US3434643A - Fastener driving apparatus - Google Patents

Description

March 25, 1969 Q. A. WANDEL. 3,434,543

FASTENER DRIVING APPARATUS Filed may 2, 19e@ sheet L /A/VeA/mf? 056A@ VWM/DEL Wwf@ @fe/5MM@ frz/MM @ma Arrow/Fys.

March 25, 1969 -o. A. WANDEI. 3,434,643

FASTENER DRIVING APPARATUS Filed nay 2, 196e sheet 2 of 2 /54 ,g4 25g: ff@ 1 /A/l/EA/roe 05m? A. MMA/DEL f7/m (Mahn/ffm, Wy@

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United States Patent U.S. Cl. 227-130 10 Claims ABSTRACT F THE DISCLOSURE There is provided a pneumatically operated tool for driving and setting fasteners including a driver blade. The driver blade is engageable by a main piston movable in a cylinder in response to the introduction of pressurized uid into one end thereof. Moreover the driver blade is secured to an inner or second piston also movable in response to the introduction of pressurized lluid into the one end of the cylinder. A lost motion connection between the main piston and the driver blade permits a followthrough movement of the driver blade at the end of the driving stroke of the main piston. An air chamber is provided for instantly retracting the driver blade upon completion of its followthrough projection.

This invention relates to a fastener driving apparatus and, more particularly, to a new and improved pneumatically operated tool for driving and setting fasteners.

Pneumatically operated tools for driving fasteners such as T-nails, finishing nails, and common or cooler nails having enlarged heads and lengths up to two and one-half inches are known. One such pneumatically operated tool is described and claimed in a copending patent application Ser. No. 340,863, filed Ian. 29, 1964, by Doyle et al., now U.S. Patent No. 3,253,760, granted May 3l, 1'966.

It is frequently desirable in the fastener art to drive the head of the fastener below the surface of the workpiece so as to countersink or set the fastener. The obvious way of accomplishing such result with a pneumatically operated fastener driving tool would be to modify an existing tool so that the driving blade projects the desired distance beyond the end of the nosepiece of the tool. However certain dificulties are encountered in providing a tool with the necessary longer driving stroke. One such diiculty is that a longer stroke requires a greater height of tool, making the tool more difficult to handle and preventing its use in certain tight spaces.

Accordingly one object of the present invention is to provide a new and improved fastener driving apparatus which overcomes the above diflculties.

Another object is to provide a new and improved fastener driving apparatus.

Yet another object is to provide a new and improved fastener driving tool having a comparatively long stroke without increasing the overall height of the tool.

Yet another object of the present invention is to provide a new and improved fastener driving tool wherein the driving blade projects beyond the end of the nosepiece.

Yet another object of the present invention is to provide a new and improved fastener driving tool for setting fasteners below the surface of the workpiece.

In accordance with these and many other objects, an embodiment of the invention is applicable to a pneumatically operated tool for driving and setting fasteners such as round headed nails and including a portable housing having both a vertically extending head portion and a rearwardly extending handle. A portion of the head and the handle are hollow and provide a reservoir in which is disposed a cylinder containing a fastener driving assembly made in accordance with the present invention. Known control means are provided for controlling the ICC admission of pressurized uid into the cylinder for actuating the fastener driving assembly and for exhausting the pressurized lluid from the cylinder to the atmosphere to provide for the return of the fastener driving assembly. In one embodiment of the present invention, the fastener driving tool was similar to that described in the above mentioned Doyle et al. patent, except for the improvements made to the fastener driving assembly.

In accordance with the present invention, the advantages thereof are obtained by providing an improved fastener driving assembly including a main piston slida'ble within the cylinder and a depending driver blade or element that is slidably received within a drive track formed in a nosepiece carried on the lower end of the head portion. The main piston is a generally cup-shaped member including a head and a cylindrical skirt defining an inner cylinder and provided with a blade opening in its head. An inner piston is slidably received within the inner cylinder and is connected to the driver blade which extends in airtight relation through the blade opening in the head of the main piston. Passage means are provided through the main piston to the inner cylinder to supply pressurized fluid to the chamber to hold the inner piston and the driver in an upper position when the main piston is in its normal or return position.

