US2015922A - Feeding mechanism for rock drills - Google Patents

Description

` Octl, 1935. J. c. CURTIS FEEDINGVMECHANISM FOR ROCK DRILLS 5 Sheets-Sheet 1 Filed NOV. l0, 1932 i Nm QQ JOHN cca/775 INVENTOR ATTORNEY Oct. 1, 1935. l J, C. CUR-ns 2,015,922

FEEDINGYMEGHANISM FOR ROCK DRILLS Filed NOV. l0, 1952 3 Sheets-Sheet 2 55 BY Eg' 6 g ATroRNl-:Y v

CLVl, 1935. 1 Q CURTlS 2,015,922

FEEDING MECHANISM FOR ROCK DRILLS Filed Nov. 1o, 1952 :s sheets-sheet s JOHN C. 60E 775 lNvENToR Hg. 12 BY v ATTORNEY Patented Oct. 1, 1935 UNITED vSTATES PATENT OFFICE FEEDING MECHANISM FOR ROCK DRILLS q John C. Curtis, Cleveland, Ohio, assigner to The Cleveland `Rock Drill Company, Cleveland, Ohio, a. corporation of Ohio Application November .10, 1932, Serial No. 642,015

` 21 Claims.`

This invention relates broadly to rock drills but more particularly to 'feeding mechanism for rock drills of the drifter type.

One object of this invention is to provide a 55. feeding mechanism for rock drill provided with means preventing jar imparted to the Vmotor by its piston upon the reversal of its strokes, to cause a longitudinal motion ofthe 'motor in Aa direction opposite to its feeding motion.

Another object of this invention 'is to construct a rock drill `feeding mechanism with all the parts thereof inclosed within the 'feed cylinder, thus protecting these parts against dust resulting from the drilling operation, and conse- 151`quently reducing the wear between the movable parts. i i

' Another object of this invention is to produce an efficient 'device for packing the screw used in the feeding mechanism, thus affording a durable fluid tight joint between the screw and its cooperating parts and consequently increasing the efficiency of the mechanism. i

Other objects and advantages more or less ancillary to the foregoing reside in the specific construction and aggroupment of the elements peculiar to this structure, as will become apparent from a more complete examination of this speciiication.

In the drawings which illustrate a preferred .embodiment of the invention: Fig. 1 is a longitudinal view partly in section, illustrating the drilling motor with the feed piston positioned in one extreme end of its travel. Fig. 2 is a view similar to Fig. l, illustrating tne drilling motor and feeding piston positioned in the other extreme end of its travel.

Fig. 3 is an enlarged sectional view of the rear portion of the feed tube.

Fig. e is a cross sectional view taken in a 401 `plane indicated by line 4-4 in Fig. 2.

Fig. 5 is an enlarged sectional view of the stationary nut shown in Fig. 1 and Fig. 2.`

Fig. 6 is an enlarged View of the backhead mounted on the end of the feed tube.

Fig. 7 is a cross sectional view taken in a plane indicated by line 'I-'I in Fig. 5.

Fig. 8 is a cross sectional view taken in a plane indicated by line 8--8 in Fig. 6, illustrating the throttle valve in one operative position.

Fig. 9 is a View similar to Fig. 8 illustrating the throttle valve in `another operative position.

Fig. 10 is an enlarged longitudinal view of the feed piston.

Fig. 11 is a view similar to Fig. 10 but taken at right angle therefrom, .illustrating the ratchet plunger in one operative position.

Fig. `12 is a view 'similar to Fig. 11, illustrating the ratchet plunger inthe other operative position. 5 f

Fig. 13 is a cross sectional View taken in a plane indicated by line I3--I3 in Fig.. 10.

Referring to the drawings, the rock drill shown for the purpose of illustration comprises a cylinder I 0, within which there is reiprocably 10 mounted a piston capable of delivering its blow to a cutting tool or drill steel Il. This drill steel is equipped with lugs engageable with corresponding jaws provided into the chuck I2, in

a manner common to 'tools of this type. e The 15 external wall of the lower portion of the cylinder IU is provided with two gibs or guides I3. The feeding mechanism comprises a feed tube I4 made of rectangular cross section constituting a support for the rock drill. vided on its upper face with two guide-ways I5 within which the guides I 3 of the cylinder I0 are free to slide, permitting thereby the longitudinal displacement of the rock drill on the feed tube I4. For mounting purposes on a tripod or oth- 25j4 er supporting devices, the feed tube I4 is equipped with a cone I6, attached thereto by any suitable means, as for instance by means of a weld. The right end of the feed tube which will hereafter be designated as front end, is closed as at 30 I'I, while the left end, which will hereafter be designated as rear end, is closed by a backhead I8 secured thereto by bolts I9.

