US2575455A

US2575455A - Impact tool

Info

Publication number: US2575455A
Application number: US707949A
Authority: US
Inventors: Joseph C Lang
Original assignee: BOCJL Corp
Current assignee: BOCJL Corp
Priority date: 1945-12-12
Filing date: 1946-11-05
Publication date: 1951-11-20
Anticipated expiration: 1968-11-20

Description

NOV. 20, 1951 c, LANG 2,575,455

IIIIII II 0L N mu; I I I Nov. 20, 1951 J. c. LANG IMPACT TOOL Filed Nov. 5, 1946 8 Sheets-Sheet 3 H II INVENTOR. Jqsepfi Clan! ,WMMZ M Nov. 20, 1951 J, LAN 2,575,455

Nov. 20, 1951 J. c. LANG 2,575,455

IMPACT TOOL.

Filed Nov. 5, 1946 8 Sheets-Sheet 5 Nov. 20, 1951 AN 2,575,455

IMPACT TOOL 8 Sheets-Sheet 6 Filed NOV. 5, 1946 INVENTOR. Joseph 6; Lang Nov. 20, 1951 c, LANG I 2,575,455

IMPACT TOOL.

Filed Nov. 5, 1946 8 Sheets-Sheet 7 I I l I INVENTOR. Joseph CLang Z f M Nov. 20, 1951 J. c. LANG I 2,575,455

IMPACT TOOL Filed Nov. 5, 1946 8 Sheets-Sheet 8 INVENTOR. Jbseph (flung Patented Nov. 20, 1951 nurso'r TOOL Joseph C. Lang, Pittsburgh, Pa., assignor to Bocjl Corporation, Pittsburgh, Pa., a. corporation of Delaware Application November 5, 1946, Serial No. 707,949

12 Claims. (Cl. 1-51) This invention is for an impact tool and relates particularly to a tool in which rotary motion is transformed into a reciprocating motion, and wherein a driver is operated with sudden force.

The invention relates particularly to a machine for driving tacks, and particularly tacks in strip form, disclosed in my copending application Serial No. 636,467, filed December 21, 1945. It will be specifically described in this connection, but the invention may be otherwise embodied and is not restricted to the particular driver herein dis- 5 closed.

In many industries, such for example as the furniture upholstery industry, large quantities of tacks are required to be driven. Persons trained in the art of driving tacks are frequently known as tack spitters, by reason of the fact that when working they place a hand full of tacks in their mouths. They remove them one at a time to drive them. At the end of a particular operation, if one of them should happen to have a quantity of tacks in his mouth, he spits them away, and in many industries it is probable that the number of tacks thus wasted equals or exceeds the number used. stringent sanitary rules regulate plants of this kind to prevent the re-use of the tacks. Large quantities of tacks are requently strewn over the floor.

A further difficulty is that such workmen require a high degree of training before they are sufficiently skillful to work rapidly and accurately, and since the furniture is usually completely finished so far as woodworking is concerned, before the upholstering is done, it not infrequently happens that furniture is ruined or expensive refinishing operations are required by reason of such an operator hitting the wood finish in driving home the tack.

In my copending application Serial No. 636,467, filed December 21, 1945, I have disclosed a tacklike fastener which is designated a T-tack. It is formed from a narrow strip or ribbon of metal which is slit diagonally from one edge toward the center, and then longitudinally of the strip to form a succession of tack or fastener blanks. The

margin of the ribbon of metal which is so slit constitutes the leg-forming element of the tack. In operation it is bent about anaxis transverse to the longitudinal axis of the ribbon into a position perpendicular to the original plane of the metal to form a T-shaped blank with the head of the tack being to one side of the leg, and being comprised of that part of the strip of metal which is not slit. The strip so formed is cut at regular intervals with the leg-forming element about midway of the length of the head to form the individual fasteners. It is intended that the steps of bending down the leg, cutting off the blank, and driving it, be accomplished in the driving machine, and in my application Serial No. 634,537,

filed December 12, 1945, I have disclosed a feeder for advancing such a blank strip into a driver.

To drive a tack or fastener of this kind, it is necessary that the tack be hit a quick, sharp, hard blow, and it is also necessary that insofar as possible, the leg of the fastener shall be guided against bending, particularly when the fastener is initially entering the wood or other substance into which it is being driven.

According to the present invention, there is provided an implement having a reciprocating driver with an electric motor for operating the driver. While the mechanism is particularly designed for use in driving tacks of this type, the same mechanism for translating rotary motion into reciprocatin motion and controllably striking a quick, hard blow may be adapted to other machines and devices requiring a similar action. With the present invention the rotary movement of the motor shaft is translated into an oscillating or reciprocating movement of a pawl. The driver or impact tool is provided with a succession of teeth so that each strokeof the pawl serves to ad- Vance the driver the distance of one tooth in one direction, and a detent or holding pawl restrains the driver from moving back after it has been so advanced. This advance is effected against pressure of a spring or other biasing means, a spring being the most compact form of biasing means. When the driver has been moved a predetermined distance, there will be no further teeth for the motor-driven pawl to engage, and it will thereupon merely move back and forth without effecting any result. A trigger mechanism is provided for releasing the holding pawl so that when the trigger is pulled, rendering the holding pawl ineffective, the spring or other biasing force will propel the driver at high speed and with great force in the opposite direction. Means are provided whereby after the trigger has been operated, it is ineffective to again release the driver until the driver has been completely restored to v a cooked position, when the driver is again at the limit of its travel and the spring fully compressed.

The invention further provides a convenient form of tool for operating upon the T-tack strip above described and referred to in the former of my said prior applications, there being feeding means for advancing the strip automatically as each tack is driven. Theinvention provides in the particular embodiment shown, a compact, easily handled tool which is motor-driven, and which may be easily located with respect to the work, and the tack rapidly driven. The machine is so designed that the tacks may be well aimed, and damage to the finish of adjoining woodwork can be avoided, and less skill on the part of the operator is required.

The invention may be more fully understood by reference to the accompanying drawings, in which:

Fig. 1 is a side elevation of a machine embodying my invention;

Fig. 2 is a view similar to Fig. l,with part of the cover or casing removed, and with certain parts of the machine shown in section, the trigger being in the normal position and the mechanism being operative to cock the machine;

Fig. 3 is a machine similar to Fig. 2, just at the instant of releasing the trigger;

Fig. 4 is a longitudinal horizontal section in the plane of line IV-IV of Fig. 3;

Fig. 5 is a similar view in the plane of line V-V of Fig. 3;

Fig. 6 is a transverse vertical section through the strip feeder, the view being in substantially the plane of line VI-VI of Fig. 3;

Fig. 7 is a fragmentary transverse section'in the plane of line VII-VII of Fig. 3;

Fig. 8 is a similar view in the plane of line VIII-VIII of ig. 3;

Fig. 9 is a fragmentary view showing the driving nose of the machine with an attachment to limit the extent to which the tack is driven applied thereto;

I Fig. 10 is an assembly view showing in side elevation one arrangement for using the driver and supplying it with fasteners from a strip carried on a reel suspended from an overhead trolley;

Fig. 11 is a detail view showing a counterbalancing arrangement for the organization shown in Fig. 10;

Fig. 12 is a side elevation of a slightly modified form of machine in which the reel of strip fasteners is positioned directly at the side of the maally patterned after a gun, having a pistol grip 2 with a trigger 3, and at the top of the pistol grip is a barrel portion 4. Forwardly of this is a casing 5. The muzzle or driving nose from which the tacks are driven is designated 6, and the strip feeding mechanism is designated generally as I. The electric motor which is set into the casing 5 is designated generally as 8.

Referring now to Figs. 1 to 12 inclusive, the machine is preferably formed of two longitudinally divided sections or casings which are bolted or otherwise secured together in face-to-face relation, and which serve to hold and confine between them the various mechanisms to be hereinafter described, the arrangement being such i4 thereon, which are both offset at the same angle, and to the same extent. Each crank is engaged by the inner end of a pawl member ii, the free ends of these pawl members being tied together by a cross pin l6 isee Fig. 5). Each of these pawls is provided with a tooth I! as clearly shown in Figs. 2 and 3. When the shaft l2 rotat'es, the cranks or eccentrics cause the two pawl elements ii to move back and forth, and at the same time they are free to move to a limited extent in an are about the cranks as a center.

The driver, designated generally as l8, has an end l9 (see Fig. 3) which is adapted to shear the fastener from the end of the strip, propel it along a guideway 20, and be discharged from the muzzle or nose 6. The driver also has a bending die portion 22. the formation of which is to engage the leg-forming element of the next-succeeding fastener blank of the strip and bend it down to a perpendicular position. This enables the fastener strip to remain flat until immediately before the driving operation. As the driver completes its stroke in the driving of one staple, the die portion 22 cooperating with die block 22a operates to engage the leg portion of the next succeeding blank and bend it. The exact arrangement by means of which this may be accomplished is more fully shown and described in my copending application Serial No. 634,537, filedDecember 12, 1945.

The driver 18 has secured thereon an inclined cam element 23, the purpose of which is to engage a roller 24 on a slide plate 25, which as viewed in Fig. 3 moves up and down, as contrasted to the back and forth movement of the driver itself. The slide plate 25 is pushed down by the action of the cam 23 engaging the roller 24. It is pulled up in the opposite direction by a pair of tension springs 26 secured to post 21 on the slide plate, and secured to fixed post 28 on one of the plates constituting the housing for the machine. The feeding mechanism illustrated is disclosed in my copending application last referred to. The slide plate which in Fig. 3 is shown in its uppermost position, and in Fig. 2 is shown in its lowermost position, has spring-pressed pawls 29 thereon which engage in notches 30 in the edge of the fastener strip 3! that is fed upwardly through a that one of the two casing parts may be removed to give access to the mechanism.

The motor 8 runs continuously while the machine is in use. It has a worm gear 9 at the end of its armature shaft. An oiling pad l0 mounted on a bracket at the inner end of the motor bears against the worm wheel 9 to keep it lubricated. and a suitably located oil hole in the casing enables oil from a can to be dropped upon the pad for supplying lubrication to the pad. The worm gear meshes with a worm wheel I I which is keyed to a transverse shaft I! supported in bearings I! at each side of the housing as best seen in Figs. 5 and '7. This shaft has two eccentrics or cranks narrow slot or channel 32 provided for it in the machine. As shown, these pawls are tooth-like elements carried on resilient leaf springs 29a secured to the slide plate, thepawls passing through the plate and being movable in a direction normal to the plane of the plate. Two fixed holding pawls 33 also engage in the notches 30 to prevent the strip from moving backwardly, once it has been advanced. The holding pawls are similarly carried on leaf spring arms 330, all as more fully described in my said-copending application Serial No. 634,537.

Briefly, when the driver moves from the position shown in Fig. 3 to the position shown in Fig. 2, the cam 23 operating against the roller 24 pushes the slide plate 25 down against the tension of the springs 25. During this time the pawls 33 lock the strip 3| against reverse movement, while the pawls 29 slide down along the edge of the strip. When the driver reacts to allow the slide plate to move up under the influence of the'springs 2B, the pawls 29, catching the notches 30 of the strip 3|, cause the strip to travel upwardly with the upward movement of the slide plate. The disposition of the pawls and the manner in which they engage in the edges of the fastener strip is perhaps most a clearly shown'in Fig. 6, while the general organization of the slide plate and its relation to the cam 28 is best shown in Figs. 2 and 3.

