Fastener driving tool

[57] ABSTRACT

A fastener driving tool including a piston having a driving element supported eccentric to the axis thereof and reciprocated in a bore by fluid under pressure. A contactor mechanism comprises an inner portion located in the bore in the path of movement of the piston and an outer portion defining a fastener outlet alinged with the path of movement of the driving element. Where the contactor mechanism is a dimpier mechanism, the outer portion has a spherical dimpling surface surrounding the outlet and an expansive energy dissipating surface surrounding the dimpler surface. The dimpler mechanism and piston have cooperating means that cause a deceleration of the piston and an acceleration of the dimpler, rigid striking engagement between the piston and dimpler mechanism being made when their speed or velocity differential has been substantially reduced. The tool also incorporates a safety mechanism that prevents firing until the tool is in engagement with a workpiece, and includes shock absorbing means to prevent damage to the tool when inadequate back-up exists.

Claims, 10 Drawing Figures

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Patented Nov. 27, 1973

3,774,293

Sheets-Sheet 1

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Patented Nov. 27, 1973

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Patented Nov. 27, 1973

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Sheets-Sheet 3

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128

3,774,293 dimpler fatigues the parts and can readily result in destruction of either or both of the parts.

The second type of drive mechanism discussed above, i.e., that utilizing a resilient member, while reducing the shock loads and softening the impact between the driver and the dimpler by eliminating direct metal-to-metal contact, minimizes the degree of control over the terminal movement of the dimpler mechanism relative to the fastener and fastener driver and therefore control over the depth of the dimple and depth of penetration of the fastener.

A further disadvantage of all of the driving tools that have been proposed for driving a fastener and for simultaneously dimpling a workpiece surface, is that the 15 tools were not capable of compensating for variations in the driving resistance for the fastener which may result from variations in fluid pressure, and from variations in such characteristics as grain structure, moisture content, knots, etc., in the lumber and studs to which 20 the workpiece (such as a wallboard) is secured. That is of extreme importance when securing wallboard in areas where a clean finished surface is desired. For example, if a nail happens to strike a hard spot like a knot, its head might protrude from the surface and the wallboard would not be held tightly against a supporting stud. On the other hand, if a nail is driven too deeply, the wallboard core may be crushed or the sheathing may even be tom or ruptured, conditions which are unacceptable for known reasons. Since wallboard gener30 ally includes gypsum or other material of little structural strength covered on both sides with a sheathing of paper, the rupturing of the paper sheathing may preclude proper and dependable mounting of the wallboard, and may result in a finished structure that is un,. .. , ---[ may fail to meet building code requirements.

Problems such as these with fastener driving tools previously suggested for securing wallboard to studs and the like have been reasons contributing to the fact ____ ' i substantial present need, i.e., a tool which is capable of driving a fastener to a predetermined depth while simultaneously forming a recess of predetermined dimension and depth around the fastener head.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of the tools that have heretofore been proposed for simultaneously dimpling a workpiece surface as a fastener is being driven.

The fastener tool of the present invention is capable of automatically compensating for variations in driving resistance of a fastener. It minimizes the possibility of damaging the surface of wallboard and makes it possi³³ ble consistently to push and hold wallboard against a stud or the like. In addition, the tool is capable of being operated extremely close to comers so that virtually all of the fasteners that must be driven can be driven by the tool, rather than manually. Furthermore, the tool also incorporates mechanism that will prevent free firing,” i.e., firing before the tool is placed against a work surface, and structure that will minimize the possibility of damage to any of the parts should the tool be fired when no fastener is present or when inadequate backup support exists.

The pneumatically operated fastener driving tool includes a driver assembly that is reciprocated within a

FASTENER DRIVING TOOL

BACKGROUND OF THE INVENTION

The present invention relates generally to pneumatically actuated fastener drivers and more particularly to an improved fastener driver tool that drives a fastener and simultaneously forms a recess or dimple around the fdstencr.

Pneumatically operated fastener driving tools have been used in a substantial number of industries. Tools of this type have been used to drive fasteners such as staples, tacks, T-nails, and ordinary headed nails through readily pierceable materials.

One application for such tools that has great commercial potential is in driving fasteners for securing wallboard or dry wall, as to wooden supporting structures, such as studs and rafters. Since the use of dry wall and wallboard has become very extensive, especially in the prefabricated building industry recently, the need for such a practical tool has become very acute.

In securing wallboard to a wooden structure, it is highly desirable that the heads of the fasteners be countersunk and that a limited area of the surface of the wallboard, the area about the countersunk fastener head, be formed with a uniform but slight depression to receive a hardenable filter material so that the head of the fastener is not visible in the finished structure. The countersinking must be accomplished without tearing or ripping the surface, such as the paper surface, of the wallboard.

In order to accomplish this, several fastenmg tools have been proposed, each of which incorporates a dim- _______j___________ pling head or dimpler mechanism that is actuated by 35 jp appearance and that has a limited life, and the fastener driving mechanism to provide a shallow re- ..... ' ♦cess or dimple in the wallboard surface concurrently with the driving of a fastener into the wallboard. Examples of such tools are disclosed in the following U.S. ________________

Pat: Bacon et al. No. 2,679,044; Smith 2,918,675; Nel- 40 _{that no too}i_s commercially available to fill a very son 3,027,560; and Michel 3,040,327.

The tools disclosed in these patents utilize two basic types of driving means for the dimpler mechanism. The first type, which may be referred to as the direct impact type, has the driving piston, the carrier of the kinetic 45 energy, strike the dimpler in a direct metal-to-metal impact. The second type of drive mechanism utilizes a resilient member carried by the driving piston to soften the impact of the piston against the dimpler.

The advantage of the direct impact type is that the extent of penetration of the fastener relative to the dimpler can be accurately controlled. However, there are a number of disadvantages in a direct impact drive arrangement that overshadow the principal advantage. Because this arrangement requires metal-to-metal contact between the piston driver and the dimpler, the impact speed of the driver has to be considerably lower than in customary pneumatic fastener driving tools to reduce the shock and extreme stresses and to provide a reasonable service life for the various parts. This means that there is either more recoil of the tool or more weight must be added to the housing portion. If more weight is added to reduce recoil, the tool becomes heavy and awkward to handle. Of even greater ₆₅importance is the fact that when no fastener is located in the tool and the tool is actuated, the shock resulting from the direct impact between the drive piston and the

3.774.293 bore located in a housing and a dimpler mechanism supported for reciprocation on the housing. The dimpler mechanism has an inner portion in the bore located in the path of movement of a piston portion of the driver assembly. The inner portion of the dimpler mechanism, i.e., the portion closest to the piston, comprises a metal stud portion extending above a substantially flat surface and a resilient member seated on said flat surface surrounding the stud portion and extending above the upper surface of the stud. The stud portion and resilient member cooperate with the piston so that the dimpler is initially accelerated via contact between the piston and resilient member while the piston is decelerated, the piston acting to compress the resilient member. Thereafter, the metal piston first directly strikes the upper end of the metal stud to provide concurrent rigid movement of the dimpler mechanism and piston.

In the fastener driving tool of the present invention, a fastener driving element is secured to the piston eccentrically of the axis of the bore so that the driver element can be located closer to the front of the housing and as such in closer proximity to comers of workpieces, thereby to drive fasteners closer to comers and the like. In prior art tools, nails at comers had to be driven manually so that they entered the wallboard and members to be secured to each other generally perpendicularly. To counterbalance the weight of the driver element, the drive piston has counterbalancing means secured to the opposite side.

The tool also advantageously provides means for dissipating excess energy that is applied to the dimpler after a dimple has been produced in the workpiece, thereby to control the depth of the dimple and its size. More specifically, the dimpler has a convex or a spherical segment surrounding the outlet through which the fastener passes and an annular expansive collar adjacent to or surrounding the spherical segment. Preferably, the expansive collar is flat and tapers slightly upwardly and outwardly away from the spherical segment.

In addition, the tool also incorporates a safety-trigger interlock mechanism which prevents actuation of the tool until the dimpler mechanism engages a workpiece. The safety mechanism is actuated in response to movement of the dimpler mechanism from its extended position to its retracted position. In prior art tools it was necessary to retract the dimpler before the trigger could be squeezed, otherwise free firing of fasteners would take place. With the safety mechanism here incorporated, the trigger may be squeezed and held and as soon as the tool is placed against a workpiece, it will fire to drive and to dimple, speeding a cycle of operation of the tool.

