US2127108A - Well drilling apparatus - Google Patents

Description

Aug. 16, 1938. D. DRISCCSLL WELL DRILLING APPARATUS Filed March 4, 1936 4 Sheets-Sheet l H16 Hilary Aug. 16, 1938. D DRISCOLL 2,127,108

WELL DRILLING APPARATUS Filed March 4, 1936 4 Shets-Sheet 2 a .Z'n en for flaw/15 L. D2166 OLL Aug. 16, 1938. D. L. DRISCOLL v WELL DRILLING APPARATUS Filed March 4, 1936 4 Sheets-Sheet 3 1938- D. L. DRISCOLL 2,127,108

WELL DRILLING APPARATUS Filed March 4, 1936 4 Sheets-Sheet 4 Patented Aug. 16, 1938 UNITED STATES WELL DRILLING APPARATUS Dennis L. Driscoll, Los Angeles, Calif., assignor to Lawrence F. Baash, Los Angeles, Calif.

Application March 4,

18 Claims.

This invention relates to well drilling apparatus and relates more particularly to a rotary table bushing and slips therefor. A general object of this invention is to provide an improved rotary table bushing and slip assembly that is particularly effective and long wearing.

Another object of this invention is to provide a practical rotary table bushing and slip assembly in which the slips all have extensive and equal seating engagement with the bushing and have uniform gripping contact with the pipe or object handled. The extensive engagement of the slips in the bushing allows the slips to be of light construction and of substantial length.

Another object of the invention is to provide a master bushing for a rotary table that has inclined grooves or slots in its interior of uniform width throughout their lengths and slips shaped and proportioned to fit the slots whereby they may have extensive continuous engagement with the walls of the slots while gripping the pipe and when in any vertical position they may assume while contacting the pipe. Heretofore it has been the usual practice to provide a round tapered opening or a, round opening of downwardly diminishing diameter in the bushing of a rotary table to receive the pipe gripping slips. When a bushing is provided with such a tapered opening there is only one vertical position in which the slips have full cooperation with the walls of the bushing and when the slips assume different vertical positions as they often do when gripping a pipe, certain of the slips have only line contact or partial contact with the bushing. In the assembly of my invention the slips have full surface contact with the walls of the bushing slots regardless of the vertical positions they may assume when contacting the pipe.

Another object of this invention is to provide a slip receiving bushing for a rotary table having an opening of uniform dimensions throughout its length to more readily pass drill pipe protectors and other drilling equipment.

Another object of this invention is to provide an improved assembly of a rotary table bushing and pipe gripping slips in which the slips cannot foul one another and cannot turn or tilt laterally in the bushing.

Another object of this invention is to provide a rotary table bushing and slip assembly in which all of the several slips have uniform gripping engagement with the object or pipe throughout their lengths to dependably grip the pipe without tending to distort it.

Another object of this invention to provide 1936, Serial No. 67,080

a rotary table bushing and slip assembly that embodies practical effective rests or cradles for the slips when they are removed from the bushing which cradles support the slip in positions for immediate insertion in the slots of the bushing.

Another object of this invention is to provide slips having simple and very inexpensive replaceable pipe engaging parts or liners whereby they may be readily reconditioned or adapted for the handling of pipe of various diameters.

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

Fig. 1 is a top or plan elevation of one form of assembly provided by this invention. Fig. 2 is an enlarged fragmentary horizontal detailed sectional view taken substantially as indicated by line 22 on Fig. 3. Fig. 3 is an enlarged fragmentary vertical detailed sectional view taken as indicated by line 3-3 on Fig. 1. Fig. 4 is a fragmentary elevation view of the upper portion of one of the cradles being a view taken substantially as indicated by line 44 on Fig. 3. Fig. 5 is an enlarged fragmentary horizontal detailed sectional View taken as indicated by line 55 on Fig. 3. Fig. 6 is a topor plan elevation of another form of assembly provided by this invention. Fig. 7 is a fragmentary vertical detailed sectional view taken as indicated by line I'I on Fig. 6. Fig. 8 is a fragmentary horizontal detailed sectional view taken as indicated by line 8-8 on Fig. 7. Fig. 9 is a perspective view of the inner side of one of the bushing sections of the form of the invention illustrated in Figs. 6, 7 and 8; and Fig. 10 is a top or plan elevation of still another form of assembly provided by the invention.

