Abstract:
An apparatus for enlarging an existing hole in an object includes a separate hole saw with a center pilot shaft. A guide tube with a disk attached at one end inserts into the preexisting hole in the object and receives a bridging web with a plurality of tapered radial arms cumulatively forming a cone shape on the other end. The space between the bridging web and the disk is reduced by a threaded fitting to clamp the guide tube on the object within the existing hole. When the cone-shaped web wedges into the pre-existing hole, the guide tube is moved toward the axis of the pre-existing hole. The bore of the guide tube slideably receives the pilot member to guide the hole saw to rotate coaxially relative to the bore when cutting the second hole. A flat web may be used for non-coaxial cutting.

Description:
FIELD 
     The present invention relates to hole saws and more particularly to hole saws having a central pilot bit and an outer cutting element, such as a saw, for cutting a hole. 
     BACKGROUND 
     Hole saws with a central pilot bit and an outer concentric cutting element, such as a cylindrical saw or a plurality of cutting blades or gouges are known. In using such hole saws, the pilot bit drills into the material into which a hole is to be cut prior to the engagement of the outer cutting element, e.g., a cylindrical saw, with the material. When the pilot bit drills into the material making a drilled hole, the interaction between the pilot bit and the drilled hole establishes a center of rotation for the cutting element, assisting in holding the cutting element on this center of rotation as the cutting element is turned by a drill and cuts through the material to make a larger hole. This type of saw is typically used for cutting holes in a material which is without pre-existing holes. 
     SUMMARY 
     The disclosed subject matter relates to a guide for a hole saw having a pilot member and a cutting member for cutting a second hole in an object having a pre-existing hole, the second hole at least partially overlapping the pre-existing hole. The guide has a guide member with a bore therein, the guide member capable of being positioned in the pre-existing hole and held in the pre-existing hole by at least a first support member attached to the guide member, the bore adapted to slideably receive the pilot member to guide the hole saw to rotate coaxially relative to the bore when cutting the second hole. 
     In an another approach, the first support member has a component of extension perpendicular to the axis of the bore of the guide member. 
     In another approach, the guide has a second support member having a component of extension perpendicular to the axis of the bore of the guide member, removably attachable to the guide member. 
     In another approach, the first and second support members are capable of at least partially bridging the pre-existing hole when the guide member is positioned in the pre-existing hole with the first and second support members attached. 
     In another approach, the second support member has a plurality of radial arms extending from a hub and the guide member is attached to the second support member proximate the hub. 
     In another approach, the hub has a first side and a second side, the first side disposed towards one end of the guide member and the second side disposed toward the other end of the guide member when attached thereto, a diameter of the hub being less than a diameter of the pre-existing hole, the radial arms tapering in thickness in a direction parallel to the direction of extension of the hub from the first side to the second side and having a greater thickness proximate the hub and a lesser thickness distal to the hub. 
     In another approach, at least one of the first support member and the second support member is held in association with the guide member by an adjustable fastener that is adapted to selectively move one of the first and second support members to within a selected proximity of the other. 
     In another approach, the tapering radial arms are capable of guiding the hub of the second support member toward a position proximate an axis of the pre-existing hole when the adjustable fastener moves the first and second support members closer together and the tapering radial arms contact the object proximate the pre-existing hole. 
     In another approach, the tapering radial arms define sloped surfaces which cumulatively approximate a portion of a cone adapted to be selectively pointed toward the first support member, the cone progressively wedging into the pre-existing hole as the adjustable fastener urges the first and second support members closer together. 
     In another approach, the tapering radial arms each have a plurality of steps on the sloped surfaces thereof defining a set of steps on each of the plurality of tapering radial arms. 
     In another approach, the plurality of tapering radial arms are symmetrical about an axis through the hub, the set of steps on each of the plurality of tapering arms being approximately identical. 
     In another approach, the steps approximate a plurality of concentric ledges of different radii. 
     In another approach, the steps function as gripping teeth that bite into the object when the adjustable fastener is tightened. 
     In another approach, the guide member has a threaded end, the threaded end extending through an aperture in the hub, the fastener being a nut that engages the threaded end and the first and second support members adapted to clamp the object there between when the fastener is tightened. 
     In another approach, a resilient member is positioned adjacent to the first support member and between the first and second support members. 
     In another approach, the first support is a disk attached to the guide member proximate one end and the guide member is tubular. 
     In another approach, the second support member has four radial arms symmetrically disposed about an axis through the hub, the set of steps on each of the plurality of tapering arms being approximately identical. 
     The present disclosure also relates to a hole cutting assembly for cutting a second hole in an object having a pre-existing hole, the second hole at least partially overlapping the pre-existing hole, the assembly including a hole saw having a pilot member and a cutting member, a guide tube with a bore therein and being threaded at at least one end. A first support member in the form of a disk is attached to the guide tube proximate one end at an approximately perpendicular relative orientation. A second support member having a hub and a plurality of radial arms extending from the hub is attached to the guide tube proximate the hub. The hub has a first side and a second side and an axial aperture running from the first side to the second side, with the axial aperture receiving the guide tube. The first side of the hub is disposed towards one end of the guide tube and the second side is disposed toward the other end of the guide tube when the guide tube is extended there through, the radial arms tapering in thickness in a direction parallel to the direction of extension of the hub from the first side to the second side and having a greater thickness proximate the hub and a lesser thickness distal to the hub. A threaded fastener is receivable on the threaded end of the guide tube to retain the second support member on the guide tube and to control the position of the second support member on the guide tube relative to the first support member. The first support member is positionable on one side of the object with the guide tube attached and extending through the pre-existing hole, with the second support member being attached to the guide tube by the threaded fastener on the other side of the object. The tapering radial arms define sloped surfaces which cumulatively approximate a portion of a virtual cone, such that when the guide tube is positioned in the pre-existing hole with the virtual cone pointed toward the first support member, the virtual cone progressively wedges into the pre-existing hole as the adjustable fastener urges the first and second support members closer together, moving the guide tube toward the axis of the pre-existing hole and holding the guide tube at a given position relative to the axis of the pre-existing hole. The bore of the guide tube is adapted to slideably receive the pilot member to guide the hole saw to rotate coaxially relative to the bore when cutting the second hole. 
     In another approach, tapering radial arms of the guide each have a plurality of steps on the sloped surfaces thereof capable of functioning as gripping teeth that bite into the object when the adjustable fastener is tightened. 
     In another approach, the second support member has four radial arms symmetrically disposed about an axis through the hub. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention, reference is made to the following detailed description of exemplary embodiments considered in conjunction with the accompanying drawings. 
         FIG. 1  is an exploded view of a power hub installed in a solid surface, such as a desk top in accordance with an embodiment of the present disclosure. 
         FIG. 2  is perspective view of a hole saw and guide assembly. 
         FIG. 3  is a side view of the hole saw and guide assembly of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIG. 1  shows an electrical power and connector hub  10  which is receivable in a hole  12  formed in surface S, e.g., of a desk or table. The hub  10  is provided with one or more sockets, e.g., three prong electrical outlets  14 , USB sockets  16 , phone jack(s)  18 , etc. The hub  10  may also be provided with LEDS  20  to indicate power is present at the hub, circuit breaker reset button(s)  22  and other electrical power and data connectors, controls and status indicators. The hub  10  inserts into the hole  12  such that the hub  10  is approximately flush with the surface S, a peripheral lip  24  covering the outer edge of the hole  12 . Electric cords  26  extend from the hub  10  beneath the surface S. It is known to provide holes in desks and tables to allow the passage of cords and to position electric devices within the holes. Frequently, desks and tables are predrilled and blocked with a removable grommet and or a sleeve to selectively accommodate various devices. The predrilled holes do not, however, necessarily match the size of a given electrical fitting, such as hub  10 , which may be, e.g., 3.5 or 4.0 inches in diameter, whereas the predrilled hole may be, e.g., 2.0 or 2.5 inches in diameter. Stated more generally, it is possible for there to be a size mismatch between the electrical apparatus installed into the desk or table and the predrilled hole. In the event that it is desirable to enlarge a pre-existing hole with a larger sized hole saw, it is sometimes difficult to maintain the position of the hole saw relative to the existing hole if the guide bit is significantly smaller than the pre-existing hole and therefore does not provide a guiding function to hold the cutting element on a center of rotation coaxial with the existing pre-drilled hole. While this situation exists when enlarging a pre-existing hole in a desk or a table to accommodate an electrical fitting, the situation exists in any case wherein a pre-existing hole needs to be enlarged by a larger hole saw, e.g., in enlarging a hole for a lock set in a door, or enlarging a passageway through a floor for water pipes or electrical conduit. 
