The full form of PDC bit is Polycrystalline Diamond Compact bit. It is a fixed-cutter drill bit whose cutting elements are small discs of synthetic diamond bonded to tungsten carbide. PDC bits have no cones and no bearings; they drill by shearing rock rather than crushing it. This guide explains what each word in the name means, how a PDC cutter is made, how a PDC drill bit works in the hole, how to read a PDC model code, and where PDC bits do — and do not — make sense.
PDC bit full form, word by word
- Polycrystalline — the diamond layer is made of many small diamond crystals bonded together, not a single crystal. Because the crystals are randomly oriented, the layer has no single weak cleavage plane and is tougher than a natural single-crystal diamond of the same size.
- Diamond — the hardest known material, which gives the cutter its exceptional wear resistance. The diamond in PDC cutters is synthetic, manufactured for industrial use.
- Compact — the cutter is a compact: a thin diamond table bonded to a thicker tungsten-carbide substrate, forming a small cylindrical disc that can be brazed into the bit body.
Note that "PDC" has other meanings in banking and elsewhere (post-dated cheque, for instance). In drilling, PDC always refers to polycrystalline diamond compact.
How a PDC cutter is made
Diamond powder is placed against a tungsten-carbide substrate and sintered at very high pressure and temperature. Under these conditions the diamond grains bond to each other and to the carbide, producing a solid diamond table on a carbide base. The carbide gives the cutter toughness and a surface that can be brazed; the diamond table gives it the cutting edge.
Cutters are made in standard diameters measured in millimetres. Across the Volgaburmash FastDrill range, cutter sizes run from 8 mm to 19 mm: smaller cutters are more impact-resistant and suit harder or interbedded rock, while larger cutters take a deeper bite and suit softer formations.
How a PDC drill bit works
A PDC bit shears rock the way a lathe tool peels metal. Each cutter is set at a small backward tilt (back rake) and often a sideways tilt (side rake). As the bit rotates under weight, the cutters plough into the formation and shear off a continuous chip. Drilling fluid from the nozzles cools the cutters and washes the cuttings up through junk slots between the blades.
Shearing takes less energy than crushing, which is why PDC bits often drill faster than roller cone bits in suitable rock, and why they perform well with downhole motors at higher rotary speeds. Because there are no moving parts, there is no bearing to wear out — a PDC bit can stay in the hole for a long run, reducing trips.
Parts of a PDC bit
- Body — either steel (machined from alloy steel; strong and repairable) or matrix (tungsten-carbide matrix; highly resistant to erosion and abrasion).
- Blades — raised ribs that hold the cutters. Fewer blades mean a more aggressive, faster bit for soft rock; more blades spread the load for harder or interbedded rock.
- Cutters — the PDC compacts brazed into pockets on the blades.
- Nozzles or ports — direct drilling fluid across the cutters. Some bits have replaceable nozzles.
- Junk slots — channels between blades that carry cuttings away.
- Gauge pads — the outer surfaces that hold the hole diameter.
- Shank and pin — the threaded connection, usually an API Reg pin, that screws into the drill string.
Reading a PDC model code
Volgaburmash PDC model codes are built from blades, cutter size and formation category. For example:
- FD516SM — FastDrill, 5 blades, 16 mm cutters, for soft formations with medium interlayers (SM).
- FD613MH — FastDrill, 6 blades, 13 mm cutters, for medium formations with hard interlayers (MH).
- WD513SC — WaterDrill, 5 blades, 13 mm cutters, for soft formations (S), with replaceable nozzles (C).
The formation letters used across the range are S (soft), SM (soft with medium interlayers), M (medium) and MH (medium with hard interlayers). The industry also has an IADC classification for fixed-cutter bits, a four-character code describing body material, cutter density, cutter size and bit profile. It is less widely quoted than the three-digit IADC tricone code, so always confirm the actual blade count and cutter size with the supplier.
PDC vs tricone bits
| Feature | PDC bit | Tricone bit |
|---|---|---|
| Cutting action | Shearing | Crushing and gouging |
| Moving parts | None | Three cones on bearings |
| Best formations | Soft to medium, uniform | Soft to very hard, including fractured and interbedded |
| Rate of penetration | Usually higher in suitable rock | Moderate; steady in hard rock |
| Run length | Long; no bearing wear | Limited by bearing and cutting structure life |
| Weakness | Impact damage in hard, broken rock | Bearing failure on long runs |
| Purchase price | Usually higher | Usually lower |
The right choice depends on the formation and the economics of the whole run, not the purchase price alone. Our DTH vs tricone vs PDC guide compares all three for borewells.
Where PDC bits are used in India
Oil and gas. PDC bits drill a large share of footage in soft-to-medium sedimentary sections and are the usual choice for directional and horizontal wells run on downhole motors. The Volgaburmash FastDrill steel-body series covers 3 9/32" to 17½" for vertical, directional and horizontal drilling, and FastDrillMatrix offers a matrix body where erosion and abrasion are the concern.
Borewells and water wells. In soft sediments without boulders — much of the alluvium of the north — a PDC bit can drill fast. The WaterDrill series is a steel-body PDC from 4" to 11 7/32" for soft formations and soft formations with medium interlayers. In hard basalt and granite, DTH or TCI tricone bits are usually the better tools.
See the ranges on our PDC bits and borewell & water-well bits pages, compare with tricone bits, or check the PDC bits in stock in Dubai.
Common PDC failure modes
- Impact damage — chipped or broken cutters from hard stringers, vibration or bouncing on bottom. Keep parameters steady when entering hard layers.
- Abrasive wear — flat, worn cutters in quartz-rich rock. A matrix body or smaller, more numerous cutters help.
- Thermal damage — overheating from poor cooling or excessive speed in hard rock degrades the diamond table. Maintain enough flow.
- Bit balling — sticky clay packs between the blades and the bit stops drilling. Good hydraulics and fluid design prevent it.
Frequently asked questions
What is the full form of PDC bit?
PDC stands for Polycrystalline Diamond Compact. A PDC bit is a fixed-cutter drill bit whose cutters are synthetic diamond tables bonded to tungsten-carbide substrates.
Is the diamond in a PDC bit real diamond?
Yes, it is real diamond, but synthetic: diamond grains are sintered under very high pressure and temperature into a polycrystalline layer bonded to tungsten carbide.
Can a PDC bit drill granite or basalt?
PDC bits are at their best in soft to medium, uniform formations. In hard, fractured rock such as granite or basalt the cutters can chip, so TCI tricone bits or DTH button bits are usually the better choice.
Can PDC bits be used for borewells?
Yes, in soft sediments without boulders, where they drill fast. The Volgaburmash WaterDrill series is a steel-body PDC bit for water wells in soft formations and soft formations with medium interlayers.