US2719294A

US2719294A - Staple gun tacker

Info

Publication number: US2719294A
Application number: US337328A
Authority: US
Inventors: Herbert W Marano
Original assignee: Wilson Jones Co
Current assignee: Wilson Jones Co
Priority date: 1953-02-17
Filing date: 1953-02-17
Publication date: 1955-10-04
Anticipated expiration: 1972-10-04

Description

Oct. 4, 1955 H, w. MARANO STAPLE GUN TACKER 5 Sheets-Sheet l Filed Feb. 17, 1953 INVENTOR HERBERT M Mp4/v0 A BY ATTO RNEY Oct. 4, 1955 77 will y H. W. MARANO STAPLE GUN TACKER 3 Sheets-Sheet 2 'TJEEL INVENTOR 45H55? TM A44/,wvo

MS2-L ATTO RN EY Oct. 4, 1955 H. W. MARANO STAPLE GUN TACKER 3 Sheets-Sheet 3 Filed Feb. 17, 1955 INVENTOR United States Patent l() ice STAPLE GUN TACKER Herbert W. Marano, Summit, N. J., assignor to Wilson- Jonesi Company, Chicago, Ill., a corporation of Massachusetts Application February 17, 1953, SerialNo. 337,328

8 Claims. (CI. 1-49.)

The present invention relates generally to` an improved fastener driving device, and itrelates in particular to an improved' portable, hand-operated device which will d'rive a single fastener such as a staple,. or the like, from a pre-formed cohered strip of such fasteners into wood', cardboard, plastic or other materials. The word staple as herein usedwill indicate fasteners of that general type.

Hand-operated stapling machines of the general type with which the present invention is concerned' are Widely used, and consist generally of a spring-loaded plunger or ram having a depending staple-driving blade movable along a predetermined path, a magazine for holding a strip of staples with the foremost staple in the path of the driving blade, and a hand-operated mechanism for retracting and releasing the spring-loaded plunger whereby to eect the staple driving stroke.

The conventional heavy duty stapling gun of the aforementioned type is a highly inetlicient machine, inflexible, expensive to fabricate, subject to excessive wear, and diicult tov operate and service. The inefficiency of the conventional gun tacker has been found tol be directly attributable to the eccentricity existing between the line of force of the energy storing plunger driving spring and the line of force exerted by the plunger retracting and spring loading element. The torque imparted to the plunger asv a result of this eccentricity accountsfor a major part of the energy expended in loading the driving spring andl is dissipated in frictional losses, which in turrr` greatly contribute to the excessive wear of the stapling device and demands an expenditure of much more energy on` the part of the operator than should be necessary in employing the stapling gun.

Another disadvantage encountered in the, conventional gun tacker is its limitation to use with only one size staple', or its limitation within an extremely smallV range of sizes. The spring loading and actuating mechanism is'such that the energy stored in the spring duringteach driving stroke is normally xed and unalterable. The gun tacker requires a major conversion in order to-readjust or change the amount of energy stored in the drivingi springV during the stapling cycle. The drawbacks of this construction are readily apparent in view of the fact that it is often desirable to switch from one size staple' to another and to apply the staples to different types materials. Moreover, the optimum drive applied to the staples'varieswith the staple size and the material to which they are applied, and: conventional devices make no provision for varying readily' the driving force. Another undesirable characteristic of the conventional gun tacker isv the tendency of the staples in the magazine to jam. The guide which accommodates the strip of staples has upper confronting walls which are, of necessity, spaced a distance at least as large as the greatest diameter of the wire forming the, staples. Since the diameter of this wire varies, it often happens that the staple strip pusher causes. staples of-V lesser diameter wire to mount` each other and jamfthe guideway. Increasing the strength of the pusher spring 2,719,294 "Patented Oct. 4, 1955 p therconventionalV gun tacker is the fabrication of the staple exit guide. This guide, being subject to the maximum wear and abrasion, must be heat treatedY for reasonable service. However, since this guide is generally formed integral with the lower channel member of the gun tacker, its proper hardening without disturbing the channel member is a major problem and dilicult of proper attainment without a large percentage of rejects. There are many other drawbacks and disadvantages encountered in the conventional staple gun' tacker' in spiteof the fact that this device is universally and widely employed, and much elfort has been expended in its development.