Further, the tool also incorporates a specially located shock absorbing cushion which minimizes the possibility of damage to any of the parts should the tool be actuated, for example, when wallboard is not properly located with respect to a stud, such as where wallboard is spaced a distance away from a stud to which it is to be fastened, i.e., when inadequate back-up support exists.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF DRAWINGS

FIG. 1 is a fragmentary side elevation view, partly in section, of a fastener driving tool of this invention;

FIG. 2 is a bottom view taken generally along line 2—2 of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view showing the tool prior to application against a work 5 surface;

FIG. 4 is a section taken generally along line 4—4 of FIG. 3;

FIG. 5 is a bottom view of the dimpler mechanism taken generally along the line 5—5 of FIG. 3;

FIG. 6 is a view similar to FIG. 3 showing the tool at the end of a workstroke;

FIG. 7 is a sectional view taken generally along line 7—7 of FIG. 6;

FIG. 8 is a fragmentary sectional view taken gener15 ally along line 8—8 of FIG. 6;

FIG. 9 is a sectional view taken generally along line 9—9 of FIG. 6; and

FIG. 10 is a fragmentary rear view of the dimpler mechanism.

DETAILED DESCRIPTION

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one specific em25 bodiment, with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.

Referring first to FIGS. 1 and 3, there is illustrated a ³⁰ pneumatically operated fastener driving tool 10 including a housing structure 12 having a body portion 14 and a head portion 16 on the forward end of the body portion. The body portion serves as a handle by which the operator may grasp and manipulate the tool. The han³⁵ die portion is cored to provide a storage chamber 18 into which fluid under pressure, such as air, from a suitable source (not shown) is introduced through an opening 20, to provide air to appropriate passages for driving a piston.

⁴⁰ The head portion 16, located on the forward end of the housing, has an opening 22 that terminates at a lower end in a nose piece 24. A cylinder 26 is secured in the opening 22 and defines a bore 28 in which a driver assembly 30 is reciprocated by the source of ⁴⁵ fluid under pressure. The driver assembly 30 includes driving piston 31 which has a blade or driver 32 secured thereto.

According to one aspect of the invention, the driver element 32 is eccentrically secured to the piston 31 so ⁵⁰ that a suitable fastener or nail may be driven into a workpiece in sufficiently close proximity to a comer to meet the requirement of building codes and to minimize the necessity for hand or manual fastener driving. For example, some building codes require that the cor⁵⁵ ner fasteners must be perpendicularly driven into wallboard at least 3/8 inch, and not more than 1/2 inch from the wallboard edge. In the present tool, this is accomplished by eccentrically or laterally offsetting the driver element with respect to the central axes of the ⁶⁰ bore and the piston. As is clearly shown in FIGS. 1, 3 and 6, the driver element 32 is secured to the piston 31 between the central axis of the piston and the forward portion of the housing by an integral stud 34 (FIG. 6) which extends through an opening 36 in the piston 31 and which has an enlarged flange 38 which engages the lower surface of the piston. The driver element 32 is held in fixed position on the piston by a nut 40 threaded

3,774,293 normal position in FIGS. 1 and 3, the diaphragm assembly 52 is maintained in sealing engagement with the upper edge 54 of the cylinder or sleeve 26 to prevent the flow of compressed air into the upper end of the cylinder.

When the diaphragm assembly is seated on the upper edge of the cylinder 26, the chamber 60 is vented to atmosphere through an exhaust valve 90. This valve 90 is more clearly shown in FIG. 3 and includes a resilient valve seat 92 defined in the upper end of the cap 56 and a movable element 94 carried by the diaphragm assembly 52. In the lowermost position of the movable element 94, the area above the piston 31 is vented through openings 96 in the cap. However, movement of the dials phragm assembly upwardly will close the valve 90 to seal the area above the piston 31 from the atmosphere. It is also desirable to have a diffusing member 98 to divert the flow of air passing through openings 96.