Reciprocably mounted into the front portion of the feed tube I4, there is a piston 20 com- 35 prising a sleeve 2l having the ends thereof formed with external threads to receive the nuts 22. Clamped between the nuts 22 and supported by the sleeve 2|, there are two rectangular packings 23 disposed in opposite directions and capable of 40 duid tight engagement with the inner wall of the feed tube I4. Intermediatethe packings 23, there is a rectangular separator 24 capable of slidable engagement with the inner wall of the feed tube I4, but held against rotation therein by reason of its rectangular cross section, thus the sleeve 2I being clamped to the separator 24 by the nuts 22, is also held against rotation. The sleeve 2I is properly machined to rotatably receive the restricted end 25 of the feed screw 2E. 50 The end of the screw 26 is threaded to receive a nut 21 for preventing the accidental removal of the piston 20 from the screw. Located on each end of the sleeve 2|, there are `two disks 28 and 29 which are keyed to the restricted 55 'I'his tube is pro 201 between thel nut 'an-d the tube.

end of the screw. The inner walls of the disks 28 and 29 are provided with radially disposed ratchet teeth 36 and 3 I. Leading from the inner face of the disk 28 to the inner face of the disk 29, there are provided through the sleeve 2I two square passages 32. Reciprocably mounted into each of these passages 32, there is a square plunger 33 with the ends thereof machined to fit the teeth 30 and 3I.

Terminating the portion of the feed tube-in which the piston 20 is reciprocably mounted, there is a stationary nut 34 formed with a head shapedv to fit the internal wall of thefeed tube I4, and

secured thereto by transversally 4disposed bolts 35. Extending from the head ofthe nut 34, there is a Vcylindrical portion or sleeve 36, provided with a threaded bore corresponding to the thread of the screw 26 and capable of engagement with the latter. Secured to the nut 34, there is a packing 31 having a lip 38 in engagement with the internal wall of the tube I 4 for affording a iiuid tight joint Mounted in screw tight engagement on the sleeve 36, there is a retaining nut 39 capable of engagement with a retainer 46 for clamping the packing 31 against the feed screw nut 34. `The relative rotation of the packing with the nut 34 and retainer 4B is prevented by pins 4I which are transversely mounted through these parts. Intermediate its ends, the

retainingnut 33, is provide with'a transversally prerssion spring 48 havingone end thereof resting against the front side wall of the slot 42, while the other end is engageable with an outer flange 49 terminating the busing 45. Intermediate the end of the sleeve36 and the inner flange 46 of the bushing 45, there is a packing 50.

The screw 26 is formed of two distinct portions, the portion adjacent the piston 20, which will hereafter be designated as the screw 26 is formed with a left hand thread, WhileV the other end portion of the screw, hereafter `designated as the screw 5I, is formed with a right hand thread. Projecting from the rear end of the cylinder I6 into the feed tube I4 there is a tongue 52, formed with a threaded bore into which the'screw 5I is `rotatably mounted. To allow the passage of the tongue 52, the upper wall of the feed tube I4 is provided with a slot 53, extending between the backhead I8 to the nut 34. Y

Attached to the rear ofthe tongue 52 by a bolt l54 at a point adjacent the upper inner wall of the feed tube I4, there is the end of a strap 55, preferably made of flexible material such as leather or the like. The other end of the strap 55 is affixed toa spring actuated roller 56,- rotatably mounted into the rear end of the feed tube I4. The strap can be wound on the roller 56 and kept under tension by means of the torsion spring 51.

Rotatably mounted within the backhead I8, there Vis a throttle valve 58 having attached thereto a handle-59. The throttle valve is formed with a central bore 60 into which motive uid may be admitted from its source of supply. Leading from-thebore SIL-there are two radially disposed ports 6I and 62. A recess 63 is also formed on the external wall of the throttle valve, this recess is in constant communication with a vent hole 64, provided in the backhead I8. Leading from the throttle valve 58 into the rear end of the frontr portion of the feed tube I4, there is a small tube 65, capable of communication with the throttle 5 valve port 6I for admitting motive fluid into the rear end of the cylinder, and leading from the throttle valve 58 into the front end of the front portion of the feed tube I4, there is another tube 65 capable of communication with the throttle 10 valve passage 62 for admitting motive iluid into the front end of the feed tube.