In operation, the main piston Will be driven downwardly through a power or driving stroke by the admission of pressurized fluid into the top of the main cylinder. At the end of the driving stroke when the driver blade has just reached the end of the nosepiece, the main piston will strike against a bumper or stop. However, the momentum of the inner piston and driver blade assembly will cause these elements to continue moving downwardly, compressing the air in the inner chamber within the main f piston. The compressed pressurized Huid in this chamber acts as an air spring to cushion and arrest the movement of the inner piston and driving blade `assembly as the `driving blade projects beyond the end of the nosepiece to set a fastener, and will cause an immediate return of the inner piston and driving blade assembly to its up position relative to the main piston even 'though the main piston does not begin its return stroke.

Advantageously the followthrough of the blade protrusion Ibelow the end of the nosepiece on the drive stroke provides for maximum drive of the fastener with a controlled followthrough independent of the main piston. The followthrough movement of the driver blade assembly is momentary, giving the necessary overdrive of the blade for the additional drive to set the fastener and permits the inner piston and blade assembly to instantly retract to its up position, reducing bounce and minimizing the possibility of double cycling. This allows the stroke of the driver blade to be longer than the stroke of the main piston and reduces the overall length of the tool. Moreover the design provides for a gradual stopping of the blade assembly instead of a sudden stop, thus prolonging the life of the blade. Additionally in commercially available tools, when the tool is red and the trigger iS not released, the main piston will generally remain down; however in the instant design the inner piston and blade assembly will continue its downward movement through the setting movement of the fastener, `but will instantly retract regardless of the length of time that the trigger is held depressed.

Many other objects and embodiments of the present invention will become apparent when considering the following detailed description in conjunction with the drawings in which:

FIG. l is a fragmentary side elevational view of a pneumatically operated fastener driving tool embodying the present invention;

FIG. 2 is a fragmentary side elevational view of the pneumatically operated fastener driving tool of FIG. 1, but illustrated with the fastener driving assembly thereof in its fastener setting position; and

FIG. 3 is also a fragmentary side elevational view of the pneumatically operated fastener driving tool of FIG. l and illustrated with the blade thereof retracted after completion of a fastener driving operation.

Referring now to the drawings, there is fragmentarily illustrated a fastener driving tool which embodies the present invention and which is indicated generally as 10. The tool may be of known construction and, as illustrated, is similar to that described in the above mentioned Doyle et al. patent except for the incorporation of the present invention. Briefly, the tool 10 comprises a housing 12 including a generally vertically extending head or forward portion 12a and a rearwardly extending hollow handle portion 12b. The interior of the head portion 12a and the handle l12b provide Ia reservoir 16 of pressurized fluid, such as compressed air, which is supplied to the tool by a exible line. The drive system for the tool 10 includes a cylinder 18 movably mounted within the head portion 12a and having an open upper end that is adapted to be selectively connected to the reservoir 16. The cylinder 18 is normally biased to place its open upper end in engagement with a main valve assembly 20 (FIG. 1) under the control of a safety or touch-trip valve assembly 22 and a manual valve assembly 24. A fastener driving assembly 25 includes a main piston 26 slidably mounted within the cylinder 18 and carrying an inner piston 27 hav-ing a depending driver blade member 28 secured thereto. The driving assembly 25 is normally lbiased to .a position with the main piston 26 adjacent the main valve 28 under the control of a piston return valve assembly indicated generally as 30. An exhaust valve assembly indicated generally as 32 for controlling the selective connection of the upper end of the cylinder 18 to the atmosphere is disposed on the housing 12 olfset from the axis of the cylinder 18 to reduce the overall height of the tool 10.

