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Tungsten Synthetic
carbide diamonds
Hybrid

Roller Cone Bits

Roller cone bits have steel cones that roll, or turn, as the bit rotates. The bit
cutters are on the cones. As the cones roll over the bottom of the hole, the cutters
scrape, gouge, or crush the rock into relatively small chips, or cuttings. Drilling fluid,
which comes out of special openings in the bit, removes the cuttings. Most roller
cone bits have three cones, although some have two or four. The cutters on a roller
cone bit are either steel teeth or tungsten carbide inserts. Manufacturers mill (cut) or
forge (hammer) the teeth out of the steel body of the cones. For tungsten carbide
insert bits, they drill holes in the cones and press-fit the tungsten carbide cutters into
the holes.
Most steel-tooth and tungsten carbide roller cone bits have nozzles that eject
high-speed streams, or jets, of drilling mud. The jets of mud sweep cuttings out of the

way as the bit drills. With the cuttings out of the way, the bit cutters do not redrill
cuttings, which would slow the drilling rate, or rate of penetration (ROP – pronounce
each letter). Because of their jetting action, oil people sometimes call roller cone bits
“jet bits.”
Fixed-Head Bits
Although fixed-head bits have jets, they do not have cones that roll
independently on the bit as it rotates. Instead, fixed-head bits consist of a solid piece
– the head – that rotates only as the drill string rotates. The bit manufacturer sets the
cutters into the bit head. One type of fixed-head bit has natural, industrial-grade
diamond cutters. Another employs synthetic diamonds. One synthetic diamond is
polycrystalline diamond-, manufacturers also use a synthetic diamond called a
“thermally stable polycrystalline diamond.”
In a natural diamond bit, the bit maker embeds industrial diamonds in the
bottom and sides of the bit head. As the bit rotates, the diamonds contact the face of
the formation and plow and grind it to make hole. Manufacturers make many kinds of
diamond bits for many kinds of formations and drilling conditions.
A widely used bit is the poly crystalline diamond compact (PDC) bit. PDC bits
feature tungsten carbide compacts to which are bonded synthetic diamonds.
(Acompact, in this case, is a small disk made of tungsten carbide.) The manufacturer
machines pocket into ribs or blades on the bit body and insert the diamond-coated
compacts into the pockets. A special kind of PDC bit is a thermally stable
polycrystalline diamond (TSP) bit. TSP bits can withstand much higher temperatures
than PDC bits. Thus, when drilling a hole that requires a lot of weight and high rotary
speeds that generate enough heat to destroy the synthetic diamond coating of a PDC
cutter, the operator may select a TSP bit.
Bit designers have taken advantage of the unique properties of each of the
various materials used to make fixed-head bit cutters and have combined them on one

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