| 摘要 |
A drilling tool has a drilling shaft member, a crown drilling member with an annular wall provided with a plurality of cutting edges and detachably mounted on the shaft member, a center drilling member detachably mounted on the shaft member inside the crown drilling member and having a further cutting edge, and elements for limiting a drilling depth of the tool when the center drilling member is mounted on the shaft member. Thereby, the operator of the drilling tool, after drilling a guiding groove in a rock, is forced to remove the center drilling member from the drilling tool and drill further without the center drilling member, which increases the drilling efficiency. |
