US2179010A - Well bit - Google Patents

Description

Nov. 7, 1 939.

T. A. CREIGHroN ErvAL WELL BIT Filed June 17, 1938'. 2 sheets-sheet 1 Nov. 7, 1'939. `T. A. cRElGHToN r AL v 2 Sheets-Sheet 2 Filed June 17, 1958 M l www @HN y@ www@ ww w Ivn I| IIN Patented Nov. A7, 1939 UNITED. STATES PATENT oFFlcF.`

Thomas A. .Creighton ma Thomas E. Meantime4 Long- Beach, Calif., assignors oi' one-third to Martha H. Wright, Los Angeles. Calif.

Application June 17, 1938, Serial No. 214,234

9 Claims. (Cl. 2551-72) the bit free and clear for the reception of the sur- This invention relates to well drilling toolsand relates more particularly to well bits for use in the rotary method ofwell drilling. A general object of this invention is to provide a simple, practical and effective well bit that facilitates the surveying of the well as the drilling progresses.

` Rotary well drilling bits have been vintroduced having openings for receiving surveying instruments, and the like, to permit the making of well l0 surveys and well tests without the necessity of withdrawing the bits and drilling strings from the wells. A bit of the class just mentioned usually has a central vertical opening of substantial diameter for passing the surveying instrument. It is necessary to arrange a removable core receiving barrelror a removable core destroying device in this opening to receive or cut away the core as the drilling progresses so thai-l the surveying instrument may be entered through the opening in the bit. In employing a bit of the class referred to it is necessary to remove the core barrel or the core destroying device from the bit when a survey is to be made. 'Following the surveying operation it is necessary to lower or run the core barrel or core destroying device down through the drilling string to its position in the bit. These operations are time` consuming and, therefore, expensive.

Another object of this inventionis to provid a rotary well drilling bit having an opening through which a surveying instrument may be passed to make a survey and embodying means for breaking or cutting away the core of earth formation, that would. otherwise occupy said opening, that is retractable to permit the successful operation of the surveying instrument.

Another object of this invention is to provide a rotary well drilling bit of the character mentioned in which the core cutting or core breaking means does not have to be removed from the bit to make a survey by an instrument passed down through the bit.

Another object of the invention is to provide a bit of the character mentioned in which the core breaking means automatically returns to the opveying instrument. v

Another object of this inventlonis to provide a well drilling bit of the character mentioned in which the core breaking means is simple to manufacture and inexpensively embodied in the bit.

A further object of this invention is to provide a rotary well drilling bit of the class mentioned in which the core breaking means cannot foul or injure the well surveying instrument.

The various objects and features of my invention willbe fully understood from the following detaileddescription of typical preferred forms and applications of the invention, throughout which description reference is made to the accompanying drawings, in which:

Fig. 1 is a side elevation of a rotary well drilling bit embodying one form of core breaking means.

Fig. 2 is an enlarged bottom elevation of the lower part of the bit shown in Fig. 1. Fig. 3 is an enlarged fragmentary vertical detailed sectional view taken' as indicated by line 3--3 on Fig. 1.

Fig. 4 is a horizontal detailed sectional view taken as indicated by line 4 4 on Fig. 3. Fig. 5 is a fragmentary vertical detailed sectional view'I of the lower portion of the bit shown in Fig. 1 illustrating a part of a surveying instrument in broken lines and showing the dog in the retracted position. Fig. 6 is a side elevation of a rotary well drilling bit embodying another form of core breaking means of the invention. Fig. 'l is a vertical detailed sectional view taken as indicated by line 1 1 on Fig. 6 with broken lines illustrating the retracted positions of the dogs. Fig. 8-is a horizontal detailed sectional view taken as in,- dicated by line 8-8 on Fig. 7, and Fig. 9 is a fragmentary vertical sectional view of still another form of the invention.

The present invention may be embodied in rotary well drilling bits of various types and constructioris. In the following detailed description we will describe two typical forms of the invention embodied in drag type rotary bits. It is lto be understood that the invention is not to be construed as limited or restricted to these specic forms or applications of the invention. Further it is to be understood thatx where reference isv made herein to surveying instruments and surveying operations it is contemplated that such referf ence is to be construed as meaning various instruments and operations that may be employed for determining, testing and receiving the various conditions in the well, such as directional conditions, temperature conditions, pressure conditions, formation conditions, etc.

The bit construction of the present invention illustrated in Figs. 1 to 5, inclusive, of the drawings may be said to comprise, generally, a bit body I0 having a central vertical opening II for receiving a surveying instrument A, cutting means I2 on the body I0 for cutting the well bore to gauge and means I3 for cutting or breaking away the core or central portion of the earth formation.

The body I0 of the bit illustrated in Figs. 1 to 5, inclusive, of the drawings is in the nature of an elongate Istem or shank. The lower major portion of the bit body I 0 is cylindrical and of uniform diameter while the upper portion I4 of the body is enlarged and tapered downwardly and inwardly. Means is provided at the upper end of the body Infor facilitating its connection with a well drilling string. In the typical case illustrated a tapered screw threaded socket I5 is provided in the upper portion of the body I0 to receive a correspondingly shaped pin on the lower end of the string. The opening II extends downwardly through the body I0 from the socket I5 to the lower end of the body. The opening II serves to handle or conduct the circulation uid and is proportioned to receive or pass the surveystrument A. Means are provided in the bodyV ||l to assist in locating and supporting the surveying instrument A. An annular flange I6 is provided on the wall of th opening II. The ange I6 is spaced below the socket I5. The lower portion of the opening II is reduced in diameter to receive the instrument A with suitable clearance. The flange I6 and the reduced lower portion of the opening II serve to center and locate the surveying instrument A in the body I0 of the bit. i

The cutting means I2 is provided to cut away the earth formation and form the well'bore. The present invention is not primarily concerned with the character of the cutting means embodied in the bit and contemplates the employment of cutting means and elements of various natures. In the form of the invention being described the cutting means I2 includes two cuttingblades I1 on the lower end portion of the body I0 and a set of spaced cutting blades I8 on the upper enlarged body portion I4. The cutting blades Il may be termed pilot blades and operate to form an annular cut inthe earth formation to receive the lower portion of the shank IU with suitable clearance. The blades Il project downwardly and outwardly from the lower end of the body I0 and have upwardly and inwardly inclined lower cutting edges and substantially vertical reaming edges. The inner edges of the blades I'I .are clear of or aligned with the wall of the opening I| to permit the passage of the surveying instrument A through the opening. The lower end portion of the body I0 may be provided' with stabilizing blades I 9. The blades I9 project downwardly and outwardly from the lower end of the body I9 and have quite broad outer surfaces 20 adapted to cooperate with the outer Wall of the cut made by the blades I1 to assist in stabilizing the bit. It will be observed that the pilot blades I'I' operate to form an annular cut and leave a central portion or core of earth formation in line with the opening II. It is preferred to provide notches 2| in the low'er end of the body II) to communicate with the opening I I. The notches 2| are provided to permit the free lateral discharge of fluid from the opening II and are preferably arranged in front of the blades I1 with respect to the direction of rotation of the bit.

The upperblades I8 are the reaming or bore enlarging blades of the cutting means I2. The blades I8 project downwardly and outwardly from the enlarged tapered /body portion I4. The lower edges 22 of the cutting blades I8 slope downwardly and outwardly and the outer edges or reaming edges 23 of the blades I8 may be substantially vertical. The blades I8 are operable to enlarge the well bore to receive the drilling string with substantial clearance to provide for the return oW off circulation fluid through the well bore. I

