Abstract:
A hole saw for cutting standardized holes in the web portion of an I-joist features a light weight three spoke body having a rim with continuous circumference and three inserted cutting blades fixed in an offset to the circumference, which is dimensioned in accordance to standard web heights.

Description:
PRIORITY CLAIM 
   The present invention claims priority to the U.S. Provisional Application Ser. No. 60/451,225 filed Feb. 28, 2003, which is hereby incorporated by reference. 

   FIELD OF INVENTION 
   The present invention relates to hole saws. Particularly, the present invention relates to hole saws for cutting holes in a in corner regions with spacing requirements such as a web portion of an I-joist. 
   BACKGROUND OF INVENTION 
   I-joists are increasingly utilized structural elements in architectural constructions and the like. I-joists are beams that have an I like profile to provide maximum stiffness and strength with a minimum of weight. I-joists are commonly fabricated in a number of dimensional standards from wood and wood like materials. 
   Architectural constructions often require the cutting of holes into the web portion of the I-joist to lay pipes, electrical lines and the like across one or more installed I-joist. There exist a number of standards for maximum hole sizes that may be cut into the web portion. Of primary concern is thereby a remaining offset between the web hole and the horizontal top and bottom portion of the I-joist in order to keep the I-joists buckling tendency within safe limits. Therefore there exists a need for a hole cutting apparatus that provides spacing between adjacent sticking out structures while cutting the hole. The present invention addresses this need. 
   The cutting of large diameter holes at the construction site is mainly accomplished by hand held power tools in which the cutting apparatus is rotatable held. Therefore, for cutting large diameter holes there exists also a need for a cutting apparatus that provides cutting action with minimum friction, reduced peak torque and safe operation without pronounced or sharp features extending beyond the circumference of the rotating apparatus. The present invention addresses also these needs. 
   SUMMARY 
   Cutting holes with a hand held power drill or the like may be accomplished in combination with a hole cutting apparatus concentrically attached to a rotating portion of the power drill. As the hole diameter increases, the resulting torque increases as well. A hole cutting apparatus in accordance with the preferred embodiment of the invention has a number of circumferentially arrayed cutting members configured to keep cutting forces and a resulting cutting torque to a minimum for a given cutting diameter, given axial cutting pressure and a given material of the work piece. 
   The hole cutting apparatus has a lightweight body including radial beams that connect a central portion with a circumferential ring. Concentrically attached to the central portion is on one side an arbor for attaching the apparatus to the power drill or the like. A pilot drill is attached on the opposite side in coaxial alignment with the arbor. The pilot drill drills a pilot hole into the work piece such that the apparatus is centered during the following hole cutting. The pilot drill extends sufficiently beyond the cutting members to drill the pilot hole sufficiently deep before the cutting members contact the work piece. As the rotating apparatus is forced towards the work piece, cutting edges of the cutting members gradually remove material along an increasingly deep concentric groove until a portion of the work piece inside the concentric groove becomes separated from the remaining work piece. 
   In the preferred embodiment, the apparatus is configured in combination with dimensional standards of an I-joist. With respect to the present invention, an I-joist is defined as an I-beam profile having a top chord, a bottom chord and a central web portion. The apparatus provides a cutting of holes in the web portion in accordance with dimensional safety criteria for maximum hole dimensions in the web. The safety criteria are established by I-joist manufacturers for their respective products. Particularly, the ring portion of the apparatus has an outer diameter that corresponds to a height of the web portion between the chord elements such that the apparatus becomes aligned between the top chord and the bottom chord prior to a contacting of the pilot drill with the web portion. The cutting members are in an offset to the ring diameter such that the cutting groove and consequently the hole edge remain in a certain distance to the chords in accordance with the safety criteria. 
   In the preferred embodiment, three cutting members are circumferentially arrayed to provide an even distribution of cutting pressure onto the individual cutting members. For an I-joist made of wood and/or wood like material, the cutting members may be made of steel, carbide or other material suitable for cutting wood and/or wood like material. The cutting members are preferably mounted in an exchangeable fashion for easy replacement. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  shows a perspective view of a first embodiment of the invention. 
       FIG. 2  illustrates a side view of the apparatus of  FIG. 1  in operational approach to a preferred work piece. 
       FIG. 3  depicts a perspective view of the apparatus of FIG.  1  and the work piece of  FIG. 2  after cutting a hole with the apparatus into the work piece. 
       FIG. 4  shows a perspective view of a second embodiment of the invention. 
       FIG. 5  is a top view of the apparatus of FIG.  4 . 
       FIG. 6  is a detailed section view of the apparatus of  FIG. 4  in accordance with a section line A—A indicated in FIG.  5 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , the present invention is a hole cutting apparatus  100  configured to be attached to a rotating portion of a well known power drill. The power drill may be substituted by other well-known devices configured for receiving and rotating other well known apparatus performing rotating operations. The apparatus  100  is axially attached via an arbor  102 , which may have a hexagonal shape for a rigid interlocking with a three jaw-clamping device of the power drill. The arbor  102  may have other configurations as are well known in the art for transmitting a torque while keeping the apparatus  100  aligned with respect to its rotation axis. 
   The arbor  102  extends from the backside of a central portion  103  from which preferably three beams or spokes  107  extend in radial direction. The radial beams or spokes  107  connect the central portion  103  with a circumferential ring or rim  101 . The spokes  107  provide a stiff connection between the rim  101  and the central portion  103  while keeping the over all weight of the apparatus  100  to a minimum. 
   From the front side of the central portion  103  extends a pilot drill  105 , which is in axial alignment with the arbor  102 . An optional spacer  104  may provide a safety space between the pilot drill  105  and the central portion  103  to prevent an inadvertent contacting of the central portion  103  and/or the spokes  107  and/or the rim  101  with a work piece  200  (see  FIGS. 2 ,  3 ). 
   On the rim  101  are circumferentially arrayed and attached a number of groove cutting member  121 , which are configured to gradually remove material from the work piece  200  while keeping friction in the cutting groove to a minimum and while preventing sudden biting of a cutting edge  122  in the cutting groove. For that purpose, the cutting members  121  have a sliding feature  123  placed in front of the cutting edge  122  with respect to an operational rotation direction of the apparatus  100 . 
   There are preferably three groove cutting members  121  arrayed on the ring  101  to assure equally distributed contact pressure between the individual cutting members  121  and the work piece  200 . The cutting members  121  are preferably attached in a removable fashion in recesses or cavities  109  of the rim  101  and radially fixed via cap screws  124 . Hence, when the cutting members  121  suffer damage or wear, they may be quickly replaced. The invention includes embodiments in which the cutting members  121  are integral part of the ring  101 , which in turn may be replaceable as a whole. 
   Now turning to  FIG. 2 , the preferred operation of the apparatus  100  may be explained in more detail. The apparatus  100  is preferably configured for cutting holes  205  (see  FIG. 3 ) in a web  204  of an I-beam  200  made of wood and/or wood like material. The I-beam  200 , also known as I-joist  200  has a top chord  201  and a bottom chord  202 . Both chords  201 ,  202  are spaced apart with distance  212 , which equals the free height of the web  204 . The rim  101  has an outer diameter or circular circumference  111  that is marginally smaller than distance  212 . Consequently, the apparatus becomes vertically substantially aligned once the rim  101  is moved in between the chords  201 ,  202 . The circular circumference  111  is sufficiently small to prevent excessive friction between the rotating rim  101  and a chord  201  and/or  202 . 
   The pilot drill  105  protrudes above the rim  101  with an extension  151 , which is sufficiently small to assure positioning prior to contacting of the pilot drill  105  with the web  204 . During operation, the apparatus  100  is brought into rotation via the arbor  102  and brought into contact with the web  204  at a predetermined location. Since the rim  101  assures vertical alignment, the operating person may focus mainly on contacting the pilot drill  105  at a proper longitudinal position along the I-joist  200 . 
   The drill extension  151  is selected such that the pilot drill  105  drills a sufficiently deep guiding hole into the web  204 , before the cutting members  121  begin gradually removing material and thereby forming an increasingly deep concentric cutting groove. Due to the short circumferential length of the cutting members  121 , chip buildup and associated friction between the cutting members  121  and the cutting groove is kept to a minimum. 
   While axial pressure is applied via the arbor  102 , the cutting members  121  continue to gradually remove material from the cutting groove until a central portion of the web  204  inside the cutting groove becomes disconnected from the remainder of the web  204 . The cutting members  121  have a height selected in correspondence with a thickness  214  of the web  204  to assure a cutting groove sufficiently deep for separating the central web portion. 
   The cutting members  121  are positioned in a substantially equal offset  125  to the rim&#39;s  101  circular circumference  111 . The offset  125  is selected according to hole cutting standards established by a manufacturer of I-joist  200 . The I-joist  200  may be fabricated in a number of standardized dimensions including a variety of standardized widths  212 . The apparatus  100  may be provided in varying configurations that comply with the varying I-joist standards. As a result, the apparatus  100  may be selected in a prefabricated configuration that corresponds to the dimensional standard of the I-joist  200  for cutting a hole  205  (see  FIG. 3 ) that is within the static safety limits for that particular I-joist  200 . 
   To further reduce friction between the ring  101  and a chord  201  and/or  202 , the outer surface of the ring  101  may be specially treated for reduced friction. Such treatment may include a coating with a low friction material such as Teflon. 
   The present invention includes embodiments in which a bushing ring or a bearing may be assembled on the rim  101 . 
   In that case, the circular circumference  111  would be that of the bushing or the bearing. 
   The present invention is not limited to cutting holes into wooden and/or wood like I-beams. It may also be configured for cutting holes with reduced friction into any kind of work piece. For example, holes may be cut with the apparatus  100  into a metal or stone. In such cases, the cutting members  121  may be accordingly configured for cutting metal or stone as is well known in the art. 
   In the first embodiment of the invention depicted in the  FIGS. 1-3 , the circular circumference  111  is substantially continuous, which warrants a smooth sliding of the rim  101  against adjacent chords  201 ,  202  during cutting operation. In context with the present invention, the substantially continuous circular circumference  111  pertains to the fact that a projection of the circular circumference  111  in axial direction renders a substantial continuous circle, despite recessing cavities  109 . 
   In a second embodiment of the invention depicted in the  FIGS. 4-6 , the circular circumference  311  has s substantially continuous surface, which means that all main outside boundary edges of the continuous surface are substantially circular and substantially concentric. Cap screws  324  may be accessible through radial rim openings that are not considered as outside boundary edges due to their insignificantly small diameters. The substantially continuous surface provides increased operational safety preventing inadvertent radial thump in case of premature rotation of the apparatus prior to operational positioning of the apparatus  300 . 
   An additional safety aspect is the fact that the groove cutting members  121  are fixedly held in cavities  309  that are finite in other than axial direction. Particularly, the cavities  309  are finite in direction radial away from the axis of rotation. Under extreme conditions, where the attachment of the groove cutting members  121  may suffer from impact or the like, the groove cutting members  121  would be held in the apparatus  300  against centrifugal forces. 
     FIG. 6  illustrates in detail how the groove cutting members  121  are fixedly held in the apparatus  300  via the cap screw  324  radially withholding itself in a press contact in one of the spokes  307  while pressing the groove cutting member  121  against an outside radial wall of the cavity  309 . The cap screw  324  is reaching thereby through an opening of the groove cutting member  121  such that the cap screw  324  head is peripherally accessible through the radial rim opening. The cap screws  324  act thereby additionally as a double supported latch holding with their shaft and head their respective groove cutting members  121  in the cavity  309 . 
   In contrast the groove cutting members  121  are pressed in the first embodiment against an inside radial wall of the cavity  109 . Also, the cap screws  124  are withholding them self in a tensile fashion, which may require a threads in the spokes  107 . 
   The cap screws  324  are preferably pressing there associated groove cutting members  121  via a nut  327  that has a circumferential locking contour corresponding to a rotation lock feature of the cavity  309 . The circumferential locking contour is preferably a flat surface corresponding to a flat bottom of cavity  309  in assembled position. In that case, a flat bottom of the cavity  309  may serve as the circumferential locking contour. 
   Also in the second embodiment, the groove cutting members  121  may be pressed against the outside radial wall with two bridge contacts  1211  that are in an opposing distance relative to the cap screw  324  such that the groove cutting members  121  are resiliently deflected. This assists in establishing a resilient fix of the groove cutting members  121  that absorbs operational vibrations without becoming loose. Curvature of the groove cutting members  121  may be fabricated accordingly such that it may correspond to the cut groove radius in assembled position. 
   Rims  101 ,  301 , spokes  107 ,  307  and central portions  103 ,  303  are preferably monolithically fabricated from a lightweight material such as for example, an aluminum alloy, an magnesium alloy, an injection molded plastic or from sheet metal. 
   The hole cutting apparatus  100 ,  300  may be fabricated in accordance with exemplary standard diameters for circular circumference  111 ,  311  listed in inches in the table below. 
   
     
       
             
           
         
             
                 
             
           
           
             
               4.5 
             
             
               5 
             
             
               5.5 
             
             
               6 
             
             
               6.5 
             
             
               7 
             
             
               7.5 
             
             
               8 
             
             
               8.5 
             
             
               9 
             
             
               9.5 
             
             
               10 
             
             
               10.5 
             
             
               11 
             
             
               11.5 
             
             
               12 
             
             
               12.5 
             
             
               13.0 
             
             
                 
             
           
        
       
     
   
   The preferred offset  125  is about 0.25 inches making the cut holes in diameter approximately 0.5 inches smaller than the circular circumference  111 ,  311 . An additional spacer insert may be placed in between the groove cutting member  121  and the respective outside wall to slightly reduce the diameter of the cut hole. Such spacer insert would have a preferred thickness of about 0.125 inches. 
   Accordingly, the scope of the invention described in the specification above is set forth by the following claims and their legal equivalents: