Abstract:
A fastener includes a cylindrical shaft located between a head and a tapered point, threads integrally extending from the shaft and extending along a portion of a length thereof, and a burr cutoff area near the tapered point and including flank surfaces therein forming an angle greater than 90° therebetween. A flattened area can be located between the flank surfaces.

Description:
BACKGROUND 
       [0001]    Fasteners, particularly screw type fasteners drive through and/or into two objects, securing them to one another. In sheet metal applications, screw threads may cut into the sheet metal, creating a pigtail-looking burr that is not only sharp and dangerous, but may compromise the integrity of the screw attachment and the sheet metal itself due to the burr damaging the sealing washer typically provided under the screw head, resulting in a defective water seal. 
         [0002]    Previous methods for preventing screws from forming pigtail burrs include mill-cutting the screw-tip. The prior known milled point screws are generally referred to as a “Type 17” point screw, an example  400  of which is shown in  FIG. 23 . Here a tip  406  of the screw  400  has a cut area  430  that is cut into a screw tip  406  and threads  420  using a standard right angle milling cutter  500 , shown in  FIG. 24 , with generally right-angled teeth  510 . Such a standard cutter may be 3″ in diameter and ⅛″ thick. When the cutter  500  cuts into the screw  400 , a right angle is created in the screw tip  406  and the cut through the threads  420  is similarly at a right angle. This sharp angled cut area  430  helps to break off burrs that form during screw insertion. These screws include a cutting edge milled with a 90° cutter, shown in  FIG. 24 . One side of the cutter is can be aligned with the fastener centerline so that the cutting face created is perpendicular. However, installation of these types of fasteners does not consistently result in a burr not being formed. 
       SUMMARY 
       [0003]    A fastener includes a cylindrical shaft located between a head and a tapered point, threads integrally extending from the shaft and extending along a portion of a length thereof, and a burr cutoff area formed in the shaft near the tapered point and including flank surfaces therein forming an angle α of more than 90 degrees therebetween, and a flattened area between the flank surfaces. This is referred to by applicant as a beveled milled point and applicant has shown that this arrangement reduces the installation torque required due to the reduced surface area of the thread near the point as well as the increased cutting performance due to the beveled point surfaces and also addresses the issue in the prior known milled point fasteners. 
         [0004]    In one aspect, the angle α is from at least 90° to 145°, and more preferably about 105°. 
         [0005]    In one preferred arrangement, a sealing washer located on the shaft under the head. 
         [0006]    In one embodiment, the flank surfaces are arranged at an angle of α/2 from a center of the cutoff area, with the cutoff area being symmetric in cross-section. 
         [0007]    Alternatively, a first one of the flank surfaces can be arranged at an angle α l  of about 90° from the flattened area, and a second one of the flank surfaces is arranged at an angle α 2  of about 5° to 50° to the flattened area, more preferably at about 45°. 
         [0008]    Here, the second one of the flank surfaces preferably faces in an advancing direction of the thread. 
         [0009]    In another aspect, a method of forming an anti-burr-forming fastener is provided, which includes the steps of providing a rotating cutting tool with a cutting surface including, in cross-section, two sides set at an angle of greater than 90° to each other, connected by a flat portion; and applying the cutting surface to a screw in an area adjacent to a tip of the screw, cutting a groove generally parallel to an axis of the screw forming a cutoff area with two flank surfaces at an angle of greater than 90° to each other connected by a flattened area. 
         [0010]    In one preferred arrangement, one of the two sides of the cutting tool is arranged at an angle of about 90° to the flat portion. 
         [0011]    Alternatively, the two sides of the cutting tool can be arranged at equal angles to the flat portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         [0012]      FIG. 1  is a perspective view of a first embodiment of a screw, 
           [0013]      FIG. 2  is a side view of the screw of  FIG. 1 . 
           [0014]      FIG. 3  is a cross-sectional view of the screw of  FIG. 1 . 
           [0015]      FIG. 4  is a cross-sectional view taken along line  4 - 4  in  FIG. 1 . 
           [0016]      FIG. 5  is a side view of the screw of  FIG. 1  shown with a sealing washer under the head. 
           [0017]      FIG. 6  is a cross-sectional view of the screw of  FIG. 5 . 
           [0018]      FIG. 7  is a partial side view enlargement of the screw of  FIG. 1 . 
           [0019]      FIG. 8  is a view of a milling cutter form forming the cutoff area of the screw of  FIG. 1  according to one embodiment of the invention. 
