What is a drill bit?

A “bit” is a rotating device found at the bottom of a “drill string”; it is used to cut and pulverize rock. The drill bit is the business end of the drilling string and it crushes rock so that the drill string can be advanced. The bit is part of the “bottom hole assembly” (BHA.) The BHA consists of the drill bit, drill collar, and drilling stabilizers.

Types of Bits:

Bits come in various types and sizes. The most common types of bits are tricone rotary bits, Down the Hole (DTH) bits, and fixed cutter bits. Tricone rotary bits are recognizable for their three headed design and are manufactured in steel tooth and Tungsten Carbide Insert (TCI) varieties. The Hughes Tool Company invented these bits in 1909. These varieties describe different cutting structures of the teeth. The steel tooth variety is typically used for softer drilling conditions and the TCI is used for harder drilling conditions. The International Association of Drilling Contractors (IADC) grades drilling bits according to the IADC code. The IADC code is a three digit numbering system that describes the series of the cutting structure, the type of cutting structure, and the bearing system and gauge surface. Tricone drill bits are the workhorses of the drilling industry and are found in all drilling applications including oil and gas, mining, water well and geothermal, directional drilling, and foundation/construction drilling.

Ingersoll-Rand invented DTH bits in the mid 1950s. The best way to describe a DTH bit is to think of a jackhammer at the bottom of the drill string. DTH bits are used in very hard rock formations and perform well under extreme conditions, like those found when drilling granite. This is a popular bit in all drilling operations particularly in very hard rock. DTH bits are especially popular with quarrying operators.

A third type of drill bit is the fixed cutter bit or diamond bit. Fixed cutter bits come in three major varieties: natural diamond bits, diamond impregnated bits, and polycrystalline diamond cutter (PDC) bits. The PDC bit is by far the most common type of fixed cutter bit, and was first introduced to the drilling industry in the late 1970s. PDC bits are different from tricone and DTH bits in that they shear rock vs pulverizing. Shearing is more efficient than crushing, and thus PDC bits can drill faster than either tricone or DTH bits. Manufacturers build PDC bits in two types: steel body and tungsten matrix.

Drillers use unique bits for unique purposes, especially in the mining industry. Raise bore bits and top hammer (or surface) bits are two common miscellaneous bits. Raise boring is a drilling technique used to create ventilation shafts in underground mines. Top hammer bits are used in areas that require precise drilling but cannot utilize large drilling rigs. Top hammer bits are normally found in underground applications and in rugged terrain or austere environments.


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