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With the expiration of some Hughes basic patents, all rolling
cutter rock bits became similar. They were tricone roller bearing
assemblies with a great variety of tooth structures, including both
milled and tungsten carbide insert types. Some six U. S.
manufactures make them.
The jet bit principle was first applied to drag bits and proved
effective. In the late 1950s jet nozzles were applied to rock bits,
even with tungsten carbide inserts. Higher cost of jet bits was
justified in deep drilling because bottomhole scavenging could be
done with less drilling fluid being circulated and less friction loss
in drill string.
Substituting fluid velocity for fluid mass was effective in
cleaning debris from under the bit. At great depth, if small drill
pipe is required, it is illogical to attempt to circulate large fluid
volumes. The surface equipment (pump and prime mover) would
soon be considerably overloaded.
The most recent improvement in sock bits is lubricated
bearings, particularly lubricated journal-type bearings. Remember
the Hughes simplex bit of the 1920s? It had lubricated journal-type
bearings.
The concluding portion of this section will be confined
exclusively to tricone rock bits since they account for a large
portion of bit usage today. But before doing so, something must be
said about specialty bits that have made significant contributions to
the art.
In the drag bit category, fishtail bits with inexpensive
replaceable alloy steel blades made it possible to use hardfacing
material more effectively and expedited bit dressing at the rig. Bit
expense was lowered since only the blade was expendable. One
other approach to the problem was replaceable, welded-in alloy
steel blades used with a cast steel body (available in 2-blade, 3-
blade and 4-blade models).
The Guiberson disc bit was used extensively in Texas during
the early 1930s. Hughes offered a bit of similar construction

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