           [0020]      FIGS. 9 and 10  show a beveled grinding wheel being applied to as a part of the manufacturing process to form the cutoff area of the screw of  FIG. 1 . 
           [0021]      FIG. 11  shows a side view of the grinding wheel. 
           [0022]      FIG. 12  shows a side view of the grinding wheel. 
           [0023]      FIG. 13  shows an enlargement of the cutting surface of  FIG. 12 . 
           [0024]      FIG. 14  is a perspective view of a second embodiment of a screw, 
           [0025]      FIG. 15  is a side view of the screw of  FIG. 14 . 
           [0026]      FIG. 16  is a cross-sectional view of the screw of  FIG. 14 . 
           [0027]      FIG. 17  is a cross-sectional view taken along line  17 - 17  in  FIG. 14 . 
           [0028]      FIG. 18  is a partial side view enlargement of the screw of  FIG. 14 . 
           [0029]      FIG. 19  is a view of a milling cutter form forming the cutoff area of the screw of  FIG. 14  according to one embodiment of the invention. 
           [0030]      FIG. 20  shows a side view of the grinding wheel. 
           [0031]      FIG. 21  shows a side view of the grinding wheel. 
           [0032]      FIG. 22  shows an enlargement of the cutting surface of  FIG. 21 . 
           [0033]      FIG. 23  is a partial side view enlargement of a screw according to the known prior art. 
           [0034]      FIG. 24  is a view of a milling cutter form forming the cutoff area of the prior art screw of  FIG. 23 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]      FIGS. 1-7  show a first embodiment of a screw  100  described herein. The screw  100  comprises a shaft  102 , head  104 , point or tip  106 , threads  120 , and anti-burr cutoff area  130 . (Although traditionally the plural is used to describe the “threads,” a screw thread  120  is typically one helical connected inclined plane). 
         [0036]    A screw  100  is one of the six classical simple machines, and combines the simple machines of an inclined plane and wedge. The threads  120  of the screw  100  are made of an inclined plane that encircles the cylindrical shaft  102 . The threads  120  or planar inclination allows the screw  100  to fasten more easily and also improves the screw  100 ′s holding power. 
         [0037]    The screw tip  106  acts as a wedge that operates by separating objects. When used with the screw  100 , the wedge tip  106  creates a hole in the material that the screw  100  engages. The sharper the tip  106 , the less force it takes for it to create a hole. 
         [0038]    Once the tip  106  creates a small hole, the threads  120  engage the material and drive it apart. The threads  120  may be wound into existing thread grooves within the previously created hole or they may cut their own grooves during insertion. A rotation force applied to the screw  100  drives the screw through the material. This force may be applied with a driving mechanism like a drill or screwdriver. The threads  120  resting within the grooves create a bind that joins materials engaged along the axis of the screw shaft  102 . This engagement is the result of converting torque to linear force. 
         [0039]    The strength of hold of the screw  100  depends on the width of the threads  120  and the distance between them. The closer and wider the threads  120 , the stronger the hold will be. More threads, however, require more rotations to attach the screw  100 , while wider threads  120  require more force in the rotations. 
         [0040]    As shown, the screw threads  120  taper from their maximum height along the cylindrical shaft  102  along the conical screw portion  107  that leads to the tip  106 . At the tip  106 , the screw thread  120  height diminishes until it meets and/or forms the point. 
         [0041]    Along the length of the screw shaft  102 , the screw threads  120  maintain a constant height in most uses (although this is not necessary). 
         [0042]    Depending on the application, the screw  100  may include one or more sealing washers installed under the head  104 . One preferred arrangement used for sheet metal siding and roofing provides a two part bonded washer with a steel washer  140  that goes under the head  104  and a rubber or elastomer seal  142  that goes under and is preferably bonded or vulcanized to the steel washer  140  to provide sealing around the entry point of the screw  100  into the material being fastened. Alternatively, the washers  140 ,  142  could be two separate parts. 
         [0043]    In the screw  100 , a burr cutoff area  130  is provided having an overall angle α of at least 90° to 145°, and more preferably about 105°. The cutoff area  130  is formed with three surfaces, shown most clearly in  FIG. 7 , with two flank surfaces  134   a,    134   b  that define the angle α therebetween that are connected by a bottom, flattened surface  132 , shown as flat in cross-section in the present embodiment. Here the flank surfaces  134   a,    134   b  are each at an angle of α/2 from a center of the cutoff area  130 , forming a symmetric groove. This arrangement results in what applicant terms a “double bevel milled point” screw  100 . 
