AUTOMATED BIT HANDLING AND CHANGING SYSTEM AND PROCESS

Abstract

A system for supporting a table bushing of a drill rig during a drill-bit changing operation is provided. The system includes a bushing support bracket mounted to a breakout wrench and having support arms arranged to engage the table bushing as a drill string is raised. The support arms are arranged to support the table bushing away from a deck opening and hold the table bushing in an elevated supported position while a drill bit is removed from or installed onto the drill string.

Description

RELATED APPLICATION DATA

This application is a continuation-in-part of U.S. patent application Ser. No. 19/301,143, filed Aug. 15, 2025, which claims priority of U.S. Provisional Application No. 64/684,210, filed Aug. 16, 2024.

TECHNICAL FIELD

The present disclosure relates to an automated drill bit handling and changing system for a mobile drill rig, and more particularly to a system that combines a deck wrench with an automated bit changing mechanism for enhanced safety and efficiency in surface mining operations. The disclosure further relates to a bushing support bracket arranged to engage and support a table bushing as the drill string is raised.

BACKGROUND

Mobile drill rigs are commonly used in surface mining operations for drilling patterns of holes to specific depths and angles into the drill bed. Self-propelled rigs preliminarily drill these holes, after which the mine uses sequences of explosive charges to break up the bedrock (or other subsurface constituents) so that large end loaders or drag lines can scoop up the material to transfer to dump trucks for relocation to the processing areas at the mine.

Many operations involved in servicing and maintaining the rigs are difficult and hazardous. Finding ways to automate these processes can result in machines that are easier to maintain while reducing costs and increasing efficiency. One particularly challenging task is replacing the rotary drill bit.

The current process for changing out bits is performed manually by a mechanic and an operator. However, the leading standard in drill technology today is automation. Customers and suppliers seek to reduce the need for operators of the drill rig to increase both safety and efficiency. While many tasks performed by drill rigs have been successfully automated, automation of drill bit changing has proven difficult to perfect.

Automating the bit changing process is needed to meet the growing demands of the mining industry. Through automated bit replacement, time can be drastically reduced and a faster, more reliable mechanism for changing bits will ultimately save money. Automation will also improve the safety by eliminating potential bodily harm to mechanics and operators by removing the need for human interaction with heavy drill bits in confined operating environments.

One factor hindering automated bit changing is limited rig space, meaning that any automated system must be engineered to fit on a variety of rigs without using too much space.

Thus, there is a need for an automated rotary drill bit changing system that is capable of being automated, reliable, capable of being easily fitted to a blast-hole drill rig, designed to allow for easy restocking of bits, capable of storing new bits and holding the old bit(s) after being replaced, robust, compact and able to handle extreme conditions, and safe to operate.

SUMMARY

The present system is arranged to automate the bit changing process on a blast hole drill rig.

The invention combines a deck wrench with a bit changing mechanism to form one compact unit. The auto bit handling mechanism is made up of a slewing/sliding group to rotate between bits and move the bit into position for changing, a carousel weldment where the bits are stored, a bit breaker group which is easily replaceable for different bit sizes and a cover assembly.

The present combined deck wrench and bit changing mechanism is capable of carrying two new bits and storing one used bit. The bit changing mechanism slides in position under the rotary head where the bit is changed and slides back out when not in use.

The arrangement fits inside a specially designed deck wrench, which supports the bit handling mechanism, which holds and rotates the bit to break it free from the drill string as part of the bit breaking and removal process.

This system was designed to make the process easier for automation while maintaining a compact footprint.

According to an example embodiment, a drill bit handling and changing system for a drill rig comprises a deck wrench assembly mounted on a deck of a mast of the drill rig, the deck wrench assembly being arranged to break the drill bit from a drill pipe of the rig; and a bit changing mechanism slidably disposed on the deck wrench assembly between a standby position and an engaged position where the bit changing mechanism is centered with the drill bit and/or drill pipe, the bit changing mechanism including carousel having a plurality of receptacles, at least one of the receptacles being empty to receive an used drill bit and at least two receptacles holding new drill bits to be connected with the drill pipe after the used drill bit is removed from the drill string, wherein the bit changing mechanism includes a slewing drive arranged to rotate the carousel to present an empty receptacle or a new drill bit to the drill pipe.