When it is desired to actuate the tool, a ball 74 is 20 moved by a valve plunger 84 from its position shown in FIG. 3 to that shown in FIG. 6 by a trigger mechanism 86, which will be described later. Movement of the ball upwardly will block the flow of compressed air to the passage 70 and will simultaneously place the passage 25 70 in communication with exhaust port 78. This will exhaust the air from the area 64 and the compressed air in the annular chamber 50 will move the diaphragm assembly 52 upwardly to close valve 90 and seal the area above the driver assembly 30 from the atmosphere. 30 The compressed air on the upper surface of the piston 31 will drive the piston in the fastener driving direction. When the piston has moved to its downward position, the ball is again allowed to seat on the valve seat 76 and apply fluid under pressure to the area 64 and again seal ³⁵ the diaphragm assembly onto the upper edge of the sleeve while venting the chamber 60 through valve 90.

Upon reseating of the diaphragm assembly 52, the piston is returned to its initial position by compressed air entering from annular chamber 50 through open⁴⁰ ings 100 into the cylinder or sleeve wall between piston flanges 102 and 104 (FIG. 6) and the differential area of the piston flanges will move the driver assembly upward, as is explained in more detail in the abovementioned Langas U.S. Pat. No. 3,106,136.

According to the primary aspect of the present invention, the fastener driving tool 10 also includes a movable contactor mechanism. The contactor mechanism pushes a workpiece toward a second member to which it is to be secured by a fastener to hold the members to ⁵⁰ each other or to tighten their connection, or may be proportioned to dimple the work-piece surface. The dimpler mechanism described in detail herein produces a dimple or recess around a nail head as a nail is being driven to its final position in wallboard. The dimpler mechanism is reciprocatably driven by the piston 31. When the piston strikes the dimpler mechanism, the piston decelerates while simultaneously accelerating the dimpler mechanism. After that initial acceleration, during which an interposed resilient member is com⁶⁰ pressed, a metallic piston portion and a metallic dimpler mechanism portion rigidly engage each other. Thereafter the piston and metal dimpler portion move together to complete the dimpling operation. The dual phase impact design results in initial resilient impact ⁶⁵ between the dimpler mechanism and the piston, and a positive driver-dimpler relationship at the end of the piston stroke.

on the free end of the stud. The forward offset location of the driver element will allow a nail or other fastener to be driven in closer proximity to the forward end of the housing, as will be explained in more detail hereinafter.

As will be appreciated, fastening tools of the type to which this invention pertains are operated with highpressure fluid and act as guns that shoot fasteners rather than bullets. As such, the eccentric mounting and weight of the drive element on the piston will pro- 1 duce a side load on the piston during the driving of a fastener. To minimize this potential problem and to reduce the wear of the relatively moving parts, piston 31 also mounts a counterweight or counterbalancing means 44 between the central axes of the bore and piston and the rear of the housing structure. As clearly shown in FIGS. 1 and 6, the counterweight or counterbalancing means consists of a sleeve 46 that receives a stud 48 which is threaded into an opening 49 in the piston. For example, the sleeve and stud may have a com- ' bined weight that is substantially equal to the weight of the driver element 32, and the driver element may be offset to one side of the central axis of the bore substantially the same distance that the counterbalancing means is oppositely spaced from that axis. In order to further insure that the eccentrically mounted driver element will operate smoothly, the confronting surfaces of the cylinder 26 and the piston 31 are preferably finished with a coating of hard, smooth, and wear resistant material. With this arrangement, the eccentrically mounted driver element will not significantly adversely affect the operation of the tool during the fastener driving operation and will not significantly adversely affect the life of the tool.

Reciprocation of the piston is generally accomplished in the manner described in Langas et al. U.S. Pat. No. 3,106,136, the disclosure of which is incorporated herein by reference. Briefly, fluid under pressure is maintained in the storage chamber 18 as well as in an annular chamber 50 between the cylinder 26 and the inner surface of the opening 22 in the head portion of the tool. The flow of fluid or compressed air between the storage chamber 18 and a chamber 60 (between the interior of the cylinder 26 and the upper surface of the piston 31) is controlled by a diaphragm valve assembly 52 that seats against the upper edge 54 of the cylinder 26. The diaphragm assembly 52 is clamped between a cap 56 and the upper edge of the head portion 16 and serves to block off the flow of compressed air between the annular area or chamber 50 and the chamber 60 defined within the cylinder.