The driver II also has a rod 88 projectin axially from the top thereof, and the right-hand end of this rod as viewed in Figs. 3 and 4 i slideably guided in a bore 84 in a barrel or guide block 31 that is threaded into the casing above the handle or grip 2 of the machine, this barrel or block having a tubular extension "a which extends down toward the driver. A compression spring 88 is confined between the end of the driver II and the shoulder llb formed between the tubular portion 81a, the guide block and the main body 31 of the guide block. This organization is most clearly shown in Fig. 4.

Two racks ,40 (see Fig. 4) are secured to the driver it, one of them being at each side of the guide rod 35. These rack bars 48 have a succession of ratchet-shaped rack teeth 48a thereon. These rack teeth are arranged for cooperation with the tooth elements II on the reciprocating pawls l5. Two pawls l8 and two parallel ratchet bars or racks 40 are used to give symmetry to the design and avoid uneven distribution of forces and loads, but obviously a single pawl andrack bar may be used.

As shown in Fig. 2, the pawl teeth II engage o part 48b on the holding pawl 43 between its two teeth 48'. This extension, with its little angles 48c, also passes over the cross pin II that joins the free ends of the two motor-driven pawls II (see Fig. 5).

Assuming the parts to be in the normal position shown in Fig. 2, but with the driver retracted to the cooked position shown in Fig. 3, the operator may press on the trigger 3, swinging the lever 88 toward the right as viewed in Fig. v3. This exerts a pull on the plate 48, the

- motion being transmitted through pin Si in slot in the ratchet teeth 48a, and the throw ofthe cranks on the shaft i2 is such that each stroke of the pawls is designed to advance the driver one notch or tooth toward the right, as viewed,

52. The pins 46 engaged in the slots 41 cause the plate 48 to move downwardly as it also moves toward the right from the position shown in Fig. 2 to the position shown'in Fig. 3. The downward movement of the plate 48 causes the extension 48b at the front of this plate to push down onthe holding pawl assembly 48, disengaging its' teeth 45 fro'mtherack teeth a. It also presses [down on the cross pin it, moving the pawl teeth onthe pawl l5 out of the line of travel of the rack teeth 40a. When this happens, there is nothing to hold the driver in the cocked position, and the spring 38 propels the driver with great force towardthe left as viewed in Fig. 3, to theposition shown'in Fig. 2.

' The plate 48, as'shown in Figs. 5,7 and 8, has an angle 48d welded to one face'thereof to pro vide an overhanging lip or flange. One of the two'arms 40 having the ratchet rack teeth 40a is provided as shown in Figs. 7 and 8 with a laterally extending tongue 54. When the driver and 3, supports a vertically slideable pawl element 43 (see Figs. 2, 3, 5 and 8), there being springs 44 for urging this element upwardly. It has two teeth 48 thereon, which are best shown in Fig. 8, and which teeth are adapted to normally be projected by the springs 44 into engagement with the ratchet teeth 48a of the ratchet racks 48. Thus as each throw of the pawls l5|1 advances the racks one tooth, the pawl teeth 48 engagin the racks to lock the racks against reverse travel.

As best shown in Fig. 5, the block 42 has a rearwardly projecting extension 42a of reduced thickness forming a supporting bracket on which are mounted two pins 48. Positioned alongside the bracket 42 is a plate 48 which has inclined slots 41 therein (see Figs. 2 and 3) through which the pins 44 pass. A tension spring 48 anchored to one of the pins 48 and to a pin 50 on the plate 48 exerts a force tending to move the plate 48 upwardly and toward theleit as viewed in Fig. 2. The plate 48 has a rearwardly extending projection 48a in which is a transverse pin 8|. This pin is received in a slot 52 in the upper end of a trigger lever 53 in the butt of handle 2 of the tool, the trigger I being formed on the lever 88 and projecting through an opening in the handle 2 near the top of the handle.