The form of the invention illustrated in Figs. 1 to 5, inclusive, of the drawings, includes generally, a bushing I0 for arrangement in a rotary table T and having slots II in its interior, slips I2 adapted to fit in the slots II to grip a pipe P or the like, and rests or cradles I3 for carrying the slips l2 when they are removed from the bushing Ill.

The bushing 10 is what is usually termed a master bushing and is intended for arrangement in the opening M of the rotary table T. In'the particular form of the invention being described the bushing I0 is round or cylindrical tofit the correspondingly shaped opening M of the table T. An annular outwardly projecting flange I5 is provided at the upper end'of the bushing H) to fit in an enlargement or annular groove IS in the upper end of the table opening I4 and to seat on a shoulder |6 in the opening I4. Lugs l7 project radially from the periphery of the flange It: to fit bayonet slots I8. in the table T. Lock blocks l9 are inserted in the bayonet slots |8 to lock the lateral arms of the lugs II in the lateral portions of the slots I8. A rotary table of the general type just described having bayonet slots for receiving lugs on a bushing is fully described and claimed in'my co-pending application entitled Rotary well drilling apparatus, filed November 11, 1935, Serial No. 49,175.

t is to be understood that the bushing ||l being described may be shaped to fit any type of rotary table opening without departing from the invention. It is to be noted that when the bushing I is designed for use in the particular rotary table T illustrated that it has a cylindrical periphery throughout its length and, therefore, has a substantial and uniform wallthickness. The Wall of the bushing I0 may be chambered and provided with suitable internal reinforcing webs 20.

The bushing I0 is preferably sectional to facilitate its insertion in the rotary table T. In the preferred construction the bushing |0 comprises two sections A and B of substantially equal extent as illustrated in Fig. 1 of the drawings. A central vertical opening 2| is provided in the bushing ID to receive and pass the pipe P, tubing and other drilling equipment. It is afeature of the invention that the opening 2| is of uniform diameter or dimensions throughout its length, that is, the opening 2| has vertical walls and is not tapered or of downwardly diminishing capacity. This formation of the opening 2| permits the ready passage of drill pipe protectors and other devices throughthe bushing l8 which often interfere with the lower ends of the usual master bushings having central openings of downwardly diminishing diameter. 'In the particular form of the invention being described the opening 2| is round in cross section or is cylindrical, it being understood that the opening 2| of the bushing l0 may be polygonal, as illustrated in Figs. 6, 8, 9 and 10 of the drawings.

It is a feature of the invention thatlongitudinal or vertical slots areprovided inthe wall of the opening. 2| to receive the slips l2. The slots I are circumferentially-spaced to provide for the spaced engagement of the slips |2 with the pipe P. In the drawings I have shown four equally spaced slots ||,it being understood that the bushing ||l may be provided with two slots, three slots or any desired number of slots II, as desired. In accordance with the invention the slip receiving slots H are of uniform configuration and width throughout their lengths and are of substantial length to present'extensive walls or surfaces for engagement by the slips l2. The opposite side walls of the slots I are parallel andare preferably vertical to provide for the easy insertion of the slips |2. In the particular form 'of the invention illustrated'in Figs..1 to 5,

inclusive, of the'drawings the inner walls.22 of the slots l are cylindrically concaved. These inner walls 22 of the slots II are inclined downwardly and inwardly to slidably receive the slips 2 and to provide for the wedging of the slips against the object or pipe P. The curvature of the inner walls 22 of the slots is the same throughout their lengths having a uniform radius of curvature. The above described shape and proportions of the slots provide for the full or extensive contact of the slips l2 with the slot walls. The slots may extend from the face or upper end of the bushing H] to the lower end of the bushing.

