| 摘要 |
A drill bit comprises a bit body having a plurality of upstanding main blades formed thereon. The main blades have a plurality cutting elements mounted thereon, and they are shaped such that a cutting profile of the bit includes a nose portion, an inner cone region located radially inwards of the nose portion and an outer region located radially outwards of the nose portion. The bit further has at least one additional blade. The additional blade carrying cutting elements located radially inwards of the outer region of the cutting profile, but being substantially free of cutting elements located in the outer region of the cutting profile.
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