The plate 48 also has a narrow extension 48b thereon which passes over the middle of the pawl element 43 between its two teeth 45, as clearly shown in Fig. 5, and as shown in Figs. 5 and 8 it has little angles 48c welded to each side of it, the horizontal flanges of the angles being in the plane of the bottom of the extension 48b, and serving to increase the bearing area of the is in the position shown in Fig. 2, this lug or tongue 54 isclear of the left-hand end of the flange 48d and when the driver is cocked and in the position shown in Fig. 3, this tongue 54 is clear of the right-hand end of the flange 48d. As the driver travels on its impact stroke from the position shown in Fig. 3 toward the left, to the position shown in Fig. 2, the tongue 54 rides over the top of the flange 48d and even though pressure on the trigger is released, the spring 49 cannot operate to restore the plate 48 to its raised position until the driver reaches the lefthand limit of its movement, when the tongue is again clear of the other end of the plate 48d. As soon'as this happens, the plate 48 lifts and moves toward the left under the action of spring 49 to the position shown in Fig. 2, taking pressure oif the holding ratchet assembly 43-45,

and also ofi the pin l6 which depresses the two operating pawls. Thereupon the operating pawls may again engage the ratchet teeth 40a to recock the driver. As soon as the driver starts to move toward the right in being cocked, the tongue 54 will be under the ledge or lip 48d as shown in Figs. 7 and 8, and even though pressure is put on the trigger to pull it, the tongue operating on the under face of the flange 48d will supportthe plate 48 and prevent it from being pulled down.

By reason of the relation of the tongue 54 and the flange 48d, a mechanism is provided where'- by. it isimpossible to operate the trigger at any 7 sheet metal designated 55 in Figs. 2 and 3 has its two arms secured to the under edges of the operating pawls l5, while the single opposite end of the stamping designated 55a is attached to one end of a tension spring 56, the other end of this spring being anchored to a pin 51 in the casing of the machine. This spring does not interfere with the back and forth movement of the operating pawls as effected by the cam shaft, but it does exert an upward thrust tending to resiliently raise the ends of these pawls to an operating position, except when they are depressed by the operation of the trigger mechanism as hereinbefore described.

Reviewing the operation of the machine, start-' ing with the parts as shown in Fig. 2, and with the motor operating, the motor turns the worm wheel II to rotate the shaft 12, reciprocating the pawls I5 so that their teeth l1 advance the racks 40a. one notch at a time against the compression of the spring 38 until the driver has been moved to a position where the teeth of the rack are clear of the teeth 11 of the operating pawls. During this step-by-step advancing movement of the driver toward its cocked. position, the holding pawl assembly 43-45 is effective to prevent the driver from moving in the reverse direction and the flange 48d riding over the tongue 54 prevents the trigger from being operated to prematurely release the driver. As the driver nears the end of its stroke, the springs 26 operate to advance the slide plate 25, whereupon the pawls 29 advance the fastener strip from the position shown in Fig. 2 to the position shown in Fig. 3, where the previously formed fastener is now directly in the path of travel of the driver.

When the trigger is pulled, the plate 48 is moved down and toward the right, and the ex tension 48b at its lower end simultaneously depressed the holding cam 43-45, and by pressure against the pin l6, moves the teeth H on the pawl arms [5 out of the path of travel of the racks so that the fully compressed spring 38 may then operate to move the driver toward the left, hitting the tack a sharp, quick blow, and driving it. Of course the first step in the driving is to shear the formed tack from the end of the strip. In this movement of the driver toward the left in driving the tack, the cam 23 engaging the roller 24 on the slide plate 25 moves the slide plate down from the position shown in Fig. 3 to the position shown in Fig.2, so as to be ready to advance the fastener strip when the driver is next retracted. The shoulder 22 on the driver cooperating with a die block 22a near the nose of the machine operates to turn down the leg of the next succeeding tack blank as the tack in the guideway is being driven. As previously stated, this feeder and leg-bending arrangement is fully shown in my said copending application, Serial No. 634,537.

