| 摘要 |
The bit has a front tip (2) drilling a surface, and a conical central section (3) for gradually reaming a conical opening of the bit in the drilled surface. The front tip and the conical central section extend in an extension of each other. A rear section (4) forms a reamer extended in the extension of the central section and adapted to mill a front end of the opening. The front point and the central section include a helix (6) with four bits. A slope of the central section ranges between 0 degrees 10' and preferentially between 0 degrees 15' and 0 degrees 45'. |