The means |3 is an important feature of the invention. The means I3 is provided to remove or cut away the core or inner portion of earth formation during the drilling operations and is retractable to permit the surveying instrument A to be arranged in or passed through the body opening II to make a well survey. The means I3 includes one or more retractable core breaking or cutting dogs 24. In the particular case illustrated there is one dog 24, it being understood that the invention contemplates the employment of one or more dogs. The core cutting or breaking dog 24 is preferably located at the lower end portion of the bit body IU and the 'lower part of the body is constructed to receive and mount the dog. An enlargement or boss 25 is provided on the exterior of the body I0 in adjoining relation to one of the stabilizing blades I9 and a notch 26 extends upwardly into the lower end of the body I0 between the boss 25 and the said stabilizing blade I9. The notch 26 preferably has fiat parallel side walls and a at substantially horizontal upper wall. The body I0 is provided with a machined or fiat surface 21 at the outer side of the notch 26 and ya similar flat surface 28 on the rear side of the stabilizing blade I9 that is adjacent the notch 26. The surface 21 is pro-l vided on the outer side of the boss 2-5 and the adjacent parts of the body I0.

The core cutting or breaking dog 24' is a shiftable or pivotable knife-like element. The outer portion of the dog 24 is received in the notch 26.

Means is provided for pivotally supporting the dog 24 in the notch 26. A bore or socket 29 enters the body I0 from the above-mentioned surface28 and intersects the notch 26. The inner end of the opening 29 may enter the boss 25. A pivot pin -30 is arranged in the opening 29 to pass through a transverse opening 3| in the outer portion of the dog 24. The pin 30 supports the dog 24 for pivotal movement about a substantially horizontal axis. Welding 308L may be provided on the rear surface 28 of the adjacent stabilizing blade I9 to secure the pin 30 in its opening 29, it being obvious that other means may be employed to hold the pin 30 in place. The opposite sides of the dog 24 are preferably flat to 'effectively bear on the side walls of the notch 26 and the upper side of the dog 24 is iiat to bear upwardly against the upper wall of the notch 26. When the dog 24 is in its normal substantially horizontal cutting position its upper side is in flush bearing engagement with the flat upper wall of the notch 26.

The dog 24 is proportioned to project into the opening II or to project into the central zone directly below the opening II. In practice the dog 24 may be proportioned to have its inner end a short distance from the central longitudinal axis of the opening II when in the active core breaking position. The inner projecting portion of the dog 24 may be pointed or. provided with inwardly convergent sides as best illusmated in rigs. s and 4 of the drawings. A cutv 5 ting rib 32 is provided on the active lower side ofthe dog 24. The rib 32 may be built up of welded-on hard cutting material and is provided to cut away the core of earth formation left standing between the pilot blades I1. The

' 10 cutting rib 32 operates du'ring rotation of the bit to cut away the central core of earth formation by a dragging or shearing action. The upper .inner corner 33 of the dog 24 is vbevelled or rounded downwardly and inwardly for the purpose to be hereinafter described. l

The invention may provide means for automatically returning the dog 24 to its active cutting position immediately upon the removal of the surveying instrument A from the opening. II

of the bit. A slot 34 is provided' in the outer portion of the dog 24 to intersect the opening 3|. A torsional spring 35 is arranged in the slot 34 and surrounds the pin 36. One end portion of the torsional spring 35 bears upwardly against 25 the under side of the dog 24 and the other end portion of the spring bears inwardly against a surface of the body I0. The spring 35 exerts a turning force on the pivoted dog 24 to urge the dog to the active position illustrated in Figs.

1 to 4 of the drawings where its upper side bears against the upper wall of the notch 26..- The engagement of the dog 24 with the earth formation may automatically return vthe dog to its active position and'it may be preferred or desirable in some instances to dispense with the spring means just described.

In the preferred construction the outer side of the dog receiving notch 26 is closed to protect the dog' 24 and the other parts against an o excessive -:flow of iiuid through the notch. A plate 36 is arranged against the body surface 21 and extends across the outer side of the notch 26. The plate 36 is shaped to conform tov the surface 21 and to extend about the adjacent portion of the dog 24. Welding31 may secure the plate 36 to the body I0. The plate 36 serves to prevent the flow of circulation uid laterally through the notch 26 and protects the dog 24.

In the use or operation of the bit the body I0 o is connected with the lower end of the well drilling string and the bit is operated on the lower end of the string in the usual manner. ,During the drilling operations the drilling string is rotated and the blades I1 and I8 act .on the earth formation to form the well bore.` The blades I1 on the lower end of the bit body I6 form a pilot bore of small diameter in advanceV of the bore enlarging blades I6. The blades I8 act on the earth formation to enlarge the pilot 0 bore and to make the well bore ofthe desired gauge. The core cutting or breaking dog 24 is in the position illustrated in Figs. 1 to 4, inclusive, of the drawings, during the drilling-.operations-and its cutting rib 32 operates to cutaway 5 the core or central portion of earth formation left standing between the blades I1. It will be observed that the engagement of the cutting dog 24 with the earth formation serves to hold the dog in the position where its upper side bears against the upper wall of the notch 26. Thus the operating forces are directly transmitted from the body I0 to the dog -24 without subjecting the pivot pin 30 to severe strains. The circulation fluid passed downwardly through the drilling string iiows through the opening II and is discharged from its lower end and from the notches 2|. This circulation fluid may assist in removing the core.' When it is desired to make a survey of the well or to project a well instrument into the 5 open well below the bit the drilling operations are temporarily suspended and the drilling string is moved upwardly to raise the bit from the bottom of the well. The surveying instrument A or other well instrument is then dropped, pumped 10 or run down through the drilling string to pass through the opening II of the bit body I0. When the instrument A approaches the lower end of the opening II it contacts the. rounded upper inner corner 33 of'thedog 24 and the down- 15 wardly moving instrument moves or swings the dog downwardly and outwardly to a position such as illustrated in Fig. 5 of the drawings. The weight of the surveying instrument A is sumcient to overcome'the spring 35 yand readily move '20 the dog 24 to its`retracted position. Thus the instrument A is free to pass downwardly through the opening II and project from the lower end of the bit. The instrument A is adapted to come to rest in a position where its head, or an en- 25 largement on the instrument, seats on the flange I6. This locates the instrument and the engagement of the instrument head with the iiange I6 cuts off or substantially cuts off the flow of circulation fluid causing the pumps to stop or 3o labor, thus indicating to the operator or driller that the instrument is in the correct position for operation. When the instrument A is in its correct position projecting from the lower end of the bit it is controlled or operated in the usual 36 manner to take a reading. Upon4 the completion of the survey or instrument operation the instrument A is withdrawn from the drilling string. When the instrument A is moved upwardly from the opening II the spring 35 swings 40 or pivots the dog 24 upwardly and inwardly to the active position where its upper side contactsthe upper wall of the notch 26. Thus the core breaking dog 24 is automatically reconditioned for operation immediately upon the removal of 45 the surveying instrument A from the bit. 'I'he drilling operations may now be resumed.

It is to be observed that the improved bit illustrated in Figsl to 5, inclusive, embodies an improved core breaking means that effectively 50 removes the core or central portion of earth formation during drilling and that does not require withdrawal from the well preparatory to making a well survey or Well condition determining operation. The core breaking dog 24 is car- 55 ried by the bit throughout the drilling and surveying operations eliminating the necessity of running a grappling vtool `into and out of the drilling string before and after the surveying operation to withdraw and reset a core break- 50 ingdevice.

The embodiment of the invention illustratedin Figs. 6, '1 and 8 of the drawings may be said to comprise, generally, a body 40 having a central vertical-opening 4I, cutting means 42 on the 65 body 46, and a plurality of retractable core breaking dogs 43, carried by the body 40 to break or cut away the central portion of the earth formation that would otherwise enter the opening 4 I.

The bit body 40 may be a generally cylindrical 70 member, as illustrated. Suitable means is provided at the upper end of the body 46 foryconnecting itr with the' `drillingstring. In the case illustrated a tapered screw threaded socket 44 is provided in the upper end part of the body 40 to' 'I6 60 active positions.

receive the pin of the drill collar of the string. The opening 4| extends downwardly from the socket 44 to the lower end of the body 40.