According to an example embodiment, a method of changing a drill bit of a drill rig, the method comprising the steps of providing a drill bit handling and changing system including a deck wrench assembly and a bit changing mechanism movably disposed thereon; sliding the bit changing mechanism along the deck wrench assembly to position the bit changing mechanism underneath a raised, used drill bit in the engaged position; positioning an empty receptacle of the carousel underneath the used bit; lowering the drill bit to position the used drill bit in the receptacle; pivoting a break-out wrench mounted on the mast to engage the drill pipe; breaking a connection between the used drill bit and the drill pipe; unclamping the break-out wrench and raising the drill pipe to uncouple the drill bit from the drill pipe; sliding the bit changing mechanism with the used drill bit located in the receptacle to the standby position on the deck wrench assembly; rotating the carousel to position a receptacle holding the new unused bit toward the drill pipe; sliding the bit changing mechanism with the new, unused drill bit located in the receptacle to the engaged position on the deck wrench centered with the drill pipe; lowering the drill pipe and rotating the drill pipe to attach the new, unused drill bit to the drill pipe.

The disclosure further relates to a bushing support bracket arranged to engage and support the table bushing as the drill string is raised and to hold the table busing in an elevated supported position while the drill bit is removed or installed onto the drill string.

According to an example embodiment, a table-bushing support apparatus, for use in a drill bit handling and changing system, includes a bushing support bracket mounted to a breakout wrench of a drill rig, the bushing support bracket having a base plate arranged to be secured to a platform on an upper surface of the breakout wrench, and a pair of support arms extending from the base plate and arranged to capture, lift, and support a table bushing of a drill string, the support arms each including a guiding surface angled relative to the base plate and a tapered front end configured to interact with the table bushing, wherein the support arms are spaced apart by a distance sized to receive the table bushing, and wherein the bushing support bracket is configured to hold the table bushing upward from a deck wrench of the drill rig and support the table bushing during a drill-bit changing operation.

According to an embodiment, a method of supporting a table bushing during a drill-bit changing operation of a drill rig is provided. The method includes providing a bushing support bracket mounted to a breakout wrench, the bushing support bracket including a base plate and a pair of support arms extending from the base plate, raising a drill string such that a table bushing engages the tapered front ends of the support arms; holding the table bushing upward from a deck wrench using the support arms, positioning the breakout wrench beneath the table bushing while the support arms support the table bushing, and performing a drill-bit changing operation while the table bushing remains supported by the bushing support bracket.

According to an embodiment, a table-bushing support system, for a drill rig, includes a bushing support bracket mounted to a breakout wrench of the drill rig, and a pair of support arms of the bushing support bracket being configured to engage a table bushing carried on a drill string, wherein the support arms are arranged to hold and support the table bushing away from a deck opening of the drill rig as the drill string is raised, and wherein the bushing support bracket is further configured to hold the table bushing in a supported position during a drill-bit changing operation.

The foregoing summary, as well as the following detailed description of the embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the embodiments depicted are not limited to the precise arrangements and instrumentalities shown.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic view of a mobile drill rig with an automated drill bit changing system according to the present disclosure.

FIG. 2 is a schematic view of a drill string in accordance with the present disclosure.

FIG. 3 is a perspective view of the deck wrench assembly and bit changer mechanism assembly according to the present disclosure.

FIG. 4A is a top view of an uncovered bit changer mechanism in the standby position on the deck wrench and FIG. 4B is a top view of the uncovered bit changer mechanism in the bit removal position on the deck wrench.

FIG. 5 is an exploded view of the deck wrench and bit changer mechanism assembly of FIG. 3.

FIG. 6 is a perspective view of the slewing component of the bit handling mechanism of FIG. 5.

FIG. 7 is a partial exploded view of the carousel of the bit handling mechanism of FIG. 5.

FIG. 8 is a perspective view of the bit breaker plate of FIG. 5.

FIGS. 9A-10G illustrate the drill bit changing process according to the present disclosure, with FIGS. 9A-9J showing the used bit removal part of the process and FIGS. 10A-10G illustrating the installation of a new bit.

FIG. 11 is a perspective view of break out wrench and table bush support bracket according to another embodiment of the bit changer mechanism.

FIG. 12A is a top perspective view of the bush support bracket.

FIG. 12B is a bottom perspective view of the bush support bracket.

FIG. 12C is a front view of the bush support bracket.

FIGS. 13A-13D further illustrate the table bushing and drill bit being lifted/retracted.

