Patent Publication Number: US-2020277980-A1

Title: Self drilling screw

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of engineering and in particular fasteners. Specifically, the invention is an improved screw found to be particularly useful in assembling security screens for windows, doorways, and the like. 
     BACKGROUND TO THE INVENTION 
     Various types of screws are known including wood screws, metal screws, coach bolts, batten screws, self-tapping or self-drilling screws, etc. Each has a particular use and is configured with certain features for that use. One particular type of screw used in the fabrication of security screens is a thread-forming screw. A thread-forming screw cuts a thread as it is forced into a pre-drilled hole. In use a pilot hole is drilled and as a separate action the thread-forming screw is driven into the hole. 
     It is known in other applications to use a self-drilling screw. A prior art self-drilling screw is shown in  FIG. 1 . It is characterised by a head and a shank. The head may be pan, countersunk, round, or various other variations. The shank terminates in a drill bit that drills a hole in the material being fastened. The shank has a thread along part of the length extending from the head to the drill bit. 
     Another type of thread-forming screw is used in wood and has self-embedding ribs at the end of the shank. This is sometimes referred to as a bugle head screw. The self-embedding ribs are not actually a drill bit but rather a flute to assist with moving material as the screw bites into the timber. These screws are only useful for soft timbers and require a pilot hole for use in hardwood. They are not useful for metal and therefore cannot be used for security screen assembly. 
     As mentioned, self-drilling screws are used in the fabrication of security screens. Reference is made to International Patent Application publication number WO96/07006, which describes one such intruder resistant screen, the content of which is incorporated herein by reference. WO96/07006 describes an intruder resistant screen including a frame comprising elongate frame members, each having a channel section engaging a respective corner stake in each end thereof. A woven wire intruder resistant mesh covers an opening enclosed by the frame. There are a plurality of clamping members co-acting with respective screws to thereby clamp the mesh to the frame. The intruder resistant screen described in WO96/07006 is known in the market as the Crimsafe® Security System. 
     SUMMARY OF THE INVENTION 
     In one form, although it need not be the only or indeed the broadest form, the invention resides in a screw comprising: 
     a head and a shank;
 
a drill bit formed at one end of the shank away from the head; and
 
a thread extending along the full length of the shank, including the drill bit.
 
     Preferably the head is a pan head or a counter-sunk head. 
     The head includes a fastening tool engagement portion which may be slot, Philips, hex, or other suitable form of engagement. 
     The drill bit may be hardened or bi-metal. 
     Further features and advantages of the present invention will become apparent from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To assist in understanding the invention and to enable a person skilled in the art to put the invention into practical effect, preferred embodiments of the invention will be described by way of example only with reference to the accompanying drawings, in which: 
         FIG. 1  is a side view of prior art self-drilling screw; 
         FIG. 2  is a side view of an embodiment of a self-drilling screw according to the invention; 
         FIG. 3  is an exploded view of an application of the self-drilling screw of  FIG. 2 ; 
         FIG. 4  is an assembled view of the frame shown in  FIG. 3 ; 
         FIG. 5  is an enlarged view of a portion of  FIG. 4 ; and 
         FIG. 6  is a side view of a second embodiment of a self-drilling screw according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the present invention reside primarily in a self-drilling screw. Accordingly, the elements of the screw have been illustrated in concise schematic form in the drawings, showing only those specific details that are necessary for understanding the embodiments of the present invention, but so as not to obscure the disclosure with excessive detail that will be readily apparent to those of ordinary skill in the art having the benefit of the present description. 
     In this specification, adjectives such as first and second, left and right, and the like may be used solely to distinguish one element or action from another element or action without necessarily requiring or implying any actual such relationship or order. Words such as “comprises” or “includes” are intended to define a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed, including elements that are inherent to such a process, method, article, or apparatus. 
     Referring to  FIG. 1  there is shown a prior art self-drilling screw  10 . The self-drilling screw  10  comprises a head  11  and a shank  12 . In the embodiment of  FIG. 1  the head  11  is a pan head, but other shapes as known in the art are also acceptable. An engagement portion  13  (shown in hidden detail) is formed in the head  11 . The engagement portion  13  receives a tool that is used to drive the fastener by rotation. In the embodiment of  FIG. 1  the engagement portion is a hex slot. 
     The shank  12  terminates in a drill bit  14 . The drill bit is the same diameter as the shank and, in use, cuts a hole to receive the shank of the self-drilling screw. A thread  15  is formed on the shank between the head  11  and the drill bit  14 . The thread  15  sits proud of the shank so as to cut into the material around the hole cut by the drill bit  14 . 
     Referring to  FIG. 2 , there is shown a first embodiment of a self-drilling screw  20 . The self-drilling screw  20  comprises a head  21  and a shank  22 . In the embodiment of  FIG. 2  the head  21  is a pan head, but other shapes as known in the art are also acceptable. The inventor has found that a countersunk head may be particularly useful in some applications. An engagement portion  23  (shown in hidden detail) is formed in the head  21 . In the embodiment of  FIG. 2  the engagement portion is a hex slot, but Phillips, straight slot and other known shapes will also be useful. 
     The shank  22  terminates in a drill bit  24 . The drill bit is the same diameter as the shank and, in use, cuts a hole to receive the shank of the self-drilling screw. It may be made from an alloy, hardened steel or bi-metal. The drill bit  24  may be slightly small than the shank  22 , which may increase the holding strength but will increase the force required to use the screw. On the other hand, the drill bit  24  may be slightly larger than the shank  22 , which will make the screw easier to insert but may reduce the holding strength. The length of the drill bit  24  relative to the shank  22  may also be varied. A thread  25  is formed on the shank  22  and extends from the head  21  to the end of the shank, including the drill bit  24 . The thread  25  sits proud of the shank so as to cut into the material around the hole cut by the drill bit  24 . 
     The self-drilling screw  20  of  FIG. 2  differs from the prior art of  FIG. 1  in that the thread extends to the end of the shank, including the drill bit  24 . This additional length of thread has been found to offer hitherto unexpected advantage for fastening in certain circumstances. One such circumstance is for holding the clamping member to the frame in a security screen, such as that described in international patent publication WO96/07006. 
     By way of example,  FIG. 3  shows an exploded view of a portion of the frame of a security screen. An elongate frame member  32  comprises a channel section  31 . A wall  33  of the channel section  31  extends to form one side of a clamping assembly. A flange  34  extends away from the wall  33  and includes serrated surface  34   a . Extending from another wall  35  is a lip  36  having a groove  36   a  that forms a catch for a hook  37  of a clamp element  38 . At an end of wall  33  is a channel  39  that receives a seal element  39   a  that co-acts with seal element  39   b  to form a seal to inhibit ingress of moisture along a mesh  40 . The clamp element  38  has a serrated surface  38   a  that is similar to the serrated surface  34   a . A hole  30  in the clamp element  38  receives screw  20 . A cover  41  has at one side an edge  42  that engages a rim  43  on the frame member  32  and towards an opposite side a hook  44  that engages a clip  45  on the clamp element  38 . At an edge of the cover  41  is a channel  46  that receives seal element  39   b.    
     The assembled frame and clamp is shown in  FIG. 4 . As can be seen, the screw  20  fastens the clamp element  38  to the flange  34  thus clamping the mesh  40  with a leveraged clamping action. As seen most clearly in  FIG. 5 , the thread  25  of the screw  20  holds throughout the length of the shank  22 , thus improving holding strength. 
     An alternate embodiment of the screw of  FIG. 2  is shown in  FIG. 6 . The self-drilling screw  60  comprises a head  61  and a shank  62 . In the embodiment of  FIG. 6  the head  61  is a countersunk head. An engagement portion  63  (shown in hidden detail) is formed in the head  61 . The shank  62  terminates in a drill bit  64 . The drill bit  64  may be slightly smaller or slightly larger in diameter than the shank  62 . The length of the drill bit  64  relative to the shank  62  may also be varied. A thread  65  is formed on the shank  62  and extends from the head  61  to the end of the shank, including the drill bit  64 . The thread  65  sits proud of the shank so as to cut into the material around the hole cut by the drill bit  64 . 
     In testing conducted on the embodiment shown in  FIG. 2  for the application of  FIG. 5 , a 14% strength increase was measured compared to the prior art screw. The screw  20  has the additional advantage of greatly streamlining the fabrication process for security screens. Typically, these screens are fabricated on site. The prior art process is to drill holes for each screw but the screw of  FIG. 2  can be inserted without any preparation, thus making assembly much quicker. Some advantages of using the screw of  FIG. 2  compared to the screw of  FIG. 1  are: stronger product; faster assembly; less tools required. As a result, a person assembling a screen has less incidence of repetitive strain injury. There is also less chance of scratching due to a drill slipping and there is less waste material, such as metal filings from drilling. 
     The above description of various embodiments of the present invention is provided for purposes of description to one of ordinary skill in the related art. It is not intended to be exhaustive or to limit the invention to a single disclosed embodiment. As mentioned above, numerous alternatives and variations to the present invention will be apparent to those skilled in the art of the above teaching. Accordingly, while some alternative embodiments have been discussed specifically, other embodiments will be apparent or relatively easily developed by those of ordinary skill in the art. Accordingly, this invention is intended to embrace all alternatives, modifications and variations of the present invention that have been discussed herein, and other embodiments that fall within the spirit and scope of the above described invention.