The diaphragm valve assembly 52 (FIG. 3) is biased against the upper edge of the cylinder by a spring 62 and high-pressure air introduced into a closed area 64 between the diaphragm assembly and the cap 56. The high-pressure air is introduced into the area 64 through a tube 66 that extends through the annular chamber 50 and has its upper end in communication with the area 64 through a passage 68. The lower end of the tube 66 is in communication with a passage 70 defined in the housing wall and communicating with valve means 72.

The valve means 72 (FIGS. 3 and 6) consists of a ball 74 that is normally maintained in a valve seat 76 located between passageway 70 and an exhaust port 78. In this position, fluid under pressure is delivered from the storage chamber 18 through an opening 80 in alignment with the ball 74. With the ball 74 shown in the

3,774,293

As is clearly shown in FIG. 3, the dimpler mechanism is generally designated by the reference numeral 120 and has an inner or upper end portion 122 located within the bore 28 and disposed in the path of movement of the driver assembly 30. The dimpler mechanism further includes a second lower or outer end portion 124 below the cylinder bore 28 that has a dimple forming member 126 at the free end thereof which defines a fastener outlet 128 (FIG. 6) through which fasteners pass and which is aligned with the path of movement of the elongate driver element 32. The inner and outer portions 122 and 124 are interconnected through a sleeve 123 on the inner portion 122 and a stud 125 on the outer portion that are secured by a pin 129.

The driving means between the driving piston 31 and the dimpler mechanism 120 consists of first resilient means interposed between the piston and the inner end of the dimpler mechanism and carried by one of them initially for accelerating the dimpler mechanism while decelerating the piston, and rigid striker means on the piston and dimpler mechanism for direct striking engagement with each other after initial acceleration of the dimpler mechanism and deceleration of said piston and after the piston and dimpler mechanism are traveling at a substantially reduced velocity differential. The driving means is most clearly shown in FIGS. 3 and 6 and includes a resilient member 130 that is supported on the upper surface of an enlarged flange 132 at the upper or inner end of the dimpler mechanism 120. The resilient member, which is preferably formed of rubber or other material having elastic memory characteristics, defines an opening 134 through which the driver element 32 extends. The rigid striker means for direct engagement consists of a bore centered stud member or stud 136 that is integral with, and extends upwardly toward the piston above the upper surface of the enlarged flange 132 and which is located in an opening 138 in the resilient member. The stud 136 has an enlarged head portion 140 that is received in an enlarged portion of the opening 138 and that engages an annular flange 142 defined in the opening 138 intermediate the opposite ends thereof. With this arrangement, the upper surface of the resilient member 130 is located above the upper surface of the stud 140 and is also located in the path of movement of the piston.

The rigid means for producing direct engagement between the piston and dimpler mechanism further includes a projection 144 depending from the lower surface of the piston 31 and which is aligned with the stud 136. The projection consists of a bolt which has an enlarged circular head 144aand which extends through an opening in the piston. The circular head or projection 144α is held in fixed relation on the piston by a nut 146 threaded on the other end of the bolt.

It should be noted that the longitudinal axes of the projection 144 and the stud 136 are coincident with each other and are also coaxial with the axes of the bore 28 and of the piston 31.

Thus, initial engagement between the piston and the dimpler mechanism is through the resilient member 130 and the driving piston initially compresses the resilient member or bumper resulting in a gradual deceleration of the piston and a simultaneous acceleration of the dimpler mechanism. When the resilient member has deflected sufficiently the piston projection 144 directly strikingly engages the confronting upper surface of the stud 136 to cause simultaneous movement of the dimpler with the piston.

It is desirable that the resilient member has compressibility characteristics such that it will deflect just 5 sufficiently for the piston projection to just touch the stud 136 at the terminal portion of movement of the piston for a fastener and lumber combination which it is anticipated will require the greatest driving force so that the piston moves the dimpler mechanism just 10 enough to produce the desired dimple. With this arrangement, it will be assured that the same dimple will be made for all grades of lumber and regardless of other factors which affect the driving resistance for the fastener. If the driving resistance is lower, the excess 15 energy transmitted to the dimpler mechanism may be dissipated in a manner to be described hereinafter.

It should be noted that the compression of the resilient member 130 will accelerate the dimpler mechanism and will result in substantial reduction in the ve20 locity differential between the dimpler mechanism and piston before rigid metal-to-metal contact takes place between them. It is desirable that the velocity of the piston be reduced so that approximately one-half of the total piston energy is used for driving the fastener while 25 the remaining half of the energy is used for the dimpling operation. With this arrangement, it is possible to “blank fire” the tool continuously at normal operating pressure without exceeding the endurance stress limit of the metallic dimpler mechanism and piston projec³θ tion.

According to another aspect of the present invention, the contactor mechanism which in this case is a dimpler mechanism incorporates means for engaging a work surface and for dissipating excess energy that is applied ³⁵ to the dimpler mechanism after a dimple has been produced in a work surface. To that end, outer end portion 124 includes a dimple forming member 126. Member 126 includes a dimpling surface 150 surrounding the fastener outlet 128 and an integral expansive energy ⁴⁰ absorbing surface segment 152 adjacent the dimpling surface. The surface segment 152 has been illustrated as being a collar surrounding dimpling surface 150, whereas dimpling surface 150 has been illustrated as a spherical segment. As more clearly shown in FIG. 6, ⁴⁵ surface segment 152 is in the form of an expansive flat annular surface. It is disposed at a small acute angle with respect to the confronting workpiece surface and the outer periphery thereof merges with an arcuate segment 154 that has a radius substantially less than the ⁵⁰ radius of the collar and has its inner edge merging tangentially with the flat surface while the opposite edge is directed upward toward the driver assembly. This arrangement makes it possible to obtain the advantages of the tool even if it is slightly tilted (not exactly per⁵⁵ pendicular) in use. Desirably, the forward end of the collar is cut off (shown at 153) to accommodate location of said dimpler in close proximity to a comer of a workpiece.

It is preferable that the acute angle defined between the flat surface segment 152 and the wallboard surface be substantially less than 30°, i.e., less than 30° to a plane normal to the axis of the bore 28, and preferably about 5° to 7°, and that the total area of the flat surface be substantially greater than the area of the dimpling surface 150.

With this arrangement, and with the driving mechanism for the dimpler mechanism that has been de3,774,293 trol means for controlling the movement of tire piston that prevents firing of the tool when the tool is not in its operative position with respect to a workpiece. The safety mechanism is generally constructed in accordance with the teachings of Langas U.S. Pat. No. 3,194,324, which is incorporated herein by reference. In the present tool, all of the movable elements of the safety mechanism are substantially enclosed within the tool housing.

As more clearly shown in FIG. 3, the safety mechanism includes a safety pin 170 that is guided for movement in spaced openings 172 defined in the head portion 16 of the tool. The pin 170 is normally biased to its extended position by a spring 174 having one end 15 engaging an annular shoulder on the pin and an opposite end engaging a surface on the head portion 16. The upper end of the pin cooperates with a trigger lever 176 that forms part of the trigger mechanism 86. The trigger lever 176 is pivoted at one end to a trigger member 20 180 that in turn is pivoted on a pin 182 which extends through aligned openings in flanges extending from the housing (only one being shown). The opposite end of the lever 176 is positioned in the path of movement of the safety pin 170 while an intermediate portion of the 25 lever 176 cooperates with plunger 84 that moves the valve 74 between its position.

With the safety pin 170 in the position shown in FIG. 3, the trigger member 180 can be moved between the solid and dotted line position shown therein without 30 moving the plunger 84 sufficiently to actuate the valve 74. However, if the safety pin is moved to a retracted position shown in FIG. 6, the upper end of the safety pin will carry the free end of the trigger lever 176 upwardly so that movement of the trigger member 180 to lever about the upper end of safety pin 170 to actuate the valve. The movement of the safety pin 170 between its extended and retracted positions, respectively shown in FIGS. 3 and 6, is accomplished by engage⁴⁰ ment of the dimpler mechanism with a workpiece supporting surface and by movement of the dimpler mechanism thereagainst to a retracted position. The safety mechanism includes a collar 184 secured to the lower end of the pin and having an arm 186 extending there⁴⁵ from and overlying the upper surface of a projection 187 extending from the enlarged flange 132 of the dimpler mechanism 120. Flange 132 is slightly eccentric to permit air to escape while the piston is descending. Projection 187 extends across the open area to provide for engagement with arm 186. Thus, if the dimpler is moved from the solid to the dotted line position shown in FIG. 3, the flange 132 will carry the collar, and the pin upwardly to move the safety pin 170 to its release position. This arrangement insures that the dimpler mechanism is in a proper retracted position with respect to the head portion of the tool before the valve means 72 can be operated.

The present arrangement also has the desired advantage of being capable of continuously operating the fastener tool without having to repeatedly pull the trigger. Thus, if the trigger member 180 is held in the “on” position, the driver assembly 30 will be moved through its power stroke each time the dimpler mechanism is moved to its retracted position, thereby speeding the driving of fasteners.

As was explained above, the present tool is designed such that during normal operation, the tool cannot be scribed above, a uniform dimpling depth is achieved even though the operating pressure, the lumber grade or the driving resistance of the fasteners may change, within normally anticipated ranges. Any excess energy that is developed, such as that which may result from reduced driving resistance, is applied to the surface segment 152 and will be absorbed and dissipated by the wallboard surrounding the dimple or recess formed by the dimpler surface. Since the total surface area of the surface segment 152 is substantially greater than the total exposed surface area of the dimpling surface 150, all excess energy developed will be absorbed by the wallboard with a negligible increase in the dimple depth and without tearing the sheathing or face paper and without crushing the gypsum core.

The dimpler mechanism is positively guided for reciprocable movement on the housing to insure that it travels along a predetermined path while it is driven from its retracted to its extended position. For this purpose, the nose piece 24 mounts a pair of transversely spaced depending members 158 (FIGS. 4 and 7), each having an elongated slot 160 therein. The main body portion of the outer portion 124 is guided for movement between the adjacent surfaces of the members 158 and has outwardly directed flanges 162 that are located in the slots 160 (FIG. 7).

It should be noted that while the dimpler mechanism has been specifically disclosed and described in connection with an eccentric driver element, the advantages of the dimpler disclosed herein could readily be gained by having the outer portion 124 and its fastener outlet 128 coaxially aligned with the piston and bore axes. .

» itfsolidlinTposition by any suitable means, and a magazine 164 has been illustrated which has an open end in communication with a slot 166 that extends from one side of the dimpler (FIG. 7). The magazine is held in fixed relation on the dimpler mechanism, as by a bracket 168.

The tool is also easily accessible for clearing a jam in the dimpler mechanism. Heretofore, it has been common to either have a split member that defines the fastener receiving opening that could be opened to one side for clearing a jam or alternatively the opening was slotted the entire length thereof to one side so that access could be gained to remove bent or slightly misformed fasteners. Because of the high shearing stresses that are developed during the use of the high speed fastener tool designed in accordance with this invention, the split nose piece cannot be utilized and still have a dimpling mechanism that is capable of withstanding continued use without destruction of parts or it would be very heavy and bulky. Also, the slotting of the open- ₅₅ing the entire length thereof is not feasible because it would eliminate the possibility of having a uniform dimple surrounding the fastener head. Accordingly, a reduced opening or slot 169 is defined in the outer end portion 124 of the dimpler mechanism to provide ready ₆₀access to any fasteners which may become jammed in the fastener outlet 128. .

As was explained above, the high-speed operation of the tool makes the tool a gun and the fastener being driven by the driver assembly could be considered to be equivalent to a bullet when the tool is not placed against a workpiece. Thus, the present tool incorporates a safety mechanism that cooperates with the con65

3,774,293 mechanism having an inner end in said housing and which is positioned to be engaged by said piston and an outer end outside of said housing and which is positioned to engage a workpiece; first means interposed 5 between said piston and said inner end for accelerating said contactor mechanism while decelerating said piston when said piston first engages said contactor mechanism; rigid striker means on said piston and said contactor mechanism for direct striking engagement with 10 each other after said piston has been decelerated; and said housing structure defining passages for supplying fluid to one end of said bore for reciprocating said piston.

2. A fastener driving tool in accordance with claim 1, ¹⁵ in which said first interposed means comprises a resilient member carried by one of said piston and said contactor mechanism.

3. A fastener driving tool in accordance with claim 2, in which said inner end defines an enlarged flange, said ²⁰ resilient member being supported thereon, and in which said rigid striker means includes a stud member on said contactor mechanism extending upwardly toward said piston.

4. A fastener driving tool in accordance with claim 3, and in which said rigid striker means includes a projection depending from said piston, said projection being aligned with said stud member.

5. A fastener driving tool in accordance with claim 2 ₃₀ including cushioning means interposed between said contactor mechanism and said housing structure for absorbing energy from said contactor mechanism.

6. A fastener driving tool in accordance with claim 1, wherein said fastener driver is secured to said piston 35 and is laterally offset from the central axis of said piston bore, said fastener driver being located between said central axis and the forward portion of said housing structure, and counterbalancing means carried by said piston between said central axis and a rear portion of 40 said housing structure.

7. A fastener driving tool in accordance with claim 6, in which said contactor mechanism defines a fastener outlet aligned with said fastener driver and located below the lower end of said bore.

8. A fastener driving tool in accordance with claim 6, in which said rigid striker means includes a stud member on said contactor mechanism extending upwardly toward said piston and aligned with said central axis.

9. A fastener driving tool in accordance with claim 1 50 in which said contactor mechanism is a dimpler mechanism defining a fastener outlet and having a dimpler surface surrounding said fastener outlet, and having an expansive energy absorbing surface adjacent said dimpler surface positioned to engage a surface of a work³³ piece after said dimpler surface engages said surface.

10. A fastener driving tool in accordance with claim 9 wherein said expansive energy absorbing surface is a collar surface surrounding said dimpler surface.

11. A fastener driving tool in accordance with claim ⁶⁰ 10 in which said collar surface is flat and is inclined at an angle of less than 30° to a plane normal to the axis of said bore.

12. A fastener driving tool in accordance with claim 1, including alignment means carried by said tool and positioned to engage a surface of said workpiece for maintaining the axis of said bore substantially perpendicular to the surface of said workpiece.

actuated without having the dimpler mechanism in a retracted position. However, if the tool were to be placed in position for operation and actuated without proper back-up support, the driving and dimpling energy would not be absorbed by the workpiece and could therefore result in high impact force between the dimpler and the nose piece. According to the present invention, a cushioning means or washer 190 is interposed between the housing nose piece and the adjacent surface of the dimpler mechanism to absorb excess energy that is developed when the tool is fired without proper or adequate back-up support. Lack of proper back-up support occurs, for example, when the tool is placed against wallboard at a location spaced from a stud or when the wallboard is spaced outwardly from a stud, for example, at a distance of one-half inch where the wallboard is to be secured to the stud, or when the stud is not properly anchored, hence is loose.

The dimpling tool further includes alignment means carried by the tool and adapted to engage the surface of the workpiece for maintaining the axis of the bore 28 cis well as the axis of the driver element 32 substantially perpendicular to the surface of the workpiece. Such a means is schematically illustrated in FIG. 1 as a Ushaped bracket 194 that may be secured to the tool by a common connection that defines the connection for the magazine. The U-shaped bracket may provide a lower flat surface 196 that engages the workpiece surface to maintain a proper aligned relation of the tool with respect to the surface. Alternatively, an alignment means may be integrally formed with the dimpler mechanism.

The advantages of the present tool have been set forth in the above description that will briefly be summarized at this point. The construction of the tool allows for a fast cycling pneumatically operated fastener driving tool that can precisely limit the terminal driver position of the dimpler mechanism with respect to the surface of the workpiece while preventing the tearing of the thin sheathing of wallboard around the nail and dimple or recess. The tool also forces the wallboard against the supporting studs while the fastener is being driven and allows for concurrent driving of the fastener and production of the recess or dimple. The eccentric arrangement of the drive element allows for all fasteners to be driven perpendicularly into a workpiece by the tool and still meet the acceptable building codes relative to the spacing between workpiece comers and the location of the fastener. The tool produces a substantially constant dimple depth even though the fastener driving resistance varies. The tool is capable of being fired without proper back-up support and still have a life time cycle of millions. The tool is also easily accessible for clearing a jam and is light in weight with a minimum number of moving parts that can readily be serviced. Further, it will be realized that hand tools with the type of action described herein are not limited to drywall or wallboard application. They may also be used for fastening thin sheathing, for fastening subflooring or hardwood flooring, or wherever simultaneous fastener driving and tightening to a support or dimpling is desired.