FIGS. 14A and 14B are perspective views of the table bushing being engaged and supported by the table bushing bracket.

FIG. 14C is a side view of FIG. 14B.

DETAILED DESCRIPTION

As shown in FIG. 1, a mining vehicle 10, such as a rotary drill rig, includes a mobile deck or carriage 12 having a frame and a mast 14 mounted on the carriage. Mining vehicle 10 can be down-the-hole (DTH) drill rig or a rotary blasthole drill rig. It should be appreciated that other types of vehicles are contemplated and the present disclosure is not limited to mining vehicles or a particular type of mining vehicle.

Mast 14 is movable between a horizontal, stored position and a vertical position as shown. The mast carries a rotary head 16 which is capable of rotating a drill string 18 to which a drill bit 20 is mounted. The rotary head 16 can be raised and lowered to enable pipes to be removed or added to the drill string.

At least one control unit 26 is arranged to control various components of the present drill rig and drill bit handling and changing system. The control unit 26 can be a computer, processing device, or any corresponding device and may include a user interface with a display device as well as control means for giving commands and information to the drill bit changer system. Control unit 26 may be a computer equipped with appropriate software that can be accessed and controlled by the operator of the drill rig. Additionally, control unit can be operated remotely.

As shown in FIG. 2, drill string 18 can be a drill pipe 19 with a top sub 24 engaged at a top end thereof and the bit 20 threadedly engaged at a bottom end of a bit sub 22 of the drill string. Bit sub 22 is a short section of the drill string that connects the drill bit to the rest of the drill pipe/string.

As shown in FIG. 3, the present drill bit handling and changing system includes a deck wrench assembly 30 having a deck wrench 32. As will be described further herein, deck wrench assembly 30 is movably disposed on and parallel to a deck 28 on the mast (FIGS. 4A and 4B).

Plate 33 of deck wrench assembly 30 also includes an opening 31 through which drill bit 20 and bit sub 22 can extend through.

A bit handling mechanism 40 is arranged to slide on the deck wrench assembly 30 so as to move between a standby position and an engaged position whereby the bit handling mechanism is centered with drill pipe and bit sub. As will be described further herein when the bit handling mechanism is in the engaged position a used bit can be removed from the drill pipe or a new bit can be attached to the drill pipe.

Referring to FIGS. 4A and 4B, deck wrench assembly 30 is pivotally disposed on deck 28 of mast 14. Actuators 38 provide the pivoting movement, which as will be described further herein, assists in breaking a used bit from the bit sub.

As discussed above, bit handling mechanism 40 is slidably supported on deck wrench assembly 30 to move between the standby position where the mechanism is not centered with the drill bit or drill pipe and opening 31 of the deck wrench is not covered by mechanism 40, which is illustrated in FIG. 4A, and the engaged position shown in FIG. 4B where opening 31 is covered and mechanism 40 is centered with the drill bit or drill pipe.

Referring again to FIG. 3 and as shown in FIG. 5, bit handling mechanism 40 includes a slewing assembly 42, which is arranged to rotate a carousel 44 holding drill bits 20, along with bit breaker plates 46, and a cover assembly 47.

Slewing assembly 42 is shown in FIG. 6 and includes a base plate 52, which supports a slewing drive 58 that is activated by motor 48. Bit handling mechanism 40 engages with the deck wrench assembly 30 to slide, activated by an actuator 54, from the standby and engaged positions as described herein. Referring again to FIG. 3, deck wrench assembly includes housing weldments 34, which guide the slewing assembly 42 and bit handling mechanism 40.

Slew drive 58 can include a gear mechanism actuated by motor 48 to provide rotational actuation of an indexing shaft 56, which carousel 44 is mounted thereon. Slew drive 58 is controlled by control unit 26. An encoder is mounted to indexing slew drive shaft 56 to monitor the position of the new or used bits positioned in receptacles of carousel 40.

Referring to FIG. 7, carousel 44 and includes receptacles 60 arranged to receive the bits. A barrel 64 is arranged to be positioned on shaft 56 and rotate therewith when the bit handling mechanism is assembled. The carousel includes supports to receive the cover assembly 47. Cover assembly 47 is stationary so that the carousel rotates within the housing formed therein.

Referring again to FIGS. 3 and 5, carousel 44 includes the receptacles 60. As shown herein, the carousel includes three receptacles, one of which holds a used drill bit and the other two new, unused bits. It should be appreciated that although three receptacles are shown, more or less receptacles can be provided to accommodate the number of bits to be provided. Each receptacle includes a pin 62 that is arranged to engage with a hook 35 of the deck wrench assembly.

