Drill bits are essential cutting tools used to drill
a satisfactory hole in any material or create cylindrical holes. Drill
bits are held in a drill, which rotates them and provides force to
create the hole. They have a variety of uses with braces and drills.
Each bit and drill is designed for a particular use and should be used
for its intended job. Bit diameters are usually marked by a single
number, which is the numerator of a fraction. There are specialized bits
for non-cylindrical-shaped holes. The drill bits must be used correctly
and be sharpened appropriately. Drill bits are very handy tools as there
are many tasks at home which require a hole of some kind to be drilled
be it in hanging a photoframe , light fitting or building a cabinet or
putting up a shelf. There are other heavy duty tasks where professionals
use various sized drill bits for various purposes.
Materials used in drill bit construction
There are different materials used in the making of drill bit,
depending on the materials. The most popular materials are as follows:
Types of drill bits
- Steels: There are different varieties of steels that are
used, such as follows:
Soft low carbon steel bits are used only in wood and require
frequent sharpening. High Carbon steel bits are made from high
carbon steel, and used on wood or metal and are better due to the
hardening and tempering capabilities of the material. They have a
low tolerance to excessive heat which results in a soft cutting
edge. In case of high speed steel bits, they are much more resistant
to the effect of heat. They can be used in metal, hardwood, and
other materials at greater cutting speeds compared to carbon steel
bits and commercially more applicable. Cobalt steel is high speed
steel with more cobalt in them. They can hold their hardness at much
higher temperatures. These bits can be used to drill stainless steel
and other hard materials.
- Carbon steel
- High speed steel
- Cobalt steel alloys
- Exotics: Another popular material for drill bits is
Tungsten carbide. It is extremely hard. The drill bit can be used to
drill almost all materials. But it is expensive and also brittle.
That is why it is more frequently used in smaller pieces screwed or
brazed onto the tip of the bit. It is nowadays seen in many tool and
job shops the use of solid carbide drills and PCB drills. There is
another tool material which is the hardest of all tool materials and
known as polycrystalline diamond (PCD). The material consists of a
layer of diamond particles, typically about 0.5 mm thick, and this
diamond layer is bonded as a sintered mass to a tungsten carbide
support. The PCD bits are typically used in heavy duty drilling in
the automotive, aerospace, and other industries. It is used in
drilling carbon fiber reinforced plastics, abrasive aluminum alloys,
and other abrasive materials.
- Coatings: Titanium nitride is used a s a coating material
in drill bits. It is a very hard ceramic material, and can extend
the cutting life by three or more times. Considered superior to TiN,
TiAlN is another coating frequently used. Diamond powder is also
used as a coating. It is used as an abrasive. Zirconium nitride has
also been used as a coating for drill bit for some Craftsman tools.
- Twist-drill bits: Twist-drill bits are used in both wood
and unhardened metals to make clearance holes for bolts, screws,
etc., and to make holes for tapping. Only bits marked HS or HSS are
suitable for drilling in metals. Common sizes run from 1/16" to
1/2" diameter by 64ths. Twist bits are usually marked in the
same manner by 64ths of an inch. Thus a No. 8 bit would stand for
8/64" or 1/8".
- Auger bits: Auger bits are most commonly used with a
brace for drilling holes in wood. Their length varies from 7"
to 10". Dowel bits are short auger bits from 5" long. Long
(ship) auger bits range from 12" to 30".
- Expansive bits: Expansive bits take the place of many
larger bits. They are adjusted by moving the cutting blade in or out
by a geared dial or by a lock screw, to vary the size of the hole.
These are mounted below the surface for a finished appearance.
- Forstner bit: Used to form holes with a flat bottom, and
used best in a power drill held in a drill stand.
- Hole saw: These drill bits are used for cutting large,
fixed, diameter holes in wood or plastic. They can cut up to a depth
of 18mm or more.
- Glass and Tile Bits: They are designed specially for
smooth, accurate drilling in marble tile, ceramic tile, mirrors and
- Step drill: These type of drill bits are used to enlarge
holes and also for drilling a variety of perfectly sized holes in
thin gauge metal, wood, plastic and PVC.
- Countersunk bits: Countersunk bits widen holes, so
flat-head screws may be flush-mounted below the surface, for a
- Masonry bit: Used in power tool, they are used to drill
brick, block, quarry tiles, stone or concrete.