         [0044]    A beveled milling cutter  300  with teeth  310  that forms the cutoff area  130  in the screw  100  is shown in  FIG. 8 . The cutter  300  preferably has a 3″ diameter and is ⅛″ thick. The dimensions of the milling cutter could be varied depending on the particular application. Alternatively,  FIGS. 9 and 10  show a beveled cutting wheel  300 ′ formed as a grinding wheel, made of a cutting abrasive, or as a diamond coated surface with cutting surface  310 ′ having the desired profile. In  FIGS. 9 and 10 , the cutter  300 ′ is shown being applied to a screw  100 .  FIGS. 11-13  show the cutting wheel  300 ′ and the feature that the angled cutting surfaces  310 ′ a  and  310 ′ b  are at an angle of 105° to each other and the flat surface  310 ′ c  is approximately 0.015 inches, as shown. The cutting surface  310 ′ a  is used to form the flank surface  134   a,  the cutting surface  310 ′ b  is used to form the flank surface  134   b,  and cutting surface  310 ′ c  forms the flat bottom of the burr cutoff area  130 . The flat surface  310 ′ c  may be eliminated in some embodiments. The angle between surfaces  310 ′ a  and  310 ′ b  is preferably between 90 and 135 degrees. The teeth  310  on the cutting wheel  300  would have similar dimensions. 
         [0045]    When the cutting wheel  300 ,  300 ′ is applied to the screw  100 , the center axis of the shaft  120  can be aligned with the leading edge of the flat surface  310 ′ c.  However, other positioning is possible, depending on the particular profile. 
         [0046]    The reduced cross-sectional area of the point  106  reduces the chance of forming pig tail burrs so that sealing washers put onto the screw  100  are less likely to become damaged (especially the rubber washers  142 ). The anti-burr area  130  helps break off the burr when it does form, yields a larger cutting surface, and helps make a sharper drill point. 
         [0047]    Referring now to  FIGS. 14-17 , a second embodiment of a screw  200  is shown. The second embodiment of the screw  200  is similar to the first embodiment  100 , and like elements have been designated with similar reference numbers that are increased by  100 . The screw  200  includes the shaft  202 , a head  204  and a point  206 , as well as threads  220 . The screw threads  220  taper from their maximum height along the cylindrical shaft  202  along the conical screw portion  207  that leads to the tip  206 . As shown in  FIGS. 14 ,  15 , and  17 , the screw  200  can also be provided with the sealing washers  140 ,  142  under the head  204 . The difference between the screw  100  and the screw  200  is in the burr cutoff area  230 . As shown in  FIGS. 16 and 18 , the first flank surface  234   a  is at an angle α l  of about 90° from a radially extending line that extends from the bottom of the cutoff area  230 , and the second flank surface  234   b  is at an angle α 2  that is from about 5° to 50° from the radial line, and more preferably about 45°. Preferably α 1 +α 2 =between about 95° and 140°, and more preferably 135°. α 2  can be varied, and α 1  remains at about 90°. The second flank surface  234   b  faces in an advancing direction of the thread  220 . A flat can optionally be provided at the bottom of the first and second flank surfaces  234   a,    234   b.  This arrangement results in what applicant terms a “hybrid single bevel milled point screw”  200 . 
         [0048]    A beveled milling cutter  320  with teeth  330  that forms the cutoff area  230  in the screw  200  is shown in  FIG. 19 . The cutter  320  preferably has a 3″ diameter and is ⅛″ thick. The dimensions of the milling cutter could be varied depending on the particular application. Alternatively,  FIGS. 20-22  show a beveled cutting wheel  320 ′ formed as a grinding wheel, made of a cutting abrasive, or as a diamond coated surface with cutting surface  330 ′ having the desired profile. Here cutting surface  330 ′ a  is used to form the flank surface  234   a,  cutting surface  330 ′ b  is used to form the flank surface  234   h.    
         [0049]    The reduced cross-sectional area of the point  206  reduces the chance of forming pig tail burrs so that sealing washers put onto the screw  200  are less likely to become damaged (especially the rubber washers  142 ). 
         [0050]    Having thus described various embodiments of the present anti burr fasteners in detail, it is to be appreciated and will be apparent to those skilled in the art that many physical changes, only a few of which are exemplified in the detailed description above, could be made in the apparatus without altering the inventive concepts and principles embodied therein. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore to be embraced therein.