US2563711A

US2563711A - Impact tool

Info

Publication number: US2563711A
Application number: US10361A
Authority: US
Inventors: Clifford E Fitch
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-02-24
Filing date: 1948-02-24
Publication date: 1951-08-07
Anticipated expiration: 1968-08-07

Description

c. E. FITCH "IMPACT TOOL Aug. 7, 1951 5 Sheets-Sheef Filed Feb. 24, 1948 C. E. FITCH Aug. 7, 1951 IMPACT TOOL 5 Sheets-Sheet 2 Filed Feb. 24, 1948 C. E. FITCH IMPACT TOOL Aug. 7, A1951 5 Sheets-Sheet 5 Filed Feb. 24, 1948 i i e L 7 o fw Aug. 7, 1951 c. E. FITCH 2,563,711

` IMPACTl TOOL v Filed Feb. 24, 1948 5 sheets-sheet 4 5 Sheets-Sheet 5 c. E. FITCH IMPACT TOOL Aug. 7, 1951 Filed Feb. 24, 1948 Patented Aug. 7, 1951 UNITED STATES PATENT OFFICE 2,563,711 intiem n eliffor Fitch.; crete, nl. Attltation 'February' 24, itis; senti i''t'i 14 Claims;

``This ir'il'lerltio'n relates to an impact tool 'and ymore particularly to an iinpact Aclutch by ieans of which a succession 'of rotational hainrner blows natte iinpnrtentnicgii an anvil to a driven -rneniberstcn atn a nut, bolt, screw, oi trie like which offers resistance 'to rotation.

The primary objectv of the invention is to rapid;- ight'en nuts,` bolts, 'screws or the like in a for werk; wilt-nett danger of stripping' 'the ads or darnaging the heads thereof. v Anotherohject is to prolong the useful life of the partsand provide, as nearly as possible, for the 'full Contact of the faces of the parts during the period that the hannir blow is being struck. v still furtlierlobjct is to acelerate the 'speed 'of rotation of "the hammer during its period di 'disengagement with the anvil so that the energy stored in the hannier during this periodinay per; `forr useful Work during the' impact period. The aljve and other objects may be attained Meiplefiig this invention which embodies anion@ its features a rotary anvil, a hammer ad"- l'acent said anvil and rotatable withY relation thereto,- al 'iinpact elein'ent carried by said hami- 'an'a sutiable 'relative thereto into and out of the path of rotatin of the anvil, means posi# tively to attente said impatt `tlernenjt into the path of rotation of the anvil and means positively t retract said el'e'neit .froin such path after the harniner blow has been struck on Y the anvil to perlifiit the passage of the impact element relative to tnt ntil. i a

Gther features include a shaft mounted to -r'otate about its longitudinal anis, an anvil -fiired t6 the shaft intrmdiatewits ends andA extending radially" therefroirna harnrnervmounted for rati'n `1 the Shaft adjacent the anvil, an ilfnJat pin advancing 'and rtinnetnni plate mounted to rotate and slide longitudinally on the shaft adi- Ljacent the si'd of the hanirner remote from the anvil; an iriipact pin 4carried bv the plate and AI!"1`v"'alele through the hammer into and out of `the A-path lof inveihent of the anvil, means between the haiiiner disc and the plate to retract the impact pinrfrom anvil-engagingpositn when the torque on the sha-lt exceeds a predetermined value. ineans to prjt the in'pact pin into the path of nioverrient of che anvil alter it has passed the anvil, and rans tb transnii't vr'tar'y "rnti'on "tothe plate. Y Y rne fore'goin: constitute stint of tneprineipai 'objects and adtantages of th present inven ion, others of which will become 1apparefit renewing 'desciptidn and the drawings. in which et. 1 is a intentie Senna new, ninth an 4impact tool embodying the features 'of this in- 2 iention, snowiiig trie snine attached to n suitable nviri.

