US3038161A - Pneumatic fastener driving and like tool - Google Patents

Description

June 12, 1962 J. c. LANG PNEUMATIC FASTENER DRIVING AND LIKE TOOL 4 Sheets-Sheet 1 Original Filed Nov. 29, 1954 ATTORNEYS.

BY M, M,M

INVENTOR. W 4 A June 12, 1962 J. c. LANG 3,038,161

PNEUMATIC FASTENER DRIVING AND LIKE TOOL Original Filed Nov. 29, 1954 4 Sheets-Sheet 2 AT TOR N EYS June 12, 1962 J. c. LANG 3,038,161

PNEUMATIC FASTENER DRIVING AND LIKE TOOL Original Filed Nov. 29, 1954 4 Sheets-Sheet 3 ATTORN EYS;

June 12, 1962 J. c. LANG 3,038,161

PNEUMATIC FASTENER DRIVING AND LIKE TOOL Original Filed Nov. 29, 1954 4 Sheets-Sheet 4 an 23 u 22. 25 xy j 2 9.6

ATTORN EYS ite 3,038,151 Patented June 12,1952

3,038,161 PNEUMATIC FASTENER DRIVING AND LIKE 'IGOL Joseph C. Lang, Pittsburgh, Pa, assignor to Bocjl Corporation, Pittsburgh, Pa, a corporation of Deiaware Griginal application Nov. 29, 1954, Ser. No. 471,656, now Patent No. 2,932,030, dated Apr. 12, 1960. Divided and this application Mar. 9, 1960, Ser. No. 17,239

3 Ciaims. ((11. 1-52) This invention is for a pneumatic tool, and more particularly for a tool having a reciprocating driver or impact device.

The invention may be used for the driving of various fasteners such as staples and tacks, and will be hereinafter described particularly in reference to the driving of fasteners such as T-tacks disclosed in my Patent No. 2,580,444, dated January 1, 1952, but this is by way of illustration and not limitation.

Tools for the driving of tacks or other small fasteners are designed to be held in the hand and used in various positions. Consequently they should be well balanced, relatively light and easy to handle. Moreover, since speed of operation over hand-driven fasteners justifies their use, such devices must be capable of fast and sure operation. Another -justification for the use of a power-operated driver in lieu of a hand-operated device is to assure of the fastener being fully driven, either into soft or hard wood, and without damaging or marring the wood finish.

Portable drivers of the class to which the present invention is particularly applicable generally employ a spring acting in opposition to pneumatic pressure to move the driver in one direction, and fluid pressure moves it in the reverse direction. For example, in my Patent No. 2,574,875, granted November 13, 1951, the driver is propelled on its working stroke by a spring, while pneumatic pressure is used to return the driver and cock or compress the spring. While this is satisfactory for many purposes, the force of the blow is limited to the strength of the spring and the rapidity of its expansion, and no increase of force can be secured with a given spring by changing the air pressure; Also the element of recoil is hard to control so that in driving a fastener into hard wood for example, the driver may bounce or spring away from the work instead of driving the fastener completely home.

In other types of drivers a spring is compressed on the driving strike of the impact element or driver, and the compressed spring serves to return the driver to starting position. This has the objection that the spring absorbs energy from the driver at the time it .is most needed, and higher pressure or larger cylinders are required. Major objections to both types are the size, weight, weight disposition, complexity of manufacture, and rebound or recoil.

Still another object is to provide in such a machine, means for feeding strip fastener blank material and cutting off lengths of the blank in the driving operation together with pneumatic means for operating the feed at the proper time, and power to operate the feed is not derived from the driver as has heretofore been customary.

These and many other objects and advantages are secured by my invention which may be more fully understood by reference to the accompanying drawings, in which:

FIG. 1 is a side elevation showing the assembled tool, part of the magazine cover being broken away to illustrate the interior of the magazine, and in this figure the dotted line position of the cover section of the housing shows how the machine may be opened;

FIG. 2 is an enlarged detail view showing the arrangement of guide fingers at the bottom of the tool for guiding the fasteners, and also showing the valve operating foot or trigger;

FIG. 3 is a transverse vertical section in the plane of line III-III of FIG. 2;

