US1987853A

US1987853A - Core catching means

Info

Publication number: US1987853A
Application number: US650130A
Authority: US
Inventors: John H Howard; Jesse C Wright
Original assignee: Globe Oil Tools Co
Current assignee: Globe Oil Tools Co
Priority date: 1933-01-04
Filing date: 1933-01-04
Publication date: 1935-01-15
Anticipated expiration: 1952-01-15

Description

a Q F M Jan. 15, 1935.

J. H, HOWARD ET AL CORE CATCHING MEANS Filed Jan. 4, 1953 2 Sheets-Sheet 1 df m Z ,mar U nWW m i n H 1 H Jan. 15, 1935. J. H HOWARD ET AL CORE CATCHING MEANS Filed Jan. 4, 1933 2 Sheets-Sheet 2 4f 2 n xmw WWW 70 26% mnw w m J Any Patented Jan. 15, 1935 UNITED STATES PATEN T OFFICE CORE CATCHING MEAN S Wright, Los Angeles, Oil Tools Company,

poration of California Application January 4,

Claims.

' This invention relates to a core catching means, and relates more particularly to core catching and retaining means for embodiment in a well tool.

It is a general object of the present invention to provide a simple, practical and effective core catching means for a well drill or well core drill that is positive and dependable in its operation.

It is anotherobject of the invention to provide 10' a well core drill construction in which the core engaging and retaining elements are operated between retracted and active core engaging positions upon relative movement between the bit head and a sub or similar member on the lower 16 end of the barrel.

It is another object of the invention to provide a core drill construction of the character mentioned thatincludes an actuating or force producing means which acts in addition to the weight of the drill head to cause relative movement between the bit head and the sub carrying the bit head to actuate the core engaging elements. The core engaging elements of the core catchers oi the general class provided by the invention have *iheretoi'ore depended for their actuation upon shifting 01 a part of the tool brought about by the weight of the inner barrel or the weight of a substantial portion of the body or outer barrel in addition to the weight of the bit head. The present invention on the other hand, includes a spring means acting together with the weight of the bit head to cause the relative movement between the bit head and the remainder of the tool to insure the positive and eiiective actuation of the core engaging element.

It is another object of the invention to provide a core drill construction in which the core catching means may be located immediately adjacent the bit head.

It is another object of the invention to provide a core catching and retaining means of the character mentioned that is capable of embodiment in core drills having different types of cutting parts and in single barrel and double barrel core drills.

It is another object of the invention to provide a "core drill construction of the character mentioned in which the torque and the cutting thrusts are transmitted between the bit head and the sub on the body or barrel in a positive, dependable and effective manner.

It is another object of the invention to provide a core catching means of the character mentioned that does not require or necessitate the provision of packing or packed Joints in the assembly. a

non Park, and Jesse C.

1933, Serial No. 650,130

It is a'iurther object of the invention to provide a core catching means that is extremely simple and compact and that embodies a minimum. number of parts.

Further objects and features 01' the invention will be-best and fully understood from the following detailed description of typical forms and applications 01' the invention, throughout which description reference will be had to the accompanying drawings, in which:

I Fig. 1 is a longitudinal detailed sectional view of a single barreled core drill involving the present invention illustrating the core engaging elements in the retracted positions and taken as indicated by line 1-1 on Fig. 2. Fig. 2 is a transverse detailed sectional view taken asindicated by line 3-3 on Fig. 1. Fig. 3 is a central longitudinal detailed sectional view 01' the lower nd portion of the tool illustrated in Fig. 1 showing' the core engaging elements in engagement with" the core. Fig. 4 is a longitudinal detailed sectional view of the lower end portion of a double barreled core drill embodying a typical form of the invention taken as indicated by line 4-4 on Fig.

.5. Fig. 5 is a transverse detailed sectional view taken as indicated by line 5-5 on Fig. 4. and Fig. 6 is a longitudinal detailed sectional view of the lower end portion of a rock core drill involving the invention.

The core retaining means provided by this, invention is capable of embodiment in or application to core drills or coring outfits of vari ous types, and involving diflerent forms of cutting parts, etc. In the following detailed disclosure we will describe typical preferred forms of the invention embodied in several typical core drills, it being understood that the invention is not to be taken as limited or restricted to the specific forms or applicwicns oi the invention about to be described, but is to be considered as including any features or modifications ,hat may fall within the scope of the claims.