Fie. 2 is atiew similar to Fig. 1 in a plane per:

j jiilarto the plane f Fig. 1i; n Fig; 3 is Aa View similar to Fig. 1 showing all the parts in 'sectin iore clearly to illustrate the dei tails of construction; A l

4 is Aa transverse Setioiial View tia-lien substantially along theline lll-dof Fig. l

Fig. 5 is `a transverse sectional view taken "sul stantially'alfine the line 5- 5 of Fig. 1;

Fign is a transverse sectional View taken sub'- Sthtially along th lll G--'G Of Fig. 1;

Fig.` 'v7 is a transverse' sectional View taken sub1 lstanti'ally along the line '1;1 of Fig. 1; Fi-g. `8 is a perspective View of the impact pin i advancing and 'retreating plate;

rFig. 9 isa perspective View of the plate illus- 'trated in Fig. 8 showing the underside thereof; Fig. 1D is a perspective View of the anvil 'and t'oreue transmitting shaft;

Fig. 11 is a top plan view of a resilient coupling unit for the drive rotor;

` Fig. l2 is 'a sectional View through the coupling element illustrated in Fig. 111;

Fig. 13 is 'a longitudinal sectional view through an inpact tool of a mo'died form and ernlclodyingf` the features `of this invention;

Fig. 14 is a View similar to 13;

Fiqgf. 15 is a perspective View partially in section ofthe hydraulic piston and cam plate em#- ployed in the 'embodiment illustrated in Fig. 13;

Fig. 16 is a perspective View of the top of the pistn illustrated in Fig. 15;

VFig. 17 is a longitudinal sectional view through a further modified form of hydraulic impact tool;

Fig. T8 is a transverse sectional View taken substantially along the line lil-I8 of Fig. 17;

Fig. 19 is a longitudinal sectional view through 'a furti-her mod'ied form of the invention;

Fig.` 20 is a longitudinal sectional View of the structure illustrated in Fig. 19 taken in a plane which lies perpendicular to that of Fig. 19t;

Fig. 2l vahorizorital sectional View taken substantially along the line 21421 of Fig. 19t;

Fig. 22 -is af transverse sectional view taken sub- Staritially 'loi'l'g the line 2'2L-22 of Fig. 19;

Fi, 23 is perspective View 0f the hamlr emplyed in the modified form of device illustrated Fie. 24 is n view similar to Fig. 23 f the under- -siii et tn'ennnimer; and

Fig. 25fis afragnefltary perspective vier.T of the i employed in the modification illustrated in 19 and 20;

Rfering to the drawings in detail, a drive motor, designated generally I5, has formed in the projecting end of its drive shaft I6 an annular row of grooves forming longitudinal splines |1, and the end I8 of the casing of the drive motor is formed with an annular row of radially spaced openings I9 for the reception of attaching studs 26 by means of which this improved impact tool or clutch, designated generally 2|, is coupled t0 the casing of the drive motor I5.

The impact tool or clutch designated generally 2| comprises a tubular body 22 having formed at one end an outwardly extending annular flange 23 which is pierced atspaced intervals to receive the attaching or coupling studs 26 by which the impact tool is'connected to the motor 'casing of the drive motor |5. The end of the casing 22 opposite that carrying the iiange 23 is provided with a tubular boss 24 into which is fitted a Suitable bushing 25 of anti-friction metal, and extending through the bushing 25 isan end portion 26 of the torque shaft, designated generally 21, of this improved impact tool. The end of the torque shaft 21 adjacent the portion 26 is squared, as at 28, so as to effect a driving coupling between a wrench socket, screw-driver bit or other tool that is to be driven.

A 'The torque shaft 21 is best illustrated in Fig. and is provided adjacent the inner lend of the shaft portion 26 with an anvil 29 carrying diametrically opposed, radially extending arms 36, each of which is provided in opposite faces adjacent their outer endswith arcuate recesses 3| and 32', into which the impact pins, to be more fully hereinafter described, are received. A cylindrical .extension 33 projects axially from the face of the anvil 29 opposite the cylindrical portion 26, and this cylindrical portion 33 is provided at its free end with a squared extension 34 in to the end Vof which projects an internally screwf threaded socket for the reception of a cap screw 35. Seated on the squared extension 34 beneath the cap screw 35 is a collar 36, the outer surface 'of which is concentric with the shaft 21 to form a bearing for the drive coupling to be more ,fully hereinafter described. Formed on the collar 36 andextending toward the anvil 29 is a cam 31, the cam faces 38 of which are of true circular curvature and concentric with axes which lie perpendicular to the longitudinal axis of the yshaft 21.

