US2388720A - Drilling apparatus - Google Patents

Description

Nov. 13, 1945. M. s. WRIGHT 2,383,7gg

DRILLING" APPARATUS Filed Oct. 5, 1942 4 Sheets-Sheet 1 Fla-"l Flea-2 MARCUS G. WRIGHT v INVENTOR.

ATTO/PNEK DRILLING APPARATUS Filed Oct. 5, 1942 4 Sheets-Sheet 2 Mgpcus G. WRIGHT IN VENTOR.

A 7'7'ORNEK Nov. 13, 1945. M. G. WRIGHT DRILLING APPARATUS Filed Oct. 5, 1942 4 Sheets-Sheet 5 N a I I a I n m n p a I i I {A a g n s l I Mucus G. WRIGHT INVENTOR.

Nov. 13, 1945.

M. a WRIGHT I miswm DRILLING. APPARATUS Filed Oct. 5,- 1942 4 Sheets-Sheet 4 Mucus G. Wmauf INVENTOR ATTORNEY Patented Nov. 13, 1945 DRILLING APPARATUS Marcus G. Wright, Denver, Colo., assignor of thirty-five one-hundredths to Thomas P. Campbell and thirty-five one-hundredths to W. Myron Owen, both of Denver, 0010.

Application October 5, 1942, Serial No. 460,828

18 Claims.

This invention relates to drilling apparatus, and more particularly relates to electric drills of the type particularly suited for core or blast hole drilling operations.

Most drilling apparatus suited for such work is of the pneumatic type, despite the fact that present day mines for the most part are wired for electricity. In such cases, this power source is utilized to drive the compressors constituting the pneumatic supply source. But due to the presence of moisture in many mines and the consequent danger of electrocution, etc., the electric type drills so far developed have not been accepted to any appreciable extent by the mining industry.

It is an object of the present invention to provide simple, durable and efiicient electric drilling apparatus which may be used in wet areas with out danger of electrocution or the like.

Another object of the invention is to provide a high speed electric drill which may be operated continuously for long periods without damage to its component parts from excessive heating.

A further object of the invention resides in the provision of drilling apparatus which is protected from damage by impact with falling missiles or the like, but in which the component parts are readily accessible for purposes of repair or replacement.

Still another object of the invention is to provide drilling apparatus which efficiently drills even the hardest types of rock with small power consumption, and which requires little operator supervision in any such operation.

A still further object of the invention is the provision of drilling apparatus, which in addition to fulfilling its primary function of drilling efficiently and economically, has an additional advantage of providing readily accessible samples in drilling operations.

And another object of the invention is to provide drilling apparatus that is adapted for operation by connection, either in standard power circuits, or with a gasoline-motor generating unit.

Other objects reside in novel details of construction and novel combinations and arrangements of parts, all of which will be disclosed in the course of the following description.

To aiford a better understanding of the features of the present invention, reference will be made to the accompanying drawings illlustratin'g a typical embodiment of the invention. In the drawings in the several views of which like parts have been designated similarly,

Figure 1 is a partially broken top plan view of the drilling apparatus assembly as it would appear with the upper half of the protective housing removed;

Figure 2 is a fragmentary side elevation of the apparatus of Figure 1, partially broken away to show the interior arrangement of parts:

Figure 3 is an end elevation drawn to an enlarged scale, from the approximate position indicated by the arrows 33, Figure 1;

Figure 4 is a fragmentary section, taken along the lines 4-4, Figure 1, and drawn to an enlarged scale;

Figure 5 is a section taken along the line 5-5, Figure 3;

Figure 6 is an end elevation of the drill bit employed in the apparatus, taken from the approximate position indicated by the arrows 66, Figure 1;

Figure 7 is a wiring diagram, illustrating the circuit arrangement of the apparatus illustrated in Figure 1; and

Fi re 8 is an end elevation of the drill housing, illustrating the shaft support and drawn to an enlarged scale.

Referring first to Figures 1 and 2, the drill comprises a sectional housing 8 formed of two sections 8a and 8b hinged together at 9 and normally held in an enclosing position by a plurality of latches ill.

The casing 8 is attached to a standard I3 having a series of joints l2 permitting universal movement of the drill and providing means for holding the drill in any selective position. Since the details of the standard construction conform to conventional practice in the art, detailed description of the same appears unnecessary and no claim is being made to features of the standard construction per se.

As best shown in Figure 3, the inner walls of housing sections 8a and 8b are formed to provide cooperative parts of tracks or guideways l4 extending lengthwise of housing 8 on opposed walls thereof. A drill driving motor l5, suitably housed, has a plurality of rollers I 6 extending into the guideway for travel therealong.

A gear casing I! forming an extension on motor housing l5 also has a plurality of wheels or rollers [6 extending into guideways l4, and it will be apparent from the foregoing description that the composite structure is thus free to travel lengthwise of housing 8, the lower half of each guideway I4 acting as a track for the wheels l6 and the upper half as a guard.

The drive shaft l8 has at its end a chuck l9 in which a drill stem or shaft may be fitted and held for conjoint rotation with shaft I8. A drill head 2|, the details of which will be described subsequently, is mounted on the end of shaft 20 extending beyond casing 8.

The shaft I8, drill stem 20 and drill h'ead 2| are hollow and provide a continuous passage for the circulation of cooling liquid which functions as a heat exchange medium t prevent damage due to excessive heating to the rotating parts in the high speed action of the drill. Liquid, usually water, is delivered to this conductive passage through a hose 22, under control of a flow switch 23.

The flow switch unit used for this purpose is a standard item built for actuation in response to rate of flow of fluid as distinguished from response to fluid pressure and, per se, forms no part of the present invention. This switch has an associated relay 24 which is energized whenever the flow into the unit reaches or exceeds two and one-half gallons per minute. Flow through the hose 22 into switch unit 23 is controlled by a manually-operable valve 26 (Figure '7) and closing of the circuit through relay 24 is necessary to start motor I5 as will be explained hereinafter.

Consequently, it is impossible with the present arrangement to start the motor I5 and rotate drill bit or head 2I, unless there is ample supply of the heat-exchange medium to insure against damage to the drill bit 2| because of undue heating,

The circuit through the drill motor l5 also extends through a feed motor 25 located within casing I'l. Preferably, this is a three phase, 55 volt high torque motor, the drive haft 21 of which actuates a train of gears 28 to drive a double sprocket wheel 29 mounted on a shaft 30 at a reduced speed.

These sprocket members mesh with a rack, preferably comprising a double roller chain 3I, anchored at its ends and provided with a take-up adjustment (not shown). This arrangement acts as the propulsion means for moving motor housing I5 and extension casing I'I lengthwise of the housing. As clearly shown in Figure 5 the teeth of one of the sprocket members 29 are staggered with respect to the teeth'of the other sprocket member so that, when a tooth of one sprocket moves out of full engagement with a roller on one chain, a tooth of the other sprocket moves into full engagement with a roller on the other chain. This construction which provides alternate full engagement of the sprockets insures substantially continuous application of power between the sprockets and chains and minimizes lost motion or backlash.

The feed motor 25 is provided with a reversing switch 32 which extends upwardly out of casing H in proximity to the inner wall of housing section 8a. An inwardly projectin lug 33 is positioned at the rear end of housing 8 in the path of movement of switch 32 and limits the range of rearward movement of drill motor I 5.

Adjacent the opposite end, a series of holes 34 in housing section 8a permit selective insertion of a removable lug 35 which extends therethrough into the path of movement of switch 32 and limits the extent of forward movement of drill motor I5.

However, if desired, a slot and sliding plate may be substituted for the aforesaid adjustable stop to prevent entranc of dirt into the casing. So long as the adjustment is provided by some operable means the purpose of the present invention will be fulfilled.

With this understanding of the general arrangement of parts constituting the drilling apparatus, reference will be made to certain details of construction which assist in the general efficiency and advantage of the present invention.

The drill motor l5 should be capable of rotation at the rate of 3600 R. P. M. and for this purpose a 5 H, P., 55 volt, 3 phase, 60 cycle motor is recommended. As shown in Figure 4 the motor is encased within a housing I5a, at the ends of which its shaft I8 is journaled in bearings 36, and its rotor 31 rotates within its stator 38. The wiring connection to motor I5; through flow switch 23may be introduced in any suitable way, but preferably is an integral part of conduit 22. As illustrated in Figures 1 and 2, the wires 39 are clamped against the outer surface of conduit 22 and lead to flow switch 23. These wires, four in number, are sufficiently flexible to withstand repeated flexing in the handling and operation of the apparatus without breaking.

In the wiring diagram, Figure 7, the lead wires 39 are shown in disconnected relation to the hose 22 for purposes of clarity. The source of energy may be any standard circuit available in the area in which the apparatus is operated, such as a mine, and usually is either a volt or 220 volt circuit.

When such power lines are not available, a portable gasoline-motor generating unit may be taken into the mine or other location where the apparatus is to be operated, and such a source of energy is suited for use in the circuit of the present apparatus,

Consequently, by employing 55 volt motors it is possible to use standard transformers and with such voltage, electrocution of human beings is practically impossible, particularly when as here an ungrounded circuit is employed.

Referring again to Figure 7, after the input of leads 39 passes the transformer 40 and is stepped down to 55 volts, the flow is controlled by line switch 4| connected with overload relays 42 which protect the motors in case the drill should stick or a short circuit should develop in the flexible lead wires.

A three lead line 43 passes from the overload relays to the drill motor I5 and one of these leads is connected as indicated at 44 through a water flow switch relay 24, which in turn connects with water flow switch 23. A conductor 46 connects water flow switch 23 with feed motor 25 and also has a wiring connection with another one of the flexible lead wires 43 as indicated at 41.

The feed motor 25 connects through reversing switch 32 with the other two flexible lead wires as indicated at 48 and 49.

By having the motors I5 and 25 and flow'switch 23 mounted within a unitary housing structure, which is attached within drill housing 8 solely by the wheel supports mounted in guideways I4, and the meshing of sprocket 29 in rack 3|, the provision of the hinged housing arrangement 8a, 81) makes it possible to remove the completemotor and drill assembly in making a. new drill setting, The removal of the drilling unit makes it a simple matter to manipulate housing 8 on its supporting standard l3 until it is fixed in proper position, after which the drill unit may be mounted in the casing again and the drilling operation resumed,

In the operation of the drill the valve 26is opened whenever the drilling apparatus has been located in working position and as soon as the rate of flow into the flow switch reaches two and one-half gallons per minute, the flow switch makescontact which starts the drill and feed motor.

In usual practice, the mechanism will be designed for approximately four feet of travel in each setting of the drill. The feed motor preferably is of the 55, volt, 3 phase type operating at 900 or 1200 R. P. M. synchronous speed. With the arrangement described,'this motor drives the mechanism to feed the drill shaft and attached bit at a variable speed against a maximum bit pressure of approximately 1000 pounds, When drilling through hard rock, such as quartz, the forward motion would be at the rate of approximately eighteen inches per minute, while a speed of as much as fifty-four inches per minute is possible when the drill is moving through space. A motor of this type is designed to have a characteristic such that it will give maximum torque at approximately 300 to 400 R. P. M. or one-third or synchronous speed, and consequently operations in soft material will permit an increase in forward speed over that stated for quartz.

After the drilling movement has progressed to the end point determined by the selective location of stop member 35, the action is reversed and the motor unit I5 returns through the casing to the original starting position determined by the location of Inc 33.

During all this operation water introduced through hose 22 to flow switch 23 in turn passes through the hollow shaft I8, drill stem and bit 2| flowing out the face of the rock being drilled. The volume and force of the liquid thus delivered at the face of the bore washes out rock particles or silt which pass through the exterior openings '50 positioned about the crown 5| of the bit, and due to its shouldered design these particles are free thereafter to pass along the drilled passage from which they finally discharge.

The inflowing stream travels throughsimilar openings adjacent the inner bore of the bit and thus provides the necessary clearance for rearward movement of the cores. A cap element I53 normally covering the end of the hollow passage is readily removable when access to cores is desired, as shown in Figure 4.

In addition to assisting in the removal of rock particles, thisflow of liquid acts as a cooling or heat exchange medium to prevent the drill head and associated parts from damage through excessive heating. The return fiow acts as a lubrieating medium in which the drill head 2| and shaft. 20 rotate and some heat exchange action is derived therefrom as well as protecting these parts from excessive wear through contact with the surface of the bore.

Referring now to Figure 6, the hollow bit' 2| comprises an annular crown portion 5| having a series of peripheral slots or passages 50 here shown as four in number arranged at 90 intervals, Carboloy impregnated metal securely held or formed integrally with the remainder of bit 2|. To prevent undue vibration of the drill stem 20, the outer end of housing 8 has two cooperative end plates 53a and 53b carried on sections 8a and 8b respectively, and a series of roller bearings 52, here shown as four in number, hold the stem 20 against lateral displacement when the housing sections are clamped together.

The crown preferably is a. diamond or tion and operation, it will be apparent that very little operator attention is required in the continued usage of this drill. With the drill mechanism removed from housing 8 it is a simple one-man operator job to adjust the housing on standard I 2 in proper drilling position.

Thereafter, it is only necessary for the operator to insert the unit in the housing and open valve 26 to initiate the'operating cycle. The ensuing action is completely automatic and when the drill unit has drilled the predetermined distance, the reversing switch effects the necessary return, and when the return travel brings reversing switch 32 into engagement with stop 33, the switch is moved to a neutral position and opens the circuit.

Consequently, during the progress of this cycle, theoperator can be used elsewhere, for example in resetting other drills, and in this way one man can keep several such drills running regularly.

Further advantage is derived in the use of the present invention in obtaining samples. At all times during the operating cycle of the drill, water *is being discharged against the face of the bore in substantial volume, and the cuttings are entrained in the return flow, and discharge at the rear end of the casing. When samples are desired, it only is necessary to place a receptacle in the discharging stream to obtain the same, and this can be done without interfering with the drilling operation. Y

The use of diamond-impregnated or Carboloy bits rotating at high speed, coupled with the advancing action of the torque motor provides a fast boring action, and this performance is obtained with relatively small power consumption. It also should be noted that in these drilling operations, the presence of substantial quantities of water in and around the bit serves to prevent any appreciable production of dust and this feature is of considerable importance where the produc-' tion of dust in drilling operations has been having a deleterious effect on the health of machine operators.

Changes and modifications may be availed of within the spirit and scope of the invention as defined in the hereunto appended claims.

'What I claim and desire to secure by Letters Patent is:

1. Drilling apparatus comprising a hollow casing, a drill unit including a drill motor mounted in said casing for movement lengthwise thereof, a shaft connected with the motor drive shaft for conjoint rotation therewith and extending outside the casing, a drill bit on the end of the drill shaft, a roller chain secured to said casing longitudinally thereof and a pair of sprockets mounted for conjoint rotation on said unit and engaging said chain, said chain and said sprockets being so constructed and arranged that the said sprockets upon rotation alternately reach their positions of full engagement with the rollers of said chain, a high torque motor for driving said sprockets and mounted on said unit with the drill motor for conjoint movement lengthwise of the casing, a reversing switch carried on said unit, a stop member adjacent each end of the casing in the path of the reversing switch for limiting the range of travel of said unit, a circuit inclusive of the reversing switch. the drill motor and the high torque motor, and means extending into the casing for connecting said circuit with a source of electric energy. V v

2. Drilling apparatus comprising a hollow casing, a drill motor mounted therein for movement From. the foregoing description of the construc- J l ngthwise thereof and having a hollow drive shaft, a hollow shaft connected with the motor drive shaft for conjoint rotation therewith and extending outside thecasing, a hollow drill bit on the end of the drill shaft, a rack in the casing, a train of gears, inclusive of a sprocket in mesh with the rack, a high torque motor driving the sprocket through the train of gears and mounted with the drill motor for Conjoint movement lengthwise of the casing, a reversing switch carried on the high torque motor, a stop member adjacent each end of the casing in the path of the reversing switch for limiting the range of motor travel in said casing, a flow switch, a circuit inclusive of the flow switch, the drill motor and the high torque motor, a conduit connecting the flow switch with a source of water under pressure for delivery through the hollow shaft and bit, and means associated with the conduit for connecting the flow switch with a source of electric ener y, the flow switch closing the circuit when the rate of liquid flow through said switch exceeds a predetermined volume.

3. In drilling apparatus, a support including a casing, a wheel supported motor unit mounted in the casing for lengthwise movement therealong, a rotary drill motor in said unit, a rotary drilling tool in direct driving connection with said motor and extending beyond the casing in all positions of the motor unit movement, an alternating current feed motor in said motor unit for advancing said unit in opposite directions along the casing, a rack extending lengthwise of the casing, a sprocket driven by the feed motor and in mesh with said rack, a circuit including said motors, and a reversing switch on the unit constructed and arranged to change the direction of rotation of the feed motor when the unit approaches the end of the rack, said feed motor having sufiiciently high torque over a wide range of speeds to maintain the rate of advance of said drill into the material to be drilled substantially proportional to the resistance to drilling tool rotation offered by the material.