The slips l2 are provided to grip and suspend pipe P, tubing or other well drilling equipment extending through the bushing opening 2|. The slips |2 are shaped and proportioned to properly fit and operate in the above-described slots The pipe gripping slips |2 are elongate members having fiat parallel opposite sides 23 for cooperating with the side walls of the slots H and having cylindrically convexed rear surfaces 24 for shiftably bearing on the inner walls 22 of the slots. The curved or conveXed surfaces 25 of the slips l2 are inclined downwardly and inwardly but have the same radius of curvature throughout their lengths touniformly engage the walls 22. It is to be understood that when the slots H are polygonal or provided with flat inner walls the rear surfaces 24 of the slips |2 may be flat to have proper cooperation therewith. When seated in the slots the slips l2 project into the bushing opening 2| to have suspending and gripping engagement with the object or pipe P.

The active faces or sides of the slips |2 may be suitably roughened or toothed to properly grip the object or pipe P. The invention, however, provides. simple and particularly effective replaceable plates or liners 25 for the active sides of the slips I2. The liners 25 are secured to the inner or active faces of the slips l2 and are adapted to have direct engagement with the object or pipe P and thus assume the wear. The faces of the slips 2 are provided with longitudinal or vertical grooves 26 for receiving tongues or keys 2'! on the liners 25. The lowerywalls 28 of the grooves 26 are inclined downwardly and outwardly. The lower ends 29 of the keys 2! are correspondingly inclined to have locking cooperation with the walls 28. The invention includes simple positive means for removably securing the liners 25 to the slips l2. Pins or rods 30 are inserted in transverse openings in the slips I2 and the keys 2'! of the liners 25. The ends of the rods 30 may be riveted over whereby the rods are dependably held against displacement to form positive connections between the slips and the liners 25. The active faces of the liners 25 are cylindrically concaved to conform to the object or pipe P and are provided with wickers or teeth 3|. The teeth 3| are adapted to have gripping and supporting contact with the pipe P and preferably face upwardly and inwardly. If desired the teeth 3| may be grooved vertically to more effectively resist relative rotation between the pipe P and the slip liners 25. The liners 25 may be replaced with liners of different thicknesses to adapt the slips It! to handle pipe of different diameters.

The bodies of the slips I2 are preferably hollow or provided with chambers 32 to be light in weight. Reinforcing webs 33 may extend through the chambered interiors of the slips. Guide fingers 34 may cooperate with the surfaces 35 to guide the slips. The slips l2 usually project above the upper surface of the bushing II) when engaging the pipe or object P. The invention provides means for preventing the slips l2 from falling through or from the slots H. Stop lugs 36 project from the upper portions of the slip sides 23 and are adapted to fit in recesses 36 in the upper face of the bushing ID to limit the downward and inward movement of the slips l2. The recesses 36 are suitably shaped and proportioned to provide for the necessary play or movement of the slips I2.

The invention provides handles H on the slips I2 to facilitate their insertion in and removal from the slots The handles H have forks or yokes 31 on their lower ends extending into recesses 31 in the upper ends of the slips |2. Pivot pins 38 pivotally connect the forks 31 with the bodies of the slips |2. Cams or stop projections 9 may be provided on the forks 31 to limit the inward swinging of the handles H. The handles I-I include stems 39 extending upwardly from the forks 31 and lateral heads 39 carried on the stems 39. If desired or found necessary the ham-- dles H of adjacent slips l2 may be connected whereby two of the slips may be handled simultaneously. The rear walls of the recesses 31 may be engageable by the handles H to limit the outward and downward pivoting of the handles.

The rests or cradles l3 are provided to support or carry the slips l2 when the slips are withdrawn from the slots and are operable to support the slips in positions where they are entirely clear of the bushing opening 2|. A cradle I3 is provided on the bushing ID for each slip l2. The cradles l3 are adapted to be removably secured to the upper end of the bushing ID in radial alignment with the slots Each cradle l3 includes a leg 40 having a substantially horizontal foot 4|. Recesses 42 are provided in the upper side of the bushing Hi to receive the feet 4|. Countersunk or flush plates 43 extend transversely across the upper ends of the recesses 42 and the feet 4| are adapted to be inserted under the plates 43. Clamp screws 44 are threaded through the plates 43 and are adapted to clamp against the feet 4| to securely hold the cradles l3 in place. The legs 40 project vertically from the feet 4| and have upwardly and outwardly inclined portions terminating in forks 45. Concave supports or saddles 46 are arranged on the inclined portions of the legs 40 to receive the slips l2. The saddles 46 are shaped and proportioned to properly receive the convex outer sides of the slips.