Mounted forY rotation about the cylindrical portion 33 of the shaft 21 adjacent the anvil 29 is a hammer 39 which is provided at radially spacedpoints 180 apart with openings 40, the axes of which extend parallel to the longitudinal axis of 'the shaft. 21. Extending from the face of the hammer 39 remote from that disposed toward the anvil 29, at diametrically opposed points adjacent the Yshaft 21, are cams 4| opposite faces of each of which slope toward the hammer 39, as at 42 (Fig. 2).*A

MountedV for rotation on the shaft portion 33 of the shaft 21'between the hammer 39 and the collar 36 is an impact pin advancing and re- -tracting plate, designated generally 43, which comprises a `circular body 44 having an axial bore 45 Atherein ,and provided with slots or openings 46 between thebore 45jand the periphery, which openings are spaced 180 apart and extend parallel With the bore 45., Formed in the plate 44 between the openings 46 are arcuate slots 741, the curvatureof which lies concentric about the axis of the bore 45. Opening outwardly through the periphery of the plate and communicating with the arcuate slots 41 are radial 4 slots 48 which are located in diametrically opposed relation and from the openings 46. Projecting from one face of the plate 44 in the direction of the collar 36 is a cam lug 49, and formed on the opposite face in concentric relation with the opening 45 is a collar 56 having diametrically opposed, V-shaped notches 5| which form cam faces for cooperation with the cam faces 42 of the cams 4| on the hammer 39 in forcing the irnpact pin advancing and retracting plate 43 away from the hammer 39.

Impact pins 52 are mounted to slide in the openings 46 in the hammer 39, and each of these pins is provided near one end with an annular groove 53 forming a reduced neck which is adapted to be received in the slots 41 in the plate 44. It will thus be seen that as the plate 44 moves away from the hammer 39 under the influence of the cams 4| and the cam faces on the collar`56,.the pins `52 will be retractedinto the openings 46 in the hammer 39 and out of the pathA of movement of the anvil 29.

Mounted for rotation about the collar 36 carried by the squared end34 of the shaft 21 is a coupling member, designated generally 54. This coupling member comprises a body 55 opening into one end of which is a splined socket 56 for the reception of the splined end of the shaft I6, while the opposite end of the body is provided with a socket for the reception of the collar 36, as will be readily understood upon reference to the drawings. Extending radially at diametrically opposite points from thebody 55 are arms 51 carrying drive pins 58 which extend parallel to the longitudinal axis of the shaft 21 and enter the openings 46 in the plate 43. It will thus be seen that when rotary motion is. imparted to the shaft I6, the plate 43 will be driven inthe direction in which the drive shaft I6 rotates. `In some instances, it may be found desirable to employ a drive unit, designated generally 59 in Fig. l2, in place of the drive unit 54 in order to -absorb a certain amount of the shock of the impact tool and prevent it from being transmitted to the drive shaft I6 of the motor I5.`

The drive unit 53 above referred to comprises a cylindrical body 69 formed at one end with and internal socket 6I for the reception of the collar 36 above referred to, and at its opposite end with a socket 62 into which a ring-shaped cushion 63, of rubber or a suitable synthetic resin or plastic substance, is fitted. AnV internally splined bushing 64 is fitted into the ring-shaped cushion 63 for receiving the splined end of the -drive shaft I5 of the drive motor I5. The body 66 is formed with diametrically opposed, outwardly extending arms 65 carrying drive pins 66 which correspond, in all respects, to the drive `pins 58 previously described, so that Whenrthe unit 59 is employed, theV plate 43 will be driven by the drive pins, but shocks transmitted to the impact mechanism will be absorbed by the cushion 63 and breakage of the drive shaft I6 will be avoided. .Y Y

In the modification of the invention illustrated in Fig. 13,V a housing designated generally 61 is provided at one end with a coupling flange v68 for connection to the frame of the drive motor, and at its opposite end with a tubular boss 69 having a bearing bushing 16 extending therethrough in which an anvil designated generally 1| is mounted to rotate. The anvil 1| comprises an axial shaft12 provided intermediate its ends with radiating arms 13 which project laterally therefrom in diametrically opposite l relation. The l ower end of the anvil shaft is provided with a squared portion 14, while its opposite end like the anvil shaft 21, has fixed thereto against rotation a cam sleeve 15 carrying auc'am 16 which lies against the surface of the shaft 12 and projects toward the squared end 14Hther'eof. 1

