| 摘要 |
1491352 Boring earth &c. FRIED KRUPP HUTTENWERKE AG 20 Jan 1975 [29 Jan 1974] 2302/75 Heading E1F A rotary drill bit has at least one cutting system consisting of a pair of cutting elements arranged so that one corner of each of the cutting elements makes a cut across the central region of the cut produced by the other cutting element. As described a core bit has a pair of triangular inserts 4, 5 which are clamped to the body of the bit by clamps 6, 7, the inserts having three cutting edges, each of which can be brought into an operative position as the others become blunted. The bit is also provided with hard metal supports 12, 13 which bear against the wall of the hole being drilled. The inserts 4, 5 (Fig. 3) are arranged so that the corner 17 of insert 4 projects beyond the centre of cutting edge 15 of insert 5, and so that the corner 16 of insert 5 projects beyond the centre of cutting edge 14 of insert 4. In this way the cut is divided into four zones I to IV (Fig. 7) which reduces the size of the shavings to facilitate the removal of debris by the flushing medium. In a modification (not shown) the cutting inserts may be of rectangular or trapezoidal shape. The invention may also be applied to full drill bits, in which case more than one such cutting system may be necessary. |