Means are provided for releasably supporting or holding the slips l2 in the cradles I3. The forks on the upper ends of the legs 40 have flaring or V-shaped notches 41 adapted to receive handles H. When the slips l2 are raised into the cradles l3 the handles I-I may be swung downwardly so that their stems 39 are engaged in the notches 41. The heads 39 of the handles H are adapted to engage against the forks 45 to hold the slips |2 in the cradles l3 in positions where they are entirely free of the bushing opening 2|. This elevated or inoperative position of the slips I2 is illustrated in broken lines in Fig. 3. The handles H may be easily disengaged from the forks 45 to allow the slips I2 to enter or move downwardly into their respective slots H.

In the use or operation of the assembly illustrated in Figs. 1 to 6, inclusive, of the drawings, the bushing I0 is normally arranged in the table T as illustrated in Fig. 1 of the drawings. When it is desired to engage or suspend a pipe P passing through the bushing opening 2| the slips l2 are introduced into the slots H and allowed to fit downwardly therein until their liners 25 grip the pipe P. The operator or operators may readily disengage the handles H from the forks 45 to allow the slips l2 to slide downwardly in the saddles 46. The fingers 34 on the lower ends of the slips readily guide the slips into the slots The slips are free to move downwardly in the slots until the toothed inner sides of the liners 25 grip or contact the pipe P. The convex outer rear sides 24 of the slips |2 have full, even bearing engagement with the walls 22 of the slots regardless of the vertical positions assumed by the slips l2 when they contact the pipe P. The engagement of the surfaces 24 with the slot walls 22 also maintains the active inner sides of the liners .25 vertical to properly grip the pipe P. The fit of the slips l2 in the slots H is such that the pipe is dependably gripped and supported. Due to the fact that each of the slips l2 has uniform and complete engagement with the inner wall 22 of its respective slot H the several slips have even or equal engagement with the pipe P to dependably grip the pipe without distorting it. The slips |2 engaging in the slots II are adapted to form a positive drive for the pipe P in the event it is desired to rotate the pipe. The fiat parallel sides 23 of the slips H are adapted to engage the side walls of the slots II for the transmission of turning forces.

When the slips l2 are no longer required they may be easily pulled upwardly and outwardly to rest in the saddles 46. swung downwardly to engage the stems 39 in the notches 41 so that the slips are held in the cradles H3. The slips |2 are very easy and convenient to manipulate and are light in weight. The cradles |3 may be easily disengaged from the bushing Ii]. The various parts of the assembly are simple and inexpensive of manufacture. The slots may be cored in the bushing I0 and the slips l2 do not require special machining. The liners 25 of the slips l2 may be sections of strips or long stock of the desired cross section and are very inexpensive to manufacture.

The form of the invention illustrated in Figs. 6 to 9, inclusive, of the drawings includes, generally, a master bushing 5|! having internal slots 5|, slips 52 for arrangement in the slots 5| to grip a pipe P or the like and means 53 for preventing displacement of the slips and for supporting the slips 52 when they are moved to positions at the upper ends of the slots 5|.

The bushing 53 is intended for arrangement in the opening of a rotary table. The bushing 53 may be shaped for arrangement in the table T illustrated in Fig. 1 of the drawings or may be polygonal or square, asillustrated in Figs. 6 and 9 of the drawings for arrangement in a typical rotary table. It is to be understood that the bushing is adapted to be supported in a rotary table to be driven or rotated thereby. A central vertical opening 54 is provided in the bushing 50 to pass the pipe P and other drilling equipment. In accordance with the form of the invention being described the opening 54 is polygonal or square in cross section. The opening 54 may be round or cylindrical if desired. The opening 54 is of uniform width or dimensions. throughout its length, having vertical Walls. This is important as it permits the easy free passage of the drilling equipment through the bushing 50.