The invention provides a tool wherein a continuously operating motor of relatively small power can be used to move a driver by a succession of rapid small increments from an uncocked to a cooked position against the resistance of a spring. Because of the small increments of movementand the reduction of speed and the leverages of the cranks, the work done by the motor on each revolution is relatively small, so that while the spring may ultimately exert a pressure in the neighborhood of 150 pounds in the particular machine shown, the motor is not overloaded or stalled in cocking the driver. The invention further provides a fool-proof trigger arrangement fora tool of this kind, whereby advancing of the tool or injury to the operating parts is-prevented through the interlocking arrangement on the driver and trigger plate 48 that prevents the operation of the trigger and the movement of the trigger plate, except at the two limits of movement of the driver.

The invention further. provides a machine of unique design in which a compact motor-driven tool is provided for successively driving tacks formed from a strip of previously prepared metal. Because of the small area of the driver and the shape of the nose, tacks can be driven into corners and-other places which are difilcult to reach, even inhand tacking operations, and likelihood of damage to the woodwork is avoided, as for example in the application of tacks in upholstered furniture..

For aiding and'guiding the fastener while it is being driven, it will be noted by reference to Fig. 3, that there is a narrow channel 60- in one of the two plates forming the guideway: to receive the leg of the fastener while the. head of the fastener rides on surfaces Eliaand 60b. A spring-pressed guide element 6| hav-' ing a leaf spring 62 is provided through an opening 63 (see Fig. 4) intothe tack guide. It normally exerts pressure against the upper edge of the leg whichis the edge viewed in Fig. 3 at about the time the fastener is being driven, but it is cammed'upwardly out of the path of travel of the head as the head of the fastener moves under, it.- Thus at the instant the fastener begins to penetrate the materialinto which it is being driven, the leg is supported on all four sides against deflection.

Sometimes in, the upholstering industry, it is desirable to only partly drive a tack so that it can be easily removed at a later period in the operation, or the'drivingcompleted at a later time. To effect this with thepresent machine, the attachment shown in Fig. 9 may be employed.-

This consists of a shell 65 shaped to fit over the:

delivery end of the muzzle of the tool, and it. has a spring clip lid-adapted to snap into a recess in the noseof the tool to releasably hold the casing in place. i The end of the .driver never projects. beyond the end-of the .nose. Therefore theshell 65 forms a spacer to keep the nose ofthe. driver =away from-the work so that the tack will be; only partly driven.

- Figs. 10: and I1 illustrate one arrangement: for using the tacking tool.- In this arrangement, a bail 1D is attachedto a gun as shown in Fig.=

l0, and-itis curved=to=rprovide-a loop at Ma and it is bowed outwardly-to provide another;

bracket]! which in turn-has a hanger 15 suspended from a cable 16. The-cable 16 fastens over apulleyTl, another pulley" l8, and has a counter-: weight 19 at its opposite erldl The pulley Tl is'hung from a trolley 80, 'movable along an overhead trackway 8i.

The hanger I5 extending upwardly' from-the bracket '14 has aieel 82' thereon to support" a roll of prepared fastener blanks 83. Thereup the slack which exists when the gun is shifted I from a horizontal position to the vertical position shown in Fig. 10, while the counterweight I9 counterbalances the up and down movement of the whole assembly as the operator raises and lowers the gun to work at different elevations. The trolley 80 and track 8| allows the operator to move along with the piece of work in which he is engaged in driving tacks. The counterbalancing arrangement relieves the operator of supporting much weight in using the tool so that he can very easily change its position and his arms do not become tired in using it.

In some cases it may be desirable to have the reel of the fastener forming blanks attached directly to the side of the machine instead of using the arrangement shown in Figs. 12, 13, 14 and 15. Nevertheless, even with this form of construction it is desirable to use a bail such as the bail 10 of Fig. 10 for suspending the machine to keep it from being dropped, although this bail has not been shown in Figs. 12, 13, 14 and 15.

