Types of Drill Bits, Starting With the Twist

Most likely the first drill bit you’ll encounter in your carrier is a twist bit. These are the bits that saturate hardware stores and garage shelves of the Do-It-Yourselfers. They are a good introductory bit to analyze. So let’s dive in…

Here is an example of a typical twist drill bit:

The part that goes into the clamps of the drill is called a shank. There are different shank types as well, but we’ll talk about those later (but as a matter of curiosity satisfaction, the shank on this picture is labeled very creatively -- “straight”).

The rest of it is the body of the drill bit.

The spiral in-cuts are called flutes.

The end tip is called a point.

That was easy.

Now, twist drills generally come as single-flute drill bits or two-fluted drill bits. Both types are used for originating holes. The two-flute type is the most commonly available.

There are also three-fluted (core) and four-fluted (core) drill bits. Those are used interchangeably to enlarge existing holes.

There are also different length ranges. Below is a representative picture of some common lengths.

(click on the picture to enlarge)

Screw Machine Length Drill Bits
These have short flutes and short overall length. They are commonly used on sheet metal. Screw Machine bits are also called “stub length drills” or “stubbies”.

Jobbers Length Drill Bits
This is the standard length used for general purpose drilling. For this bits, the length of the flutes is ten times the diameter of the drill.

Taper Length Drill Bits
These are a little longer than jobbers length bits.

Extra Length Drill Bits
These come in various sizes, and are frequently used in automotive/aerospace industries, and in conditions where the target is hard to reach.

Longboy Drill Bits
These have longer flutes than extension bits and are available in larger diameters.

There are many different variations by different manufacturers, targeted towards unique projects. So always inspect catalogues for options, when settling on size.

One last aspect of twist drills I’d like to cover in this post is right hand drill bits versus left hand drill bits. Left hand bits cut in the opposite direction, and primarily used in large scale manufacturing for efficiency purposes. They are also sometimes used for removing screws. But those would be special screw removal bits…

Tungsten Carbide Drill Bits -- As Good As Diamond Drill Bits for the Do-it-Yourselfer?

Bosch has recently released a new product: tungsten carbide drill bits suitable for cutting glass and tiles. “These tungsten carbide bits are diamond ground to a precision point that eliminates walking and its reinforced head prevents the carbide from cracking.” Quoted from the original press release, February 13, 2008.

According to the company these bits are perfectly suited for working with ceramic, making them “the best solution for cutting glass, bathroom installations, drilling and fastening mirrors or even setting screws in glass furniture.”

As tungsten carbide drill bits are cheaper than diamond drill bits , Bosch is obviously trying to provide the Do-it-yourselfers (and professionals) with a cheaper solution than diamond, while minimizing the chipping issues associated with carbide.

These new bits start at 1/8” and going all the way up to 1” in diameter, the industry’s largest bit size, they are equipped with a 3-flat shank to reduce slippage that leads to more accurate cutting.

For more information, you call toll free 877-BOSCH-99 (877-267-2499).

Diamond Drill Bits

Diamond drill bits are a type of diamond tool, and therefore contain diamond segments bonded to a base material. It is the hardest type of tool and is especially frequently used on highly abrasive materials.

Until recently scientists thought that diamond was first used some time 500 BC in India. However recent new evidence suggests that craftsmen in China used diamond for polishing as far back as 4500 years ago.

The industrial market for this mineral focuses primarily on the hardness and heat conductivity, while clarity and color are considered irrelevant. Thus 80% percent of what the miners find end up in tools (such as diamond drill bits, diamond core drill bits, blades, polishing cups, abrasivesetc…) and not on the necks of Titanic bound debutants.

Due to the fact that it’s the hardest material we use, it is excellent for working on stone, ceramics, marble, glass, fiberglass, porcelain, etc. However, diamond drill bits grind, as opposed to cutting the surface. Nevertheless, they are less noisy and less brittle then other alternatives.

Diamond core drill bits (also known as diamond hole saws) have a hollow center and cut a circle in the material to create or enlarge an existing hole.

It is generally recommended to lubricate these bits with water.

And of course, whatever you do, always pay attention to the manufacturers instructions. Different makers use different material composition, and thus may require different mode of care and application.

Drill Bits Material: From Carbon Steel to Diamond

It is important to choose a drill bit made with the right material for your purpose. Getting a softer drill bit than needed will lead to early dullness and uselessness of the tool, leading to endless replacing at best, and a ruined project as one of the sadder scenarios. When picking the material, consider the surface to be drilled into (Soft wood? Hardwood? Metal? Stone?), and the steadiness of the drill itself – a very brittle bit on a cordless drill in the hands of not a very experienced driller is probably not the best idea.

That said, lets consider the standard options:

Low Carbon Steel Drill Bits

This is the cheapest option. Best used only on softwood. Low Carbon Steel bits require frequent sharpening, have a relatively short useful lifespan, and do not hold the edge too well. Buyer beware.

High Carbon Steel Drill Bits

These are an improvement over the above, and can be used on hardwood and even some metals. However their low resistance to heat causes them to loose their sharpness relatively quickly.

High Speed Steel Drill Bits (HSS Drill Bits)

These have essentially replaced the older Carbon steel bits on the market. HSS is significantly more resistant to heat, and as such these bits are well suited to most wood and metal jobs.

Titanium Coated Drill Bits

Titanium coating makes these bits harder and last longer than the common HSS bits. That is because the coating is a hard ceramic material.

There are a number of different Titanium coatings, most common are Titanium Nitride (TiN), Titanium Aluminum Nitride (TiAN) and Titanium Carbon Nitride (TiCN). TiN can increases the life of a drill bit by three or more times. TiAN is considered even better, and can increase the lifespan five times or more. TiCN is also considered superior to TiN.

The problem with coated bits, however, is that once dulled, they can’t be properly sharpened – the coating will be gone, and so will all the benefits of it.

Carbide Tipped Drill Bits

These are very hard, dissipate heat quickly and hold an edge longer than other types. However, Carbide tipped bits are also brittle and are likely to chip if not used carefully.

Cobalt Drill Bits

Cobalt bits retain hardness at much higher temperatures than the HSS ones. However, they are also more brittle than HSS. Cobalt drill bits are most commonly used for drilling stainless steel and other metals.

Diamond Drill Bits

Polycrystalline diamond (PCD) is one of the hardest tool materials. It actually consists of a layer of diamond particles bonded to a carbide support. And since diamond is the hardest thing found in our environment (or at least it is the hardest we know of), the diamond bits can be used on the toughest materials.

Unlike carbide and other types of drill bits, which use sharp edges to cut through material, diamond drills tend to work by grinding away their nemesis on a micro level.

Diamond drill bits can be used on glass, porcelain, ceramic tiles, granite, marble, stone, fiberglass, etc. They are commonly used in the automotive and aerospace industries, and in other environments where abrasive materials need to be drilled.

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