AMounted for rotationon the shaft 12 adja- Acent the arms 'I3 is a relatively massive hammer `designated generally 11 which comprises a cylindrical body: .1Sl having formed therein an axial opening 19 through which the shaft 1.2 extends'. Surrounding the axial opening and opening through the upperv end of the hammer in an annular channel Y8|l`wliic`h communicates at its inner end with longitudinal bores 9| in whichimpact pins 82 arev slidable. These impact pins are 4adapted to be projected through the ends of thejopenings 8| which open through the end of the hammer adjacent the arms 13 in order to engage the arms 13 at predetermined intervals during the operation of the device. Projecting upwardlyfrom the upper edge of the wall ofthe hammer lying between the axial bore 19 and the annular recess 80 are oppositely disposed cams 83 (Fig. 14), the purposeof which will be more fully hereinafter explained.

Mounted for rotation on the shaft 12 between the hammer 11 and the cam collar 15 is aV cam disc 84 carrying diametrically opposed cams 85 which liel along the shaft 12 and cooperate' with the cams 83'in causing the disc 84 to movev away from the hammer 11. Carried by the disc 84 and extending toward the hammer 11 is an annular collar 85 provided at its end remote from the disc with an annular head 86 which is `adapted to reciprocate in the annular recess 80; This head is provided with suitablechannels in'which annular `packing rings 81 are seated to form a fluid tight junction with the wallsofAv the' recess 80. ltv will thus be seen that when the' channel 80 contains a non-compressible fluid. suchl as oil, and the disc 841s moved toward or away from the hammer, the impact pins 82 will be moved into or out of the path of movement of the arms 13. Extending from the face of the disc 84 remote from the hammer 11, and lying closely adjacent the shaft 12 is a cam 88 which isadaptedto cooperate with the cam to move` theL plate- 84 toward the hammer at a certain interval' of movement of the parts. Formed in the disc 84, and extending along axes parallelwith the axis of the shaft 12 at diametrically spaced points are openings 89 for the reception of driveA` pins `90 carried by a driveunit 9| which ismountedto rotate about the cam collar and `corresponds to the drive unit 54 previously described.

In the further modification of the device illustrated in Fig. 1'1 an anvil designated generally 92 is mounted in a housing 93 corresponding in all respects tothe housing 61, and carried by the anvil 92 at diametrically opposed points are arms 94' which are provided with angular extensions 95 which lie substantially parallel to the longitudinal axis of the anvil 92. The anvil 92 is also provided with a shaft 96 which cor responds in all respects to the shaft 12 previously described and rotatably mounted on theshaft 96 adjacent the arms 94 is a cup-shaped hammer 91. Likethe hammer 11, the hammer 91 is provided with an annular Yrecess 98 in which a plunger head 99 is reciprocable under the influence of a cam plate |00`which corresponds in all respects to the cam plateili` previously deassegni cooperate with the cams on the cam plate |00 in moving the cam plate away from the hammer. Formed in the hammer 91 at diametrically opposite points are transverse openings |0| in which impact' pins |02 are mounted to slide. impact pins are adapted to be projected radially into the path of movement of the angular ex" tensions at the ends of the arms 94 of the anvil 92, and when the annular recess 99 is filled with a non-compres's'ible fluid, such as oil, it is obvious that as the cam plate |00 moves toward and away from the hammer 91, the impact pins |02` will be projected and retracted respectively.

The movements of the cam plate |00 are controlled in identically the same manner as are the movements of the cam plate 84 and the cam plate 43 previously described.

It will be understood, of course, that the cam plate |00 is driven in a manner similar to the driving of the cam plate 84 previously described through the' medium of a coupling |03 and the drive pins |04 carried thereby.

In' the modification illustrated in Figs. 19 and 2S, an anvil designated generally |95 comprises aA shaft ide mounted to rotate in a suitable bearing bushing |531' mounted in a casing me which corresponds in all respect to the casings previously described. The shaft |95 is provided intermedate its ends with outwardly extending diametrioally opposed arms ISS, and like the shafts previously referred to, is provided with a squared end le to which a tool such as a wrench or screw .river is detachably coupled. The end of the shaft opposite that carrying the squared end |0 has fixed thereto a cam collar i carrying acam H2 which lies adjacent the shaft and projectsl the camlcollar H3' and the cam collar is ahaminer H9 provided with diametrically opposite arcuate openings ||1 which lie concentric about the axis of the shaft. Projecting from the face of the hammer H6 adjacent the anvil |99.

