Abstract:
An explosively actuated fastener driving tool of the type having a driving piston for driving a fastener at the forward end of a barrel upon firing of the tool has a retractor pawl assembly with a pawl for resetting the piston into a rear end of the barrel by forward movement of the barrel relative to the receiver following firing. The pawl assembly is so constructed that the pawl can be withdrawn from the barrel to permit removal of the barrel for routine cleaning and maintenance but in this condition the assembly still remains attached to the tool to prevent components from being misplaced.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1) Field of the Invention 
         [0002]    The present invention relates to explosively actuated tools for driving fasteners such as nails or pins into a substrate composed of a relatively hard material such as concrete, masonry, or steel. 
         [0003]    2) Description of the Prior Art 
         [0004]    A typical explosively actuated driving tool comprises a barrel containing a piston which drives a fastener within a fastener guide at the forward end of the barrel upon firing of an explosive charge in a charge chamber at the rear of the barrel. The tool is cocked by pressing the forward end of the fastener guide against the substrate and when the tool is fired the piston is propelled along the barrel to drive the fastener into the substrate. The general construction and operation of tools of this type will be well understood by those skilled in the art and an example of a prior tool of this type is disclosed in U.S. Pat. No. 3,549,074. 
         [0005]    After firing it is necessary to reset the piston to the rear of the barrel in preparation for the next firing. In order to achieve this the barrel is movably mounted within a receiver mounted to the tool housing which carries other components of the tool such as the trigger and firing mechanism. To reset the piston to the rear of the barrel after firing, the barrel is moved by hand forwardly relative to the receiver while the piston is retained relative to the receiver by a retractor pawl which is carried by the receiver and extends through a slot in the barrel to lie in front of a flange of the driving piston and thereby to prevent forwards movement of the piston when the barrel is moved forward. 
         [0006]    Periodically, it is necessary to remove the barrel from the receiver for cleaning and maintenance and this, in turn, requires removal of the retractor pawl from the slot in the barrel. The retractor pawl is normally part of an assembly which is removed from the tool when it is required to remove the barrel. It is sometimes necessary for the barrel to be removed during use of the tool on a building site and in these circumstances it may happen that the retractor pawl assembly when removed from the tool is dropped or misplaced and, depending on its construction, individual components of the assembly may become displaced and lost. 
       SUMMARY OF THE INVENTION 
       [0007]    According to the present invention, there is provided an explosively actuated fastener driving tool of the type having a driving piston for driving a fastener at the forward end of a barrel upon firing of the tool, and a retractor pawl assembly having a pawl extendible into the barrel for resetting the piston into a rear end of the barrel by forward movement of the barrel relative to the receiver following firing, the pawl assembly being so constructed that the pawl can be withdrawn from the barrel to permit removal of the barrel for cleaning and maintenance while the assembly remains attached to the tool to prevent components of the pawl assembly from being misplaced. 
         [0008]    Further according to the present invention there is provided an explosively actuated fastener driving tool comprising a barrel mounted to a receiver of the tool, a driving piston within the barrel for driving a fastener at the forward end of the barrel upon firing of the tool, and a retractor pawl assembly for resetting the piston into a rear end of the barrel by forward movement of the barrel relative to the receiver following firing, wherein the retractor pawl assembly comprises a retractor pawl having a head extendible through a slot in the barrel to engage and retain the piston during forward movement of the barrel, the pawl being mounted in a housing fixed relative to the receiver and being spring biased to move radially into and out of the interior of the barrel by movement of the barrel relative to the receiver, and a release member operable to fully withdraw the pawl from the barrel to permit removal of the barrel from the receiver, the release member being mounted to the housing in such a manner that in a normal condition of the tool it cannot be moved to a position at which the pawl assembly is detached from the receiver. 
         [0009]    In a preferred embodiment of the invention, the release member is a rotatable cap threadedly mounted to the housing, the pawl is linked to the cap such that the pawl is withdrawn from the barrel slot when the cap is unscrewed relative to the housing, and removal of the cap from the housing is prevented by engagement of the pawl with a stop on the housing as the cap is unscrewed. Preferably that stop is removable but only as a deliberate act using a tool to thereby facilitate disassembly in a workshop situation. 
         [0010]    In an alternative, the cap may be mounted to the housing by a bayonet type fitting which retains the cap to the housing while allowing axial movement between the cap and the housing to remove the pawl from the barrel. 
         [0011]    Particularly advantageously, in a ready-to-fire condition of the tool prior to cocking the tool, the pawl engages a detent in the barrel under its spring bias in order to prevent inadvertent forwards movement of the barrel from the receiver in this condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0013]      FIG. 1  is a section through the forward end portion of a tool in accordance with the preferred embodiment of the invention, the components being shown in a condition assumed immediately after firing the tool; 
           [0014]      FIG. 2  is a schematic perspective view corresponding to  FIG. 1  and showing the interaction between a retractor pawl and barrel in that condition; 
           [0015]      FIG. 3  is an exploded perspective view of the retractor pawl assembly; 
           [0016]      FIG. 4  is a section similar to  FIG. 1  but showing the components in a condition during resetting of the piston to the rear of the barrel following firing; 
           [0017]      FIG. 5  is a schematic perspective view similar to  FIG. 2  but showing the retractor pawl and barrel in the condition of  FIG. 4 ; 
           [0018]      FIG. 6  is a section similar to  FIG. 1  but showing the components in a condition in which the piston is fully reset to the rear of the barrel; 
           [0019]      FIG. 7  is a section similar to  FIG. 1  but showing the components in a condition assumed prior to firing of the tool; 
           [0020]      FIG. 8  is a schematic perspective view similar to  FIG. 2  but showing the retractor pawl and barrel in the condition of  FIG. 7 ; 
           [0021]      FIG. 9  is a section similar to  FIG. 1  but showing the components in a condition assumed in overdrive of the piston; and 
           [0022]      FIG. 10  is a section similar to  FIG. 1  but showing the components in a condition in which the retractor pawl is fully released from the barrel to permit removal of the barrel from the receiver. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    An explosively actuated tool in accordance with a preferred embodiment of the invention is of the type described earlier. The improvement which forms the subject of this invention concerns the retractor pawl assembly previously discussed and as such only the forward end portion of the tool at which the retractor pawl assembly is mounted is shown in the drawings. With initial reference to  FIGS. 1 to 3 , there is shown the forward end portion of the tool including a receiver  2  fixably mounted within a housing  4  and a barrel  6  mounted within the receiver  2  for axial movement relative to the receiver in a fore-aft direction. The barrel  6  carries at its forward end a fastener guide  8 . A driving piston  10  is mounted within the barrel  6 , and, on firing the tool, is driven into the fastener guide  8  to drive a fastener at the forward end of the guide into a substrate. Apart from the construction and operation of the retractor pawl assembly, the tool is otherwise of conventional construction which will be well understood by those skilled in the art. 
         [0024]    The retractor pawl assembly  12  comprises a housing in the form of a tubular spigot  14  fixed at the forward end of the receiver  2 . A retractor pawl  16  is reciprocably mounted within the spigot  14  for movement perpendicularly to the axis of the barrel  6  (and thus radially of the barrel) between an inner position in which the inner end portion of the pawl  16  (its head) extends through an axial slot  18  in the barrel  6  into the interior of the barrel to retain the piston  10  during the resetting action, and an outer position in which its head is completely removed from the barrel to permit removal of the barrel from the receiver. The pawl  16  may also assume a variety of positions intermediate these extreme positions as will be described. The pawl  16  is biased towards its inner position by a compression spring  20  interposed between the pawl  16  and a release member in the form of a cap  22  which is threadedly mounted on the external surface of the spigot  14 . 
         [0025]    During normal operation of the tool, the cap  22  is screwed fully onto the spigot  14  as shown in  FIG. 1 , and the cap  22  is only unscrewed when it is required to remove the barrel as will be subsequently described. To facilitate its unscrewing for that purpose, the cap  22  is preferably knurled on its outer surface. The cap  22  is held captive relative to the pawl  16  by a bolt  24 . The shank of the bolt  24  is fixed to the cap  22  by threaded engagement and extends into an interior passage  16   a  of the pawl so that the head of the bolt is above an internal partition  16   b  within the passage  16   a.  The configuration of the head of the bolt  24  within the passage  16   a  allows rotation of the cap  22  relative to the pawl  16  so as to permit the cap  22  to be unscrewed from the spigot  14  while permitting the pawl  16  to move axially relative to the spigot  14 . As will be seen from  FIG. 1 , the shank of the bolt  24  extends axially through the compression spring  20  which is between the base of the cap  22  and the pawl  16 . 
         [0026]    The body of the retractor pawl  16  is of generally cylindrical shape of a diameter corresponding to the internal diameter of the spigot  14  so that the pawl  16  is a sliding fit within the spigot, but part of the outer cylindrical surface of the pawl  16  is cut back to form a flat face  30  which lies inwardly of the internal surface of the spigot. The flat face  30  is bounded from above by a shoulder  32  adjacent the head of the pawl. A roll pin  34  extending transversely through the wall of the spigot  14  engages the flat face  30 . The roll pin  34  functions to prevent rotation between the pawl  16  and spigot  14  and thereby to ensure that the pawl  16  is retained in a predetermined angular orientation relative to the spigot  14  and ensures that the pawl  16  can only be installed in the correct orientation; it also acts as an abutment which is engaged by the shoulder  32  at the head end of the pawl when the cap  22  is unscrewed from the spigot  14  to permit removal of the barrel to ensure that in that condition the retractor pawl assembly is held captive to the receiver  2 . Complete removal of the pawl assembly from the tool requires removal of the roll pin  30 , an action requiring use of a tool (a punch for example) which would normally be undertaken in a workshop during servicing of the tool rather by an operator while using the tool on a work site. 
         [0027]    The head of the retractor pawl  16  is of a width to extend into the longitudinal slot  18  formed in the forward end of the portion of the barrel  6  and includes a rearwardly-facing abutment surface  36  for engagement with a flange  38  of the drive piston  10  for resetting the piston as will be described, and a forwardly-facing ramped surface  40  for engagement with the piston  10  in an overdrive situation as will also be described. Part-cylindrical shoulders  42  at opposite sides of the head engage with the outer surface of the barrel  6  at either side of the slot  18  as may be clearly seen in  FIG. 2 . The outer surface of the barrel in the zone of the slot  18  acts as a cam surface engaged by the shoulders  42  and is profiled to control the radial position of the retractor pawl  16  relative to the barrel slot  18  when the barrel  6  is moved forwardly and rearwardly relative to the receiver  2  during operation of the tool. 
         [0028]    Operation of the retractor pawl assembly will now be described commencing with  FIG. 1  which shows the condition directly after firing. In this condition, the barrel  6  is in a rear position relative to the receiver  2  and the piston  10  is in a forward position in the barrel following driving of a fastener into the substrate from the fastener guide  8  at the forward end of the barrel  6 . In this position of the barrel  6  relative to the receiver  2 , the pawl  16  is held by the profile of the barrel  6  in that zone so that the pawl head is in a fully retracted position within the barrel slot  18 . 
         [0029]    To reset the piston into the rear end of the barrel in preparation for the subsequent firing, the operator pulls the barrel forwardly or outwardly relative to the receiver. The shaping of the barrel surface at either side of the slot  18  allows the head of the pawl to displace inwardly under its spring bias into the interior of the barrel during this forward movement whereby its rear abutment surface  36  lies in the path of the forward flange  38  of the piston  10  to thereby engage and restrain the piston  10  from forward movement with the barrel.  FIGS. 4 and 5  show the condition in which the head of the pawl has engaged and retained the piston  10  during the initial part of forwards barrel movement, and  FIG. 6  shows the condition in which the piston  10  has been reset into the rear end of the barrel at the end of the forward movement of the barrel  6 . The barrel  6  with the piston  10  thereby reset into its rear end can be pushed by the operator back into the receiver  2  in preparation for the next firing. 
         [0030]    In the ready-to-fire position of the barrel  6  in the receiver  2  (that is, the position assumed by the barrel prior to cocking the tool) as shown in  FIGS. 7 and 8 , the shoulders  42  of the pawl  16  engage within a detent groove  50  in the outer surface of the barrel  6  adjacent the forward end of the slot  18 , and this prevents the barrel  6  from moving forwardly from the receiver  2  if the tool is lowered or perhaps as a result of inadvertent movement. While most tools of this type have a mechanism for preventing unwanted forwards movement of the barrel out of the ready-to-fire position, conventionally this is achieved by a mechanism which is separate from the retractor pawl assembly. The use of the retractor pawl also to prevent the unintended forwards movement of the barrel results in a simpler construction and a reduction in cost. 
         [0031]    In order to fire the tool, the tool must be cocked and this is achieved by pressing the forward end of the fastener guide  8  against the substrate to push the barrel  6  further into the receiver from the position shown in  FIGS. 7 and 8 , and this occurs against the bias of a strong spring force provided by the firing mechanism. In the cocked condition, the barrel  6  and thereby the retractor pawl  16  are positioned as shown in  FIG. 1  with the pawl retracted within the barrel slot  18  in a position where it is clearly held away from engagement with the piston during firing. 
         [0032]      FIG. 9  illustrates an overdrive situation which can occasionally occur if due to an error the operator uses the tool to drive a fastener into a soft substrate. In this overdrive condition, the rear end of the drive piston  10  is in engagement with the rear end of the fastener guide  8  in contrast to the normal position following firing as shown in  FIG. 1  in which it is displaced rearwardly from the fastener guide and also rearwardly from the retractor pawl. In this overdrive condition, the relative positions of the retractor pawl  16  and the flange  38  of the piston  10  are such that the pawl  16  will not engage the flange  38  when the barrel  6  is drawn forwardly. If the barrel is drawn forwardly in this condition, subsequent rearwards displacement of the projecting end of the piston, for example by lightly tapping that end, will result in the rear edge of the piston riding over the ramped forward face  40  of the head of the pawl to retract the pawl against the bias of its compression spring until the piston is in a proper position within the barrel such that the rear abutment face  36  of the pawl head can engage the forward flange  38  of the piston in a normal resetting condition. 
         [0033]    In order to remove the barrel  6  from the receiver  2 , the pawl  16  must be fully retracted from the slot  18  in the barrel. This is simply achieved by unscrewing the cap  22  relative to the spigot  14 . Unscrewing of the cap  22  causes the bolt  24  which is attached to the cap to draw the pawl  16  outwardly from the barrel slot (see  FIG. 10 ). Withdrawal of the pawl  16  is limited by engagement of the pawl shoulder  32  with the roll pin  34  as shown in  FIG. 10  and in this condition the cap  22  is disengaged from the thread of the spigot  14  so that the pawl  16  and the attached cap  22  are hanging from the roll pin  34 . Accordingly, although in this condition the pawl  16  is fully retracted clear of the barrel, the pawl assembly still remains attached to the tool and cannot be removed except by removal of the roll pin  34 . Thereby, the tool operator on a work site can be assured that unscrewing the cap to its fullest extent will retract the pawl fully to permit removal of the barrel, but the cap cannot be unscrewed to a point at which the pawl assembly will become detached from the tool itself. As the cap is knurled on its outer surface it is envisaged that an operator of the tool will intuitively appreciate that the cap needs to be unscrewed in order to permit removal of the barrel even if the operator is not especially familiar with this particular model of tool. The interaction between the roll pin and the flat face  30  of the pawl will ensure that the pawl is retained in the correct angular orientation to ensure that its head will re-enter the barrel slot when the barrel is returned to the tool. 
         [0034]    Although in the embodiment shown, the cap  22  is held captive to the pawl  16  by the bolt arranged in the manner shown in which the head of the bolt slides within the interior of the pawl and the shank of the bolt is engaged with cap, in an alternative configuration the shank of the bolt may be engaged with the pawl with the head of the bolt being positioned externally of the cap so that the bolt can slide relative to the cap. While this latter configuration is technically feasible, it is not particularly preferred as it will result in the presence of the head end of the bolt projecting externally of the cap and moving inwardly and outwardly relative to the cap as the pawl displaces. 
         [0035]    Although in the embodiment shown the cap is threadedly mounted to the spigot an alternative form of attachment, for example a bayonet type attachment, may be used. Other modifications are possible within the scope of the invention. 
         [0036]    Throughout this specification and claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.