The cutting means 42 may be any suitable form 5' of lmeans for cutting away the earth formation and that permits the passage of a surveying instrument through the body 40 to project from the lower end of the bit. In the typical case illustrated the cutting means 42 comprises spaced downwardly and outwardly projecting cutting blades 45 on the lower portion of the body 40. The blades 45 may be of substantial length to continue upwardly along the side of the body 40. The lower cutting edges 46 of the blades 45 slope downwardly and outwardly while the side cutting edges or rearning edges 41 of the blades are substantially vertical. The inner edges of the cutting blades 45 are clear of or aligned with the wall of the opening 4| to permit the passage of a surveying instrument downwardly from the the body opening 4|.

The dogs 43 are provided to break away or cut away the central core of earth formation left by the blades 45 to leave the opening 4| open or unobstructed and to provide a generally flat bottom wall on the well. In accordance with the invention there may be any suitable number of core breaking dogs 43. In the form of the invention being described there are two likedogs 43. The dogs 43 are arranged in diametrically opposite slots or notches 48 in the lower end portion of the bit body 40. The notches 48 extend upwardly from the lower end of the bit body and communicate with or join the opening 4|. The side walls of the notches 48 are preferably flat and 40 parallel and the upper walls 49 of the notches are flat and generally horizontal. Transverse bores or openings 50 are provided in the body 40 to intersect the upper portions of the notches 48.

In accordance with the invention the dogs 43 are pivotally supported'in the notches 48 to depend or project downwardly. Pivot pins 5| are arranged in the openings 50 and pass through transverse openings 52 in the upper parts of the 50 dogs 43 to support the dogs for pivotal movement having inner faces 53 thatslope downwardly and inwardly when the dogs are in their active positions. The lower ends of the dogs 43 are provided with hard cutting material 54 and are substantially horizontal when the dogs are in their The upper ends of the dogs 43 are provided with stop shoulders or faces 55 engageable with the upper walls 49 ofthe notches 48 to stop the dogs in their active positions and to assist in transmitting the drilling pressures and forces between the body l0 and the dogs. The inner lower corners of the dogs 43 are preferably rounded, as illustrated. The sides of the inner active portions of the dogs 43 may be inwardly convergent as best illustrated in Fig. 8 of the drawings. The dogs 43 are proportioned to have their inner lower corners in spaced adjacent relation to the central vertical axis of the opening 4| when in their active cutting posi- 75 tions. 'I'he hard cutting material 54 preferably continues upwardly along the rounded inner lower corners of the dogs 43.

Means is provided for yieldingly holding the dogs 43 in their active cutting positions and for returning the dogs to these positions following the withdrawal of the surveying instrument from the bit. Flat substantially vertical surfaces 56 are provided on the periphery of the body 40 at the outer sides of the notches 48. Leaf springs 51 are arranged against the surfaces 56 and are secured to the body 40 by screws 58, or the like.

The leaf springs 51 project downwardly into the notches 48 to cooperate with the pivoted dogs 43. The dog controlling springs 51 are shaped to bear inwardly against the outer sides of the dogs 43 to urge the dogs to their active positions where the stop faces 55 cooperate with the upper walls 49 of the notches 48. Plates 60 are welded to the body surfaces 56 to extend across the outer sides of the notches 48. The plates 80 extend downwardly from the upper ends of the notches 48 to adjacent the lower end of the body 40 and serve to protect the dogs 43 and the springs 51. The plates 60 prevent an excessive flow of circulation fluid through the notches 48 thus protecting the dogs 43 and the springs 51 against the errosive action of the uid.

In the use or operation of the bit illustrated in Figs. 6, 7 and 8 the body 40 is connected with the lower end of the drilling string and the string is rotated and fed downwardly in the well in the usual manner. The cutting blades 45 serve to cut the well bore to gauge but leave a central portion or core of earthformation. The dogs 43 are in the positionsv shown in full lines in the drawings during the drilling operation and serve to cut away the core of earth formation just mentioned. It is to be observed that the dogs 43 are formed and mounted so that the cutting pressures are transmitted longitudinally through them and through the cooperating stop faces 55 and the upper ends of the notches 48. The cut- 'ing engagement of the dogs 43 with the core of earth formation maintains -the dogs in their active cutting positions. The hard cutting material 54 makes thedogs 43 particularly effective in drilling or breaking away the core. Circulation fluid pumped downwardly through the drilling string discharges from the lower end of the opening 4| to flush the dogs 43 and the cutting blades 45.

When it is desired to make a survey of the well, or a so-called "open hole reading, the bit is raised from the bottom of the well and the surveying instrument is dropped or lowered through the drilling string. When the surveying instrument moves downwardly through the body opening 4| its lower end contacts the inner sides 53 of the dogs 43. The surveying instrument engaging the inclined sides 53 readily swings the dogs 43 outwardly to the retracted positions illustrated by the broken lines in Fig. '1. 'Ihus the downwardly moving surveying instrument automatically retracts the dogs 43. The instrument is free to project from the lower end of the bit and when in the correct position is operated to make the survey. Upon the completion of the survey the instrument is withdrawn upwardly from the bit and removed from the drilling string. Upon the upward withdrawal of the surveying instrument from the opening 4| the springs 51 acting on the dogs 43 automati-` cally pivot the dogs to their active cutting positions. The bit may then be lowered to engage or outer sides of the elements 14.

the bottoml of the well borefand the drilling operation may be continued.

Fig. 9 of the drawings illustrates a portion of a well bit embodying another form of the invention. VIn the structure shown in Fig'. 9,10 designates a well bitbody having a central vertical opening 1l adapted to receive a surveying instrument, or the like. Suitable cutting means is provided on thebit body 10 to `cut the major outer portion of the well. In the'case illustrated this cutting :means comprises suitable .drag type blades 12 projecting downwardly and outwardly from the body 10. 'The blades 12 are arranged so that an object such as a surveying instrument may be passed downwardly through the opening 1| to project from the lower end of the bit. In this form of the invention there are one or more lateral pockets 13 provided in the body 18 to communicate with its opening 1I. In the case illustrated thereare two diametrlcally opposite pocketsv 13 formed in the body 10.

A core breaking or core cutting element 14 is bodily shi'ftable in each pocket 13 between a position Where it projects into the opening 1I to cut away the core or inner portion of thev earth formation and a position retracted within the pocket. The elements 14 are knife-like or bladelike parts having lower cutting edges 15 that may be hard faced or provided with hard cutting material. The upper inner corners of the elements 14 are bevelled oi to provide downwardly and inwardly inclined edges 18. The upper ends of the elements 14 may be flat to bear against the upper walls of the pockets 13 when the elements are in. their projected active positions.

Means are provided for governing the movement of the core breaking and cutting` elements 14. In the case illustrated these means comprise downwardly and outwardly inclined slots 11 in the elements 14 and pins 18 carried by the body 10 to intersect the pockets 13 and pass through the slots 11. The engagement of the pins 18 with the slots 11 may be such that it prevents undesirable pivoting or rocking of the elements 14 on the pins. 'Ihe elements 14 are movable downwardly and outwardly on the pins 18 from the active positions illustrated to retracted positions entirely within their pockets 13. Spring means may be provided to return or to assist in returning the elements 14 to their active projecting positions. We have shown leaf springs 19 secured to the body 10 and projecting into the pockets 13 to bearinwardly against the rear The springs 19 are positioned and shaped to urge the elements 14 upwardly and inwardly.

The operation of the bit construction illustrated in Fig. 9 of the drawingsis substantially identical with the previously described forms .of the invention. During drilling operations the elements 14 are in the positions illustrated so that their lower cutting edges 15 act on the inner or central portion of the earth formation to cut the same away. The blades 12 form the outer portion of the well. When a survey or similar operationis to be performed the bit is raised and the surveying instrument or like device is'run down through the opening 1I to project beyond the lower end of the bit. The lower end of the surveying instrument contacts the edges 18 and forces or moves the elements 14 downwardly and outwardly. Thus the surveying instrument automatically retracts the elements 14. When the surveying instrument is Withdraw Imm the bit 'the springs 19 urge the elements14 upwardly and inwardly to protrude into the opening 1l and when drilling operations are resumed the engagement of the earth formation with thecutting edges 15 positively returns the elements 14 to their fully extended active positions.