and lying along the shaft I0@ are diametrically,

opposed cams llt which are adapted to cooperate with the cams ||4 in moving the hammer away from the anvil. Formed in the hammer beveenv opposite ends of the arcuate openings ||1 and extending along axes which lie parallel with' -the shaft |86 are openings H9 in which impact pins |20 are fixed as by set screws l2 The face of the hammer ||6 opposite that carrying the cams I3 is provided with a cam lug |22 (Fig. 23) which is adapted to cooperate with the cam face ||2 of the cam collar in moving the hammer I6 toward the anvil, and the impact pins |29 into the path of movement of the arms |09.

Mounted for rotation about the cam collar is a drive unit |23 which is adapted to be coupled to the drive shaft of a suitable drive motor and is provided with outwardly extending diametrically opposed arms |24 carrying` drive pins |25 which extend along axes which lie parallel` with` TheseV theaxis of the shaft H16, through the arcuate openings Hi and into the openings V|| in the arms ||4 of the cam collar ||3. It w'ill thus be seen that the cam collar H3 will be driven in unison with the drive unit |23, and by reason of the arcuate openings these pins clear the hammer H5 so that any driving effect on the hammer is obtained through the contact of the cam faces of the 'cams ||4 and IIB.

Operation In use, a suitable tool, such as a wrench socket, is fitted onto the squared end 28 of the shaft '2 and the drive member 5B is coupled to the drive shaft IG of the motor |5. Upon setting the motor into operation, it will be obvious that the drive pins 58 will rotate the disc or plate d3, thus irnparting rotary motion to the hammer 39 through the impact pins 52. So long as no resistance is encountered, the impact pins will remain against the arms 39 of the anvil in the recesses 3| and the nut or screw that is being worked upon will be driven with a continuous rotary motion. As soon as the nut or screw becomes tight enough to offer resistance to rotation, the cam faces 42 working against the inclined faces 5| of the hammer Se and the plate 43, respectively, will cause the plate to move away from the hammer 39, thus withdrawing the pins 52 into the ham-V mer so as to permit the hammer to rotate under the influence of the drive motor without imparting movement to the shaft 2l. It is to be understood, of course, that the magnitude of movement of the plate 43 is such that the pins 52 are wholly retracted into the openings 4U and yet the cam faces 4| and 5| never completely disengage. The limitation of motion of the plate 43 away from the hammer 39 is effected by the engagement of the cam lug 49 with the collar 35. In order to impart a hammer blow to the anvil 29, it becomes necessary to force the pins through the openings 4i! and advance them into the path of the arms 3i! of the anvil 29. This is accomplished by the engagement of the cam lug 48 with the cam 3l which vis so positioned with relation to the anvil 29 that the impact pins 52 are forced downwardly between the arms 30. By thus advancing the rapidly moving impact pins 52 into the path of movement of the arms 30 of the anvil 29, it will be obvious that when the pins encounter the arms, the latter will be struck a sharp blow backed by the momentum of the rotating hammer 39 which will effectively drive the work home. Obviously, the operation is repeated during the impact cycle of the tool. When it is desired to remove a tightened nut, it is obvious that the shaft IG is reversed, in which event the pins 52, during the impact cycle of the apparatus, will engage in the recesses 32 in the arms 3G.

In the operation of the modified structure illustrated in Figs. 13 through 18 inclusive, it will be understood that the annular recesses 3e and 88 contain fluid which as the cam plates 84 or lili) are advanced toward their respective anvls, the impact pins 82 or |32, as the case may be, will be projected into the path of movement of their respective anvils due to the displacement of the fluid by the advance of the head 85 or the head 99 into its respective annular recess. The functions of the impact pins are identically the same as those previously described, and as the rotation is continued, the

cams

83 and 85, will move the cam plate away from its respective hammer, so as to retract the impact pins and allow them to pass their respective arms.

In using the structureillustrated in Figs. 19. through 25 inclusive, the impact pins |20 are carried by the hammer H6, which riding loirl gitudinally of the device on the drive pins |25 will move the impact pins intoand out of Vthe path of movement of the arms |09 ofthe anvil |05. 1

Throughout al1 forms of the .invention the cams between the cam plate or cam collar and the hammer will serve to retract the impact pins from the path of movement of the arms of the anvil, while the cams on the face of'the hammer or cam plate remote from the arms of the anvil, cooperating with the cams carried by the anvil will serve to advance the impact pins into the path of movement of the arms of the anvils.

When the advancing and retracting plate 43 (Fig. 2) is in its raised position the hammer 39 is free to rotate with the lplate 43. As the plate i3 isY forced downwardly bythe cam 31 the upper cam 42 feeds downwardly onto the lower cam 4| requiring the lower cam 42 with the hammer 39 to rotate at a greater velocity than the rotating speed of the shaft l5, and hence the motor. Thus the hammer 39 is given an additional spin over and above that afforded by the motor just before the pins 52 (Fig. 3) strike the anvil 29 resulting in greater momentum in the hammer and a greater impact force.

While in theforegoing there has been shown and described the preferred embodiments of this invention, it is to be Yunderstood that minor changes in the details of construction, combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as claimed.

I claim: Y

1. In an impact mechanism, a rotatable anvil, a rotatable hammer, means for locking the two together for simultaneous rotation comprising a slidable element rotatable with said hammer and movable into the path of said anvil, a motordriven element carrying said slidable element, cam means between said motor-driven element v and said hammer element for rotating said hammer element and for retracting said slidable element inrelation to said hammer, and cam means between the motor driven element and the anvil positively returning said slidable lelement into the path of movement of said anvil.

2.l An impact mechanism comprising a rotary anvil, a hammer rotatable about the aXis of the anvil, slidable impact pins carried by said hammer and movable into and out of the path of rotation of said anvil, a motor-driven element aligned axially with said hammer and anvil, an impact pin advancing and retracting element between said hammer and said motor-driven element, drive pins carried by the motor-driven element, and having driving relation with the impact pin advancing and retracting element, said impact pin advancing and retracting element having cam coaction with said hammer element for rotating said hammer and for retracting said impact pins into said hammer, and having further cam coaction with said anvil for advancing said impact pins into the path of movement of said anvil.

3. An impact tool which includes a shaft mounted to rotate about its longitudinalaxis, an anvil fixed to the shaft intermediate its ends and extending radially therefrom, a hammer mounted for rotation on the shaft adjacent the anvil,V an impact pin advancing and retracting plate mounted to rotate and slide longitudinally on the' shaft adjacent the side of the hammer remote from the anvil, an impact pin carried by `the plate and movable through the hammerV into and .out lof the path of movement of the anvil, means'between the hammer' and the plate to retract the impact pin from anvil-engaging position after the pin has struck a blow on the anvil, means to project the impact pin into the path of movement of the anvil after it has passed the anvil and means to transmit rotary motion to the plate.

4. An impact mechanism comprising an anvil, a hammer, means for locking the two together for simultaneous movement comprising slidable hammer pins rotatable with said hammer and movable into and out of the path of said anvil, a motor driven element axially aligned with said hammer and anvil, a floating element located between said hammer and said motor-driven `element, said motor-driven element having a pair of drive pins therefor, said floating element being slidable on said drive pins and carrying said hammer pins, said floating element having cam coaction with said hammer element for retracting said hammer pins in relation to said hammer, and having further cam coaction with said anvil for returning said hammer pins into the path of movement of said anvil.

5. An impact mechanism comprising a rotary anvil, a hammer rotatable in relation thereto, means for driving said anvil from said hammer and for releasing it therefrom comprising an element carried by said hammer, means independent of centrifugal force for moving said element into the path of rotation of said anvil, said means comprising a cam actuated element and a hydraulic connection between said cam actuated element and said rst element, said hydraulic means being responsive to said cam actuated element for effecting removal of said first element from such path after delivery of an impact from said hammer to said anvil.

