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Auger Drill Bit
A drill bit is the sharp component of a drill tool that penetrates materials such as rock or wood to create holes. Powered by axial force, the bits drill cylindrical and non-cylindrical holes into materials, dependent on the type used. Inserted into the core of a rotary drill, bits are used in a variety of applications from mining to construction.

Prior to the invention of drill bits, materials were put together using rivets and bolts. Made from carbon steel or high-speed steel, the bit was developed around 1845. Some bits are made from tungsten carbide, a material capable of drilling into some of the hardest materials found on sites. Polycrystalline diamond (PCD) is another type of hard material capable of cutting through even the most challenging matter.[1]

For many drill bits, there is a coating put on top of it to increase the strength of the bit. For example, some drill bits have a titanium coating which increases the longevity of the bit's use. A zirconium coating makes the bit stronger, but also allows it to go through hard, but brittle materials such as steel. Due to overall makeup of the zirconium coating, friction is decreased which increases overall precision. Finally, there is cobalt which can be used when high speed steel doesn't work. It can handle high amounts of heat, but the draw back is that they are more brittle.[2] 

There are many types of drill bits, each designed for cutting holes in different types of materials, such as brick, glass, rock, plastic, and wood. Bits are available in different types: flat-faced, convex, concave, and kavex. Bit sizes for the cones are typically between four and seven inches (10.2 and 16.5 cm).

Flat-faced bits are used in heavy-duty drilling applications where the drilling is deep. As described, the face of the bit is flat as it drills.

The convex bit is used in applications where the rock is somewhat worn away and drills with two buttons as opposed to one.

The concave bit is one of the most common. It is used in medium to hard rock applications, and drills a straight hole.

The kavex is a combination of both the concave and the convex with a bit that works best on abrasive materials, drilling straight holes.

Bits have different types of faces, which are suitable for varying applications.

Close Up of a Polycrystalline Diamond Drill Bit
Dome bits have spherical faces and are mostly utilized for DTH drills. Well-suited for a variety of applications from medium to hard rock as well as broken formations, the dome shaped face is less likely to break than the other types.

The double-domed face is similar to the dome shape, but with an additional dome positioned on top of the other. The additional bit adds life to the bit while providing a sharper penetration.

Ballistic bits are capable of drilling in more rapid motions, but are used less because they tend to break when used in certain formations they were not designed for.[3]

[edit] References

  1. drillbits. Diy Data. 2008-09-28.
  2. Drill Bit Materials
  3. DTH Bits PDF. Rockhog. 2008-09-28.