| 摘要 |
<p>The tool is for boring stony ground and uses augers having a point at the end of an axial shaft (4), followed by a helicoidal blade to remove material. The perforating head (1) has several teeth (2) on the outside of a conical blade (13a,13b). The teeth are arranged differently radially and axially on the head. They are more widely spaced diametrically opposite to each other but have the same angular inclination to the axial shaft (4). The shaft has concentric breaking teeth (5) at its end to commence the bore.</p> |