It is, therefore, a principal object of the present invention to provide an improved fastener driving device.

Another object of the present invention is to provide an improved portable hand-operated staple gun tacker.

Still another object of the present invention is to provide an improved staple gun tacker requiring a minimum of manual effort in its operation. I A further object of the'present invention is to provide an improved staple gun tacker having a7 staple driving mechanism which is highly efficient in the transmission of the energy expended by the operator in relation to the driving of the staple.

Still a further object of the present invention is to provide an improved staple gun tacker which is capable of handling staples of a large range of sizes.

Another object of the present invention is to provide an improved staple gun tacker in which the force imparted to the staples may be easily and simply manually adjusted.

Still another object of the present invention is to provide an improved magazine for the strip of cohered staples in which the jamming, of the staples is eliminated.

A further object of the present inventionV is to provide an improved staple gunV tacker havingl a staple loading mechanism. which permits the rapid and` simple insertion of a strip of staples.

St-ill a further object of the present invention is to provide` an improved. staple gun tacker having a novel staple exitv channel: which greatly facilitates the fabrication thereof.

The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawings, wherein p Figure l is an exploded' view illustrating in perspective the various components entering into the assembly of an improved staple gun tackerin accordance with the present invention; i

Figure 2 is a side transverse sectional` View of the staple gun tacker in uncocked condition;

Figure 3 is a side transverse sectional view of thev forward portion ofthe staple gun. tacker in fully cocked condition` immediately precedingA the release of tbestaple driving plunger;

VFigure 4 is a side detail view,y partly in section and partially broken away, of the. staple magazine andy opening, and loading mechanism illustrated; in open position;

Figure 5 is aI side elevational view of the. improved staple gun tacker in normal uncocked operative position.;

Figure 6 is a side elevational view of the tacker showing the handle in the magazine opening position;

Figure 7` is a sectional View taken along line 7`-7' of Figure 2 showing the driving forceV adjusting element in the high energy position;

Figure 8 is a sectional view taken along line 8*'--81 of Figure 3v showing the driving forcel adjusting el'eme'nt-i in the: low energy. position;v

Figure 9 is a sectional view taken along line 9-9 of Figure 2;

Figure 10 is a sectional view taken along line 10--10 of Figure 2; and

Figure ll is a sectional View taken along of Figure 2.

A staple gun tacker embodying features of the present invention includes a main body or frame member having an actuating handle hinged to its upper front edge, a staple magazine housing hinged to its lower rear edge and a channel shaped member secured to its front and defining a housing and guide for the staple driving plunger and spring. Slidably supported in the front channel is a plunger or ram having a horizontal shoulder and a depending driving blade which rides along the inner front face of the channel. An energy storing compression spring is confined between the'upper face of the ram shoulder and a vertically spaced shelf and urges the plunger to its lowermost or advanced position. The plunger cocking and releasing mechanism comprises a horizontally hinged lifting lever whose free end engages the bottom face of the ram shoulder at a point colinear with the line of force of the ram driving spring, the lever having a longitudinal slot formed therein. A fulcrum is pivotally mounted in the upper part of the frame member and supports at its front end a depending cocking member terminating in a pointed end topped at its forward edge by a recessed portion deiining a hook above which the edge inclines rearwardly defining a cam surface. The cocking member registers with the lifting lever slot, the hook normally engaging the front edge of said slot. The rear end of the fulcrum is link-connected to the actuating handle.

A vertically stepped triggering element is slidably supline 1-1-11 ported by the frame in confronting relation to the front edge of the cocking member so that different portions of the trigger may be brought into alignment with the cocking element whereby to trigger the cocking mechanism at preselected points in its stroke and hence impart varying driving forces to the plunger as will be described in detail. A channel shaped staple guide is disposed on the base of the magazine housing and engages a slidable staple pusher which is urged forward by spring means. An elongated staple retaining element is hinged at its rear to the lower portion of the frame at point intermediate the ends of the frame and terminates at its front end in depending rearwardly facing hooks which slide along the base of the magazine housing and may engage tabs projecting laterally from the staple pusher. Spring means urge the staple retainer downwardly whereby to confine the staples stored on the staple guide. The forward side walls of the magazine housing are provided with elevated portions having forwardly directed recesses formed therein which, when the housing is in closed position, are engaged by a latch member consisting of an apertured plate slidably supported in the frame and having laterally projecting locking tabs extending through corresponding slots in the frame side walls. The latch member is spring-urged to the locked position, and the aperture therein registers with the pointed end of the cocking member which, when depressed by the raising of the actuating handle, travels between the front edge of the aperture and a rearwardly disposed stop, urging the latch member to its forward open position and releasing the magazine housing. The magazine housing swings downwardly as does the staple retaining member, the hooked ends of which engage the staple pusher carrying it to its retracted position and facilitating the loading of a strip of staples. Upon closing of the magazine housing, the staples are urged forward so that the foremost staple is brought against the driving blade and into its path upon the cocking of the plunger. An aperture is formed in the front bottom wall of the magazine housing and defines a staple exit opening. A hardened staple exit channel is positioned above this opening and receives the brunt of the driving cycle.

Reference is now made to the drawings which illustrate a preferred embodiment of the present invention wherein the

numerals

12, 12 generally designate a pair of laterally spaced, symmetrical side walls having abutting upper and rear inwardly directed flanges 13, and opposing oval shaped openings 14, in which is positioned a nger grip 16 formed of rubber or other suitable material. The side walls 12, which define a supporting frame, have upper and lower projecting

portions

17 and 18 respectively, which extend into and between side walls 19 of a front channel member 20 abutting said side walls and are secured thereto by means of the suitable screw and spacer assemblies illustrated, which pass through and are located between corresponding aligned holes formed in the channel side walls 19, and the

frame member projections

17 and 18. Hinged to the lower rear corner of the frame member is a bottom magazine housing channel 21, having a pair of rear upwardly directed tabs 22, which embrace the lower rear corners of the side walls 12, and have holes formed therein aligned with corresponding holes formed in the side walls 12, said holes being secured by a suitable post fastener 23. The forward end of channel 21 has a front wall 24, the upper edge of which abuts the front lower edge of the front channel member 20 when the magazine channel is in closed position, and also has a pair of upwardly directed front tabs 26, whose forward edges tit into the confronting lower corner edges of channel 20 when the magazine channel 21 is closed. Also formed in the matching portions of the channel walls 19 and tabs 26, are

recesses

27 and 28 respectively which dene a continuous slot. A rectangular opening 29 is formed in the front of the bottom wall of the magazine channel 21. An actuating handle 3i), having depending laterally spaced side walls 32, is hinged tothe frame 12 by means of a post screw assembly 33 passing through holes formed in the front portion of the handle side walls 32 and corresponding openings formed in the frame projections 17 and front channel side walls 19, the front portion of the handle side walls embracing the upper portion of the front channel side walls 19.

A plunger 36 is vertically slidably disposed in the front channel 20, and includes a ram 37 and a depending driving blade 38. The ram 37 is formed of a sheet of metal and has a front wall 39, side walls or gussets 40, a bottom wall 41 formed of the inwardly directed tab of the front wall 39 and the inwardly directed tabs 40a of the gussets 40, and a rear wall formed of a further extension of the front wall tab. The tabs forming the ram bottom wall 41 are secured by a centrally located rivet 42. Projecting forwardly from the upper portion of the ram front wall 39 are a pair of horizontally spaced detents 43 which bear against the upper edge of the depending driving blade 38 secured to the ram front wall 39 by suitable rivets 38a. It should be noted that the plunger is guided by a pair of inwardly directed ribs 44 formed in the front wall of channel 20 and the forward vertical edges 46 of the frame wall 12.

Located in the upper end of the channel 20 is a shelf 47 having lateral extensions 48 registering with corresponding slots 49 formed in the upper projecting

portions

17, 17 of frame walls 12. Depending centrally from the shelf 47 is a spring-engaging stud having a stepped cylindrical head 50. A pair of concentric helical compression drive springs 50a, 5011 are entrapped between the underside of shelf 47 and the upper face of the ram bottom wall 41, urging the plunger 36 to its lowermost or advanced position. The upper ends of the springs 50a, 50h engage the stud stepped head 50, the springs 50a, 50h, the head 50 and the rivet 42 being coaxially disposed. A torsion spring 51, whose arms bear against the cross wall of handle 30 and the upper face of shelf 47, is mounted on the bolt 33 and urges the handle 30 to its normal intermediate position, see Figure 2.

amazes The plunger actuating mechanism includes a lifting lever 52 of channel shaped cross-section having rearwardly extending vertical. tabs provided with aligned openings engagingv a bolt 52a whichv is supported by the frame walls 12 and, in turn, rotatably supports the lifting lever 52. The front end of the lifting lever 52 has a forwardly projecting arm S having a convex upper face which engages substantially the center of the head of the rivet 42. The horizontal wall of theV lever 52 has a longitudinal slot 54'` formed therein. Positioned directly below the lifting lever arm 53is a cushion assembly consisting of a pair of superimposedv plates 56, the lateral endsv of which engage and extendI intocorrespo'nding horizontal slots 57 formed in the front channel side walls 19 flush with the outer margins thereof, andy a rubber pad 58 mounted atop the plates 56, the assembly being secured by a rivet 59; It should be noted that the lifting lever, cushion assembly, driving, blade and plunger, and the driving spring mechanism are so. dimensioned and disposed that the lower edge of the blade 38v is at the level of the lower edge; of the magazine channel front wall 24 when the mechanism is in its normal at restr position.

In order to effect the staple driving stroke, there is provided a pair of horizontally spaced parallel fulcrum arms 60 which are rotatably supported; between the upper parts of the frame walls 12 by means of` a screw post 61 passing through alignedholes` formed between the ends of arms 60 and in the frame walls 12. The rear ends of the arms 60 are connected through a suitable pivot and spaced and by links 63 to a screw post 64 supported by the side walls of the actuating handle 30. Hinged to and depending from the forward ends of the arms 60 is a cocking member 66, which` is positioned intermediate thearms` 60 by meansof. suitable spacers engaging a pin 67 which registers with holes. formed in the upper part of cooking member 66 and the forward part of the arms 60. A torsion spring 68, mounted about the post 61, has its armsV confinedV between the lower edges of arms 60 and the rear edge of cooking member 66 to swing the lower end of the member 66 forwardly. The cocking member 66 terminates at its lowerv free end in a point defined by a front inclined; cam edge 69 and a back inclined cam edge 70. Above the front cam edge 69 and separated therefrom by a recessed portion 71 deining a hook, is an upwardly, rearwardly inclined cam edge 72. i

In normal inoperative position, the lower end of the cooking member 66 passes through the slot 54' in the lifting lever 52, the hook 71 engaging the front edge of the slot 54. AnV adjustable triggering element 73 is prou cesses 78 formed.' in the frameface forward edges 46.

A spring member 79, supported on thev front channel walls 1-9 by a suitable post 79a, resiliently retains the member 73 in the recesses 78. While the lower edge of triggering element 73 is illustrated as having but two steps, this edge may have a larger number of steps or be inclined, as will be readily understood from the foregoing.

Disposed in and secured'v to the. bottom wall of the magazine channel 21 is a channel-shaped staple guide 80, whose upwardly directed side walls 81 have parallel longitudinali slots. 82 formed' therein. The forward ends of the guide side Walls 81 have depending legs 83 which overhang the rear wall of the opening 29 and extend to the lower edge thereof. An apertured upright tab 84 is positioned at the front end of the staple guide bottom wall, the other end of which is provided with a rearwardly extendingV portion terminating in an upright tab 86 having a horizontal slot formed therein. A pusher member 88, having depending side walls provided with longitudinal slots 89,` slidably straddles the guide 80, the slots 89 being aligned with the. guide slots 82. The

pusher member 88`v is alsoV provided with horizontal cross walls, thev rear one of which has a dependingv apertured tab 90. A cross bar 91, Vhaving a longitudinal tubular guideopening'92', is positioned in the guide 80 and pusher 88, projecting laterally through andl beyond the aligned slots 82'. and, 89. A guide rod 94 passes through the openings in

tabs

84, 86 andv 90; and the pusher tubular opening 92, and has its flattened rear end upset at tab 86- to complete the assembly. Mounted on, and coaxial with, the guide rod 94 is a helical compression spring 96 conlinedv between the confronting faces: of guide tab 86 and pusher tab 90 to. urge the pusher 88' to its; advanced position.

A staple-confining andf pusher-retracting member 100 of inverted" channel shape is provided, and has an upper wall 101 and depending side walls 102 adapted to straddlel the pusher member 88 and nest in theimagazine channel 21. The confining member 100 is hinged to. and between the lower portions of frame walls 12 by means of a screw post 100a passing through aligned openings formedy in upward extensions 103 to the rear portions of side walls 102 and corresponding openings formed' in the framewalls 12. The front ends of side walls 102 are provided with forwardly projecting shanks 104 terminating in depending rearwardly open hooks 106 which ride along the inner longitudinal bottom edges of the channel 21 and are adapted to engage the portions of the pusher arm 91 projecting beyond the pusher slots 89. Furthermore', a rearwardly flanged upright tab 107 is positioned towards the back edge of the confining member upper wall 1'01.

A latch or locking member 110- of horizontal platelike configuration is slidably supported at the level of the recess 27 formed in the front channel side Walls 1,9 byl means of a plurality of laterally projecting

tabs

112, 111, 112 slidably engaging a similar number of slots 1113 of longer extent formed in the frame sidewalls12. The centermost tabs 111 project through their associated slots 113 beyond the outer faces of side walls 12, whereas the front and rear tabs 112 only extend to the plane of these faces. Formed in the latch member 110, inverti'.- cal alignment with the cooking member 66, is a longitudinal rectangular aperture 114, the forwardV edge of which is provided with an upwardly rearwardly inclined tab 116. A stop member 117 is disposed directly above the locking member 110 and is supported in fixed posi:- tion by means of a pair of laterally extending earsA 1181 engaging corresponding openings 118a in the frame side walls 12. The forward edge of the stop member 1.17 is providedv with a forwardly inclined depending tab 117:1I projecting into the locking member aperture` 1:1'4- at' a point intermediate the ends thereof in lockedposition. A pair of helical tension springs 11'9 engage at one end openings 120 formed in the rear portion of locking member 110 and at the other end` a pin 121 supportedA by holes formed in the upper corners` of retaining member side wall extensions 103. The springs 119 are normally upwardly deflected from their straight line path by the retaining member upright 1'07 and serve the multiple purpose of urging the locking member 117 to itsclose position and the conning member 100 downwardly and counterclockwise, as seen in Figure 4.

A channel shaped staple exit member 122 is formed of a hardened' steel and is disposed at the forward end of the magazine channel 21, registering with the exit aperture 29. The forward' wall 123 of the exit member abuts the inner face of the magazine channel front Wall 24 and is provided at its upper edge with a forwardly projecting lug 126 which abuts the upper edge of channel front Wall 24 and registers with a recess 127 formed in the lower edge of the front wall of front channel member 20. The rear portion of the side walls of the staple exit member is directed laterally arcuately outwardly and forcibly engagesA the confronting rear edge of magazine channel aperture 29. Projecting vertically from the. side walls of the exit channel are tabs 128 which extend above the corresponding edges of the magazine channel side walls. The staple exit member 122 is hardened prior to assembly and, due to its configuration, distortion will be outward which is favorable since a preloaded condition is set up when it is assembled into forward end of magazine channel 21. The curved end faces of the member 122 abutting the rear edge of aperture 29 secures it therein, correcting an inward distortion that might manifest itself after the heat treating process. In the eX- ceptional case, where the distortion of the side walls of member 122 is laterally outward, then the side walls of the magazine channel 21 will forcibly engage the exit member side walls suitably, preloading the same. Moreover, the abutting faces of the

walls

24 and 123 are secured by a tack weld. It should be noted that the forward vertical edges of the staple guide 81 are spaced from the inner face of the wall 123 of eXit member 122 a distance sufficient to permit easy passage of the driving blade 38.

Considering now the operation of the improved stapling gun; in order to load the gun, the actuating handle 30 is raised in the direction of the arrow, Figure 6, causing the fulcrum arm 60 to rotate counterclockwise. The point of the depending cocking member 66 is thereby forced downwardly into the aperture 114 of the locking member 110. The locking member lower forward cam edge 65* engages the tab 116 and the rear cam edge 70 engages the stop tab 117 urging the locking member 110 forward and the locking tabs 111 from the close position in the recesses 28 to their open position out of these recesses and into the adjacent recesses 27. The springs 119, acting through the retaining member 100, swing the magazine channel 21 to its fully open position as seen in Figure 4, the lower edges of hooks 106 riding along the bottom wall of the magazine channel 21. As the magazine channel 21 is swung outwardly, the hooks 106 engage the laterally projecting portions of the pusher bar 91 extending through openings 89 in the pusher member 8S withdrawing the staple pusher member 88 to its retracted position and compressing the feed spring 96. A strip of staples may then be placed on the staple guide 8?, and the magazine channel thereafter swung to its closed position, the locking tabs 111 engaging the locking recesses 28. The hooked ends 106 of the retaining member 100 are thus returned to the forward end of the magazine channel 21, allowing the pusher member 88 to slide forward, engaging the rear staple of the strip and, by virtue of the spring 96, urging the strip of staples forward and the foremost staple against the inner face of the driving blade 38. The springs 119, acting on the upright 107, urge the confining member 100 downwardly, which maintains a pressure on the top side or bridge of the staples when loaded on the staple guide and thereby greatly inhibits the jamming of the staples.

In performing the stapling operation, the actuating handle 30 is pressed downwardly toward the frame member 12, thereby rotating the fulcrum arms 60 clockwise, as seen in Figure 3, and raising the cocking member 66. The hooked portion 71 of the cocking member 66 passing through lifting lever slot 54, engages the lower face of the lifting lever S2 and rotates the lifting lever 52 clockwise about pin 52a. The forward edge 53 of the lifting lever 52, acting on the rivet head 42, raises the plunger 37 and, as the lower edge of the driving blade 38 is elevated above the level of the strip of staples, the foremost staple is advanced into the vertical path of the driving blade 38 under the urging of spring 96. In the raising of the plunger 36, the energy storing springs 51 are compressed and loaded. As the fulcrum arm 60 is rotated clockwise and the cocking member 66 thereby raised, the forward upper cam edge 72 of the cocking member comes into contact with and engages the

lower edge

74 or 76, as the case may be, of the triggering element 73. The triggering element lower edge, acting on the cam edge 72 (see Figure 3), swings the cocking lever 66 rearwardly as it is raised until the forward edge of the hook portion thereof is retracted beyond the forward edge of the slot 54 in the lifting lever 52, releasing the lifting lever 52 and the plunger 36. The loaded spring is thus permitted to expand and send the plunger forcibly downwardly, the blade 38 engaging the bridge of the staple in its path, shearing it from the cohered strip and driving it home. The shock of the descending plunger and liftv ing lever is cushioned by the rubber pad 58.

After the completion of the staple driving stroke, the handle 30 is released and the entire mechanism returned to the starting position, as shown in Figure 2, being urged thereto by the

springs

51 and 68.

It should be pointed out that when the triggering element is in the position shown in Figure 7, the higher stepped edge 74 engages the cocking member cam surface 72 and releases the plunger when it has been raised to a greater height than when the triggering element is in the position shown in Figure 8 and the lower edge 76 engages the cam surface 72. Since, in the former case, more compression is imparted to the springs 51 and hence more energy, a heavier driving stroke is effected when the triggering element is in the position illustrated in Figure 7, and a lighter stroke is effected when the triggering element is in the position shown in Figure 8. It is also important to observe that since the lifting lever 52 engages the ram 37 at a point and in a direction colinear with the axis of the compression springs 51, there is a minimum of torque and hence an increase in energy efficiency and a decrease in the frictional wear due to the wasted energy dissipated as a result of this torque.

While there has been described and illustrated a preferred embodiment of the present invention, it is apparent that numerous alterations and omissions may be made without departing from the spirit thereof.

I claim:

1. A staple driving device comprising a body member, a plunger slidably supported in said body member and movable between advanced and retracted positions, said plunger having a depending staple driving blade, spring means urging said plunger to its advanced position, a staple magazine adapted to feed a staple into the path of said driving blade, an actuating handle hinged to said body member, a first lever rotatably supported in said body member at a point between the ends of said first lever, said actuating handle being linked to one end of said first lever, a second lever hinged to said body member and having a free end engaging said plunger, a movable hook shaped cocking member rotatably depending from the other end of said first lever and releasably engaging said second lever, and a triggering element adapted to engage said cocking member and urge it out of engagement with said lifting lever upon said cocking element being raised to a predetermined position whereby to release said lifting lever.

2. A staple driving device as claimed in claim l, wherein said cocking element has a lower hook portion and a rearwardly inclined upper cam edge disposed above said hoook portion, and said triggering element has a triggering edge adapted to bear against said cam edge as said cocking element is raised to urge said cocking element rearwardly and to release said lifting lever upon said cocking member being raised to a predetermined point.

3. A staple driving device as claimed in claim 2, wherein said triggering element is movably supported and the level of said triggering edge varies along its length whereby to effect the release of said lifting lever at various preselected points.

4. A staple driving device as claimed in claim 1, wherein a resilient cushion is mounted in said body member below the free end of said lifting lever.

5. A staple driving device comprising a body member, a plunger slidably supported in said body member and movable between vertically spaced advanced and retracted positions, said plunger being provided with a substantially horizontal wall having an upwardly directed face and a downwardly directed face, a helical compression spring bearing against said upwardly directed face to urge said plunger to its advanced position, a driving blade secured to and depending from said plunger and movable therewith along a path between advanced and retracted positions, a staple magazine supported on said body member and adapted to feed staples into the path of said driving blade and actuating means engaging said downwardly directed face at a point substantially in alignment with the longitudinal axis of said helical compression spring whereby to permit the raising of said plunger and the loading of said spring with a minimum of torque.

6. A staple driving device in accordance with claim 5, wherein said driving blade is secured to and depends from the forward portion of said plunger.

7. A staple driving device in accordance with claim 5, wherein said actuating means includes a pivoted lifting lever having a free end engaging said downwardly directed face at the point substantially in alignment with the longitudinal axis of said helical compression spring.

8. A staple driving device in accordance with claim 7, including an actuating handle hinged to said body member, means releasably linking said actuating handle to said lifting lever and means for opening the linkage between said actuating handle and said lifting lever upon said lever being elevated to a predetermined level.

References Cited in the le of this patent UNITED STATES PATENTS 577,887 Stanton Mar. 2, 1897 1,028,778 Powers June 4, 1912 1,067,541 Palmgren July 15, 1913 1,457,446 Michener June 5, 1923 1,757,812 Polzer May 6, 1930 2,065,659 Cullen Dec. 29, 1936 2,109,203 Spencer Feb. 22, 1938 2,285,512 Harley June 9, 1942 2,433,155 Peterson Dec. 23, 1947 2,438,713 Maynard Mar. 30, 1948 2,493,640 Peterson Jan. 3, 1950 2,551,898 Nyberg May 8, 1951 2,559,131 Rundblad June 3, 1952 2,617,096 Boroughs Nov. 11, 1952 2,617,097 Spencer Nov. 11, 1952 2,624,046 Nyberg Jan. 6, 1953 FOREIGN PATENTS 51,501 Sweden Apr. 19, 1922