The handles H may be The bushing 53 is preferably sectional for ready assembling in a rotary table. As shown in the drawings the bushing 50 preferably includes two sections M and N. The bushing 55 is preferably divided or separated in a vertical plane which intersects two side walls of the opening 54. In the preferred construction the slots for receiving the slips 52 occur in the corners of the openings 54. The slots 5| are preferably alike in size and shape and there may be one slot 5| in each corner of the opening 54. It is to be understood that the invention contemplates the provision of two or more slots 5| in the bushing opening 54. In the form of the invention being described the slots 5| are polygonal or flat walled. The side walls of the slots 5| are flat and vertical and lie in planes tangent to a circle concentric with the central longitudinal axis of the opening 54. The parallel relationship and, therefore, the uniform spacing of the side walls of the slots 5| continues throughout the entire lengths of the slots. The slots 5| may extend between the upper and lower ends of the bushing 55. The innermost walls or inner walls 55 of the slots 5| are fiat and are inclined downwardly and inwardly. Curved or inclined surfaces 56 join the upper ends of the slots 5| to assist in entering or guiding the slips 52 into the slots.

The slips 52 are adapted to be inserted in the slots 5| to grip and suspend the pipe P or other object. The several slips 52 are alike and there is preferably a slip 52 provided for each slot 5|. The slips 52 are shaped to properly fit the slots 5| having flat parallel sides 51 and downwardly and inwardly inclined rear surfaces 58 for shiftably bearing on the inclined walls 55 of the slots. The slips 52 are preferably proportioned to have proper play or clearance in the slots 5|. The active sides of the slips 52 are preferably vertical and if desired teeth or gripping parts may be formed directly on the slips to cooperate with the pipe P. It is preferred, however, to provide replaceable shoes or liners 59 on the slips 52 for gripping the pipe P. The slips 52 are shaped to receive the liners 59 having vertical channels or grooves 6|] which terminate at their lower ends in downwardly and outwardly inclined walls 6|. Tongues or keys 62 are provided on the liners 59 to fit the grooves 60 to form positive driving connections between the liners and slips. The lower ends of the keys 62 are inclined downwardly and outwardly to have locking cooperation with the groove walls 6|.

Means is provided for removably attaching the liners 59 to the slips 52. Rivets or rods 63 are passing through transverse openings in the slips and keys 62 to secure the liners 59 to the slips. The opposite ends of the rods 63 may be headed or riveted. The active faces of the liners 59 are cylindrically concaved to conform, generally, to the pipe P and are provided with suitable wickers or teeth 64. The teeth 64 preferably face upwardly and inwardly and may be interrupted by vertical grooves to have more efficient engagement with the pipe. The liners 59 may be replaced by liners of various thicknesses to adapt the slips 52 for the proper handling of pipe and other objects of various diameters. The bodies of the slips 52 may be chambered or hollowed to be light in weight. Reinforcing webs 65 may extend through the hollow interiors of the slips. Handles H are provided on the slips 52 to facilitate the manipulation of the slips. The handles H may be identical with the handles H described above and reference is hereby made to the detailed description of the handles H. Corresponding reference numerals are employed to designate corresponding parts of the handles H and H and their mountings.

The means 53 is provided to prevent loss or displacement of the slips- 52 from the slots 5| and to assist in supporting the slips in retracted or inoperative positions at the upper ends of the slots. The means 53 comprises elongate grooves or slots in the side walls of the slip receiving slots 5|. There may be a slot 10 in each side wall of each slot 5|. The slots 1|] are parallel with the inclined inner walls 55 of the slots 5| and terminate some distance above the lower ends of the slots 5|. Lugs or pins 7| project from the sides of the slips 52 to shiftably operate in the slots 10. The cooperation of the pins II with the slots 10 is such that the slips 52 may properly work and shift in the bushing slots 5| The pins 1| are adapted to cooperate with the lower ends of the slots 10 to definitely limit the downward travel of the slips 52 and thus prevent the loss of the slips from the bushing 5|]. The upper ends of the slots are spaced some distance below the upper end of the bushing 59. The slots 10 and the pins 7| are related so that the pins cooperate with the upper ends of the slots 10 when the slips 52 are brought to positions where they may be pivoted onto the surface 56. The cooperation of the pins 1| with the upper ends of the slots 70 assists in retaining or supporting the slips 52 in their up or inoperative positions on the surfaces 55. Fig. 7 of the drawings illustrates in broken lines a slip 52 in its retracted position where it rests on the surface 55 with the pins H in cooperation with the upper ends of the slots 15. In practice removable plates 73 may be recessed or countersunk in the upper ends of the bushing 55 to close the upper ends of the slots 10. The plates 13 thus form the upper ends or walls of the slots 15 and may be removably secured to the bushing by screws or other suitable means. The plates. 13 are removable to permit the entrance of the pins 1| in the slots 10 when the slips 52 are assembled in the bushing 50 and are removable to permit the withdrawal of the pins 1| from the slots 15 when the slips are to be removed from the bushing.

