| 摘要 |
A hole drilling method for a plate material is provided to prevent generation of crack or damage at the periphery of a hole and improve productivity by communicating the front end of a second core drill with a taper surface. A hole drilling method for a plate material comprises the steps of: forming a first concave part(1a) on one side of the plate material by using a first core drill having a taper part where outer periphery of the front end has a condensed diameter toward the front end, and forming a through-hole opposed to a first core drill(2) at the outer periphery of the drill part from the other side of the plate material by using a second core drill(3) whose outer diameter is larger than an inner diameter of the first core drill and is smaller than the surface periphery of the first concave part. |