In the operation of the mechanism, assuming the parts positioned as illustrated in Fig. l and the throttle valve positioned as illustrated in Fig. 9, 15 pressure fluid will be admitted on the back of the piston 20 through'the tube 65 to move the piston forwardly. Any pressure fluid remaining in the front endof the feed tube, Will be free to exhaust f to atmosphere through the tube 66, valve passage 2O 52, recess 53 and vent hole 64. Pressure fluid admitted into the rear end of the feed tube will be prevented to escape between the screw 26 and nut 34 by the action of the packing 56. The compression spring 48V acting on the ange 43 of the 25 bushing 45, causes the inner flange 46 thereof to effect a constant pressure on the packing 56. This constant taking up of the packing 50 by means of the spring 48 Will be suicient, under normal pressure, to afford an efficient fluid tight joint. How- 30 ever when pressure iiuid is admitted back of the piston 23, a pressure will be exerted on the forward face of the bushing 45, thus cooperating with the spring pressure to move the bushing toward the nut 34 and consequently produce a greater com- 35 pression of the packing 58. The tightness of the joint is thereforel proportional to the tension of the spring together-with the pressure resulting from the action of the pressure fluid on the forward end of the bushing 45. back of the piston 2i) will cause the forward movement of the latter together with the longitudinal movement of the screws 26 and 5 I. The last screw -being in engagement with the cylinder I0, its longitudinal movement will naturally be trans- 45 mitted to the cylinder of the rock drill for feeding it toward the work. The screw 26 being pulled through the stationary nut 34 will effect the rotation of the screws 25 and 5I in one direction. The threads of the screw 5I being opposite to the 50 threads of the screw 26, the rotation of the former within the corresponding threaded tongue 52 of the cylinder I8 will cause the longitudinal movement of the cylinder in the same direction as the piston 28. It can be seen that if the two screws 55 are formed with an equal pitch, the movement or displacement of the rock drill will be twice as fast as the displacement of the piston 26. The rock drill is displaced by a longitudinal force resulting from the longitudinal movement of the piston 20 60 or screw 5I and by a second force resulting from the rotationof the screw 5I within the tongue 52.

` When the machine is fed forwardly, the strap 55 affixed to the rear face of the tongue 52, will move forwardly with the machine against the tension 65 of the spring 51. This strap being wider than the width of the slot 53, will close the slot behind the machine and consequently prevent the admission of dust or foreign matter inside the feed tube or upon the screwV 5I. 70

. vWhen it is desired to retract the rock drill from the work, the throttle valve may be positioned as illustrated in Fig. 8 to admit pressure iiuid in front of the piston 20. Any pressure fluid remaining into the rear end of the feed tube, will The pressure fluid admitted 40 y be 'free to exhaustto atmosphere throughthe tube 65, valve port 6|, recess 63 and vent hole 64. l

Pressure fluid acting on the piston will actuate the same rearwardly, thus causing the rearward motion of the machine in a manner similar to the one explained previously in regard to the forward movementof the machine. During the rearward movement of the machine, the strap 55, by the action of the torsion spring 5'|, will also move rearwardly to allow the passage of the tongue 52 into the slot 53'.

It will be observed that whenthe machine is fed forwardly or toward the work, the actuating area of the piston 20 is restricted to the annular area extending from the screw 24 to the periphery of the piston. On the other' hand, when `the machine is fed rearwardly or awayfrom the work, the actuating area of the piston is unrestricted. The feeding power being directly proportional to the actuating area of the piston, it will be obvious that the feeding power producing the retraction of the machine from.A the work is greater than the feeding power impelling the machine forwardly, permitting thereby the withdrawal of the drill steel l from the drilled hole under the most adverse conditions.

