Abstract:
A gun device for driving a fixing element into a work surface includes a driving mechanism for the fixing element. The gun device further includes supply means for a filler material, the supply means having an outlet arranged to deposit filler material on the work surface at a point corresponding substantially to an entry point of the fixing element into the work surface. Actuating means is provided for actuating the supply means in response to advancement of the gun device towards the work surface to deposit filler material on the work surface. Movable means is provided, movable in response to retreat of the gun device from the work surface, to pass across the work surface over the end of the fixing element so as to cause deposited filler material to smooth and fill any depression formed in the work surface as a result of operation of the gun device.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a device for driving a fixing element into a work surface, for example a constructional material. The device may be used for driving fixing elements such as nails into wood, and more particularly but not exclusively the invention relates to a nail gun for use such as in the construction of pallets and crates, fixing of floor boarding, manufacture of furniture and the fixing of trim and architraves. 
         [0002]    When using machines of the above type, the depression left in the material when the nail is driven to the required depth can be unacceptably unsightly. To improve the finish, the depressions might be filled with a wood-filler which could require further dressing when cured. This is a labor-intensive operation which increases the cost of the process. 
         [0003]    It is an object of the present invention to provide a device for driving a fixing element into a work surface and simultaneously for filling any depression formed in the material as the fixing element is inserted. 
       SUMMARY O INVENTION 
       [0004]    According to the present invention there is provided a gun device for driving a fixing element into a work surface and including a driving mechanism for driving a fixing element into the work surface, characterised in that the gun device further includes: supply means for a filler material, the supply means having an outlet arranged to deposit filler material on the work surface at a point corresponding substantially to an entry point of the fixing element into the work surface; means for actuating the supply means in response to advancement of the gun device towards the work surface to deposit filler material on the work surface; and means movable in response to retreat of the gun device from the work surface to pass across the work surface over the end of the fixing element so as to cause deposited filler material to smooth and fill any depression formed in the work surface as a result of operation of the gun device. 
         [0005]    The supply means may comprise a piston pump dispenser including a body attached to the remainder of the device, piston means biased to an extended configuration, and a reservoir. Thus, as the device approaches the work surface the piston is depressed and filler material in the dispenser is displaced and deposited on the work surface substantially at the point of entry of the fixing element into the work surface such that, in use, the fixing element passes through the filler material and draws a portion thereof into the work surface. The energy required for operation of the piston pump is derived from work done by the user of the device in bringing the device into close proximity to the work surface. 
         [0006]    The means for actuating the supply means may comprise a shaft which protrudes from the remainder of the dispenser to contact the work surface. In this way, the contact and the relative motion between the shaft and the remainder of the dispenser causes operation of the dispenser. The shaft may be hollow for the passage of filler material to the outlet. A one-way valve may be incorporated into the piston to inhibit the flow of filler material from the outlet back into the supply means. In this way, return motion of the piston under the unrestrained action of spring loading may induce flow from a reservoir of filler material. 
         [0007]    The piston pump dispenser may include a spill port which is covered by the piston means during part of its travel such that on initial movement of the piston means the spill port is open and filler material flows back to a reservoir, while on further movement the piston means closes the spill port and filler material is dispensed through the outlet. The reservoir may be made of a flexible material, for example contained within a substantially rigid frame. This allows the reservoir to accommodate the change in volume associated with the action of the dispenser and allows the reservoir to exclude gases therefrom. 
         [0008]    The supply means may be operated on advancement of the device as a result of contact with the work surface. 
         [0009]    An axial direction of the outlet may be inclined to a direction of movement of the fixing element from the device into the work surface. The axial direction of the outlet may intersect with the direction of movement of the fixing element. Thus the outlet dispenses the filler material onto the work surface at a position substantially in the path of the fixing element during operation of the device. Thus, the stroke of the dispenser piston together with the angle of inclination of the outlet relative to the path of the fixing element may determine the distance moved by the outlet across the work surface. Such movement may wipe the filler material into any depression caused by the action of the device. 
         [0010]    The outlet of the supply means may be movable in response to retreat of the gun device from the work surface so as to cause deposited filler material to fill any depression. Thus, after operation, as the device is raised from the work surface in a direction substantially normal thereto, the motion of the outlet, for example under the influence of a biasing spring, may maintain contact with the work surface so as to wipe across any depression formed in the work surface and to fill the same. 
         [0011]    Alternatively, the means movable in response to retreat of the device may be selected from a wiper and a roller. The movable means may be movable such that, on advancement of the device towards the work surface, the movable means is retracted from a first position in which it extends across a direction of movement of the fixing element from the device into the work surface to a second position in which the movable means is clear of the direction of movement and, on retreat of the device from the work surface, the movable means is advanced from the second position to the first position so as to cause deposited filler material to fill any depression. As the movable means is moved between the first and second positions the movable means may be moved initially towards and subsequently away from the work surface. The movable means may be moved along an arcuate path. 
         [0012]    The movable means may be movable by means selected from a cam mechanism, a rack and pinion assembly and a worm drive which is operated as the device is advanced towards and retracted from the work surface. 
         [0013]    The movable means may be made of a flexible material, such as a resilient material. The movable means may be made of a material having a low coefficient of friction and/or may be coated with a material having a low coefficient of friction. 
         [0014]    The wiper may be formed with a waisted portion to increase flexibility thereof. Biasing means may be provided to urge the movable means towards the work surface. 
         [0015]    The filler material may be formulated to change from a substantially liquid state in the reservoir to a solid state after being dispensed. In order to prevent the filler material hardening in the outlet, the outlet may incorporate a one-way valve which allows the passage of filler material under the action of internal pressure, but otherwise provides an air-tight seal. In this way the outlet is sealed between use so as to prevent access to air and moisture and the loss of volatile constituents of the filler material. 
         [0016]    A guard may be provided to surround the filler material deposited on the work surface. The guard may be at least in part flexible. The outlet may form part of the guard at the time the fixing element is driven into the work surface. Such a guard may assist in the prevention of splattering of the filler material when the fixing element passes through the filler material at high speed. 
         [0017]    The movable means may be located in a movable foot of the device. A surface of the foot adapted to contact the work surface may be provided with a non-slip surface. The movable foot may be substantially U-shaped. The outlet may extend into an open side of the U-shaped foot. 
         [0018]    The whole of the dispenser for the filler material may be made as a disposable item which is replaced when the filler material is exhausted. Such a disposable item may also include the guard. Alternatively, the dispenser may incorporate a disposable reservoir of filler material for attachment to the remainder of the dispenser. The dispenser itself may then be replaced after several reservoirs have been attached. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0019]    For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: 
           [0020]      FIGS. 1 to 3  show the basic elements of one embodiment of a device for driving fixing elements, in the form of a nailgun, according to the present invention; 
           [0021]      FIGS. 4 to 7  show an operating sequence of a dispenser piston relative to a nailgun mechanism; 
           [0022]      FIGS. 8 and 9  are a cross-sectional view and an elevational view of a dispenser pump,  FIG. 8  being a section taken along the line A-A in  FIG. 9 ; 
           [0023]      FIGS. 10 and 11  are cross-sectional views corresponding to  FIG. 8  and illustrate the operation of a spill valve arranged on the dispenser pump of  FIGS. 8 and 9 ; 
           [0024]      FIG. 12  is a cross-sectional view corresponding to  FIG. 8  and illustrates a reservoir attached to a filler dispenser; 
           [0025]      FIGS. 13 to 16  illustrate the operation of a wiper mechanism attached to a filler dispenser; 
           [0026]      FIGS. 17 to 19  illustrate a guard attached to the wiper mechanism of  FIGS. 3 to 16 ; 
           [0027]      FIGS. 20 and 21  show a nozzle tip of a dispenser co-operating with a flexible guard to provide a sealed surround for filler at the instant or activation of the nailgun; 
           [0028]      FIGS. 22 and 23  show a sealing device for filler material; 
           [0029]      FIG. 24  is a diagrammatic perspective view of a part of another embodiment of a device for driving fixing elements, in the form of a nailgun, according to the present invention; 
           [0030]      FIG. 25  is a perspective view from above of a foot of the nailgun shown in  FIG. 24 ; 
           [0031]      FIG. 26  is a perspective view from below of the nailgun foot shown in  FIG. 25 ; and 
           [0032]      FIG. 27  is an elevational view of a wiper blade for use in the nailgun of  FIGS. 24 to 26 . 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0033]      FIGS. 1 to 3  show important features of a conventional nailgun, in which nails  43  are formed into a strip to be fed through a slot  45  in a gun barrel  35  from a magazine (not shown) held by mounting holes  48 . A drive pin  42  is powered by piston  41  by gas pressure applied to the upper surface of the piston  41 , the flow of gas being regulated by a first trigger mechanism (not shown). A second, interlocking trigger mechanism is attached to a movable foot  44  so that, in order for the nailgun to operate, both trigger mechanisms must be activated. This is a well-known safety feature and prevents accidental firing of the nailgun. 
         [0034]    The foot  44  is spring loaded to an extended position, as shown in  FIG. 2 . In order to activate the trigger mechanism, the foot  44  must be depressed as shown in  FIG. 3  so that the end of the nailgun barrel  35  is brought close to a wooden block  36 . 
         [0035]    In accordance with the present invention, when the two trigger mechanisms are activated, the drive pin  42  moves down through an orifice  47  in barrel  35  to position a dispenser nozzle  34  substantially on an inclined line intersecting the axis of the orifice  47  and hence the axis of motion of the nail  43  when driven. The dispenser nozzle  34  is spring loaded to an extended position as shown in  FIG. 2 . A shoe  32  is mounted on the end of the dispenser nozzle  34  to guide filler from the dispenser nozzle onto the surface of the wooden block  36 . As the nailgun is brought close to the wooden block  36  to depress the foot  44  and activate an interlock trigger, the motion activates a dispenser (not shown in  FIGS. 1 to 3 ) causing filler material to be deposited through the dispenser nozzle  34  onto a surface of the wooden block  36  in the path of the driven nail such that the nail  43  passes through the filler material and draws a portion of the filler material into the wooden block  36 . 
         [0036]    The filler material is designed to change from a substantially liquid state prior to being dispensed to a solid state after being dispensed. 
         [0037]      FIGS. 4 to 7  show the motion of the dispenser nozzle  34  and the shoe  32  as the nailgun barrel  35  is moved in a direction perpendicular to the surface of the wooden block  36 . A nail site  31  is shown to indicate the intended position of the nail.  FIG. 4  shows that initially the shoe  32  is pressed against the wooden block  36  by spring force from the dispenser (not shown in  FIGS. 4 to 7 ). The shoe  32  covers the nail site  31 . As the nailgun moves to the position shown in  FIG. 5 , the nozzle moves along an inclined guide  33  and the shoe  32  moves across the surface of the wooden block  36  away from the nail site  31 . The motion of the nozzle  34  causes the dispenser pump to activate and filler material is deposited on the surface of the wooden block  36  on or close to the nail site  31 .  FIG. 6  shows a configuration in which the barrel  35  is closer to the wooden block  36  than in  FIG. 5  so that more of the nail site  31  is uncovered by the shoe  32 .  FIG. 7  shows the nozzle  34  fully depressed at a point where the foot  44  (not shown in  FIGS. 4 to 7 ) has activated the interlocking trigger and the nailgun is ready to fire. The dispenser has delivered a desired quantity of filler to the surface of the wooden block  36 . The nailgun is then activated and the nail is fired into the wooden block  36 . As the nailgun is moved away from the wooden block  36  after firing, the shoe  32  maintains contact with the wooden block  36  and slides back over the nail site  31 . The action of the shoe  32  causes the filler material in the vicinity of the nail site  31  to be smoothed into the cavity (depression) formed by the nail in the wooden surface  36 . 
         [0038]      FIGS. 8 and 9  show the filler dispenser in section and in elevation. A dispenser outlet  21  is connected to the nozzle  34  of  FIGS. 4 to 7 . The dispenser outlet  21  is a hollow tube rigidly attached to a pintle  15  which is attached to a return spring  19 . The pintle  15  is connected to the dispenser outlet  21  so that filler material might flow through the annular gap therebetween, provided that a piston  11  is not abutting the pintle  15  and thus sealing the passage. The piston  11  is slidingly mounted on the dispenser outlet  21  and is urged against a back face of the pintle  15  by a piston spring  18 , thus closing a connection between filler in the body of a dispenser  10  and the dispenser outlet  21 . When the pressure in the body of the dispenser  10  exceeds a pressure determined by the piston spring  18 , the piston  11  moves away from the back of the pintle  15  allowing filler material to pass through the dispenser outlet  21 . A spill hole  20  and an inlet  14  are connected to a reservoir  25  ( FIG. 12 ). As the dispenser outlet  21  is depressed, the piston spring  18  moves the piston  11  down the body of the dispenser  10 . The piston  11  is in contact with the pintle  15 , sealing the dispenser outlet  21 . This motion causes filler material to flow from the dispenser body  10  through the spill hole  20  and back to the reservoir  25 . 
         [0039]    Backflow through the inlet  14  is prevented by a check ball  12  which engages a seat  16 . 
         [0040]      FIGS. 10 and 11  show the dispenser outlet  21  at the extremes of its movement. As the dispenser outlet  21  moves from the position shown in  FIG. 10  to the position shown in  FIG. 11 , it causes the piston  11  to move over and cover the spill hole  20 . While the spill hole  20  remains uncovered, the filler material in the body of the dispenser  10  is pushed out of the spill hole by the action of the piston  11 , and at the same time the piston  11  remains in contact with the pintle  15  maintaining the dispenser outlet  21  closed. When the spill hole  20  is covered by the piston  11 , backflow to the reservoir  25  through the spill hole is prevented. Backflow through the inlet  14  is also prevented by the check ball  12 . Further movement of the dispenser outlet  21  causes the pressure within the dispenser body  10  to rise and to displace the piston  11  against the piston spring  18  and so to break the seal between the piston  11  and the back of the pintle  15 . Filler material is now displaced through the dispenser outlet  21  for the remainder of the stroke of the dispenser to the position shown in  FIG. 11 . The quantity of filler material dispensed is therefore a function of the cross-sectional area of the piston  11  and the position of the spill hole  20  relative to the end of the stroke of the dispenser outlet  21 . Moreover, delivery of filler material will not commence until the spill hole  20  is covered so that the first part of the stroke will not cause delivery, so that accidental contact with the dispenser outlet  21  will not give rise to delivery of the filler material. 
         [0041]      FIG. 12  shows the dispenser body  10  connected to the reservoir  25 . The reservoir is ideally constructed of a flexible, non-stretch material which can readily change its shape and volume, without pressure change, as the quantity of filler material in the reservoir changes. The flexible reservoir  25  is preferably housed within a rigid frame or container for protection. 
         [0042]      FIGS. 13 to 16  show a filler dispenser system which incorporates a wiper  52  to provide the function of the shoe  32  described in relation to  FIGS. 1 to 12 . The wiper  52  is supported by links  53  attached to a main body  55  of the dispenser system, which is in turn attached to a nailgun barrel  35 . The geometry of the links  53  and the wiper  52  constrain a leading edge of the wiper to follow an arcuate path approximating to the axis of the dispenser  10 . The wiper  52  is spring loaded to the extreme position shown in  FIG. 16 . As the nailgun approaches the wooden block  36 , the wiper initially contacts the surface of the wooden block  36  so that the leading edge covers the position of the nail site  31 . As the nailgun is brought closer to a position corresponding to  FIGS. 10 and 11 , the wiper  32  retracts back across and away from the nail site  31  and the inner surface of the wiper  52  contacts a dispenser nozzle  51  in a recess  57 . Further motion of the nailgun to the position of  FIG. 13  causes dispenser nozzle  51  to depress and deliver a quantity of filler material to the surface of the wooden block  36  from the recess  57  in the wiper  52  via a connecting channel. The nailgun, in the configuration of  FIG. 13 , is ready to fire and the interlocking trigger on the foot  44  (not shown in  FIG. 13 ) Is connected. After the nail has been fired through the filler material, the nailgun lifts away from the surface of the wooden block  36  in a direction perpendicular to the surface and the wiper  52  remains in contact with the surface by means of a spring (not shown). The wiper  52  moves back towards the nail site  31  and smooths the filler material into the depression caused by the nailing action at the nail site  31 . It is intended that the main body  55 , the links  53  and the wiper  52 , together with the dispenser and filler reservoir, might be manufactured cheaply as a disposable item, to be replaced in part or totally on exhaustion. With this design, the dispenser can be simplified to eliminate the spill hole and return passageway, since the stroke can be much shorter as it is not required for the smoothing action. 
         [0043]      FIGS. 17 to 19  illustrate the fitting of a flexible guard  58  to the wiper  52 . The flexible guard  58 , together with the wiper  52 , surrounds the filler material on the surface of the wooden block  36  at the point when the nail is fired. The flexible guard  58  contains the filler material and prevents splatter as the nail penetrates the filler material at high speed. The flexible guard can be part of the disposable system previously described. 
         [0044]      FIGS. 20 and 21  illustrate a guard system for the dispenser system described in relation to  FIGS. 1 to 12 . A splatter guard  64  is mounted on a bracket  65  attached to a filler dispenser body  62 . These components, together with the dispenser, reservoir and filler material, might form part of a disposable system. 
         [0045]    The shoe  32  on the dispenser nozzle  34  forms an infill between the open ends of the substantially C-shaped splatter guard when the dispenser nozzle  34  is in its fully depressed position. As the nailgun is fired and the nail impacts with the filler material, the splatter guard forms a complete seal around the nail site  31  against the surface of the wooden block  36 . 
         [0046]      FIGS. 22 and 23  show a simple sealing system that acts as a one-way valve to prevent the filler material hardening in the dispenser during periods when not in use. The figures represent the dispenser body  10  attached to a fixing armature  82  through which the dispenser outlet  21  is attached to shoe  32 . In this arrangement the shoe is substantially cylindrical with an orifice  88  in the side wall, through which the filler material is delivered. An elastic sleeve  84  is slipped on the cylindrical surface of the shoe  32  so that the material of the elastic sleeve  84  is in tension. Positive pressure from the inside of the shoe  32  will cause the sleeve to lift from the surface of the shoe and allow filler material out. Air, dirt and moisture are prevented from entering the orifice  88  and low pressure vapors from volatile constituents of the filler material cannot escape through the orifice, thus preventing premature hardening of the filler material. 
         [0047]    Various modifications may be made without departing from the invention. For example, the dispenser might employ different valves and piston design or the splatter guard system might be permanently affixed to the nailgun barrel. 
         [0048]    The nailgun shown in  FIGS. 24 to 27  includes a dispenser  10  having a nozzle  51  and mounted within a dispenser body  62 . The nozzle  51  is configured such that, as the nailgun is operated by movement towards a work surface (not shown) the nozzle engages against the work surface and causes the dispenser  10  to retract into the dispenser body  62  so as to dispense a predetermined volume of filler onto the work surface in the path of a nail (not shown). 
         [0049]    A foot  44  is mounted on supports  46  which extend upwardly to a body of the nailgun in conventional manner. As explained previously, the foot  44  is movable relative to the body of the nailgun and is biased towards an extended position. As the foot is caused to retract as a result of contact with the work surface a second, interlocking trigger mechanism (not shown) is conventionally provided as part of the actuating mechanism for the nailgun. 
         [0050]    A cam actuator  90  is provided on the body  55  of the nailgun in a predetermined position so as to engage with a cam  91  provided on the foot  44  as the foot is retracted. The foot  44  is substantially U-shaped in configuration so as to substantially surround a region on the work surface into which the nail is to be inserted. The lower face of the foot  44  is provided with a non-slip surface, for example of thermoplastic elastomer having a medium to high Shore hardness, in order to ensure the nail is inserted into the intended region. The non-slip surface may be ridged to enhance grip with the work surface. If desired, the non-slip surface may be removed and replaced with fresh material to ensure a continuing satisfactory engagement with the work surface into which the nail is to be inserted. The nozzle  51  of the dispenser extends into an open side of the U-shaped foot  44  so as to dispense the filler at the desired location as the foot is retracted. 
         [0051]    A wiper blade assembly  92  is mounted within the U-shaped foot  44  and includes a wiper blade  93  mounted on a carrier  94 . The wiper blade is made of a flexible, or preferably a resilient, material having a low coefficient of friction, such as polytetrafluoroethylene (PTFE), silicone or polypropylene material, to allow the wiper blade to pass smoothly over the work piece. If desired, the wiper blade  93  may be provided with a surface coating to further reduce the coefficient of friction thereof. The wiper blade  93  will tend to wear as a result of repeated movement over the work surface and can be damaged, for example as a result of contact with irregularities in the work surface. The wiper blade, at least, is therefore a replaceable component which can readily be removed and replaced with a new component whenever necessary. The wiper blade  93  may be mounted on the wiper blade assembly  92  by way of biasing means, such as a coil spring or a torsion spring, to urge the free edge of the wiper blade in the direction of the work surface. 
         [0052]    The carrier is mounted within the foot  44  in a slidable manner, for example in recesses  95  which allow the carrier to move generally laterally towards and away from the dispenser nozzle  51 . The recesses  95  extend substantially laterally in the region thereof closest to the dispenser nozzle  51 , but are inclined upwards (away from the work surface) at each end. This results in the wiper blade being lifted at least partially from the work surface at each end of its travel. Such an action may conveniently be obtained by movement along a curved, or arcuate, path. 
         [0053]    The cam  91  is mounted on a rotatable shaft  96  which passes through the foot  44 . Also mounted on the rotatable shaft, within the foot  44 , so as to be rotatable in response to rotation of the cam is one end of an operating arm  97 . The other end of the operating arm  97  is rotatably connected to the carrier  94 . Biasing means, such as a torsion spring  98  as illustrated or a coil spring, may be provided to bias the carrier  94 , and therefore the wiper blade  93 , in a direction towards the dispenser nozzle  51 . 
         [0054]    As can be seen from  FIG. 27 , the wiper blade  93  may be formed with a waisted region  99  which facilitates flexing of the wiper blade. 
         [0055]    In use of the nailgun shown in  FIGS. 24 to 27 , as a user pushes the nailgun towards a work surface in a direction substantially perpendicular to the surface the cam actuator  90  engages with the cam  91  and causes the cam to rotate in a clockwise direction in  FIG. 24 . Rotation of the cam  91  causes corresponding rotation of the shaft  96  and the operating arm  97  to move the carrier  94  and attached wiper blade  93  away from the dispenser nozzle  51  and to lift the wiper blade  93  at least partially from the work surface at the end of its range of travel. 
         [0056]    At the same time, the dispenser nozzle  51  contacts the work surface and is depressed so as to dispense a predetermined amount of filler in the form of a bead onto the work surface in the region where the nail is to be inserted. 
         [0057]    When the nailgun has been moved to within a predetermined distance of the work surface with the foot  44  in contact with the surface, the nailgun is primed and a nail is fired by depressing a conventional trigger (not shown). The nail travels out of the nailgun and passes into the work surface through the bead of filler material drawing a portion of the filler material into the work surface. 
         [0058]    The user then lifts the nailgun away from the work surface in a direction substantially perpendicular to the surface and the cam actuator  90  is retracted so as to allow the cam  91  to rotate under the biasing force of the torsion spring  98  so as to move the carrier  94  and the wiper blade  93  towards the dispenser nozzle  51  and again to lift the wiper blade  93  at least partially from the work surface at the end of its range of travel. 
         [0059]    As the wiper blade  93  moves towards the dispenser nozzle  51  the carrier  94  runs along the recesses  95  so as to approach the work surface as well as moving towards the dispenser nozzle. The downward movement, combined with flexing of the wiper blade  93  in the region of the waist thereof so that the wiper blade is angled (i.e., not substantially perpendicular) to the work surface, creates a “smearing” action which first pushes filler material in a downwardly direction into the depression created by the nail head as it entered the work surface and then removes excess filler material which remains proud of the depression. 
         [0060]    The lifting motion of the wiper blade  93  at the ends of its range of travel, combined with the flexibility resulting from the waisted region, allows the wiper blade readily to ‘flip’ from one angled direction to the other when changing direction of movement at the end of each direction of travel and allows the wiper blade to pass more easily over the work surface without catching on any irregularities. That is, the waisted region  99  acts as a form of hinge. Thus the lower edge of the wiper blade  93  is always trailing behind the upper region thereof irrespective of the direction of movement. 
         [0061]    It will be appreciated that the use of a cam  91  and operating arm  97  is not essential and that alternative mechanisms can be used to transmit the downward motion of the nailgun into transverse movement of the wiper blade assembly  92 , such as a rack and pinion assembly or a worm drive. Moreover, the wiper blade  93  may additionally or alternatively be pivotable, for example around the lower edge thereof, so as to engage the filler material with a face of the blade and to urge the filler material into the depression in the work surface caused by the head of the nail. Alternatively, the wiper blade may be replaced by other means, such as a downwardly biased roller or the like to urge filler material into the depression in the work surface caused by the head of the nail.