When the tool 10 is to be operated, the safety valve assembly 22 and the manual valve assembly 32 are closed and compressed air from the reservoir 16 enters the upper end of the cylinder 18 Iand drives the fastener driving assembly 25 downwardly to engage and set a fastener or nail 34 supplied to a drive track 36 in a nosepiece or nosepiece structure 38. When the cylinder 18 moves downwardly, a venting assembly indicated generally as 42 places the lower end of the cylinder 18 in communication with the atmosphere so that the air disposed below the piston 26 can be discharged to the atmosphere to prevent pneumatic damping of the downward movement of the piston. When the valve assemblies 32 and 24 are released, the cylinder 18 is moved upwardly to engage the main valve assembly 20 and close off communic-ation between the reservoir 16 and the upper end of the interior of the `cylinder 18. When the cylinder 18 moves to a position engaging the `main valve assembly 20, the exhaust valve assembly 32 is actuated to place the upper end of the interior of the cylinder 18 in communication with the atmosphere. This discharges the entrapped air above the fastener driving assembly 25 and controls the piston return valve assembly so that compressed air is supplied below the fastener driving assembly 25, the vent assembly 42 being closed by the upward movement of the cylinder 18. The compressed air supplied by the assembly 30 retracts the fastener driving assembly 25 including the driver blade member 28 to the normal position shown in FIG. 1 to complete a cycle of operation of the tool 10.

Referring now more specifically to the drive system embodied in the tool 10, this system is of the same general type as that shown and described in detail in the above mentioned Doyle et al. patent and includes a pair of cylindrical portions 44 and 46 (FIG. 1) in the head portion 12a in which are slidably received two different diameter portions on the cylinder 18. The larger diameter or upper portion of the cylinder 18 is sealed by two O-rings 48 which slidably engage the cylinder 44, and a lower or smaller diameter portion of the cylinder 18 is sealed by an O-ring 50 engaging the cylindrical portion 46. An intervening space or cavity 52 defined by the O- rings 48 and 50 is selectively supplied with compressed air or connected to the atmosphere by the control valve assemblies 22 and 24. ln the normal condition of the tool 10, one or both of the valve assemblies 22 and 24 supply compressed air to the space 52 which acts on the downwardly facing surfaces on the cylinder 18 within the space 52 which are greater in area than the upwardly facing surfaces acted on by the compressed air within the reservoir 16 to provide an upwardly directed component of force biasing the open upper end of the cylinder 18 against the main valve assembly 20 to prevent communication between the upper end of the cylinder 18 and the reservoir 16.

The interior of the cylinder 18 is lined with an inner cylinder 54 preferably formed of a self-lubricating material or metal which is secured in position by a fastening means 56. The outer wall of the cylinder 54 is spaced from the inner wall of the cylinder 18 to provide an air conveying space 57 forming a part of the piston return system controlling by the piston return valve assembly 30. The piston 26 includes a greater diameter upper portion 26a carrying a pair of O-rings 58 which slidably engage the inner wall of the inner cylinder. A smaller diameter lower portion of the piston 26 is adapted to engage a resilient bumper 60 disposed within a cylindrical retaining sleeve 62 which rests on the upper wall of nosepiece structure 38, which nosepiece structure is fastened to the lower end of the head portion 12a of the housing 12 to close the lower end of the head portion 12a. The driver blade 28, which extends slidably through the main piston 26 and is secured to the inner piston 27, passes through an opening 66 in the resilient bumper 60 to enter the upper end of the drive track 36 formed in the nosepiece structure 38.