The driver itself is of the same construction as that previously described, and is designated generally as A, and no reference will be made to the individual parts except as may be necessary for the purpose of understanding the present modification. One of the side plates of the reel to rotate freely. At one point on its periphery, as best shown in Figs. 12 and 15, the

bracket is provided with an axially ofiset spiralled portion 96, through which the strip is guided. as it unwinds from the periphery of the reel to point in alignment with the beginning of the s ip-feeding slot designated 91 in the tacking machine, and which is similar to the guide previously described in connection with Figs. 1

to 10 inclusive.

With this arrangement the previously prepared reel of fastener blanks is merely put in position on the bracket, threaded into the machine, and as the strip is fed into the machine with the fasteners being consumed, the reel turns on the bracket. When the reel is exhausted, a new reel is substituted for it.

It may be noted that the casing is divided longitudinally into two sections, a cover section and a supporting section which carries all of the operating mechanism, the cover section having only a bearing for one end of the crank shaft. With thisarrangement the cover may be removed without disturbing the operating mechanism. v

While-I have illustrated and described one 10 particular embodiment of an impact tool designed in accordance with my invention, and one particular form of tacker, it will be understood that this is by way of illustration, and that various changes and modifications may be made within the contemplation of my invention. and under the scope of the following claims.

I claim:

1. In a mechanism of the class described, a crank, means for rotating the crank, a pawl operated by the crank, a plunger having a success ion of ratchet teeth with which the pawl cooperates to move the plunger in one direction, said rack having a smooth surface at the end or the ratchet teeth positioned to be engaged by the pawl along which the pawl may ride when the plunger has been moved a predetermined distance by the pawl, and a selectively releasable holding pawl also cooperating with the ratchet teeth of said rack and so located that said smooth surface is always clear of it.

2.A machine of the class described comprising a plunger. a rack having ratchet teeth connected with the plunger, a reciprocating pawl mechanism for moving the plunger in one direction. means for urging the plunger in the opposite direction, means for holding the plunger against movement by the last named means, means for releasing said holding means, simultaneously moving the reciprocating pawl to an inoperative position, and means for preventing operation of the releasing means when the plunger is intermediate the limits of its travel.

3. A tool of the class described, a plunger having a rack with ratchet teeth thereon, a spring for operating the plunger in one direction, an operating pawl cooperating with the ratchet teeth of said rack for operating said plunger in the opposite direction to compress the spring, a latching pawl cooperating with the rack, and means for simultaneously moving the operating pawl and the latching pawl out of engagement with the rack, the rack having a smooth area at one end thereof positioned to be engaged by the operating pawl when the plunger has reached the limit of its travel in a direction to compress the spring, whereby the pawl may continue to operate without further movement of the plunger.

4. A tool of the class described, a plunger having a rack with ratchet teeth thereon, a spring for operating the plunger in one direction, an-

operating pawl cooperating with the ratchet teeth of said rack for operating said plunger in the opposite direction to compress the spring, a latching pawl cooperating with the rack, means for simultaneously moving the operating pawl and the latching pawl out of engagement with the rack, said last-named means including a plate extending parallel with the plunger and movable toward and away from the plunger, the plate having a flange thereon, the plunger having a hookwhich rides above said flange when the operating pawl and the latching pawl moves above said flange when the plate is in a posi-, tion to hold the operating pawl and the latching pawl clear of the rack, and which rides under said flange when the plate is in a position for the said operating. pawl and latching pawl to engage the rack, said flange thereby preventing the engagement of the pawls with the rack tending only between the limits of travel of the hook and the hook being clear of said flange at both limits of movement of the plunger.