4. In drilling apparatus, a support including a casing, a wheel-supported motor unit mounted in the casing for lengthwise movement therealong, a rotary drill motor in said'unit, a rotary drilling tool in direct driving connection with said motor and extending beyond the casing in all positions of the motor unit movement, an alternating current feed motor in said motor unit for advancing said unit in opposite directions along the casing, cooperative means on the casing and motor unit for moving said unit lengthwise of the casing through an oscillatory cycle, cooperative means on the casing and motor unit for determining the extent of said oscillatory cycle, and a switch-controlled circuit, including said motor unit, said feed motor having sulficiently high torque over a wide range of speeds to maintain the rate of advance of said drill into the material to be drilled substantially proportional to the resistance to drilling tool rotation offered by the material.

5. In drilling apparatus, a support including a casing, a wheel-supported motor unit mounted in the casing for lengthwise movement therealong, a rotary'drill motor in said unit, a rotary drilling tool in direct driving connection with said motor and extending beyond the casing in all positions of the motor unit movement, an alternating current feed motor in said motor unit for advancing said unit in opposite directions along the casing, cooperative mean on the casing and casing through an oscillatory cycle, cooperative means adjustably positioned on the casing and motor unit for selectively determining the extent of said oscillatory cycle, and a switch-controlled circuit, including said motor unit, said feed motor having sufficiently high torque over a wide range of speeds. to maintain the rate of advance of said drill into the material to be drilled substantially proportional to the resistance to drilling tool rotation offered by the material.

6. In drilling apparatus, a support, a wheelsupported member mounted for forward and backward movement thereon, a hollow drilling tool carried by said member and extending beyond the support throughout the range or movement of said member, means on said member for rotating said tool, means on said member for advancing it alternately in opposite directions along the support, associated means on the support and member for controlling the operation of said advancing means, conductive mean connected with said hollow tool for delivering a flow of liquid therethrough to cool the same during its rotation, and means dependent upon the rate of flow of the liquid for controlling operation of said tool rotating and advancing means, said controlling means being constructed and arranged to stop said tool rotating and advancing means whenever the rate of flow of such liquid drops below a predetermined minimum,

7. In drilling apparatus, a support, a wheelsupported member mounted for forward and backward movement thereon, a hollow drilling tool carried by said member and extending beyond the support throughout the range of movement of said member, means including an electric motor on said member for rotating said tool, means, including an electric motor on said member for advancing it alternately in opposite directions along the support, conductive means connected with said hollow tool for delivering a flow of liquid therethrough to cool the same during its rotation, and a circuit, inclusive of a switch actuated in accordance with the rate of flow of said liquid for controlling the operation of said motors, and constructed and arranged to stop said tool rotating and advancing means whenever the rate of flow of such liquid drops below a predetermined minimum.

8. In drilling apparatus, in which a hollow drill tool is rotated and simultaneously advanced along a supporting structure, the improvement which comprises cooling said tool during its rotation by flowing a stream of liquid through its hollow in-' terior, and controlling the initiation and termination of said rotation and advancing movement in accordance with the rate of flow of liquid so as to initiate said rotation and advancing movement when such rate of flow increases above a predetermined minimum and terminate said rotation and advancing movement whenever such rate of flow decreases below a predetermined minimum.

9. In drilling apparatus, in which a hollow drill tool is rotated and simultaneously advanced along a supporting structure, the improvement which comprises cooling said tool during its rotation by flowing a stream of liquid through its hollow interior, starting said rotation and advancing movement whenever the rate of flow of liquid increases above a predetermined value, and terminating said rotation when the rate of flow of liquid falls below a predetermined value.

10. Drilling apparatus comprising a hollow casing, a drill motor mounted therein for movemotor unit for moving said unit lengthwise of the 7 ment lengthwise thereof and having a hollow drive shaft, a hollow shaft connected with the motor drive shaft for conjoint rotation therewith and extending outside the casing, a hollow drill bit on the end of the drill shaft, a rack in the casing, a train of gears, inclusive of a sprocket in mesh with the rack, a high torque motor driving the sprocket through the train of gears and mounted with the drill motor for conjoint movement lengthwise of the casing, a reversing switch carried on the high torque motor, a stop member adjacent each end of the casing in the path of the reversing switch for limiting the range of motor travel in said casing, a flow switch, a circuit inclusive of the flow switch, the drill motor and the high torque motor, a conduit connecting the flow switch with a source of water under pressure for delivery through the hollow shaft and bit, means associated with the conduit for connecting the flow switch with a source of electric energy, the flow switch closing the circuit when the rate of liquid flow through said switch exceeds a predtetermined volume, and means at the end of said hollow shaft remote from said drill bit normally sealing said end against the discharge of fluid.