Bit handling mechanism 40 also includes bit breaker plates 46 that are arranged to be positioned over receptacles 60. A bit breaker plate 46 covers each receptacle 60. Each plate 46 includes an opening 50 that is shaped to accommodate the shape or profile and size of a particular bit. The plates 46 can be interchanged to accommodate different bits, for example, 9″, 10.625″ or 12.25″ bits. Thus, openings 50 are configured to correspond with profiles of the actual bits. The bits are held in the receptacles due to the shape of the openings. Also, plates 46 can be provided with a standard opening that can later be modified to a particular bit profile or size.

FIGS. 9A-10G illustrate the bit changing procedure according to the present disclosure, with FIGS. 9A-9J illustrating bit removal and FIGS. 10A-10G illustrating the steps of attaching a new bit to the drill pipe. In the first step shown in FIG. 9A, drill string 18 finishes drilling and drill pipe 19 is raised upward such that used bit 20 is positioned above bit handling mechanism 40, which is in turn positioned on deck wrench assembly 30 supported on deck 28 in the standby position whereby mechanism 40 is not centered with bit sub 22 and bit 20. In the second step as shown in FIG. 9B, bit changing mechanism 40 is slid along deck wrench assembly 30 such that an open receptacle 60 is positioned underneath the used drill bit 20.

In the next step shown in FIG. 9C, bit sub 22 is lowered and used bit 20 is inserted into open receptacle 60 through opening 50. Because a used drill bit is being removed, the system control is operated to index bit mechanism 40 to present an empty receptacle at the drill pipe center as discussed above. As shown in FIG. 9D, a break-out wrench 36 is pivoted to fully engage drill bit sub 22. Break-out wrench 36 is swivelably supported on mast 14. The wrench is positioned on mast 14 at a particular position to coordinate with deck wrench assembly 30 and bit handling mechanism 40. Break-out wrench 36 can be operated by hydraulics, which are controlled by the rig system.

Referring to FIG. 9E, break-out wrench 36 has a pair of jaws, with at least one of the jaws thereof being movable in relation to the other, such that the jaws are engaged to fully grip bit sub 22. In FIG. 9F the connection of the drill bit from the bit sub can be broken. Referring again to FIGS. 4A and 4B, as shown deck wrench is pivotally actuated on deck 28, this pivotal movement is used to in connection with a slap cylinder (not shown) to break the connection.

Referring to the steps shown in FIGS. 9G-9J, the jaws of break out wrench 36 are unclamped from the bit sub, break-out wrench 36 is swung outward and away from bit sub 22, drill string 18 is moved upwards and the used bit 20 is uncoupled from the string. The used bit remains in the carousel receptacle, and bit handling mechanism is slid outward from the drill center along deck wrench assembly 30 into the standby position.

After the competition of the above steps to remove the used bit, the present system can then be utilized to install a new bit stored in the carousel of bit changing mechanism 40. Referring to FIG. 10A, carousel 44 is indexed/rotated to position a receptacle housing a new, unused bit 20 to the drill center. As shown in FIG. 10B, bit changing mechanism 40 is then slid along deck wrench assembly 30 to present the new bit to the drill pipe.

In the step shown in FIG. 10C the drill pipe is lowered and air is blown to ensure a secure connection before attaching the new drill bit because compressed air can be used to blow away any debris or dust from the threads of both the drill pipe and drill bit. New bit 20 is then threaded onto bit sub 22. Control unit 26 can be used to provide rotational force to the drill string to automatically thread the drill bit into the drill pipe. The drill pipe can then be retracted upwards to remove the drill bit out of the bit changing mechanism 40 as shown in FIG. 10D.

After new bit 20 has been attached to the drill pipe, deck wrench 30 is slid out from the drill center to the standby position once again as shown in FIG. 10E. In FIG. 10F, bit change mechanism 40 remains in the same position whereby the empty receptacle is ready to receive a used bit as described above.

In the step of FIG. 10G, the bit sub 22 with new drill bit 20 is lowered into deck wrench 30 through opening 31 to be presented for the drilling operation.

The present drill bit changing and handling system is designed to automatically operate. The system is structurally sufficient to holding multiple bits.

