| 摘要 |
PCT No. PCT/CH93/00194 Sec. 371 Date Apr. 15, 1994 Sec. 102(e) Date Apr. 15, 1994 PCT Filed Aug. 3, 1993 PCT Pub. No. WO/9404303 PCT Pub. Date Mar. 3, 1994.A method and apparatus for producing deep drill holes, particularly in wood and similarly structured materials, in which two drill elements, embodied as hollow shafts with cutting ends formed as cutting elements and concentrically disposed one within the other, are operated at different speeds, the cutting end of the interior drill element running behind the cutting end of the exterior drill element.
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