During the reciprocation of the hammer piston within the rock drill, the latter is subjected to longitudinal vibrations or jars imparted thereto by the hammer piston upon the reversal of its strokes therein, thus subjecting the rock drill to undesirable alternative forward and backward motions causing the rotation of the screw 26 and disks 28 and 29 in alternative direction, due to the interengagement of the screw 5| with the threaded tongue 52 depending from the rock drill I6. When the rock drill is fed away from the work, the `action of the pressure fluid on the front face of the piston 20, will drive the screw 26 through the stationary nut 34, thus causing the rotation of the former, and of the disks 28 and 29, in a directionillustrated by the arrows in Fig. 12. Simultaneously, the jars imparted to the rock drill in a direction away from the work, will assist the screw to rotate in the last mentioned direction, due to the interengagement of the screw 5| with the threaded tongue 52. When the rock drill is subjected to the undesirable alternative forward motion resulting from the jars imparted thereto, the threaded tongue 52 engaging the screw 5| will cause the rotation of `the latter, and consequently of the screw 26 and disks 28 and 29, in a direction adverse tothat resulting from the feeding motion. However this undesirable forward motion of the drill is prevented due to the operation of the ratchet mechanism located within the piston 20. When the pressure fluid is acting on the front face of the piston 2i! to feed the machine away from the work, pressure iiuid will flow past the teeth 3| into the passage 32 to act on one end of the plunger 33 for shifting and maintaining the same in engagement with the teeth 30 of the disk 28. In this instance, the rotation of the disk 28 and screws 26 and 5| in a direction adverse to that resulting from the feeding motion, is prevented due to the engagement of the plunger 33 with the straight wall of the teeth 39 of the disk 28. Since the rotation of the screws 26 and 5| in that adverse direction is prevented, it is obvious that the undesirable forward vmotion or rebound of the rock drill is also prevented due to the interengagement of the threaded tongue 52 with the screw 5|. During the rotation of the screws and disks in a direction indicated by the arrows in Fig. 12, that is in pressure fluid on the piston 20 for feeding the rock drill away from the work, the inclined wall of the teeth 30 engaging the correspondingly shaped end ofthe plunger 33, will force the latter away from the disk 28 against the pressure fluid the direction resulting from the action of the acting Von the other end ofthe plunger, thus wardly, motive fluid will pass by the teeth 3|) into the passages 32 for moving the plunger 33 in engagement with the teeth 3|. In this instance, the screw 26 and disks 28 and 29 are rotated `in the direction indicated by the arrows in Fig. 11.

`The rotation of the screw 26 causing the feeding of the rock drill toward the work is now permitted while its rotation in the opposite direction is prevented as previously explained. The rebounds imparted to the rock drill in a direction adverse to its feeding motion, are automatically checked by the engagement of the uid actuated plunger 33 with the teeth of the disks 28 or 29.

Although the foregoing description is necessarily of a detailed character, in order to completely set forth the invention, it is to be understood that the specific terminology is not intended to be restrictive or confining and it is to be further understood that various rearrangements of parts and modification of structural detail may be resorted to without departing from the scope or spirit of the invention as herein claimed.`

I claim:

1. The combination with a drilling motor, of feeding means therefor comprising a feed tube having a fluid actuated reciprocable member therein, a tongue connecting said member to Said motor for transmitting the reciprocatory motion of the former to the latter, an opening in said tube through which said tongue passes, a iiexible member connected to said motor and movable therewith for closing said opening subsequent to the passage of said tongue therein, and means for winding said flexible member within said tube for opening said slot during the return movement of said motor.

2.`The combination with a drilling motor, of feeding means therefor comprising a feed tube having a fluid actuated reciprocable member therein,` a member connecting said motor to said reciprocable member for transmitting the reciprocatory motion of the latter to the former, a slot in said tube through which said connecting member passes, said slot being gradually uncovered by said motor during the displacement of the lattery in one direction, a closing' member having one end thereof attached to said motor and movable thereby for closing said slot when said motor' uncovers the latter, the other end of saidclosing member being constantly connected to said tube at a point exterior to the ends of said slot.

3. The combination with a drilling motor, of feeding means therefor comprising a feed tube having a fluid actuated reciprocable member therein, a member connecting said motor to said reciprocable member for transmitting the reciprocatory motion of the latter to the former, a slot in said tube through which said connecting member passes, a flexible member attached to said motor and movable therewith in one direc-` tion forclosing said slot, and means for returning said flexible member to its original position for opening said slot during the movement of vsaid motor in the other direction.

iportions, a fluid actuated reciprocable memberV 4. The combination with a rock drill feeding mechanism comprising a feed tube constituting a support for the rock drill, guide-ways on the upper face of said feed tube, of a rock drill slidable on the guide-ways, a stationary element Within said feed tube dividing the latter into two into one of said portions, passages for admitting motive iiuid into said last portion for actuating said member, means within said stationary element engageable with means on said reciprocable ,member responsive to the reciprocation of the latter for causing its rotation, said reciprocable member extending into the other of said portions'for engagement with said rock drill, means forV transforming the rotary and reciprocatory Ymotion of said member into a feeding motion and transmitting said feeding motion to said rock drill by the engagement of the latter with said member, and further means subjected to the action of the motive fluid for affording a fluid tight joint between said stationary element and the inner wall of said feed tube.

5. The combination with a drilling motor, of feeding means therefor including a reciprocable and rotatable feed screw associated with a stationary nut, means for eifecting the reciprocation of said screw to effect its rotary motion by its association with said nut, means for transforming said rotary motion to a feeding motion and transmitting said feeding motion to said motor, where- Y:by the rotation of said screw in one direction effects the forward feeding of said motor while the rotation of said screw in the other direction ef- `fects the rearward feeding of said motor, the rearward feeding power transmitted to said motor being normally greater than the forward feeding power transmitted thereto.

6. 'I'he combination with a-drilling motor, of feeding means therefor, comprising a feed tube constituting a support upon which said drilling motor may slide, said feed tube being closed at both ends, a shaft movably mounted within said tube, a stationary bearingV for said shaft disposed intermediate the ends of said tube, a piston reciprocably mounted within said tube se- 1cured on the front end of said shaft against relative longitudinal movement therewith, a member depending from said drilling motor affording a reciprocable rear end bearing for said shaft, passages for admitting pressure fluid into .said feed tube to actuate said piston and shaft,

ing a fluid actuated member slidable therein connected to said motor for imparting feeding motion to the latter toward or away from the work, and fluid actuated means carried by said mem- ,ber for preventing the recoil of said motor resulting from said jars irrespective of the direction of the travel of said motor.

8. vThe combination with a drilling motor comprising a reciprocatory hammer piston in the motor imparting jars thereto, of a feeding mechanism for said motor comprisinga feed tube, a member reciprocably and rotatably mounted into said feed tube associatedy with a stationary element, means for effecting the reciprocatory motion of said member to effect its rotary motion by its association with said stationary member, means for transforming said reciprocatory and rotary motion into a feeding motionl and transmitting said last motion to .said motor, and further means carried by said member for preventing the recoils resulting from the jars imparted to said motor, said last means being automatically shifted into recoils preventing position at the beginning of each stroke of said member within said tube.

9. The combination with a drilling motor, of feeding means therefor comprising a feed tube having a piston longitudinally movable therein, means for transmitting the longitudinal movement of said piston to said motor, passages for admitting motive fluid into said feed tube to actuate said piston, and fluid actuated means carried by said piston for preventing the longitudinal movement of the latter against the motive fluid admitted into said feed tube.

l0. The combination with a drilling motor, of feeding means therefor comprising a feed tube having a fluid actuated rotatable member therein, means for transforming the rotary motion of said member into a feeding motion and transmitting said last motion to said motor, passages for alternatively admitting motive uid into the ends of said feed tube to actuate said member, the rotation of said member in one direction being responsive to the pressure of motive fluid admitted into one end of said feed tube and its rotation in the other direction being responsive to the pressure of motive fluid admitted in the other end of said feed tube, and means responsive to the action of the pressure uid effecting the rotation of said member for preventing the rotation of the latter in a direction adverse to the direction of rotation responsive to the pressure of motive Huid acting on said member.

1.1. The combination with a drilling motor, of feeding means therefor comprising a support upon which said motor may slide, a fluid actuated mechanism reciprocably and rotatably mounted into said support, means for transforming the reciprocatory and rotary 4motion of said mechanism into a feeding motion and transmitting said last motion to said motor, means for admitting motive fluid to said mechanism for actuating the latter in one direction, and further means permitting a step by step rotation of said mechanism in the Idirection responsive to the action of the motive iiuid admitted thereto and preventing its rotation in the opposite direction said last means being automatically shifted into the proper operative position when pressure fluid is admitted to said mechanism for actuating the latter in the other direction.

12.*The combination with a rock drill, of feeding means therefor comprising a uid actuated motor, means for transforming the motion of said motor into a feeding motion and transmitting said last motion to said rock drill, means for admitting pressure fluid to said motor for actuating the latter into feeding motion, and further means for simultaneously preventing the actuation of said motor in a direction adverse to that of said feeding motion, said last mentioned means being automatically shifted into operative position irrespective of the sense of direction of said feeding motion,

13. The combination with a drilling motor, of feeding meansV therefor comprising a feed tube having a member reciprocably and rotatably mounted therein, means subjected to the action of motive uid for effecting the reciprocatory motion of said member, other means associated with the latter for effecting its rotary motion responsive to its reciprocatory motion, further means for transforming the reciprocatory and rotary motion of said member into a feeding motion and transmitting said last motion to said motor, and a ratchet mechanism automatically connected to said member for permitting a step by step rotation of the latter in one direction and preventing its rotation in the other direction irrespective of the sense of the feeding motion of said motor.

14. The combination with a drilling motor, of a frame for said motor on which the latter is free to slide, of a feeding mechanism within said frame, a feed transmitting member connecting said feeding mechanism to said motor, a slot in said frame through which said member passes, the distance between one end of said frame and one end of said slot being considerably less than the overall length of said slot, and means capable of entirely covering said slot subsequent to the passage of said member therein, said means remaining between the ends of said frame irrespective of the position of said motor on the latter.

15. The combination of a frame, of a member reciprocably mounted thereon, of a slot within said frame through which a portion of said member is free to pass, of means for covering said slot subsequent to the passage of the portion of `said member therein, said means comprising a flexible member attached to said reciprocable member and movable therewith in one direction for closing said slot, and further means for returning said flexible member to its original position for opening said slot during the movement of said reciprocable member in the other` direction, I

16. The combination with a drilling motor, of a feeding mechanism therefor including a feed tube, a motive uid actuated member reciprocable therein, a feed transmitting connection between said member and said drilling motor, and means associated with said feeding mechanism including a denticulated element and a pawl element, one of said elements being automatically movable in operative engagement with the other for preventing motions of said member other than the motion'imparted thereto by the action of the motive fluid thereon and irrespective of its sense of direction. j

17. The combination with a drilling motor, of a feeding mechanism therefor comprising a feed tube, a power actuated member longitudinally movable within said tube for imparting feeding motion to said motor, a feeding motion transmitting connection between said member and said motor, a longitudinal movement preventing device associated with said mechanism comprising a duality of elements one movable relatively to the other, means on each of said elements capable of interengagement for preventing the longitudinal movement of said member in a direction adversed to that of its feeding motion, and means for automatically causing the interengagement of said elements irrespective of the sense of direction of the feeding motion of said member.

18. The combination with a drilling motor, of 5 mechanism responsive to the reciprocatory inow tion of said member for imparting rotation thereto, means for transforming the reciprocatory and rotary motion of said member into a feeding motion transmitted to said drilling motor, passages for admitting pressure iiuid into said feed tube 15 for actuating said piston, a ratchet mechanism associated with said member comprising a duality of toothed elements connected to said member for rotation therewith, and non-rotatable means automatically movable into engagement 20 with one of said toothed elements for preventing the rotary motion of said member in a direction adverse to the direction of rotation responsive to the action of the pressure fluid on said piston.

19. The combination with a drilling motor 25 comprising a reciprocatory hammer piston in the motor imparting jars thereto in two directions, means associated with said motor for imparting feeding motion thereto independently of said jars, and a jar resisting mechanism including a duality 30 of elements one movable relatively to the other due to the jars imparted to said motor, teeth formed on one of said elements, and means for automatically causing the engagement of the other of said elements with the teeth of the for- V35 mer for checking the jars imparted to said motor in a direction adverse to that of said feeding motion.

20. The combination with a drilling motor comprising a reciprocatory hammer piston in the 40 motor imparting jars thereto in two directions, power actuated means associated with said motor cooperating with the jars transmitted to the latter in either direction for imparting feeding motion thereto, and jars resisting means associated 45 with said motor comprising a duality of interengageable elements, automatically movable in operative engagement for checking the jars imparted to said motor in a direction adverse to that of said feeding motion.

21. The combination with a drilling motor comprising a reciprocatory hammer piston in the motor imparting jars thereto in two directions, power actuated means associated with said motor for imparting feeding motion thereto, and jars re- 55 sisting means associated with said motor oomprising a toothed member and an element in engagement with the teeth thereof, said teeth and element being formed and disposed in a manner permitting the feeding motion of the motor irre- 60 spective of said engagement but checking the movement of the motor in a direction adversed to that of its feeding motion.

JOHN C. CURTIS. 65

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