The purpose of automating a system or process is to allow that process to run without any human interaction. To ensure a maximum of automation and a minimum of human interaction the changing system will house as many unused drill bits as possible.

Blast hole drill rigs operate in some very remote areas of the planet these areas and often time come with extreme conditions including blizzards, earthquakes and hurricanes. Environmental conditions are worsened when dirt, dust and rock begin to be kicked up and thrown around during drilling operation. To withstand these conditions, the present system is structurally robust to compensate for dangerous conditions.

In addition to the embodiments previously described, certain further embodiments are provided herein.

Referring again to FIG. 2, drill string 18 includes a table bushing 70 that is located at bit sub 22. Table bushing 70 helps to centralize the drill string in the deck opening and adds support to the drill string during the drilling process. The drill string is vertically movable within table bushing 70.

In a further embodiment, as shown in FIG. 11, and with reference to the steps of FIGS. 9C-9J, the breakout wrench 36 engages the table bushing 70 with a bushing support bracket 80. As will be described further herein, bush support bracket 80 is mounted to breakout wrench 36 and is arranged to hold the table bushing 70 via arms 82 out of the deck wrench 32 and up to the point just above the bracket 80. Thereafter, break out wrench 36 will swing underneath the table bushing 70 and the bracket 80 will support it while the bit changing operation occurs.

Bracket 80 is fixedly mounted to an upper surface 76 of breakout wrench 36 via a platform 78 such that the bracket 80 is elevated therefrom.

Bushing support bracket 80 is described in detail with reference to FIGS. 12A-12C. Bracket 80 includes a base plate 82 which is affixed to platform 78 of breakout wrench 36. Base plate 82 serves as a foundation and mounting interface for a pair of support arms 84.

Each arm 86 includes a guiding surface that is angled with respect to base plate 82. As shown, arms 84 are positioned to project forward from base plate 82 at an angle to guide and facilitate a congruent engagement with the table bushing 70 as will be described further herein.

Each bracket arm 84 has opposed front and rear ends 85, 87. Front end 85 of arms 84 includes a taper 88 to interact and guide the table bushing 70 into engagement with the support arms As shown in FIG. 12B, arms 84 are spaced by a distance D to accommodate the width of the table bushing.

FIGS. 13A-13C further illustrate steps prior to the steps previously described, wherein the breakout wrench 36 is stowed, i.e., swung outward. As shown in FIG. 13A, as the used bit 20 is raised upward the table bushing 70 sits on the deck 28. Referring to FIG. 13B, the table bushing 70 is lifted by the drill bit 20 as it passes through the deck 28. Thereafter in FIG. 13C the table bushing 70 moves along the drill string once retracted beyond the deck 28.

Referring to FIGS. 14A-14C, the support bracket operation is further illustrated. For simplicity sake the steps are illustrated outside the environment of deck 28 and mast 14. But is should be appreciated that such relate to FIG. 11 and the positioning of the drill bit as shown therein. As shown in FIG. 14A, breakout wrench 36 is swung underneath the table bushing 70 and used drill bit 20 in furtherance to FIG. 13C. In FIG. 14B the used bit is positioned such that used bit 20 will be positioned through opening 83 formed by arms 84 and plate 82 of the bush support bracket 70. As shown in FIGS. 14C and 14D, bracket 80 will support the bushing 70 while the bit changing operation as described above occurs. In other words, during operation, the bushing support bracket holds the table bushing in an elevated position above the breakout wrench to permit insertion of a used drill bit into the receptacle of the bit-changing mechanism.

Bushing support bracket 80 is configured such that the table bushing is supported independently of the drill bit handling mechanism 40 during removal of a used drill bit and installation of a new drill bit. Thereafter, the used drill bit can be removed and replaced per above.

A method of supporting the table bushing during a drill-bit changing operation of the drill rig includes the step of providing the bushing support bracket 80 mounted to a breakout wrench 36. The drill string is raised such that the table bushing 70 engages the tapered front ends 85 of the support arms 84 and the table bushing is held upward from the deck wrench using the support arms. In order to do so, the breakout wrench is positioned beneath the table bushing while the support arms support the table bushing. Thereafter the above-described drill-bit changing operation is performed while the table bushing remains supported by the bushing support bracket.

Accordingly, the bushing support bracket is arranged to maintain the table bushing in a supported position independently of the drill bit handling mechanism during removal of a used drill bit and installation of a new drill bit and arranged to receive the table bushing as the drill bit is moved through the deck opening.