5. A tool of the class described. comprising a plunger having a rack secured thereto, said rack being provided with ratchet teeth, there being a smooth surface on the plunger at the end of the teeth, a holding pawl cooperating with said rack and being movable transversely of the axis of the plunger into and out of engagement with the rack, an operating pawl movable back and forth along the rack a distance of one-tooth and movable into and out of engagement with the rack for moving the plunger in one direction, said operating pawl being positioned to ride on the smooth surface of the plunger when it has moved the plunger to the limit of its travel, a member for moving both the operating pawl and the holding pawl clear of the rack, a spring for moving the plunger in the other direction when the holding pawl and operating pawl are clear of the rack, and a manually operable trigger for selectively operating said member.

6. A fastener driving machine of the class described having a bodywith a pistol grip there-- on, a driver movable back and forth in the body, a'spring for moving the plunger in one direction, pawl and ratchet mechanism for moving the plunger in the opposite direction against the stress of the spring with a step-by-step movement, a trigger mechanism for releasably restraining the driver when the spring is compressed and while the pawl continues to be operated, and motor means for driving the pawl.

7. A fastener driving machine of the class described having a body with a pistol grip thereon, a driver movable back and forth in the body, a spring for moving the plunger in one direction, pawl and ratchet mechanism for moving the plunger in the opposite direction against the stress of the spring, a trigger mechanism for releasably restraining the driver when the spring is compressed, and means for driving the pawl, said means including a crank shaft with one end of the pawl attached to the crank thereof and a motor for continuously driving the crank shaft.

8. A fastener driving machine of the class described having a body with a pistol grip thereon, a driver movable back and forth in the body. a spring for moving the plunger in one direction, pawl and ratchet mechanism for moving the plunger in the opposite direction against the stress of the spring and with a step-by-step movement, a trigger mechanism for releasablv restraining the driver when the spring is compressed and rendering the pawl and ratchet mechanism ineffective, motor means for driving the pawl, and means operated by the driver for feeding a succession .of tack blanks into position to be driven by the driver.

9. A tool ofthe class described comprising a casing formed principally of two sections which separate on a plane extending longitudinally of the tool, one of said sections being a cover section, and the other of said sections beinga mechanism-supporting section, a driver slidably mounted on the mechanism-supporting section, a spring for moving the driver in one direction, a pawl and crank mechanism carried on said last-named section, a trigger mechanism car- 1: ried on said last-named section movable to render both the operating pawl and the latching pawl inoperative, and a feeding mechanism for a strip of fastener blanks on said last-named section, removable of the cover section affordms access to all of said mechanisms without dismantling the same.

10. A fastener driving mechanism comprising a body, a driver movable back and forth in the body, means for operating the driver in one direction to drive the fastener, motor-driven means including a pawl operated by the motor and a ratchet on the driver for returning the driver in a succession of small increments of movement and rendering said first means effective, and a release mechanism for selectively restraining the driver against operation by the first means.

11. A tool of the class described having a reciprocable plunger, a spring for yieldably resisting movement of the plunger in one direction and for driving it in the opposite direction, a succession of ratchet teeth on the plunger, a driving.pawl movable back and forth-along the ratchet teeth a distance of one tooth for en-' gaging each tooth in turn and advancing the plunger against the resistance of the spring, a motor for continuously driving the driving pawl, a holding pawl for holding the plunger against movement in the reverse direction under the action of the spring, and means for simultaneously moving both pawls clear of the ratchet to enable the spring to drive the plunger in the opposite direction, the plunger having a smooth surface at the end of the succession of ratchet teeth, the driving pawl being positioned to ride on said smooth surface when the plunger has been advanced by the pawl to the limit of its movement against the resistance of the spring. 12. A tool as defined in claim 11, in which the motor serves to continuously operate the driving pawl through a crank with which the pawl connects, said crank being driven by a worm gear operatively interposed between the crank and the motor, the holding pawl being positionedbeyond the driving pawl in reference to the said smooth surface of the plunger.

JOSEPH C. LANG.

REFERENCES CITED The following references are of record in the file of this patent:

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