' The venting assembly 42 for controlling the selective connection of the lower end of the interior of the cylinder 18 to the atmosphere comprises a cylindrical or annular valve element 68 that is slidably mounted in a lower cylindrical portion 70 of the head portion 12a with the interface between the cylindrical portion 70 and the sleeve 68 being sealed by an O-ring 72 carried on the sleeve 68. A compression spring 74 interposed between a flange of the retaining element 62 and the lower end of the sleeve 68 normally biases a resilient O-ring 76 carried on the sleeve 68 into engagement with an inclined wall surface connecting the cylindrical portions 46 and 70 to close the lower end of the interior of the cylinder 18. However, when this cylinder moves downwardly, its lower end engages the upper end of the sleeve 68 and moves this sleeve downwardly against the force of the compression spring 74 to move the valve element 76 out of engagement with the inclined wall. This places the lower end of the interior of the cylinder 18 in communication with the atmosphere through one or a plurality of exhaust ports 78. When the cylinder 18 is restored to its normal position at the end of the driving stroke, the compression spring 74 slides the sleeve 68 upwardly so that the valve element 76 again engages the inclined wall surface to close communication between the lower portion of the interior of the cylinder 18 and the atmosphere.

The piston return valve assembly 30 is shown and described in detail in the above identified patent to Doyle et al. As set forth therein, the piston return valve assembly 30 is automatically responsive to the pressure within the upper end of the cylinder 18 or the position of the piston 26 to selectively supply compressed air from the reservoir 16 to the lower end of the interior of the cylinder 18 to return the piston 26 to its normal position engaging the main valve assembly 20. The piston return valve assembly 30 is mounted in a protuberance 18u on the cylinder 18 and includes a valve element 80 having a piston portion 82 slidably mounted within a two-diameter cylinder formed in the portion 18a. The upper end of the larger diameter portion of the cylinder is closed by a member 84 having a passageway 86 through which compressed air from the reservoir 16 is continuously supplied. This air acts on the piston portion 82 to provide a downwardly directed component of force that seats the valve 80 on a resilient valve element provided by an O-ring 88. This closes off communication through a passageway 90 and a port 92 between the reservoir 16 and the air conveying space 57 which is dened by the cylinder 18 and the cylindrical insert 54 and which communicates with the lower end of the interior of the main piston 26.

Whenever the tool is actuated to move the cylinder 18 downwardly, the main piston 26 is driven downwardly to engage the bumper 60 and remains in this position when the cylinder 18 is returned to its normal position engaging the main valve assembly 20 by the release of the control valve assemblies 22 and 24. When the exhaust valve assembly 32 is operated to connect the upper end of the interior of the cylinder 18 to the atmosphere, the compressed air interposed between the piston portion 82 and the member 84 is largely exhausted to the atmosphere through a passageway 94, the upper end of the cylinder 18, and the exhaust valve assembly 32. The compressed air acting on the lower end of the piston portion 82 lifts the valve element 80 out of engagement with the valve seat 88 so that compressed air enters the lower end of the cylinder 18 below the fastener driving assembly 25. This compressed air moves the piston 26 upwardly to engage the main valve 20. In this position, the port terminating the inner end of the passageway 94 is sealed by the O- rings 58. The compressed air entering through the passageway 86 now accumulates above the piston portion 82 and overcomes the upwardly directed force due to the compressed air supplied from the reservoir 16. At this time, the exhaust valve 80 moves downwardly to engage the resilient O-ring 88 and terminates the supply of pressurized fluid to the lower end of the cylinder 18. The piston 26 is retained in its upper position by the frictional engagement of the O-rings 58 with the innner wall of the cylindrical insert 54.

The main valve assembly 20 is carried on a closure cap 100 which is secured to the head portion of the housing with a resilient sealing gasket 104 interposed between the head portion 12a and the closure cap 100 s0 as to close an upper end opening 106 in the head portion 12a. The main valve assembly 20 includes a resilient element 108 of a diameter slightly larger than the upper end opening in the cylinder 18. The resilient element 108 is vulcanized or otherwise rigidly and permanently secured to a plate 110 that is secured to the lower surface of the closure cap 100 by a plurality of machine screws 112. The main valve element 112 is vulcanized or rigidly secured to the supporting plate 110 throughout its length so that the upper end of the cylinder 18 is immediately separated from the valve element 108 as soon as the cylinder 18 begins to move downwardly. This permits immediate response of the tool 10 to the actuation of the control valve assemblies 22 and 24.