FIG. 4 is a bottom plan view of the discharge end of the fastener guide or driving nose of the machine, the trigger mechanism being in section in the plane of line IV-IV of FIG. 3; 7

FIG. 5 is a side elevation on a larger scale of the driver portion of the tool, the driving cylinder being shown in section and part of the feed mechanism being shown in section with the feed piston retracted. Also in this view the trigger is omitted for clarity of illustration;

FIG. 6 is a plan view of a fastener formed to be driven;

FIG. 7 is a side elevation of the fastener;

FIG. 8 is a front elevation of the fastener;

FIG. 8A is a plan View of a portion of a strip of fastener blanks from which the fasteners are formed;

FIG. 9 is a view similar to FIG. 5, showing the feed mechanism at the opposite limit of its travel;

FIG. 10 is a fragmentary bottom view of the feed finger mechanism only;

FIG. 11 is a transverse section in the plane of line XIXI of FIG 9;

FIG. 12 is an enlarged side elevation of the air valve operating trigger mechanism;

FIG. 13 is a transverse vertical section in a plane at right angles to FIGS. 1 and 9, showing the main cylinder, the valve cylinder, and the valve operating mechanism in the normal inactive position;

FIG. 14 is a similar view showing the position of the parts just before the piston starts its downward movement; and

FIG. 15 is a view similar to FIG. 13, showing the main piston at the bottom of its stroke.

The machine here specifically illustrated is designed to drive fasteners of the type which are frequently referred to as T-tacks, and which has a horizontal bar corresponding to the head of the T, forming the head of the tack, and which has a leg-forming element that joins to the head intermediate its ends, and at one side edge thereof. Such a tack is disclosed in my prior United States Patent No. 2,580,444, above noted, and it is formed from a connected series of blanks made in strip form as shown in FIG. 8A. In FIG. 8A the strip designated "S is slitted at regular intervals along one edge by diagonal slits S and each diagonal slit terminates in a longitudinal slit S This provides the single leg-forming element S of the blank. S designates the head-forming element of each blank, and it will be noted that each leg connects to the side of the head-forming portion through a connector portion S Each headfor ming portion follows a ratchet-like notch S cut in the opposite edge of the strip from the diagonal cuts S the notches S having one abrupt shoulder and one sloping shoulder as shown for cooperation with the feeding and indexing mechanism of the driver hereinafter described. This fastener strip which forms no part of the present invention is disclosed in my patent above referred to, and

the strip is prepared in coils which may contain several hundred or several thousand fasteners, depending upon the size of the magazine of the driver intended to receive the strip.

In the subsequent use of the strip, the end of the strip is moved under a plunger or driver which, on one stroke, shears off a previously formed blank from the end of the strip and drives it, while the plunger at the same time turns down the leg-forming element of the next-succeeding blank from the plane of the strip to the perpendicular position shown in FIGS. 6, 7 and 8. In FIGS. 6, 7 and 8 the tack itself is designated as T, and it has a head portion T corresponding to the portion of the original strip S It has a downwardly-turned leg T corresponding to the leg-forming portion S of FIG. 8A, and the diagonal slit S of FIG. 8A forms the point '1' of the tack. The bending line occurs transversely across the connecting portion S this bend being indicated at T in FIGS. 6 and 7.

'One form of driver for converting the T-tack strip into individual fasteners and driving them is disclosed in my prior United States Patent No. 2,580,444, above noted, and a feed mechanism for engaging in the notches S is also shown in said patent, and is also the subject of a copending application, Serial No. 264,294, filed December 31, 1951.

The present invention is for an improvement particularly in the application of pneumatic power to the driver, and the application of a pneumatic action to the feeder as well as to certain improvements and refinements in other portions of the driver. Also while being described primarily in connection with the driving of T-tacks, the mechanism is also applicable to drivers for other forms of fasteners, and to like impact-operated devices, but will be hereafter particularly described in connection with the driving of T-tacks.

In its general assembly, the device has the contour shown in FIG. 1, in which there is a horizontal bar portion designated generally as 2, and which constitutes the handle for the machine. At one end of the bar portion is a generally circular chamber constituting the magazine for the fastener strips, and at the opposite end of the bar 2 is the driver assembly and associated parts designated generally as 4. The driver includes a downwardly-projecting guide or nose portion hereinafter more fully described, the end of which is held flat against the work into which the tack is to be driven, and the length of this nose is sufficient to elevate the cross baf 2 just far enough away from the work so that ones fingers may pass under the cross bar when it is grasped in the hand, but the hand is still close enough to the work surface to enable the operator to readily position it on the work and keep it steady. The magazine has its center above the axis of the handle, both to keep it from interfering with the tool being brought close to the work, and also to even the balance of the tool. T he fastener strip is conducted from the magazine to the driver through the handle.

In FIG. 1 the driver has the power cylinder assembly 5 extending upwardly from the axis of the handle and a fastener guide or nose 6 that extends downwardly, as above explained. Below the cylinder assembly 5 the housing for the mechanism is divided into two parts, which are hingedly connected through hinges located at 7 so that one part, indicated generally as 8, can be opened out to the dotted line position shown in FlIG- 1 where it is 180 from the normal closed position. The purpose of having it thus open is to afford access to the magazine 3 for changing coils; access to the channel through which the strip feeds for threading the end of a new coil of blanks into the machine, and for giving access to the guideway through which the fastener is driven to facilitate the removal of a fastener should it become jammed in the machine, and the machine be unable to clear itself. As shown in FIG. 1, the staple strip S is mounted on a spool 9, which may be a throw-away spool, and which may contain several hundred, or even several thousand fastener blanks. It is preferable to use a coil which is not excessively large so that the weight of the machine does not become tiresome to the operator, and also to keep the proportions such that the tool will balance nicely when the hand is gripped around the handle portion 2. On the interior of the cover 8 (as shown in FIG. 1), there are spring friction fingers 10 in that portion that forms part of the magazine, designed to bear against the face of the spool when the cover is closed, and apply enough friction to the spool 8 to keep it from overrunning, or running too freely.

Considering first the pneumatic driver and its associated parts, the cylinder, assembly 5 has at its upper end a head 11 in which is an internally threaded nipple 22 into which the end of an air hose may be screwed. The lower end of the cylinder is closed by a block or cylinder base 12, which is fastened thereto, and within the cylinder assembly is a cylinder or cylindrical chamber 13, the lower portion of which is slightly enlarged in diameter as indicated at 14.

Within the cylinder 13 is a piston 15, this piston having an annular groove between its ends to receive an O-ring 16. Projecting from the lower end of the piston is a solid metal extension 17 passing through a bushing 18 in the cylinder base 12, and this bushing serves as a guide for the cylindrical extension 17.

Since the driving force exerted by the driver is a function of the mass times the velocity squared according to the formula E=MV it is to my advantage to make the piston and the projection 17 of solid metal in order to incorporate a relatively large mass into a relatively small space.

Attached to the lower end of the extension 17 of the piston is a driver element 19 which, for the purpose of driving T-tacks, may have the shape of the driver shown in my Patent No. 2,580,444, dated January 1, 1952. 20 designates a pin by means of which the driver is detachably secured to the extension.

Extending alongside the cylinder is a valve chamber 21 (see FIGS. 13-15). The cylinder and chamber 21 are here shown as an integral casting. The cap 11 at the upper end of the cylinder has a threaded recess 22 above mentioned, to which an air hose may be connected, and from this socket 22 there is an air passage 23 that opens into the valve chamber 21 intermediate its ends at the port designated 24. The valve chamber is open at its bottom and has a vent port 25 at its top. There is a port 26 in the upper part of the valve chamber that leads from the valve chamber into the upper end of the cylinder 13, and there is a port 27 at the bottom of the cylinder that communicates with the lower end of the valve chamber.

Extending up through the valve chamber is a valve rod 28 having a piston-like valve element 29 at its upper end, this valve element 29 always being located in the space between the air inlet port 24 and the vent 25.

Slidable on the valve stem 28 is a second valve element 30 located near the lower end of the valve cylinder, and which is confined to the region between the lowermost end of the valve cylinder and a point above the port 27. The valve stem 28 projects down through the open end of the bottom cylinder and is connected at its lower end to an ear 31 on a slide plate '32, which slide plate has slots 33 therein through which pass guide pins 34 (see FIG. 12), these guide pins allowing a limited relative movement of the plate 32 relative to the guide pins.

As best shown in FIGS. 12, 13 and 14, the guide pins 34 are mounted on a metal stamping or plate 35, which plate has a downwardly-projectin g extension 36 terminating in a bifurcated foot 37 that straddles the end of the staple guide to he hereinafter more fully described. The stamping 35 is slidably retained on the flat supporting plate 38 forming the main frame of the machine, and on which the cylinder is mounted, there being guide pins 39 on the plate 38 operating in slots 40 and 41, the slot 41 being in the extension portion 36 of the plate 35. The top of the plate 35 has an olfset extension 42 that projects upwardly, and as shown in FIG. 12 terminates just inside the lower open end of the valve cylinder 21, FIG. 13 showing the parts in the normal position. The arrangement is such that when the end of the staple guide nose 6 is pressed against the Work, the foot 37 will be pushed upwardly, and in the first portion of its travel the extension 42 will bear against the valve element 30 and lift this element above the port 27 to the position shown in FIG. 14.

As shown in FIG. 12, the slide plate 32 has a shoulder at 32a. A leaf spring 43 secured to the lower end of the valve and cylinder assembly projects over this shoulder when the parts are in normal position, and keeps the slide plate 32 from lifting. However when the presser foot 37 is moved upward relatively to the body of the machine, an inclined shoulder 44 on the slide plate 35 will hit the end of the spring 43 and cam it to the left as viewed in FIG. 12. At the time that this happens the plate 35 Will have been lifted from the position shown in FIG. 12 so that the pins 34 will be in the upper portions of the slots 33 and the slide plate 32 can move up. With the release of the detent spring 43 as described, and with the valve *30 pushed up to the position shown in FIG. 14, the air pressure in the valve cylinder 21 will almost instantaneously move the valve 29 up past the port 26, whereupon air under pressure can enter the top of the main cylinder 13 and drive the piston 15 downwardly with great force. Since the valve 30 at such time has opened the port 27 at the bottom of the cylinder to atmosphere, air which may be in the cylinder under the piston can freely escape and will not impede the downward travel of the piston. When the piston moves down, no further operation can take place until the tool is lifted away from the work, but upon the tool being lifted away from the work, compression spring 45, confined between an abutment on the lower end of the cylinder and an offset 35a on the stamping 35 (see FIGS. 13-15) will push the plate or stamping 35 down, returning it to the position shown in FIG. 13. The spring pressure required is very light because fluid pressure in the valve chamber pushing down on valve 30, hearing down on finger 42, equalizes the pressure acting upwardly on valve 29. As valve 30 moves down, air under pressure may enter the port 27 and again raise the piston to the position shown in this figure. Also as the plate 35 moves down the pins 34 will pull the slide plate 32 downwardly until the detent spring 43 catches over the shoulder 32a, and this downward movement of the plate 32 will pull the valve element 29 down against air pressure in the valve chamber to the position shown in FIG. 13 so that air from the valve chamber cannot get into the top of the cylinder 13, and at the same time the top of the cylinder will be vented through port 26 and air vent to the atmosphere. Hence the air in the upper part of the cylinder will not impede the return or up stroke of the piston.

To follow through the operation of the piston, when the tool is connected to an air hose the parts immediately assume the position shown in FIG. 13. The air enters the valve chamber 21 and at this time the presser foot or triggering mechanism 37 is at the lowermost limit of its travel so that the valve is held below the port 27. and the valve 29 is restrained from upward movement by the spring detent 43. Therefore the air pressure passes through the port 27 and raises the piston to the position shown in FIG. 13. When the operator presses the tool against the work at the point where the tack is to be driven andexerts a light pressure, the foot 37 will be pushed up relatively to the driver, moving the slide plate upwardly, and the extension 42 will lift the valve 33 to the position shown in FIG. 14 where the port 27 will be opened to atmosphere, and as the plate 35 reaches the upper limit of its movement, the shoulder 44 will cam the detent 43 to the left as viewed in FIG. 12, whereupon 6 air pressure acting against the under side of the valve 29 will instantly lift it, opening the port 26 from the valve chamber into the cylinder. It will be seen that by reason of the pin and slot connection of slots 33 and pins 34, plate 5 32 has a lost motion connection with member 35 on which it is carried and hence the opening of the port at the top of the cylinder occurs just an instant after valve 30 has opened the lower end of the cylinder to exhaust, and this is also an important reason for making the valve 30 relatively movable to valve 29 and stem 28 on which it is guided. When the air enters the cylinder, it will drive the piston down with great force, the air under the piston escaping to atmosphere through the port 27. When the cycle has been completed, the parts will be in the position shown in FIG. 15 and nothing more will happen until the operator lifts the tool away from the work. As soon as he does this, the spring 45 will push the slide plate 35 down, restoring it to the position shown in FIG. 13, and as the slide plate 35 moves down, the extension 42 is withdrawn from under the valve 30 so that the valve 30 is forced down by the air pressure in the valve chamber to the position shown in FIG. 13. As the plate 35 moves down, the pins 34 will transmit a downward movement to the valve stem 28, pulling the valve 29 back to the position shown in FIG. 13, and the machine will be completely ready for the next cycle of operation.

' It will be seen that the piston cannot move on its driving stroke until the presser foot or trigger has been moved fully up relative to the tool to thereby release detent 43, and after this happens the full cycle of operation must follow, so that the driver cannot operate on part stroke and leave a partly driven fastener in the tool.

All of the valve operating mechanism described is positioned on one side of the plate 3 8 and is readily accessible for assembly or repair. As best seen in FIGS. 9 and 12, the plate 33 is of substantially T shape with the cross-bar of the T vertical and the stem extending horizontally to the right asshown in FIG. 9. The driver element 19 attached to the piston extension 17 is on the opposite side of the plate *38 from the valve operating mechanism, asis most clearly seen in FIG. 9. The lower end of the plate 38 tapers in width forming the main part of the nose portion 6, :and the lowermost end provides an extension or tip 46 of a width designed to operate between the bifurcations of the presser or trigger foot 37. The driver 19 slides or bears against the face of the plate 38, and is confined between two metal strips or blocks 43 and 53 respectively which form with the plate 38 the tack guide or driver guide down which the tack or other fastener is moved in being driven. The driver element is long enough and the stroke of the piston 15 is great enough to move the driver from the raised position shown in FIG. 9 to a position where its end is flush with the tip of the tack guide (see FIG. 15).

The details of construction of the tack guide are best shownin FIGS. 2, 3 and 4. The block 49 has secured to it a stamping formed of sheet spring metal designated 51, and which has two inwardly-turned fingers 52 and 53 that are over the center of the channel between the blocks 60 49 and '50. These spring fingers have shouldered ends 54 that are urged in against the bottom of the channel formed by the plate 38. On the plate there is a somewhat similar but reversed stamping 55 having spring fingers 56 and 57, the terminal portions of the fingers 56 and 57 being the same as the terminal port-ions of the fingers 52 and 53, and finger 56 is located between fingers 52 and 53 (see FIG. 2) and finger 53 is located between fingers 56 and 57. This construction provides a succession of four resilient fingers as shown in FIG. 3, the tips of which fingers bear against the plate 38 (see FIG. 3), but the shoulders 54 of which are, clear of the plate. The lowermost finger 57 is very close to the bottom end of the nose-like extension 46 of the plate 33 (see FIG. 2).

The block 49 as best shown in FIG. 4 has a ledge 58 thereon that extends under the shoulders 54 of the sev- F l eral spring fingers, and the clearance space for the point and leg of the staple being driven is designated 59 in FIG. 4, and is provided between the edge of the ledge 58, the face of the plate 3 8, the shoulders 54 of the spring fingers, and the tips of the spring fingers. The fingers are inclined as shown in FIG. 3 so that when the driver 19 slides from the raised position shown in FIG. 3 downwardly to the end of the nose 46, it will progressively cam the fingers S2, 56, 53, 57 outwardly or to the right as shown in FIG. 4 in the order named. Each spring finger will thus serve to confine the leg of the fastener as it travels down, and hold it against the edge of the ledge '58 and the face of the plate 38 to keep the tack from bending, but as the head of the tack is pushed down by the driver, each spring finger in turn is forced out of the way. In FIG. 2 one of the tacks is shown in dotted lines merely to show its location as it finally emerges, but it would never be in this relation with the presser foot 37 in the position shown.

The driver not only serves to drive the tack from the strip, but it serves to cut the tack off from the strip and at the same time bend down the leg-forming element of the next-succeeding blank on the strip. The top of the block 50 provides the die which cooperates with the driver for effecting these operations. As shown in FIG. 2 the block 50 has a transverse groove 61 formed therein through which the head-forming portion of the blank slides in moving to a position under the driver. As shown in FIG. 4 the block 50 has a portion 62 that overhangs the plate 38, leaving a clearance space 63 where the leg-forming element of the fastener is engaged by a part on the driver and moved from the plane of the strip down into a vertical plane. The block 50 has a shoulder at 64 providing clearance for the head of the tack as it is pushed down the guideway. The construction and arrangement of the leg-forming and shearing die are fully shown and described in my said Patent 2,580,444, and further detailed description with reference to them is not here required. It is sufficient to point out that when the blank reaches the position of the blank 60 in FIG. 3, the downward stroke of the driver shears the head portion of the blank from the continuous strip to which it is connected and drives the tack under the four resilient fingers with its leg guided in the manner described until the leg penetrates the material in which the tack is being driven, the tip 46 through the end of which the tack is discharged being held firmly against the work when the driving is taking place.

The said mechanism for advancing the tack strip on each operation of the driver is of the general type shown in my copending application Serial No. 264,294, filed December 31, 1951, now issued as Patent No. 2,701,360, granted February 8, 1955, but whereas the feed mechanisms heretofore employed have derived their power from the driver, the present invention provides a feed mechanism which is pneumatically operated.

As previously explained, the staple strip unwinding from the coil in the magazine moves horizontally through the lower portion of the handle portion 2 of the instrument, and in the lefthand end of the instrument as viewed in FIG. there is a narrow channel through which the leg-forming elements of the strip are guided while the head-forming edge, which is seen edgewise in FIG. 5, is turned outwardly, exposing the indexing notches S described in connection with FIG. 8A. Located in the handle portion of the tool above the strip guide is a small air cylinder 65 in which is a piston 66 having a circular extension 67 which is guided at its outer end in a guide block or bearing 68 (see FIGS. 5 and 9). On the rodlike extension 67 is a hook-like ear 69 to which is hooked one end of a tension spring 70, the other end of which spring is anchored to a stud 71 on a part of the frame back of the cylinder. The function of the spring is to urge the piston to the right as viewed in FIG. 5, or to retract it after it has been extended in its feeding stroke. A pipe 72 is received in a fitting 73 (see FIGS. 5 and 9) formed along one side of the cylinder 65, and a port 74 establishes communication between the pipe 72 and inner end of the cylinder 65. The other end of the tube 72, as shown in FIGS. 5 and 9, is fitted into the lower end closure piece 12 at the bottom of the cylinder 13. The piece 12 simply has a socket into which the end of the tube is inserted, and an O-ring around the end of the tube forms the seal, a similar arrangement being used where the tube projects into the fitting 73.

A port 74 establishes communication between the upper end of the tube 72 and the inside of the bottom of the cylinder 13. The arrangement therefore is such that when air enters the cylinder 13 under the piston 15 to raise it, the pressure will also be transmitted through the port 74 into the tube 72 and enter the right-hand end of the cylinder as viewed in FIG. 5, urging the piston to the left-hand position shown in FIG. 9. The enlargement 14 in the lower end of the cylinder assures of this taking place. Thus an impulse of air is delivered to the cylinder 65 each time the piston 15 is lifted. When the .port 27 at the bottom of the cylinder is opened to atmosphere, the pressure in the pipe 72 and consequently in the cylinder 65 is released and the spring can operate to retract the piston 66. This operation of the piston 66 is used to feed the fastener blank so as to advance the fastener strip one step each time the driver is operated. For transmitting movement from the piston 66 and its extension 67, the extension 67 is provided with a metal piece secured thereto, this piece 75 having two fingers 76 and 77 that are turned inwardly (see FIG. 10) to engage in the notches S in the edge of the strip S, the one finger engaging in one notch, and one in the succeeding notch of the strip. A resilient metal spring finger 78 extends out over the metal piece 75 to create a resilient pressure urging the ends of the fingers 76 and 77 yieldably down into engagement with the notches. The arrangement is such that when the piston moves to the left as viewed in FIG. 5, the ends of the fingers 76 and 77 being pressed into the notches S of FIG. 8A will move the strip forwardly to the left, traveling to the position shown in FIG. 9. When the piston is returned to its retracted position the ends of the fingers 76 and 77 slide up on the inclined edges of the notches S the extension 67 of the piston being rotated very slightly against the pressure of the spring 78, so that the fingers 76 and 77 move back to their starting position without withdrawing the strip S. The stroke of the piston 66 is just equal to the distance between one notch S and the next, so that in each cycle of movement, the strip is advanced the length of one blank. In order to prevent any retracting movement of the strip there is a second spring finger 79 (see FIG. 10) having a terminal portion that rides against the edge of the strip S, and which catches against one of the vertical shoulders of the strip, should the strip tend to move backward, but this finger will ride up on the sloped edge of the notch when the strip is being advanced. In other words, the spring finger 79 is a holding pawl cooperating with the notches, and the fingers 76 and 77 are feeding pawls cooperating with the notches, the notched strip constituting the ratchet. There are two fingers 76 and 77 just to effect a positive feed and avoid any possible failure of the device to feed, but one pawl alone would be sufiicient. As stated, the fingers 76 and 77 are operatively positioned the distance between notches S on the fastener strip.

As shown in FIG. 1, the lower portion of the tack guide may be exposed, while the portion of the guide which includes the dies and the feeding mechanism is enclosed under the hinged part of the housing so that when the housing is closed this part of the mechanism is concealed and protected, but upon opening the hinged part to the position shown in dotted lines in FIG. 1, all of this mechanism will be exposed. All of the mechanism is mounted on the flat plate 38 and the hinged part of the housing, designated 8, is in the form of a casting having a flange that fits over and encloses the mechanism when the housing is closed.

The mechanism thus described comprises a convenient, light, well-balanced form of tool. The operator grasps the bar portion 2 in his hand when he is using the tool and positions the nose 46 over the place Where the tack is to be driven. He then presses down on the cross bar, causing the presser foot 37 to move up and initiate the step of driving and feeding as hereinbefore described. The pres sure of his hand is exerted close to the point of driving which is helpful in positioning the tool and holding it steady. All of the parts of the mechanism are readily available for assembly or for tension as they require it, and they are designed to be relatively light so that the tool is not tiring to the arm of the operator who may use it for long periods at a time. By having a driver which is operated entirely by air instead of by a spring in one direction and air in the other, the force with which the driver drives the tack may be varied by varying the air pressure. This is desirable because tacks may be driven one day into soft wood, and another day into hard wood, and if the same driving pressure is used both times, the head of the tack may be sunk too far into the wood in one case, or not sulficiently embedded in the wood in another. Moreover, there being no spring to absorb power from the driver, the full force of the blow is spent on the tack. Also since the feed is operated by air, there is no absorption of power from the driver to operate the feeding mechanism as is the case where the driver is provided with cams or linkages for moving the feeder. The tool is safe in that the driving of each tack requires a separate operation of the triggering foot 37, so that tacks cannot be driven unless the triggering foot is directly operated. The bifurcations on the triggering foot form a guard which prevent the operator from getting his fingers under the driver during the driving operation, and since the tool must be pressed against the surface into which the tack is to be driven, there is little danger of personal injury, as may be the case where there is a finger-operated trigger and a fastener can be expelled or shot from the device merely by pressing the trigger while the instrument is in the open air. In other words, the trigger mechanism here provided does not permit the accidental discharge of any fasteners into the air, but a fastener can only be ejected when the triggering mechanism is pressed against a resistant surface. As stated, after the driving stroke has been started, it must go through to a point where the tack is entirely clear of the machine, and the tack guide cannot become jammed with partly driven fasteners, except perhaps in the case of an imperfect tack or improper feed adjustment, but never from the operator not triggering the device properly.

The simplicity of construction and assembly is a further feature of my invention. There is a single fiat supporting plate 38, shaped to the general contour of the assembled tool, this plate having the horizontal bar between a disklike terminal at one end forming one face of the magazine and a vertical cross bar providing the downwardly-extending tapered nose 46 and the upward extension on which the main cylinder 5 is secured. On one side of the vertical cross bar of the plate is mounted the valve and trigger mechanism where it is readily accessible. On the other side of the plate is mounted the driver and fastener guide, the feed mechanism and the spool holder. The cover is hinged to the supporting plate, two screws or rivets being required, as shown in FIG. 1, and the cover, having flanges about its edges, in its closed position, encloses the feed mechanism, magazine and upper part of the fastener guide. When the cover is open the driver, forming die, feed and magazine are all accessible. This is a convenient, economical and unique assembly.

While -I have shown and described in detail one pre ferred embodiment of my invention, it will be understood that various modifications and changes may be made in the construction and arrangement of parts within the conlfi templation of my invention and under the scope of the following claims.

I claim:

1. A driver for driving a fastener having a leg portion and a head portion which is offset to one side of the leg portion, said driver comprising a metal member having a guideway-forming channel therein, said channel having one flat face along which the fastener is moved with the head portion of the fastener extending at right angles to Said flat surface, the channel being open at one end for the discharge of a fastener leg-first therefrom, a driver element slidably received and guided in said channel positioned to engage the head end of the fastener and propel it along the channel and out the open end thereof, and a succession of spring fingers fixedly mounted on said metal member at intervals along the channel with the fingers having terminals which are in the path of travel of and engageable by the driver element and the head of a fastener moving along the channel and which are resiliently flexible in a plane normal to said fiat surface whereby the terminals of said fingers may be forced away from said surface when the driver element moves along the channel toward the open end thereof and spring in toward the flat surface when the driver element is withdrawn from engagement therewith, the terminals of the fingers forming guides for two sides of the leg portion of the fastener and serving to hold a fastener being engaged by the driver against the said flat surface.

2. A driver for driving a fastener having a leg portion and a head portion which is offset to One side of the leg portion, said driver comprising a metal member having a guideway-fonming channel therein, said channel having one flat face along which the fastener is moved with the head portion of the fastener extending at right angles to said flat surface, the channel being open at one end for the discharge of a fastener leg-first therefrom, a driver element slidably received and guided in said channel positioned to engage the head end of the fastener and propel it along the channel and out the open end thereof, and a succession of spring fingers fixedly mounted on said metal member at intervals along the channel with the fingers having terminals which are in the path of travel of and engageable by the driver element and the head of a fastener moving along the channel and which are resiliently flexible in a plane normal to said flat surface whereby the terminals of said fingers may be forced away from said surface when the driver element moves along the channel toward the open end thereof and spring in toward the flat surface when the driver element is with drawn from engagement therewith, the terminals of the fingers forming guides for two sides of the leg portion of the fastener and serving to hold a fastener being engaged by the driver against the said flat surface, said terminals of the fingers having two surfaces at right angles for guiding two surfaces of the leg which are at right angles.

3. A driver for driving a fastener having a leg portion and a head portion which is offset to one side of the leg portion, said driver comprising a metal member having a guideway-forming channel therein, said channel having one flat face along which the fastener is moved with the head portion of the fastener extending at right angles to said flat surface, the channel being open at one end for the discharge of a fastener leg-first therefrom, a driver element slidably received and guided in said channel positioned to engage the head end of the fastener and propel it along the channel and out the open end thereof, and a succession of spring fingers fixedly mounted on said metal member at intervals along the channel with the fingers having terminals which are in the path of travel of and engageable by the driver element and the head of a fastener moving along the channel and which are resiliently flexible in a plane normal to said fiat surface whereby the terminals of said fingers may be forced away from said surface when the driver element moves along the channel toward the open end thereof and spring in 1 1 toward the flat surface when the driver is Withdrawn from engagement therewith, the terminals of the fingers forming guides for two sides of the leg portion of the fastener and serving to hold a fastener being engaged by the driver element against the said fiat surface, said terminals of the fingers having two surfaces at right angles for guiding two surfaces of the leg which are at right angles, said spring fingers being arranged in pairs with the fingers of one pair secured to the metal member at one side of the channel and the fingers of the other pair being secured to the metal member at the other side of the channel but with the terminals of all of the fingers in a straight line,

12 the fingers of one pair being alternated with those of the other pair.

References Cited in the file of this patent UNITED STATES PATENTS 279,427 Perry June 12, 1883 582,103 Smith May 4, 1897 2,853,707 Julifs Sept. 30, 1958 FOREIGN PATENTS 446,389 Great Britain Apr. 29, 1936

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