       FIGS. 2 and 3  show a hole cutting assembly  30  having a hole saw  32  and a guide  34 . The hole saw  32  has a saw cup  36  with a cylindrical side wall  38  extending from a central portion  40 . The side wall  38  has a plurality of cutting teeth  42  disposed at the free end thereof. A guide drill bit  44  extends through the central portion  40  of the saw cup  36  with the shank portion  46  extending upwardly for attachment to a drill chuck (not shown) and the drill tip  48  extending downwardly for drilling into the material into which a sawn hole is to be made. The drill bit  44  may be secured to the central portion  40  by welding or may be conjoined to the saw cup  36  via an arbor and threaded clamp nuts, as is conventional for hole saws. In general, an existing conventional hole saw may be utilized for the hole saw  32 , in accordance with the present disclosure, so long as the dimensions thereof are compatible with the guide  34 , as described further below. The side wall  38  may have reliefs  50  (shown by a dotted line) to promote cutting efficiency and the teeth  42  can have various shapes and patterns for cutting different types of materials, as is known in the art. Further, other known types of hole saws can be utilized, e.g., hole saws having a saw blade held in a place in a circular groove or one having one or more cutting blades or gouges radially spaced from the guide drill bit. 
     The guide  34  has a guide member, such as shaft  52  that has an internal bore  54  extending through at least a portion of the shaft  52 . The shaft  52  may be externally threaded at one end  55  to receive nuts  56 ,  58  to retain a support member, such as plate  60  on the shaft  52  approximately perpendicular thereto. Alternatively, plate  60  may be retained on the shaft  52  by welding or by swaging the shaft  52  and/or the plate  60 . An elastomeric layer or gasket  62  may be positioned against or adhered to one side of plate  60  to provide a slip resistant interface between the plate  60  and the object O, which will not scratch the finish of the object O as the guide  34  is positioned. A second support member, such as spanning web  64  may be retained on the shaft  52  at the end thereof  66  opposite to the plate  60 . The shaft  52  may be externally threaded at the end  66 , which extends through an aperture  68  in the spanning web  64 . A wing nut  70  retains the spanning web  64  on the threaded shaft  52  and may be used to adjust the position of the spanning web  64  relative to the plate  60 . The spanning web  64  has a plurality of radially extending arms  72 ,  74 ,  76 ,  78 , i.e., at least two in number, but preferably three or more, extending from a central hub  80  for spanning a given pre-drilled hole. Each arm  72 ,  74 ,  76 ,  78  has a sloping stepped upper surface  72   S ,  74   S , ( 74   S  not visible in  FIGS. 2 and 3 ),  76   S ,  78   S  with a plurality of small teeth/steps  73  that step down toward the distal tips  72   T ,  74   T ,  76   T ,  78   T  of the arms  72 ,  74 ,  76 ,  78 . As a result, the sloping upper surfaces  72   S ,  74   S ,  76   S ,  78   S  cumulatively define an approximate cone shape. 
     In use, the shaft  52  with the plate  60  attached at one end is inserted into a pre-existing hole H in an object O that needs to be enlarged, with the plate  60  spanning the hole H in the object O on one side and the shaft  52  depending from the plate  60  and extending into and through the existing hole H. The threaded end  66  of the shaft  52  is then inserted through the aperture  68  in the spanning web  64  and wing nut  70  is screwed onto the threaded end  66 , capturing the object O between the plate  60 /elastomeric coating/gasket  62  and the spanning web  64 . As the wing nut  70  is tightened, the spanning web  64  is urged towards the plate  60  and into contact with the peripheral edge of the pre-existing hole H in the object. As the spanning web  64  approaches the plate  60 , the engagement of the cone shape of the sloping upper surfaces  72   S - 78   S  of the arms  72 - 78  with the periphery of the hole H draws the spanning web  64  and the threaded end  66  of the shaft  52  captured in aperture  68  towards the center of the hole H in the object O. 
     Upon feeling resistance to further tightening of the wing nut  70 , the plate  60  may be repositioned interactively by the installer, who can sense if repositioning results in the loosening of the wing nut  70 , such that it can be further tightened, which is then done. More particularly, positioning the shaft  52  coaxially in the pre-existing hole H results in the distance between the plate  60  and the spanning web  64  being minimized when the wing nut  70  is tightened. If the shaft  52  is cocked relative to the axis of the hole H, then the shaft is disposed at a hypotenuse relative to the coaxial path and is therefore of greater length. The guide  34  may be used to find the approximate coaxial position for the shaft by the foregoing process of tightening of the wing nut  70 , attempted repositioning of the plate  60 , retightening of the wing nut  70  if loosened, etc. 
     Alternatively, the spanning web  64  may be visually placed in the approximate coaxial position relative to the pre-existing hole H with the wing nut  70  simultaneously held against the spanning web  64  concentric with the aperture  68 . The shaft  52  with attached plate  60  may then be inserted into the hole H through the aperture  68  and threaded into the wing nut  70 , all the while preserving the approximately coaxial position of the spanning web  64  relative to the hole H until the plate  60  is tightened down against the object O. Final tightening can then be accomplished by further tightening of the wing nut  70 . 
     The steps  73  on the arms  72 - 78  can perform two functions, viz., they can act as teeth that bite into the object O when the spanning web  64  is tightened down on the object O, preventing the spanning web  64  from moving relative to the object O when the hole saw is used. In addition, if the steps  73  are dimensioned at a large enough scale and each arm  72 - 78  has a substantially identical set of steps  73  of the same size and position, each set of similar steps corresponds to a virtual hole size into which that particular set of steps will insert. For example, the sixth step  73  up from the distal tips  72   T - 78   T  of each of the respective arms  72 - 78  may define a given hole size H 1 , e.g., 2.5 inches. The set of steps  73  on arms  72 - 78  that are three up from the distal tips  72   T - 78   T  may represent a larger hole size H 2 , e.g., 3.0 inches, etc. Assuming an object O with parallel upper and lower surfaces and a round, pre-existing hole extending through the object O in a direction perpendicular to the upper and lower surfaces, when the spanning web  64  is positioned coaxially in the hole H, the peripheral edge of the hole H will contact the same step  73  (e.g., the 3 rd  or the 6 th  step, etc.) on each of the arms  72 - 78 , resulting in a shaft  52  position that is approximately coaxial with the hole H. This is due in part to the symmetry of the spanning web  64  and to the fact that the aperture  68  extends perpendicularly to the radial extent of the spanning web  64  and preferably approximates the outside diameter of shaft  52 , such that positioning the spanning web  64  in an orientation parallel to the upper or lower surface of the object O results in the aperture  68  holding the shaft  52  perpendicular thereto when the shaft  52  is inserted into the aperture  68 . 
     Given that the foregoing process of positioning the guide  34  in a pre-existing hole H has been accomplished, resulting in the shaft  52  being approximately coaxially positioned in the hole H, with the wing nut  70  tight and the spanning web  64  and the plate  60  tightly clamping the object O on either side, the guide drill bit  44  of the hole saw  32  may be introduced into the internal bore  54  of the shaft  52 . Given this mechanical cooperation, it is preferred that the bore  54  and the guide bit  44  are sized to establish a slip fit. Preferably, the material composition of the guide bit  44  and the shaft  52  are selected such that there is a workable degree of frictional interaction, with less being better than more. While a guide bit  44  in the form of a conventional twist drill is shown (that would be used on a conventional hole saw), a plain shaft without cutting edges could also be used in place of the drill guide bit  44 , because the guide bit  44  is not used to drill through the object O, but is instead used simply to insert into and rotate within the bore  54  of the shaft  52 . Once the guide bit  44  is positioned in the bore  54 , the drill (not shown) may be activated to turn the hole saw  32 . As the hole saw  32  rotates and engages the object O to cut an enlarged hole, the guide bit  44  is held on a rotational center by its engagement with the bore  54  of the shaft  52 . Given a suitably sized guide bit  44 , a conventional hole saw may be used in conjunction with the guide  34  as described herein. 
     As noted above, the teeth  73  either insert within the pre-existing hole H establishing a mechanical registration and/or grip/bite into the peripheral edge of the hole H to provide a rigid mounting of the guide  34  within the pre-existing hole H. This rigidity resists the forces applied to the shaft  52  by the guide bit  44  as the hole saw  32  encounters (digs into) the object O, the teeth  42  having a varying bite depending upon small variations of force on the hole saw  32  that push the hole saw  32  into the object O and upon variations in the angular orientation of the saw  32  due to the operator twisting the drill from side to side. The resilient layer/gasket  62  on the plate  60  also aids in retaining the shaft  52  in a single orientation in that it deforms and grips the surface of the object O. 
     In the event that a pre-existing hole H requires enlargement, but it is preferred that the enlarged hole be eccentric relative to the pre-existing hole (rather than coaxial), the hole cutting assembly  30  can be used in the same manner as described above, but with the spanning web  64  inverted, such that the flat surfaces  72   F - 78   F  of the arms  72 - 78  is positioned upwardly to contact the object O. The position of the desired enlarged hole may be determined by placing the plate  60  in the desired position (which may have been previously marked with a pencil) with the shaft  52  depending there from and extending into the hole H. The spanning web  64  is then slipped on the shaft  52  and the wing nut  70  threaded on and tightened, all the while holding the plate  60  to prevent movement of the plate  60  while tightening. Since the surfaces  72 F- 78 F are flat, the spanning web  64  does not pull the shaft  52  towards the center of the hole H, but leaves the shaft  52  in the position in which it was originally placed. Once the guide  34  is positioned within the pre-existing hole H at the desired position, hole cutting can be conducted as before. 
     It will be understood that the embodiments described herein are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the claimed subject matter. All such variations and modifications are intended to be included within the scope of the appended claims.