The exhaust valve assembly 32 is selectively responsive to the position of the cylinder 18 either to connect the upper end of the interior of this cylinder to the atmosphere, in the normal condition of the tool 10, or to close the exhaust connection whenever the tool 10 is operated. The exhaust valve assembly 32, which is completely carried on the closure cap 100, is offset radially from the center or axis of the cylinder 18 to permit a reduction in the overall height of the head portion 12a of the tool 10. The exhaust system controlled by the valve assembly 32 includes a vertically extending passageway 114 passing through the resilient valve element 108, the plate 110, and the closure cap 100 in a position generally aligned with the axis of the cylinder 18. A transverse passageway 116 in the closure cap 100 connects the passageway 114 with a small diameter cylinder 118 forming a part of the housing for the control valve 32. An additional passageway 120 communicating with the atmosphere at one end is connected to the cylindrical chamber 118 by a larger diameter cylinder 122 also forming a part of the exhaust valve assembly 32.

This assembly includes a valve element 124 having an upper piston portion 124a and an intermediate valve portion 124b which are disposed within the cylinder 122. The upper end of the cylinder 122 is closed by a cap or closure 126 held in position by a lock washer or retaining ring 128. A lower sealing portion 124C of thev member 1214 is disposed within a smaller diameter cylinder 130 forming a continuation of the cylinder 118. The lower end of the valve member 124 includes an operator portion 124d which is aligned with and adapted to be engaged by the projecting portion 18a on the cylinder 18 or by the closure member 84 carried on the projecting portion 18a. In the normal condition of the tool 10, the lower end of the operator 124d engages the projecting portion 18a of the cylinder 18 to hold the exhaust valve assembly 32 in the open position illustrated in FIG. 1 in which the upper end of the interior of the cylinder 18 is connected to the atmosphere through the passageways 114 and 116, the cylinders 118 and 122, and the passageway 120.

When the tool 10 is operated so that the cylinder 18 moves downwardly, the projecting portion 18u moves out of engagement with the operator 124d` on the exhaust valve member 124. At this time, the compressed air continuously supplied to the upper surface of the piston portion 124g from the reservoir 16 through an axially extending passageway 132 in the valve member 124 acts on the upper surface of the piston portion 124er and provides a greater downwardly directed force than the uplwardly directed force resulting from the compressed air in the reservoir 16 acting on the lower surface of the sealing portion 124C. This net downwardly directed force moves the valve member 124 downwardly until a valve element provided by an O-ring 134 carried on the valve portion 124b seats on the shoulder between the cylinders 118 and 122. This prevents communication between the passageways 116 and 120 and closes the connection between the upper end of the cylinder 18 or the reservoir 16 and the atmosphere. When the cylinder 18 is restored to the normal position shown in FIG. l, the projecting portion 18a or the closure member 84 engages the lower end of the operator 124d and moves the valve member 124 upwardly against the pneumatic bias to the position illustrated in FIG. l. In moving upwardly, the valve member 124b lifts the Oring 134 out of engagement with the shoulder between the cylinders 118 and 122 so that the upper end of the interior of the cylinder 18 is connected to the atmosphere over the system of passageways set forth above. This is effective through the passageway 94 to place the upper end of the piston portion 82 at or near atmospheric pressure so that the piston return valve assembly 30 operates in the manner described above. The exhaust valve assembly 32 remains in this condition until the tool 10 is next operated to lower the cylinder 18.

The safety valve assembly 22 and the manual valve assembly 24 for controlling the operation of the tool 10 are substantially the same as those described in the above identified Doyle et al. patent. In general, the safety valve assembly 22 includes a valve stem 1-40 having a notched or reduced diameter portion 14041 adjacent its upper end which is slidably received within a sleeve 142 carried on the housing 12. The lower end of the valve stem is connected to a collar 144 so that a compression spring 146 interposed between a projection 148 on the head portion 12a. and the collar 144 lbiases the valve stem 140 to the position shown in FIG. 1 in which compressed air from the reservoir 16 flows into the space 52 through a passageway or port 150. The collar 1444 is also connected to a wire operator element 152. As more clearly shown in FIGS. 2 and 3, the lower end of the operator element 152 projects below the lower end of the nosepiece structure 38 and is adapted to engage a work piece. Thus, when the tool 10 is moved into engagement with the workpiece, the operator 152 is moved upwardly to produce a corresponding movement of the valve stem 140 against the action of the compression spring 146'. When the valve stem 140 moves upwardly, the upper end of the stern closes off direct communication between the passageway 150 and the reservoir 16, and the notched or recessed portion 14051 moves into alignment with a passageway 154. The passageway 154 communicates with the manually controlled valve assembly 24 which includes a ball valve element 155 and a passageway 156 communieating with the reservoir 16. Thus, compressed air from the reservoir 16 normally passes through the passageways 156, 154, and 150 to the space 52.

When the manual valve assembly 24 is actuated by pivoting a trigger 157 in a counterclockwise direction about a pivot pin 158, a uted valve stem 159 moves upwardly to seat the ball valve 155 in a position closing the port terminating the passageway 156. This movement of the ball valve 155 also places the passageway 154 in communication with the atmosphere through the flutes along the stem of the operator pin 159. Thus, the space 52 is placed at atmospheric pressure, and the compressed air within the reservoir 16 acting on the upwardly facing surfaces of the cylinder 18 produces a downwardly directed force which moves the cylinder 18 downwardly to cause the sequential operation of the valve assemblies 32 and 42 in the manner described above. When Iboth or either of the valve assemblies 22 and 24 is released, cornpressed air from the reservoir 16 enters the space 52 through the passageway 150 or through the passageways 156, 154 and 150 to provide an upwardly directed force acting on the cylinder 18 to move it upwardly into engagement with the main valve assembly 20. This closes the valve assembly 42, opens the valve assembly 32, and causes the operation of the piston return valve assembly 30 for the period of time necessary to return the main piston 26 and the driver blade member 28 to their normal positions.

In accordance with the present invention, the tool 10 is provided with a controlled followthrough of the driving blade to provide for maximum drive of the fasteners and setting of nails and like fasteners. To this end, the fastener driving assembly 25 includes the inner piston 27 slidably received within an inner cylinder 164 defined within the main piston 26. The driver blade member 28 slidably extends through a blade opening 166 in the head of the main piston 26. To this end the blade member 28 includes a lower blade portion 28a and an enlarged cylindrical connecting portion 28h extending through the Iblade opening 166. Suitable sealing means, such as an O-ring 168, provides a seal between the connecting portion 2819 and the blade opening 166. The upper end of the connecting portion 28b is provided with a reduced diameter threaded portion 28e passing through a central opening 27a in the inner piston 27, and the connecting portion 28b of the driving blade 28 is secured to the inner piston 27 by means of a nut 170. Suitable sealing means, such as an O-ring 172, provides a seal between the inner piston 27 and the inner cylinder 164.

To provide for cushioning the return stroke of the driver blade member 28 relative to the main piston 26, the driver blade member 28 is provided with an enlarged head or stop 174 dividing the driving portion 28a and the connecting portion 28b and seatable against a resilient washer-shaped cushion or bumper 176 fitted within a recess 178 in the head of the main piston 26.

To provide the necessary pressurized fluid to bias the inner piston 27 upwardly with respect to the main piston 26 after the fastener driving assembly 25 has ended its return stroke, a fluid passageway 184 is provided through the main piston 26 having a iirst port 184a opening in the lower end of the inner cylinder 164, and a second port 184b opening between the O-rings 58 in the main piston 26 and aligned with a passageway 188 in the inner cylinder 54, which in turn is aligned with the passageway 94 in the cylinder 18.