Having described only typical preferred forms and applications of our invention, we do not wish to be limited or restricted to the specific details herein set forth, but wish to reserve to ourselves any variations or modillcations that may appear to those skilled in the `art or `fall within the scope of the following claims:

Having described our invention, we claim:

1. A well drilling bit comprising a body having a vertical opening, cutting means on the 'body operablel to Imake an annular cut in the earth formation leaving a central core of earth formation, an element pivotally supported on the body, and yielding means urging the element to a posi-l tion where it cuts away the core. and where it is retractable by an object run down in the opening to allow the projection of the object from the lower end of the body and operable to return the element to the core cutting position.

2. A rotary well drilling bit comprisingl a body having an opening adapted to pass an object to be run into the well, cutting means on the body arranged to allow the passage of said instrument from the lower end of the opening, a corebreaking dog pivoted on `the body to swing about a generally horizontal axis, means limiting upward -pivoting of the dog to stop the dog in a position and spring means yieldingly urging the dog to the cutting position.

3. A rotary well drilling bit comprising a body having an opening adapted to pass an object to be run into the well, cutting means on the body arranged to allow the passage of said instrument from the lower end of the opening, a core breaking dog pivoted on the body to swing about a generally horizontal axis, means limiting upward pivoting of the dog to stop the dogin a position where it cuts away the central portion of earth formation during drilling and is engageable by an object passed down through the opening to be retractable downwardly and outwardly thereby, and a spring reacting against the body and dog for returning the dog to the cutting position upon upward withdrawal of the object from the opening.

4. A rotary well'drilling bit ycomprising a body having an opening adapted to pass an object, cutting means on the ybody arranged to allow the passage of said object from the lower end of the opening, a plurality oi core breaking dogs piv- 'otally supported on the body to remove' the cenbody to be secured to a' drilling string and having a vertical opening for *receiving an object to be run into the well and having a lateral notch joining said opening, cutting means on the body clear of said opening to pass said object from the lower end of the body, and a core breaking dog pivoted in said notch to normally project inwardly and cut away the core left by the cutting means and pivotable downwardly and outwardly portion of earth formation left by said cutting means and yieldable to allow downward and outward retraction of thev element from the openingv by the said object, and stop means limiting upward `and inward pivoting of the element to stop the element in a position to cut away said portion of the earth formation. A

7. A rotary well drilling bit comprising a bit body to be secured to a drilling string and having a vertical opening for receiving an object run through the string and having a lateral notch joining said opening, cutting means on the body yclear of said opening to pass said object from the lower end of the body, a core breaking element, means pivotally supporting the element in the notch for movement between a position where it bears against the upper wall of the notch and projects toward the central vertical axis of the bit to cut away -the central portion of earth formation and a position where it projects downwardly clear of the said opening, and spring means urging the element to the iirst mentioned position and yieldable to allow movement of the element to the second mentioned position when the object moves down against the element.

8. A rotary well drilling bit comprising a body having a vertical opening for receiving an object to be run into the well and having a notch communicating with said opening, cutting means on the body clear of said lopening to pass said object from the lower end ofthe body, a core breaking element, means pivotally supporting the element in the notch for movement between a position where it bears against the upper wall of the notch and projects toward the central vertical axis of the bit to cut away the central portion of earth formation and a position where it projects downwardly clear of the said opening, and means urglngthe element to the rst mentioned position and yieldable to allow movement of the element to the second mentioned position when the object moves down against the element,

the last named means including a torsional spring acting on the element.

9. A rotary well drilling bit comprising a body having a vertical opening for receiving an object to be run into the well and having a notch communicating with said opening, cutting means on the body clear of said opening to pass said object from the lower end of the body, a core breaking element, means pivotally supporting the element ln-the notch for movement between a position where it bears against the upper wall-of the notch and projects toward the central vertical axis of the bit to cut away the central portion of earth formation and a position where it projects downwardly clear of the said opening, and means urging the element to the rst mentioned position and yieldable to allow movement of the element to the second mentioned position when the object moves down against the element, the last named means including a leaf spring acting on the element.

THOMAS E. McMAHAN.

THOMAS A. CREIGHTON.

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