11. In a drilling apparatus, a supporting member, a drill assembly including a drill extending from said member, means mounted on said assembly for rotating said drill, a roller chain secured on said member, a pair of sprockets rotatably mounted on said assembly andengaging said chain, and means including a high torque motor mounted on said assembly for rotating said sprockets to advance said drill assembly along said member and to maintain said drill in engagement with the material to be drilled, said chain and said sprockets being so constructed and arranged that said sprockets upon rotation alternate in full engagement with the rollers of said chain, said motor having sufiiciently high torque throughout a wide range of speeds to maintain the advance of said drill toward the material at rates dependent upon the resistance to drill rotation offered by the material.

12. Drilling apparatus comprising a hollow casing, a drill motor mounted therein for movement lengthwise thereof and having a hollow drive shaft, a hollow shaft connected with the motor drive shaft for conjoint rotation therewith and extending outside the casing, a hollow drill bit on the end of the drill shaft, means including a second motor mounted as a unit with the drill motor for moving the drill motor to advance said drill with respect to the casing, a circuit for energizing said motors, a reversing switch for said second motor carried on said unit, spaced stop members mounted on said casin in the path of the reversing switch for limiting the range of travel of said unit, a conduit for supplying water from a source under pressure for delivery through the hollow shaft and bit, and means including a switch associated with said circuit and responsive to the rate of flow of the cooling water for controlling the enengization of said motors.

13. A drilling apparatus comprising an elongated casing having a cover portion movable to an open position for affording access to the interior thereof, a guide track within said casing, a drilling unit including a motor and a drill shaft arranged to be driven thereby, said drill shaft extending outside said casing, rollers on said unit arranged to engage said track, means on said cover portion for maintaining said rollers in position with respect to said track, and means on said unit for propelling said unit longitudinally within Said casing to move said drill shaft to and from its working position.

14. A drilling apparatus comprising an elongated casing having a cover portion movabl to an open position for affording access to the interior thereof, a drilling unit arranged within said casing and removable therefrom upon movement of said cover portion, said unit including a motor and a, drill shaft driven thereby and extending outside said casing, rollers on said unit for supporting said unit, guideways comprising cooperating portions on said casing and on said cover portion arranged to engage said rollers for maintaining said unit in position in said casing, and means on said unit for propelling said unit along said guideways to move said drill shaft to and from its working position.

15. A drilling apparatus comprising a substantially cylindrical casing divided longitudinally into half portions arranged to be relatively movable to afford access to the interior thereof, complementary guideways formed on said half portions, a drilling unit including a motor and a drill shaft driven thereby and extending outside said casing, rollers on said unit arranged to engage said guideways and support said unit in said casing for longitudinal movement therein, and means on said unit for propelling the same along said guideways to move said drill shaft toward and away from its working position.

16. A drilling apparatus comprising an elongated casing having a cover portion movable to an open position for affording access to the interior thereof, a guide track within said casing, a drilling unit including a motor and a drill shaft arranged to be driven thereby, said drill shaft extending outside said casing, rollers on said unit arranged to engage said track, means on said cover portion for maintaining said rollers in position with respect to said track, means on said unit for propelling said unit longitudinally within said casing to move said drill shaft to and from its working position, and complementary guide members on said casing and on said cover portion adjacent one end of said casing for supporting said drill shaft and for minimizing lateral movement thereof.

17. A drilling apparatus comprising a support and a drilling unit mounted for movement with respect to said support toward and away from its working position, said unit including a drill shaft and a driving motor therefor, a drill tool on said shaft, a second motor for moving said unit toward and away from its working position, means including a conduit for supplying cooling fluid to said tool, and means including a switch dependent upon a predetermined minimum rate of flow of cooling fluid through said conduit for energizing said motors and for stopping said motors whenever such flow decreases below a I,

predetermined minimum.

18. A drilling apparatus comprising a supporting structure, a hollow drill tool, means mounted on said structure for rotating said tool and for advancing said tool toward its working position, means for conducting a stream of liquid through said tool to cool said tool during its operation, means dependent upon the rate of flow of said cooling liquid for energizing said rotating and advancing means only in response to an increase in the rate of flow of liquid above a predtermined value, and means for terminating operation of said tool in response to a decrease of the rate of flow of said liquid to a predetermined value.

MARCUS G. WRIGHT.

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