed.

It is apparent that these and other refinements of the drill bit described may be employed if desired.

As the drill bit has been described, an essential feature of the apparatus includes a suitable insertion and retrieving tool for operation of the drill bit. Such a tool is illustrated in Figure 7 of the drawings. The tool consists of a massive cylindrical element or sinker bar 6%, which may be supported by a cable or wire line 61. The lower termination of sinker bar is provided With a cylindrical extension 62 equipped with a spearhead 37.

Enoircling the cylindrical extension 62 is a larger tubular sleeve member 63 maintained in sliding relation with cylinder 62. A collar element 64 fixed to sleeve 63 is provided with a conical inner surface 65. A threaded opening 66 is placed in collar 64 adapted to accommodate a slotted head set screw 70 which may pass through sleeve 63. When this, set screw 70 is turned into this threaded opening, the shank of the set screw may extend sufiiciently far to encounter a collar 67 positioned on the cylindrical extension 62. A coil spring 68 is fixed about cylindrical extension 62 so as to act against the lower portion of the sinker bar 60 and the upper termination of sleeve 63. This spring serves to urge sleeve member 63 downwardly with respect to cylindrical support 62. However, insertion of set screw 73 in the manner described limits this downward movement.

The purpose of this set screw is to hold sleeve 63 and collar 64 in an upward position spaced well above spearhead 37 when desired. Alternatively on retracting the set screw, sleeve 63 and collar 64 may be forced downwardly toward the spearhead by the spring 68. As will be described, the locked upward position of the sleeve and collar is required when using the tool to insert the retractable bit described. However, when retrieving the retractable bit, it is necessary that the sleeve and collar be forced downwardly toward the spearhead.

The retrieving tool as described and as illustrated in Figure 7 is in suitable condition for the lowering of the drill bit formerly described. The latches 30 of the drill bit may be forced inwardly so as to hold the spearhead 37 and will be retained in this position by the internal surface of the drill string while lowering downwardly to the drill collar. On reaching the drill collar, latches 30, when they have entered the annular groove 4 of the drill collar, will serve to free spearhead 37 so that the insertion tool may be removed from the well. In order to use this same tool to retrieve the drill bit, set screw 70 is retracted or removed from the apparatus. Spring 68 can then act to urge collar 64 downwardly with respect to the spearhead 37. On then lowering this tool so as to encounter the drill bit, spearhead 37 will first extend downwardly below the inner shoulders of latch '30 provided by recess 36, while the conical surface 65 of collar 64 serves to force latches 3t) inwardly. On then raising the retrieving tool, the spring 63 will serve to retain latching dogs 30 in the retracted position while maintaining the latching dogs in locked position with respect to spearhead 37.

What is claimed is:

l. A retractable drill bit comprising, in combination: a tubular drill collar, at least one circumferential groove within the bore of said drill collar providing an upward facing bearing surface and a downward facing bearing surface, a cylindrical element fitting slidably within said drill collar, the lower outer contour of said cylindrical element having a downward and inward taper, said cylindrical elementhaving at least two circumferentially spaced longitudinal slots each provided with an upward facing projection adjacent the lower end of said cylindrical element, at least two elongated drill cutter supports, each positioned in one of said longitudinal slots in sliding relationship between said cylindrical element and said drill collar, eacl". of said drill cutter supports having a downward facing shoulder engageable with said upward facing projection in said longitudinal slot, a first downwardly depending latching means pivotally fixed to each of said cutter supports and engageable with said upward facing bearing surface, said drill cutter supports including means adapted to receive said latching means in a manner permitting movement of said cylindrical element within said drill collar, means urging the lower end of each of said first latching means outwardly, a second latching means pivotally fixed to said cylindrical element and engageable with said downward facing bearing surface to limit upward movement of said cylindrical ele- 75 meat with respect to the drill collar, said cylindrical element including means adapted to receive said second latching means in a manner permitting movement of said cylindrical element with respect to the drill collar, means urging said second latching means outwardly, and a drill cutter element suspended from each of said supports, each of said cutter elements having an inward facing portion having a contour adapted to engage the lower outer contour of said cylindrical element, said first latching means being so positioned on said cutter supports that said cutter elements will be placed adjacent the lower end of said drill collar when said first latching means engages said upward facing bearing surface, said second latching means being so positioned on said cylindrical element that the lower tapered portion of said cylindrical element will be positioned to bear against said inward facing portions of said cutter elements, forcing said cutter elements against the lower end of said drill collar when said second latching means bears against said downward facing bearing surface, to thereby prevent upward movement of said cylindrical element and said cutter elements during drilling, the said forcing of said cutter elements against said drill collar thereby providing for transmission of torque from said drill collar to said cutting elements, said second latching means being positioned on said cylindrical element in a manner providing access to said second latching means by latch disengaging means lowered into said drill collar above said cylindrical element, whereby said second latching means may be disengaged from said downward facign bearing surface by a tool inserted in the drill collar, said cylindrical element may then be pulled upwardly out of engagement with said cutter elements, said cylindrical element being slidable upwardly with respect to said cutter supports until said upward facing projections in said longitudinal slots engage said downward facing shoulders on said cutter supports, thereby pulling said cutter supports upwardly as said cylindrical element is raised, and drawing said first latching means out of engagement with said upward facing bearing surface, whereby said cutter supports and cutter elements may be retracted through said drill collar.

2. Retractable drill bill as defined by claim 1 wherein the lower inner contour of said drill collar has a downward and outward taper.

3. Retractable drill bit as defined by claim 1 wherein each of said first latching means includes an inward extension and wherein said cylindrical member includes a recess to receive each of said inward extensions, said recesses being so positioned with respect to said upwardly facing projections of said longitudinal slots that said inward extensions can enter said recesses only when said upward facing projections are adjacent the downward facing shoulders of said cutter supports.

4. Retractable drill bit as defined by claim 1 wherein each of the downward facing shoulders of said cutter supports is placed at a different distance from its associated cutter element than each of the other downward facing shoulders, whereby said cutter elements will be retracted separately as said cylindrical element is raised in the drill collar.

5. Retractable drill bit as defined by claim 1 including an inward extension held by said drill collar and positioned adjacent said downward facing surface within said circumferential groove adapted to engage said second latching means against rotational movement, whereby to limit relative rotational movement of said cylindrical element and said drill collar.

6. Retractable drill bit as defined by claim 1 wherein three circumferentially arranged longitudinal slots, three drill cutter supports, three first latching means and three drill cutter elements are provided.

Hurley July 16, 1940 Walker Oct. 10, 1944