| 摘要 |
A rotating diamond core drill is contacted with a hard but brittle material, and by keeping contact relation with the material, drilling operation is continued to drill a hole to the material. Further, when a hole is bored, relative eccentrical motion is given between the diamond core drill and the material so that the whole inner circumferential surface of the hole can be contacted with the rotating diamond core drill, and drilling speed of the diamond core drill is reduced. Accordingly, drilling and cutting pressure applied to the material is reduced and no breaking-offs is generated. |