6. An impact mechanism comprising a rotary anvil, a rotatable hammer, means for driving said anvil from said hammer comprising pist0n and cylinder mechanism, the cylinder thereof having an opening in a wall thereof, a plunger slidable in said opening into and out of engagement with said anvil, and cam means operatively connected to the piston for moving said piston in one direction for extending said plunger to engage said anvil to deliver an impact, and for moving it in the opposite direction for effecting removal of said plunger from engagement with said anvil upon predetermined resistance to torque by said anvil. Y

7. An impact mechanism comprising a rotary anvil having a pair of radially extending arms adjacent one end, a hammer rotatable about the anvil adjacent the arms and movable axially of the anvil, at least one impact pin carried by the hammer and movable with the hammer into and out of the path of movement of the arms, a cam plate rotatable about the anvil between the arms and the hammer, cams on the cam plate and on the hammer adapted to move the hammer away from the arms and retract the impact pins out of the path of movement of the arms, means to impart rotary motion to the hammer and to the cam plate and means between the hammer and the end of the anvil opposite the arms to move the hammer and project the impact pins into the path of movement of the arms.

8. An impact mechanism comprising a rotatable anvil, ar'otatable hammer adjacent the anvil, an impact element carried by said hammer and movable into and out of the rotative path of the anvil, a motor drivenelement, cam means between the motor driven element and the hammer for rotating the hammer and for retracting the impact element out of the rotative path of the anvil, and cam means on the anvil for advancing the impact element into the rotative path of the anvil.

9. An impact mechanism comprising a rotatable anvil having a pair of striking faces, a rotatable hammer adjacent the anvil, a pair of impact elements carried by said hammer and movable into and out of the rotative path of the anvil striking faces, a motor driven element, cam means between the motor driven element and the hammer for rotating the hammer and for retracting the impact elements out of the rotative path of the anvil striking faces, and cam means on the anvil for advancing the impact elements into the rotative path of the anvil striking faces.

10. An impact mechanism comprising a rotatable anvil, a rotatable hammer adjacent the anvil, an impact element carried for rotation by said hammer and slidable with respect to the hammer into and out of the rotative path of the anvil, a motor driven element connected to said impact element for moving said impact element into and out of the rotative path of the anvil, cam means between the motor driven element and the hammer for rotating the hammer and for moving the motor driven element with respect to the hammer for retracting the impact element out of the rotative path of the anvil, and cam means between the motor driven element and the anvil for moving the motor driven element for advancing the impact element into the rotative path of the anvil.

1l. An impact mechanism comprismg a rotatable anvil, a rotatable hammer adjacent the anvil, an impact element carried for rotation by said hammer and slidable with respect to the hammer into and out of the rotative path of the anvil, a motor driven element, a hydraulic connection between the impact element and the motor driven element for moving said impact element into and out of the rotative path of the anvil, cam means between the motor driven element and the hammer for rotating the hammer and for moving the motor driven element with respect to the hammer for retracting the impact element out of the rotative path of the anvil, and cam means between the motor driven element and the anvil for moving the motor driven element for advancing the impact element into the rotative path of the anvil.

l2. An impact mechanism comprising a rotatable anvil, a rotatable hammer adjacent the anvil, an impact element carrie-d for rotation by said hammer and slidable with respect to the hammer into and out of the rotative path of the anvil, a motor driven element mechanically connected to the impact element for moving the impact element into and out of the rotative path of the anvil, cam means between the motor driven element and the hammer for rotating the hammer and for moving the motor driven element with respect to the hammer for retracting the impact element out of the rotative path of the anvil, and cam means between the motor driven element and the anvil for moving the motor driven element for advancing the impact element into the rotative path of the anvil.

13. An impact mechanism comprising a rotatable anvil, a rotatable hammer adjacent the anvil,. an impact element rigidly carried by the hammer and movable therewith, a motor driven element, cam means between the motor driven element and the hammer for rotating the harnmer and for shifting the hammer to retract the impact element out of the rotative path of the anvil, and cam means between the anvil and the hammer for shifting the hammer to advance the impact element into the rotative path of the anvil.

14. An impact mechanism comprising a shaft mounted to rotate about its longitudinal axis, an anvil fixed to the shaft intermediate its ends and extending radially therefrom, a hammer mounted for rotation on the shaft adjacent the anvil; an impact element carried by said ham- Amer and movable into and out of the rotative `of the rotative pathof the anvil, and cam means on the shaft for advancing the impact element into the rotative path of the anvil. i

. CLIFFORD E. FITCH.

REFERENCES CITED The following references are of record 1n the file of this patent:V

UNITED STATES PATENTS `Number Name Date Y 2,061,843 Muner NOV. 24, 1936 2,339,530 Van Sittert et al. Jan. 18, 1944 2,339,531 Van Sittert et al. Jan. 18, 1944: