| 摘要 |
A substantially cylindrical hole is drilled into a support structure, and the end of the hole remote from the point of entry of the drilling tool into the structure is enlarged in its cross-sectional area so as to provide abutment surfaces for spreading portions of a fastening element inserted into the hole subsequently to the drilling thereof. The drilling tool includes a drill shaft, and a drill bit connected to the free end of the drill shaft and having lateral cutting edges. The cutting edges may diverge in direction axially away from the drill shaft and a collar may be provided on the drill shaft which, in cooperation with the inner surface bounding the hole forms a fulcrum for a lever-type angular displacement of the drilling tool for increasing the cross-sectional area of the remote end of the hole. The collar may be mounted on the drill shaft for displacement between a plurality of axially spaced positions and for arresting in any one of these positions so as to adjust the drilling tool to a particular depth of the hole to be drilled. |