It is to be understood that the invention contemplates the embodiment of cradles similar to the cradles 53 described above, in the form of the invention illustrated in Figs. 6 to 9, inclusive, of the drawings, in substitution for the means 53 just described, and contemplates the embodiment of the means 53 in the form of the invention illustrated in Figs. 1 to 5, inclusive, of the drawings in substitution for the cradles I3.

The use or operation of the assembly illustrated in Figs. 6 to 9, inclusive, of the drawings is substantially the same as the operation of the previously described form of the invention. The slips 52 maybe easily passed downwardly into the slots 5| to contact and grip the pipe P. The handles H facilitate the lowering of the slips and the pins 1| cooperating with the slots 10 effectively enter the lower ends of the slips in the slots. As the slips 52 move downwardly in the slots 5| their rear surfaces 58 contact the inner regardless of the vertical positions assumed by the slips when they contact or grip the pipe. Accordingly, the slips 52 assume equal loadsin suspending or engaging the pipe. The flat sided slips 52 fitting in the flat sided slots 5| cannot possibly tilt or turn and are adapted to form positive effective drives in the event it is desired to rotate the pipe. The liners 59 are operable to obtain firm dependable gripping engagement with the pipe P without subjecting the bodies of the slips proper to wear. When the slips 52 are no longer required to grip the pipe P they may be easily and quickly removed from the slots 5|. The slips 52 may be easily pulled upwardly from the slots to positions where they are supported on the surfaces 56 with their pins 1| bearing on the plates 13 which form the upper walls of the slots 10. The cooperation of the pins H with the upper ends of the slots operates to retain the slips in their inactive positions on the surfaces 56. The bushings 50 and the slips 52 are simple and easy to manufacture. The slots 5| may be cored directly in the sections of the bushing 5|! and the slips 52 do not require extensive machining. The liners 59 may be easily replaced to recondition the slips 52 or to adapt the slips for the engagement of pipes of diiierent diameters.

Fig. 10 of the drawings illustrates a form of the invention embodying a master bushing 80 comprising two unequal sections X and Y. The bushings 80 may be of the same configuration as the bushing H] or the bushing 50. In the particular case illustrated the bushing 80 is of the same general configuration as the bushing 50. The polygonal opening 8| of the bushing 85 has flat walled slots 82 in its corners for receiving slips 83. The slips 83 may be identical with the slips 52. The bushing 8|) is divided into the two sections X and Y in a vertical plane 85 spaced from the central longitudinal axis of its opening 8|. The line or plane 85 of division of the bushing 80 preferably angularly intersects two adjacent sides of the polygonal opening 8|. When the bushing 85 is divided in this manner one section X has three slots 82 while the other section Y has one slot 82. Where the one section X carries three slips 83 the bushing 8|] cannot spread or work and a very positive suspension or gripping engagement with the pipe P is obtained. The operation and the mode of handling the slips 83 are the same as described above in connection with the slips 52.

When I use the term liner I refer to the shoe or shoe-like part that actually engages the pipe or the object handled.

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

Having described my invention, I claim:

1. A bushing for a rotary table comprising a body having a polygonal opening of unvarying width, and having slots in the walls of the opening for receiving slips.

2. In combination, a bushing for a rotary table having a polygonal opening for receiving a piece of drilling equipment, and having longitudinal slots in the corners of the opening, said slots having inclined walls, and slips arranged in the slots to grip the piece of equipment and having inclined surfaces cooperating with said walls.

3. In combination, a bushing for a rotary table having a polygonal opening forreceiving a piece of drilling equipment, and having longitudinal slots in the corners of the opening, said slots having substantially parallel side walls and downwardly and inwardly inclined inner walls, and slips shiftably fitting the slots to grip the piece of equipment.

4. In combination, a bushing for a rotary table having an opening for receiving a piece of drilling equipment, and having spaced slots in the wall of the opening provided with parallel side walls and cylindrically concaved inner walls, and slips in the slots for engaging the piece of equipment and having parallel sides and cylindrically convex rear sides for cooperating with the walls of the slots.

5. A slip for arrangement in a rotary table bushing comprising a slip body having substantially parallel sides, and a downwardly and inwardly inclined rear surface, and means projecting from the lower end of the slip body for guiding it in a slot in the bushing.

6. A slip for arrangement in a rotary table bushing comprising a slip body having substantially parallel sides, and a cylindrically curved downwardly and inwardly inclined rear surface extending between said sides, and means on the active face of the slip body for engaging an object extending through the bushing.

7. A master bushing comprising a body having a polygonal opening with substantially vertical walls, and having substantially vertical slots in the corners of the opening, said slots having substantially parallel side walls and inclined inner Walls.

8. A master bushing comprising a body having an opening with a cylindrically curved wall, and having spaced vertical slots in the wall of the opening, said slots having substantially parallel side walls and inclined inner walls.

9. Apparatus of the character described comprising a master bushing having a polygonal opening with substantially vertical walls and having substantially vertical slots in the corners of the opening, said slots having substantially parallel side walls and inclined inner walls, and slips arranged in the slots to grip an object extending through the opening, the slips having substantially parallel sides and inclined surfaces for cooperating with the inclined walls of the slots.

10. Apparatus of the character described including a master bushing for a rotary table, the bushing having an opening for passing drilling equipment and slots in the wall of the opening, gripping slips adapted for insertion in the slots, and stationary cradles carrying the slips for ready entrance to the slots.

11. Apparatus of the character described including a master bushing for a rotary table, the bushing having an opening for passing drilling equipment and slots in the wall of the opening, gripping slips adapted for insertion in the slots, stationary cradles on the upper side of the bushing for supporting the slips in radial alignment with the slot for insertion therein.

12. Apparatus of the character described including a master bushing for a rotary table, the bushing having an opening for passing drilling equipment and slots in the wall of the opening, gripping slips adapted for insertion in the slots, handles on the slips, cradles for supporting the slips above the openings, and parts on the cradles cooperable with the handles to releasably retain the slips on the cradles.

13. In combination with a rotary table bushing and a slip for use therein, a cradle for supporting the slip comprising a support to be mounted on the bushing, and a saddle on the support for carrying the slip.

14. In combination with a rotary table bushing and a slip for use therein, a cradle for, supporting the slip comprising a support to be mounted on the bushing, and a saddle on the support having a concave surface inclined downwardly and inwardly toward the opening of the bushing to receive the slip.

15. In combination with a rotary table bushing, a slip for use in the bushing, a handle on the slip, a support on the bushing, a saddle on the support for carrying the slip, and a fork on the support engageable by the handle to retain the slip in the saddle.

16. A rotary table bushing comprising a body having a vertical opening and circumferentially spaced slots in the wall of the bushing, the body being divided in a vertical plane spaced from the central axis of the opening to comprise two sections, one of said sections having more slots than the other.

17. In combination, a rotary table bushing having an opening for passing drilling equipment, there being a slot in the wall of the opening having an inclined inner Wall, and a groove in a side wall of the slot substantially parallel with said inclined wall, a seat at the upper end of the slot, a slip shiftable in the slot operable to engage an object in the opening and shiftable to a retracted position on the seat,-and a projection on the slip operable in the groove and cooperable with the upper end of the groove to retain the slip on the seat.

18. In combination, a rotary table bushing having an opening for passing drilling equipment, there being a slot in the wall of the opening having an inclined inner wall, and a groove in a side wall of the slot substantially parallel with said inclined wall, a slip shiftable in the slot operable to engage an object extending through the opening, and a projection on the slip operating in said groove to prevent displacement of the slip from the slot.

DENNIS L. DRISCOLL.

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