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.

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.