Figs. 1 to 3 inclusive of the drawings illustrate a single barreled core drill involving the invention, and which drill includes generally, a body or barrel 10, a sub 11 on the lower end of the barrel 10, a bit head 12 shiftably carried by the sub 11, core catching elements 13 on the sub 11 operable upon relative movement between the bit' head 12 and sub 11, and means 14 for urging the bit head 12 to shift relative to the sub 11 to actuate the elements 13.

The body or barrel 10 of the typical core drill structure illustrated in Figs. 1, 2 and 3 of the drawings is adapted to be attached to the lower end of an operating string of drill pipe, or the like, and is adapted to receive the core cut by the bit head 12. The barrel 10 is a tubular structure that may be of any desired length and operates to carry the sub 11 and the bit 'head 12. In accordance with the usual practice, the barrel 10 may be provided at its upper end with suitable means (not shown) for connecting with the operating string. A. sub or connecting member 15 may be provided on the lower end of the barrel 10 to facilitate connection of the sub 11 with the barrel. In the particular construction illustrated in the drawings, the member 15 is threaded on to the lower end of the barrel 10 and is provided at its lower end with a threaded,

pin 17.

The sub 11 is in the nature of a carrier mi supporting or shiftably carrying the bit head 12. The sub 11 is attached to the barrel 10 through the connecting member 15, being provided at its upper end with a box or socket 16 for receiving the threaded pin 1'1. A central longitudinal opening 18 is provided in the sub 11 to pass the core upwardly into the barrel 10. The walls of the sub 11 may be comparatively heavy or thick and the opening 18 may be of smaller diameter than the opening in the barrel 10. A recess or enlargement 19 is provided in the sub' opening 18, and its upper end presents a downwardly facing shoulder 20 on the interior of the sub. The lower end 21 of the sub 11 is preferably flat and normal to its longitudinal axis.

The bit head 12 is operable to make an annular cut in the earth formation to form a core to be received in the barrel 10. The bit head 12 includes a tubular body or shoe 22 and cutting parts 23 on the shoe. broader principles of catching means maybe the invention, the core included in tools having cutting parts of various characters. In the particular core drill being described, the cutting parts 23 are in the nature of blades projecting outwardly and downwardly from the lower end of the shoe 22. The cutting blades or parts 23 are spaced apart circumferenti'ally, and are operable to make an annular cut in the formation and form a core thatis adapted to pass into the sub 11 and barrel 10 with suitable clearance. Certain features of the bit head 12 illustrated in the drawings are described and claimed in the copending application of J. 11. Howard and A. C. Catland entitled Bit head, Serial No. 850,131, filed January 4, 1933.

In accordance with the invention, the shoe 22 of the bit head has telescopic engagement with the sub 11 and is adapted to shift longitudinally relative to the sub. In the case illustrated in the drawings, the shoe 22 of the bit head extends upwardly into the lower end of the tubular sub 11. A sliding key or spline connection is provided between the sub 11 and the bit head 12 whereby the rotative thrusts and/or torque is transmitted from the sub 11 to the bit head. A plurality of external splines 23 is provided on the shoe 22 and have sliding cooperation with longitudinal splines 24 on the interior of the sub 11. The upper end of the shoe 22 of the bit head is adapted to cooperate with downwardly facing shoulders 25 on the interior of the sub 11 when the tool is in operation, and a weight is on the bit head to cause its cutting parts 23 to penetrate the formation. Upwardly facing external shoulders 26 may be provided on the shoe 22 at the lower ends of the splines 23. If desired or found practical, the shoulders 26 may jbit head 12 relative to the In accordance with the cooperate with the lower end 21 of the sub when the drill is in operation.

The invention includes means for limiting the downward movement of the bit head 12 relative to the sub 11. Blocks 26 are arranged in sockets 2'7 in the splines 23 and extend outwardly into vertically elongated openings 28 in the wall of the sub 11. The blocks 26 are removably attached to the bit head shoe 22 by counter sunk screws 29. The openings or slots 28 in the sub 11 are proportioned and related to the blocks 26 to allow for the desired movement of the bit head 12 relative to the sub 11. The engagement of the lower ends of the openings 28 with the blocks 26 limits the downward movement of the sub.

The core catching and retaining elements 13 are carried by the sub 11 and are operable upon downward movement of the bit head 12 relative to the sub 11 to bite into the core within the tool. In the particular form of the invention illustrated in the drawings, the core engaging elements 13 are in the nature of pivoted dogs that are adapted to project into the opening 30 of the bit head to engage the core. There may be one or more core engaging elements 13 provided on the sub 11. In the typical application of the invention being described there are three equally or symmetrically spaced core engaging elements 13 pivotally mounted in pockets or recesses 31 in the interior of the sub 11. The recesses 31 are provided with downwardly and outwardly inclined upper walls, and substantially flat horiiwntal walls joined by curved concaved seats. Pins 32 are carried in horizontal openings 34 in the splines 24 of the sub 11 and extend through transverse openings 33 in the pivoted core catching elements 13 to pivotal y support ihe elements in the recesses 31. The openings 34 communicate with the block carrying openings 27 whereby the pins 32 may be readily arranged in position when the tool is assembled. The blocks 26 when secured in position by the screws 29 positively prevent displacement of the pins 32.

The pivoted core engaging dogs or elements 13 project inwardly from the recesses 31 and openings 35 are provided in the walls of the shoe 22 to pass the elements 13 whereby they project into the opening 30 of the head. The upper and lower ends of the openings 35 are inclined upwardly and inwardly to have effective sliding cooperation with the elements 13. The openings 35 are located with reference to the sub 11 so that the gripping elements -13 project upwardly and inwardly through them as illustrated throughout the drawings. The inner ends of the core engaging elements 13 are formed to have effective cutting or biting engagement with the core. In the particular case illustrated in the drawings, the inner end portions of the elements 13 are reduced in thickness and terminate in bevelled edges that are adapted to cut into the core as illustrated in Fig. 3 of the drawings. The engagement of the wall of the openings 35 with the core engaging elements 13 causes the elements 13 to pivot inwardly and downwardly upon downward movement of the bit head 12 relative to the sub 11 so that they have firm supporting engagement with the core. when the bit head 12 is in active cutting engagement with the earth formation and is in its up position in relation to the sub 11, the core engaging elements 13 are in the retracted positions illustrated in Fig. 1 of the drawings where they do not interfere with the passage of the core into the barrel 11. In practice, the

' a barrel, or the like.

core engaging elements 13 may be mounted and formed so as to normally bear against the core during the drilling operation to insure their effective core cutting and retaining action when the tool is raised to cause relative movement between the sub 11 and the bit head 12.

The means 14 for urging the bit head 12 downwardly relative to the sub 11 acts to move the bit head 12 downwardly upon the tool being raised, to lift the bit head out of engagement withthe bottom of the well bore, so that the core engaging elements 13 are forced into the core. The means 14 is in the nature of a spring means normally yieldingly urging the head 12 downwardly. In accordance with the broader aspects of the invention, the location and specific structure of the means 14 may be varied. The actuating means 14 includes aspring or springs arranged under compression between parts of the sub. 11 and bit head 12. In the typical embodiment of the invention illustrated in the drawings, the means 14 includes a single coiled or spiraled spring 37 arranged in the enlargement 19 of the sub opening. The spring 37 is arranged under compression between the shoulder 20 and the upper end of the bit head 12. The spring 3'! may be a comparatively heavy strong spring held under a substantial strain or pressure'so that it e is operable to urge the bit head 12 downward with considerable force.

It is believed that the operation of the embodiment of the invention illustrated in Figs. 1, 2 and 3 of the drawings will be readily understood from the foregoing detailed description. when the tool is being lowered into the well bore, the bit head 12 is held in its extreme down position through its weight and through the action of the spring 37. ,Upon the cutting parts 23 coming into engagement with the ;formation at the bottom of the well bore, and upon the drilling weight being imposed on the tool, the spring 37 is compressed so that the upper end of the-shoe 22 comes into engagement with the shoulder 25.

The tool is adapted to be rotated in the usual manner so that the cutting parts 23 penetrate the formation leaving a core whichis received in the sub 11 and barrel 10. The core engaging elements 13 remain in. their up or retracted positions during the drilling operation and therefore do not interfere with the passage of the core ing of the bit head 12 relative to the sub l-l, the

core engaging dogs-13 are engaged by the upper walls of. the openings 35 and are pivoted downwardly so that their inner ends are further projected into the opening 30 of the bit head. In

this manner the dogs 13 are forced into the core and the core may be readily broken loose from the formation by pulling upwardly on the'tool.

The spaceddogs 13 are operable to dependably retain and support the core during the withdrawal of the tool from the well bore. It is to be noted that the construction provided by the present invention has a minimum number of moving parts and the actuation of the core engaging elements 13 is not dependent upon the .weight of The construction is extremely simple, and may be applied to or embodied in a drill without necessitating the provision of packing or packed joints. The. lock blocks 28' retain the shiftable-bit head. 12 on the sub 11 and positively prevent displacement of the dog carrying pins 32. By detaching the blocks 26 from the bit head v12, the head pins 32 and 24 cooperate to transmit the rotative thrusts directly from the sub. to the bit head.

Figs. 4 and 5 of the drawings illustrate a typical ,form of the invention embodied in a two-barrel or double barrel core drill. Thetool illustrated in Figs. 4 and 5 of the drawings'l-Jncludes gen- 1 7. a body or outer barrel 10 a sub 11' connected to the lower end of the barrel 10, an inner barrel 40 carried by the sub 11' for receiving the core, ashiftable bithead 12 carried by the sub 11', core engaging elements 13' on the sub 11' actuated upon shifting of the bit head, and means 14' yieldingly urging the bit head downward toactuate the elements 13.

The body or: outer barrel 10* is an elongate tubular structureadapted to be attached to the lower end of an operating string of drill pipe or the like.

The outer barrel 10' is provided to carry the various other. parts of .the tool and to carry the circulation fluid downwardly to the sub 11' and the bit head. A suitable bit or connecting member 15' may be screw threaded onthe lower end of the outer barrel 10. The connecting member 15- is provided at its lower end with a screw threaded pin 42 to facilitate connection with the sub 11'. The sub 11* is attached to the lower end of'the outer barrel 10* through the connecting member 15' and is provided to carry the inner barrel 40 and the shiftable bit head .12'5- Thesub 11' is tubular, having a central longitudinal opening 41 adapted to pass the core into the inner barrel 40 and is provided at its upper end with a threadedsocket 16" for receiving the pin 42.

The inner barrel 40 may be screw threaded into the upper end of the sub opening 41 and extends upwardly into the outer barrel 10'; The inner barrel 40 is spaced from the inner walls of the outer barrel 10' and connecting member 15 to provide a circulation passage between the barreis. An enlargement 43 is'providedin the open-.

ing 41 of'the sub and itsupper end forms adownwardly facing shoulder 44 in the sub opening.

The lowerv endof the sub 11' may be flat and normal to thevertical axis of the tool.

The bit head 13' projects from the lower end of the sub 11* and is provided to make-an annular cut in the earth formation. The bit head 12'- may be similar generally, to the .bit head 12 described above, and is a tubular structure having a central opening 45 registering with the opening 41 in the sub. Cutting parts in the form of blades 48 project from the lower end of the bit head 12. Itis to be understood that the bit head' may. be provided with any suitable or desirable type of cutting parts. In accordance with the invention, the bit head 12 has a sliding key or spline connection with the sub 11. The bit head 12' extends upwardly into the lower end of the tubular sub 11* and a plurality of longitudinal external splines 46' is provided on the bit head to cooperate with complementary splines 47 on the sub 11'. The downward movement of the bit head 12' is limited by lock blocks 48 arranged in openings in the splines 46' of the bit head. The blocks 48 are detachably connected to the bit head by screws 49 and extend into openings 59 in the sub 11' to limit downward movement of the bit head in the same manner as the lock blocks 26 described above.

The tool illustrated in Figs. 4 and 5 of the drawings is provided with means for circulating fluid downwardly through the sub 11' and bit head 12' to discharge from the lower end of the bit head.. An annular enlargement or recess 50 is provided at the bottom of the socket 16 and is in communication with the annular space between the barrels 10' and 40. A plurality of fluid passages 51 extend longitudinally through the walls of the sub 11'. In practice, the fluid passages 51 may extend through the portions of the sub 11' having the splines 47. The upper ends of the fluid passages 51 communicate with therecess 50, while the lower ends of the passages are adapted to communicate with discharge openings 52 in the bit head 12'.

The core engaging elements 13' are carried by the sub 11' and are actuated by downward shift ing of the bit head 12' relative to the sub to bite into a core extending into the tool. The core engaging and retaining elements 13' may be in the nature of dogs pivotally attached to the sub 11'. The outer ends of the pivoted elements 13* are carried in recesses 53 in the sub 11'. Pins 54 extend through transverse openings in. splines 47 to pivotally mount the elements 13' in the recesses. trated in the drawings, there are three pivoted core engaging elements 13' carried by spaced splines 47. The core engaging or retaining elements 13' extend inwardly through vertically elongated openings 55 in the wall of the bit head 12' to project into the opening of the bit head. The inner projecting ends of the elements 13' are sharpened or provided with beveled edges so as to properly bite into or cut the core when actuated.

The means 14' for urging the bit head 12' downwardly is in the form of a spring means adapted to force the bit head 12' downwardly when the bit head is raised from the formation at the bottom of the well bore. The present invention contemplates the employment of-different types of springs arranged in various positions etc. for urging the bit head 12' downwardly.

relative to the sub 11'. In the simple, preferred structure illustrated in the drawings the means 14' includes a coiled spring 56 arranged under compression between opposing parts of the sub and bit head. The spring 56 is arranged between the shoulder 44 of the sub and the upper end of the bit head 12'.

During drilling operations, a weight or load is imposed on the tool to cause the cutting parts 46 to cut into the formation as the tool is rotated to form a coreto be received by the inner barrel 40.-

Circulation fluid passes downwardly between the barrels 10" and 49 and is discharged from the openings 52 to flush the cutting parts 4-6 and provide circulation at the bottom of the well. When the tool is raised to lift the bit head 12 out of engagement with the formation at the bottom of the bore, the spring-56 and the weight of the bit head 12' causes the bit head to move downwardly relative to the sub 11' so that the elements 13' In the particular arrangement illus-' are pivoted downwardly and inwardly to bite into the core. The dogs or elements 13' are adapted to efiectively retain and support the core in the tool. The proper actuation of the elements 13 is insured by the spring 56 which positively moves the bit head 12 downwardly relative to the sub 11'.

Fig. 6 of the drawings illustrate a typical form of the invention embodied in a double barrel rock core drill. The tool illustrated in Fig. 6 of the drawings includes generally, an outer barrel 10', a sub 11 attached to the lower end of a barrel 10", an inner barrel 40 carried by the sub 11 a bit head 12 shiftably carried by the sub 11", core engaging elements 13 carried by the sub 11 and actuated upon relative movement between the bit head and sub, and spring means 14: urging the bit head to shift relative to the sub.

The outer barrel 10*, the sub 11*, and the inner barrel may be similar to or identical with the corresponding elements of the form of the invention illustrated in Figs. 4 and 5 of the drawings. The bit head 12 has telescopic and spined engagement with the sub 11'' in the same manner as the bit head 12' described above. A plurality of roller cutters 60 is rotatably mounted on the lower end of the bit head 12 to make an annular cut in the formation. The cutters 60 are mounted in recesses 61 in the lower end of the bit head 12 and project from the bottom of the bit head. The cutters 60 may be in the form of cone cutters as illustrated in the drawings and may be rotatably supported in any suitable manner. In the specific construction illustrated, the cutters 60 are rotatably mounted on studs or pins 62 welded to the bit head 12''. There may be any desired number of cutters 60 spaced and arranged as found practical.

The core engaging and retaining elements 13 may be identical with the elements 13' described above. The elements l3 are in the nature of dogs pivotally mounted in recesses 63 in the sub 11". The dogs extend inwardly through openings 64 in the wall of the bit head 12 and their sharpened inner ends are operable to cut or bite into the core. It will be apparent how downward movement of the bit head 12 relative to the sub 11 causes the elements 13 to be pivoted downwardly and inwardly so that they effectively bite into the core to be in supporting engagement with it. The means 14 for urging the bit head 12 downwardly includes a spring '70 arranged under compression between an internal shoulder 44' in the sub 11 and the upper end of the bit head 12. After the drilling operation when the bit head 12 is raised or freed from the formation at the bottom of the well bore, the spring forced the bit head 12 downwardly relative to the sub 11 thereby actuating the elements 13 into retaining engagement with the core.

From the above descriptions of typical applications of the invention, it will be apparent that the invention is capable of use in connection with core drills of various characters. As the core catching and retaining elements are positively actuated without requiring the shifting of large or major portions of the tool, and the barrels etc. may be of simple inexpensive construction. Further, due to the simplicity of the construction and mode of operation, the invention does not necessitate packing or packed joints.

Having described only typical preferred forms and applications of our invention, we do not wish to limit ourselves to the specific details set forth,

- head in telescopic relation to the members, slidably cooperating splines on the member and head, means for moving the head relative to the member, and core retaining means actuated by movement of the head relative to the member, there being a longitudinal fluid passage in a spline of the member communicating with the first mentioned passage and discharging at the lower end of the member. 4

2. A core drill including, a tubular member having means at its upper end for connecting with a barrel, the member having a downwardly facing shoulder, a bit head carried by the member for relative vertical movement, the head having a face adapted to engage said shoulder during drilling to transmit downward pressures from the member to the head, a core retaining element carried by the member and adapted to be actuated by the head upon downward movement of the head relative to the member, and a spring between said face and an opposing part of the member for urging the head downwardly.

3. A core drill including a tubular member adapted to be connected to a barrel, a tubular bit head in telescopic relation to the member, the bit head being shiftable vertically relative to the member, cooperating splines on the member and head, there being a recess in one of the splines on the member, a core retaining element extending into the recess, aremovable pin in an opening in one of said splines and extending into the recess to pivotally support the element, the element being operable upon downward movement of the head, means for moving the head downwardly, and a removable block on the bit head limiting downward movement of the head and retaining.

the pin in the opening.

4. A core drill including a tubular member adapted to be connected to a barrel, a tubular bit head in telescopic relation to the member, the bit head being shiftable vertically relative to the member, roller cutters on the head for making an annular cut in the formation, cooperating splines on the member and head, there being a recess in one of the splines on the member, a core retaining element extending into the recess, a removable pin in an opening in one of said splines and ex tending into the recess to pivotally support the element, the element being operable upon downward movement of the head, means for moving the head downwardly, and a removable block on the bit head limiting downward movement of the head and retaining the pin in the opening.

5. A core drill including. a barrel adapted to be attached to the lower end of an operating string, a tubular member attached to the lower end of the barrel, terminating at its lower end in an annular face and having an enlarged bore extending into it from its lower end and forming a downwardly facing shoulder in the member, a bit head connected to the member to shift vertically relative thereto and adapted to engage said face, the head having a short tubular part extending upwardly into said bore to slide therein, said part terminating in said bore, a core retaining element carriedby the member and directly operable by the head upon downward movement of the head, and a spring held under compression between the shoulder in said'memher and said part of the head for moving the head downward.

8. A core drill including, a barrel adapted to be attached to the lower end of an operating string, a tubular member attached to the lower end of the barrel terminating at its lower end in an annular face and having an enlarged bore in its lower end and terminating therein, the bore terminating in a shoulder, a bit head connected to the member to shift vertically relative thereto and adapted to engage said face, and having a tubular part fitting said bore and terminating' therein, the head having cutting parts for making an annular cut in the formation, a core retaining dog pivoted in a recess in the member immediately adjacent the cutting parts of the head, the head being operable to actuate the dog inwardly against a core upon moving downward relative to the member, and a spring under compression between the shoulder and the upper end of the head for urging the head downward.

7. A core drill including, a tubular body, a tubular bit head having telescopic engagement with the body, internal splines on the body ,extemal splines on the head slidably cooperating with the body splines whereby the head is shiftable vertically relative to the body, there being a recess in the inner face of one of the splines on the body and an opening from the recess to one side of the spline, a dog extending into the recess, and a pivot pin carried in said opening and entering the recess to pivotally hold the dog so that it is operable upon downward movement of the head to grip a core.

8. A core drill including, a tubular body, a

on the body, and a bore through the spline from one side to the other and intersecting the recess, and there being an opening in the head inward of the recess, a core retaining dog having its inner end in the recess and its outer portion extending through the opening to be actuated by the head upon downward movement of the head relative to the body, and a pivot pin carried in said opening and pivotallyholding the dog in the recess.

9. A core drill including, a tubular body having an enlarged bore'in its lower end terminating in a shoulder, a tubular bit head at the lower end of the body and having a tubular part extending into said bore and terminating therein, internal splines on the body, external splines on the head slidably cooperating with the body splines whereby the head is shlftable vertically relative to the body, there being a recess in the inner face of one of the splines of the body and an opening extending into the spline from one side to intersect the recess, and there being an arranged between the upper end or the tubular part and said shoulders.

10. A core drill tneluding a tubular body having a downwardly helm internal shoulder and 5 an enlarged bore in its lower portion, a bit head at the lower end of the body and having a part engeged in said Don (or vertical movement and terminating thexoina om retaining element carried by the body and operable to engage a