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Figure 6.1 – Diamond and PDC bits
In 1909 Hughes brought out a 2-cone rolling cutter bit that
proved effective in hard rock formations, hence the term rock bit
was coined. This early model did not have intermeshing (self-
cleaning) teeth so it was poor in gumbo or shale which caused the
cones to ball up or lock. Cross rolling cutter-type bits came out
later but rock bits were not a commercial success for several years,
and seemed to have limited application.
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