In View of the above detailed description of the improved fastener driving tool 10, its operation is believed clear. However, briefly, it will be understood that the operation of the present tool is similar to that described and claimed in the above mentioned Doyle et al. patent except for the provision of the controlled followthrough of the driver blade member in accordance with the present invention. The initial downward movement of the fastener driving assembly 25, after actuation of the trigger 157 to initiate a driving stroke, moves the main piston 26, the inner piston 27, and the driver blade member 28 downwardly as a unit until the main piston 26 strikes against the resilient bumper 60. The momentum of the inner piston 27 and the blade member 28 causes the blade member 28 to continue its downward movement. Such downward movement compresses the fluid air in the inner cylinder 164. This will permit the blade member 28 to continue through a controlled followthrough best illustrated in FIG. 2, so that a fastener, such as the nail 34, can be set below the surface of the workpiece. Once the fluid in the inner cylinder 164 has been compressed, the compressed fluid in the cylinder acts as an air spring to return the inner piston 27 and lblade member 28 to its up position relative to the main piston 26, as best illustrated in FIG. 3.

Upon release of the trigger 157, the fastener driving assembly 25 will return upwardly through its return stroke to the position illustrated in FIG. 1. After completion of the return stroke of the main piston 26, the passageways 94, 188, and 184 are in alignment so that pressurized fluid enters into the inner cylinder 164 to positively raise the inner piston 27 and blade 28 relative to the main piston 26.

The followthrough or the blade protrusion below the end of the nose on the drive stroke of the tool is desirable for maximum drive of the fastener. The illustrated design has a controlled followthrough of the inner piston 27 and blade member 28 independently of the main piston 26. Moreover the controlled protrusion of the blade portion 28a is momentary, gives the necessary overdrive of the blade portion 28a for the additional drive distance, permits the inner piston 27 and blade member 28 to instantly retract to its up position, and reduces the bounce with the corresponding possibility of double cycling. This allows the stroke of the 'blade member 28 to be longer than the stroke of the main piston and reduces the overall height of the fastener driving tool 10. Moreover there is a gradual stopping of the blade member 28 instead of a sudden stop to prolong the life of the blade member.

Although the present invention has been described by a single embodiment thereof, it will be apparent that numerous other modications and embodiments may be devised by those skilled in the art and it is intended by the appended claims to cover all modifications and ernbodiments which will fall within the true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In a fastener driving apparatus of the type including a housing containing a movable fastener driving assembly adapted to drive a fastener; the improvement comprising main piston means movable in a cylinder through a drive stroke upon introduction of pressurized fluid into one end of said cylinder, inner piston means independently movable through a drive stroke upon introduction of pressurized uid into said one end of said cylinder, means for arresting movement of said main piston means at the end of its drive stroke, driver blade means connected to said inner piston and engageable lby said main piston during a drive stroke thereof, and interconnecting means interconnecting said driver blade means and said main piston means for providing a followthrough continuation of said driver blade means after termination of the driving stroke of said main piston means.

2. The improvement as set forth in claim 1 wherein the fastener driving apparatus includes a nosepiece defining a -drive track for a fastener and is adapted to set a fastener below the surface of a workpiece, the followthrough of said driver blade projecting beyond the end of said nosepiece.

3. The improvement as set forth in claim 1 above wherein said main piston means is a generally cup-shaped member including a head and a skirt defining an inner cylinder open toward said one end thereof and provided with a blade opening in said head, land said inner piston is in said inner cylinder in communication with said one end of said cylinder, and said driver blade means extends through said blade opening and is secured to said inner piston.

