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Workshop/5 min exploration

Two drill bits, two ways to break rock

What changes when a drill bit uses rolling cones instead of fixed cutters?

At the bottom of an oil or gas well, the drillstring rotates a bit under load. A tricone carries three independently turning cones covered in hard inserts. A PDC bit carries diamond-faced discs fixed to curved blades. Orbit below each model to see the cutting face, then separate the cutting assembly to inspect how it attaches.

3D model

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The cones turn on their journals as the bit rotates, repeatedly indenting and gouging rock. PDC cutters remain fixed to their blades and shear rock as the whole bit turns.

Which part rotates relative to the bit body during ordinary cutting?

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How the parts work together

  1. Three cones, four rotations

    The body turns about the drillstring axis while all three cones also turn around their individual inclined axes. Orbit below the bit to follow the insert rows.

  2. Look behind a cone

    Separate the cutting assembly to reveal the supporting journals. This is an inspection pose: the displaced cones are no longer at their operating contacts.

  3. A fixed cutting face

    Switch to PDC. The diamond-faced discs remain fixed to six curved blades. Their leading faces sweep around the drillstring axis instead of rolling on journals.

  4. Clear the cutting face

    Turn on the nozzle paths and reference plane. Fluid is directed toward the cutting region and returns through the spaces between blades. Inspection speed changes the visible rotation, without predicting drilling performance.

The main parts

Threaded shank and body
The tapered threaded pin connects to the drillstring. The central bore carries drilling fluid down into the bit; the body transmits torque and load.
Carbide inserts and cones
Three conical steel shells carry staggered rows of rounded tungsten-carbide inserts. Each cone rotates around its own inclined journal as the body turns.
Cone journals
Each forged leg supports an inward-tilted journal. Separate the assembly to expose the shaft and thrust shoulder. The internal bearing and lubrication system are not sectioned.
Curved blades and gauge pads
Six swept blades support cutters. The spaces between blades are junk slots for fluid and cuttings. Outer gauge pads help maintain the hole diameter.
Fixed diamond cutters
Each dark circular diamond table sits on a cylindrical tungsten-carbide substrate in a blade seat. The faces lead into the direction of travel; the individual discs do not spin.
Reference rock plane
The optional transparent plane locates the approximate cutting envelope. The concentric marks are guides, not a prediction of the hole-bottom pattern. No rock is removed in this model.
Drilling-fluid nozzles
Open nozzle bores point toward the cutting region. Optional blue paths suggest fluid passing across the face and outward through the gaps, carrying cuttings away. Flow speed and pressure are not calculated.

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