Although the present embodiment(s) has been described in relation to particular aspects thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred therefore that the present embodiment(s) be limited not by the specific disclosure herein, but only by the appended claims.

Claims

1. A table-bushing support apparatus for use in a drill bit handling and changing system, the apparatus comprising:

a bushing support bracket mounted to a breakout wrench of a drill rig, the bushing support bracket having a base plate arranged to be secured to a platform on an upper surface of the breakout wrench; and

a pair of support arms extending from the base plate and arranged to capture, lift, and support a table bushing of a drill string, the support arms each including a guiding surface angled relative to the base plate and a tapered front end configured to interact with the table bushing, wherein the support arms are spaced apart by a distance sized to receive the table bushing, and wherein the bushing support bracket is configured to hold the table bushing upward from a deck wrench of the drill rig and support the table bushing during a drill-bit changing operation.

2. The apparatus of claim 1, wherein the support arms are arranged to define an opening between the arms and the base plate that is sized for passage of a used drill bit during removal.

3. The apparatus of claim 1, wherein each support arm includes an opposed front and rear end, the front end including a tapered surface arranged to guide the table bushing into engagement with the support arms.

4. The apparatus of claim 1, wherein each of the support arms includes a guiding surface angled with respect to the base plate to facilitate a congruent engagement with the table bushing.

5. The apparatus of claim 1, wherein the spacing between the support arms corresponds to a width of the table bushing to ensure stable support while the bit-changing mechanism operates.

6. The apparatus of claim 1, wherein the bushing support bracket is configured to capture the table bushing as the drill string is raised, such that the table bushing is lifted from the deck opening.

7. The apparatus of claim 1, wherein, during operation, the bushing support bracket holds the table bushing in an elevated position above the breakout wrench to permit insertion of a used drill bit into a receptacle of a bit-changing mechanism.

8. The apparatus of claim 1, wherein the guiding surfaces of the support arms are arranged to centralize the table bushing.

9. The apparatus of claim 1, wherein the bushing support bracket is configured such that the table bushing is supported independently of the drill bit handling mechanism during removal of a used drill bit and installation of a new drill bit.

10. A method of supporting a table bushing during a drill-bit changing operation of a drill rig, the method comprising:

providing a bushing support bracket mounted to a breakout wrench, the bushing support bracket including a base plate and a pair of support arms extending from the base plate;

raising a drill string such that a table bushing engages the tapered front ends of the support arms;

holding the table bushing upward from a deck wrench using the support arms;

positioning the breakout wrench beneath the table bushing while the support arms support the table bushing; and

performing a drill-bit changing operation while the table bushing remains supported by the bushing support bracket.

11. The method of claim 10, further comprising capturing the table bushing between the angled guiding surfaces of the support arms during engagement to support the table bushing, wherein supporting the table bushing allows the drill pipe and drill bit to be raised and lowered without interference from the table bushing.

12. A table-bushing support system for a drill rig, the system comprising:

a bushing support bracket mounted to a breakout wrench of the drill rig; and

a pair of support arms of the bushing support bracket being configured to engage a table bushing carried on a drill string, wherein the support arms are arranged to hold and support the table bushing away from a deck opening of the drill rig as the drill string is raised, and wherein the bushing support bracket is further configured to hold the table bushing in a supported position during a drill-bit changing operation.

13. The system of claim 12, wherein each support arms includes a guiding surface angled with respect to the base plate to guide engagement of the table bushing.

14. The system of claim 13, wherein each support element includes a tapered front end arranged to direct the table bushing into engagement with the support arms.

15. The system of claim 12, wherein the support arms are spaced apart by a distance selected to receive the table bushing.

16. The system of claim 12, wherein the support arms and the base plate define an opening through which a used drill bit can be lowered during a bit-changing operation.

17. The system of claim 12, wherein the support arms are arranged to hold the table bushing above the breakout wrench while the breakout wrench engages the drill string, and wherein the bushing support bracket is arranged to maintain the table bushing in a supported position independently of the drill bit handling mechanism during removal of a used drill bit and installation of a new drill bit.

18. The system of claim 13, wherein each of the support arms includes an opposed front and rear end, the front ends including tapered surfaces arranged to engage the table bushing during upward movement of the drill string.

19. The system of claim 12, wherein the bushing support bracket is arranged to receive the table bushing as the drill bit is moved through the deck opening.