4. The improvement as set forth in claim 1 above and including air chamber means for instantly retracting said driver blade means after its followthrough projection,

5. In a fastener driving apparatus of the type including a housing containing a movable fastener driving assembly adapted to drive a fastener; the improvement comprising main piston means movable in a cylinder through a drive stroke, means for arresting movement of said main piston means at the end of its drive stroke, driver blade means, interconnecting means interconnecting said driver blade means and said main piston means for providing a followthrough continuation of said driver blade means after termination of the driving stroke of said main piston means, air chamber means for instantly retracting said driver blade after its followthrough projection, said inner piston in said inner cylinder defining said air chamber, the followthrough movement of said inner piston and driver blade means compressing fluid in said chamber which acts to return the inner piston and driver blade means and to cushion the followthrough continuation thereof.

6. The improvement as set forth in claim 4 above including air conveying means adapted to introduce pressurized fiuid into said air chamber after said fastener driving assembly completes its return stroke.

7. In a fastener driving apparatus of the type including a housing containing a movable fastener driving assembly adapted to drive a fastener; the improvement comprising main piston means movable in a cylinder through a drive stroke, means for arresting movement of said main piston means at the endA of its drive stroke, driver blade means, interconnecting means interconnecting said driver blade means and said main piston means for providing a after termination of the driving stroke of said main piston followthrough continuation of said driver blade means means, air chamber means for instantly retracting said driver blade after its followthrough projection, and cushioning means cushioning the retraction of said driver blade means.

8. The improvement as set forth in claim 7 above wherein said cushioning means includes a resilient bumper carried by said main piston means, and said driver blade means is provided with stop means for engaging said bumper.

9. The improvement as set forth in claim 8 above wherein said bumper is in the form of a washer fitted within a recess in said main piston means, and said driver blade means extends through said bumper.

10. In a fastener driving tool, a housing providing a reservoir of pressurized fluid, a movable cylinder having an open end, a fastener driving assembly including a main piston slidable in the cylinder having a head and a cylindrical skirt and defining an inner cylinder, an inner piston slidable within said inner cylinder and defining a chamber, a `blade assembly secured to said inner piston and extending through an opening in said head, a nosepiece forming a `drive track in which the blade assembly is movable, said nosepiece having an opening through which fasteners can be driven, resilient bumper means in said housing adjacent said opening through which said blade assembly passes for engaging said main piston to arrest movement thereof, the momentum of said inner piston and blade assembly moving said inner piston in said inner cylinder compressing fluid therein after motion of said main piston is stopped at the completion of its drive stroke to provide a followthrough continuation of the drive assembly, main valve means engageable by said cylinder to close the open end of the cylinder, means defining an exhaust passageway communicating with the cylinder, exhaust valve means in said exhaust passageway for opening and closing the exhaust passageway, means for supplying fluid from the reservoir to the piston means to bias the valve means to a closed position, mechanical means for controlling the exhaust valve and adapted to engage the cylinder, said cylinder engaging the mechanical means to hold the exhaust Valve in an open position against the fluid bias when the open end of the cylinder is closed by the main valve means, means for releasing said cylinder from eu-` gagement with said main valve means to open the open end of the cylinder and to release the mechanical means so that the piston means closes the exhaust valve means, and passageway means through said movable cylinder and said main piston interconnecting said chamber and said reservoir when said main valve is closed to provide pressurized uid to said chamber, movement of said main piston in said movable cylinder being effective to close said passageway means.

References Cited UNITED STATES PATENTS 1,855,266 4/ 1932 Van Eps. 2,671,214 3/1954 Iuilfs 227-130 2,887,686 5/ 1959 Wandel et al 227-130 2,888,679 6/ 1959 Peterssen et al 227-130 3,040,327 6/ 1962 Michel 227-130 X 3,094,043 6/ 1963 Powers et al. 3,107,584 10/ 1963 Powers 227130 X GRANVILLE Y. CUSTER, JR., Primary Examiner.

U.S. Cl. X.R. 227--66

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