| 摘要 |
Cutting elements, for example of polycrystalline sintered diamond, the cutting faces of which are set differently to the cutting direction, are disposed on a rotary drill bit. One group of cutting elements has its cutting faces substantially perpendicular to the cutting direction (straight set cutting elements) while other groups of cutting elements are at an acute angle to the cutting direction (obliquely set cutting elements). Because of their greater pressure per unit area, the obliquely set cutting elements penetrate more easily into plastic formations and can tear these up. The straight set cutting elements, which do not develop a great pressure per unit area, but work over a wider range, can better pare off the formation prepared by the obliquely set cutting elements.
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