Different types of drill bits are used in part manufacturing and are classified into two main categories: coating and workpiece materials. Below is an introduction to the different drill bits that make up each category.
Category #1: Types of Coating Drill Bits
Coatings are materials applied on a part to give it better functional or aesthetic value and are one of the main categories of drilling bits. Below are the types of drill bits that fall under this category.
1.1 Titanium Nitride Drill Bits
Drill bits coated with titanium nitride are hard, fast, have a longer lifespan, and are suitable for drilling hard and soft metal. Due to their properties, they have wide industrial applications. However, the only disadvantage is that it is not restorable when they lose its cutting edge unless the coating is reapplied.
1.2 Titanium Carbonitride Drill Bits
These drill bits are similar to the titanium nitride drill bits. Consequently, they are slippery with a characteristic blue or purple color. However, they have enhanced hardness. As a result, they are majorly applicable in drilling through hard materials.
1.3 Titanium Aluminum Nitride Drill Bits
Drill bits coated with titanium aluminum have high stability and suitability for drilling stainless steel, steel, and other materials at high temperatures. However, they are not suitable for drilling aluminum.
1.4 Black Oxide Drill Bits
Black oxide is an inexpensive coating applied on high-speed steel. They make the drill bits heat-resistant, rust and corrosion-resistant, and frictionless. Due to the lowered friction, drilling becomes easier.
Black oxide drill bits are suitable for drilling steel, PVC, acrylic, maple, nylon, etc., and are considered the best general-purpose drill bits.
1.5 Diamond Drill Bits
Drill bits coated in diamonds have the highest hardiness in this category. Consequently, they are suitable for drilling into hard materials such as metals. Also, they are highly accurate and suitable for materials such as glass, sea glass, etc.
Category#2: Types of Drill Bits for Different Workpiece
Many types of drill bits are categorized based on the materials they can make holes. Under this category, we have four common subcategories: universal, metal, wood, and others. Below are the different drill bit types under each subcategory and their applications.
2.1 Drill bits for Universal Workpieces
Drill bits that fall under this subcategory are suitable for all materials. There are four common universal drill bits used in part manufacturing.
-Twist Drill Bit
These drill bits feature a cylindrical shaft and helical flute. As a result, they are similar to corkscrews and can drill quickly and accurately. The helical flute is a feature that allows them to control dust from the hole as they work.
Twist drill bits are the most common drill bits with a wide industrial application applicable in drilling holes into wood and walls.
-Step Drill Bit
A step drill bit is custom-made and has a conical shape and a running flute that can be straight or angled. The flute ensures that the chips are ejected during drilling.
Step drill bits are suitable for drilling soft materials such as aluminum. Furthermore, due to them being custom-made, they are expensive.
-Unibits
They are similar to step drill bits but with a straight running flute. Their design makes them applicable in hole enlarging and, like the step drill bits, ensures efficient ejection of chips during drilling.
Unibits are widely applicable in sheet metal fabrication and drilling through soft materials such as plywood.
-Hole Saw Drill Bit
Hole saws are drill bits with short open cylinders with saw teeth on the edge. They are applicable in drilling through thin materials such as wood and sheet metal.
2.2 Drill Bits for Metal Workpieces
Drill bits under this subcategory are suitable for working on metallic materials. The common ones used in part manufacturing include:
-Center and Spotting Drill Bit
Also known as Slocombe drill bits, these tools are suitable for making starting hole or a conical indentation on the workpiece.
-Core Drill Bit
Core drill bits do not have a cutting point and 3 to 4 flutes. Therefore, they are suitable for drilling into already made holes.
-Ejector Drill Bit
The ejector drill bit has a unique design. It is similar to a tube in a tube and has a carbide drill bit tip. They are suitable for making deep holes 19-102 mm in diameter.
-Indexable Drill Bit
These are expensive drill bits made from carbide or ceramic and are more prominent in CNC drilling. They are wear-resistant and has multiple coolant channel for a prolonged lifespan. They are suitable for cutting holes about five times their diameter and are preferred due to their speeding drilling process.
-Straight Fluted Drill Bit
This is similar to the twist drill bit. However, they have a parallel running flute. Due to the parallel flute, chips don’t pop out during drilling. Consequently, there is a limitation on the industrial application. Nevertheless, they are suitable for drilling soft materials such as brass, copper, etc., and are easy to use.
Other drill bits under this subcategory include the countersink, ejector, left-hand, and metal spade.
2.3 Drill Bits for Wood Workpieces
Drill bits under this subcategory are suitable for working on wood. The common ones used in part manufacturing include:
-Brad Point Drill Bit
Brad-point drilling bits have rubber cork which aids their accuracy to a certain depth. As a result, they are suitable for drilling materials that need a highly accurate hole and are available in 3-16mm diameters. They are suitable for wood and soft plastics.
-Center Drill Bit
The center drilling bit has a tapered and threaded bit tip. It is an important drilling bit for working with wood and involves turning it to bore a hole in the wood. They are made mainly using soft steel and are ideal as a hand tool.
-Wood Spade Drill Bit
The drill bit has a long shaft but a head shaped like a spade with a needled bit tip. They come in diameter from 6-36 and are suitable for rough boring wood.
-Auger Drill Bit
These drill bits make holes in strong and dry wood. With their special design, you don’t need to apply too much pressure when drilling through the thick wood.
Other drill bit types under this category include the gimlet, spoon, and hinge sinker.
2.4 Drill Bits for Other Materials
Drill bits under this subcategory are suitable for working on other materials such as stones, concrete, and ceramic. The common ones used in part manufacturing include:
-Diamond Drill Bit
The drill bit has a design suitable to work only as a combination router and drill bit. It has a steel shell with a diamond embedded in a metal segment. They are suitable for cutting several materials but at relatively low speeds.
-Masonry Drill Bit
They are commonly used for making holes in concrete or stones. However, you must often substitute them due to the hard nature of the materials they drill through.
-Glass Drill Bit
Glass bits generate high temperatures. As a result, they have short longevity. However, they are applicable in cutting holes at low speed.
There are several materials used in making different drill bit types. Each drill bit has unique characteristics based on the inherent mechanical properties of the material. Consequently, they have unique applications. Below are the common types of drill bits based on the material used.
High-speed Steel
High-speed steel comprises tungsten, chromium, carbon, and vanadium. Consequently, these drill bits have higher hardness, strength, wear resistance, and heat resistance. They have the nick High-Speed Steel due to their ability to drill at high speed. They are suitable for drilling metal and hardwood.
Carbon Steel
A carbon steel drill bit can be low or high depending on the amount of carbon present.
Low-carbon steel drill bits are suitable for working with softwoods, plastic, and other soft materials because they cannot hold their edge well.
High carbon steel drill bits have higher durability due to the material’s heat treatment and hardening process. Unlike low-carbon steel, they are suitable for drilling through hardwood, metals, and plastic. However, they can lose their cutting edge when overheating.
Cobalt Steel Alloy
Cobalt steel alloy contains about a 5-8% cobalt blend making them hard, heat resistant, and brittle. As a result, they are suitable for drilling stainless steel and other hard materials.
Tungsten Carbide
These drill bits come from tungsten carbide, known for their extreme hardness. Consequently, they are expensive but compatible with virtually all materials. However, due to their high cost, they are mostly designed to be on the drill bit tips.
Polycrystalline Diamond
The drill bit material is made from diamond particles bonded to a sintered mass of tungsten carbide. Consequently, drill bits made from this material are the hardest. Nevertheless, they have wide applications and are suitable for all materials. Nevertheless, their high cost limits their use industrially.
Due to the myriad of drilling bits in the market, selecting the right one might be a challenge. However, you can use the hint below to select the drill bit amidst the market’s different types of drill bits.
Choose A Drill Bit Made From the Right Materials
The drill bit material is important in selecting the right drill bit type. This is because every material has a unique hardness and mechanical features. For example, high-speed steel can drill through fiberglass, PVC, aluminum, and wood, while cobalt drill bits are very hard and disperse heat faster.
Consider the Drill Bit Coatings
Coatings are important because they can improve the drill bits’ functional and aesthetic value. For example, when high-speed steel drill bits are coated with titanium nitride, they become very hard, increasing their suitability for drilling hard materials. Therefore, check through their properties if you are drilling a hard material and need a coated drill bit.
Workpiece Materials
Workpieces are made from metal, wood, stone, ceramic, or other materials. Each one has its properties necessitating you choose using the right drill bit. For example, you can use universal drill bits like the twist and step drill bits or the straight flute drill bit for workpieces made from metallic materials. Another example is using an auger and spade drilling bit for woods. Ensure you know the drilling bit’s intended use before choosing them.
Geometry/Specification of Drill Bits
You have to consider a few things about the geometry and dimension of the drill bits.
-Webbing
The right drilling bit should be thick enough to avoid snapping during the drilling process. Therefore, you should consider spending more money on heavy-duty geometry.
-Length
Short drill bits are more rigid, and they deliver higher precision. If you have no choice but to use a long drill bit, ensure that it has a short flute length, i.e., two times the drill diameter. Long drill bits with long flute lengths will have lower stability and the tendency to cut.
-Drill Point Angle
The two common drill point angles are 118°and 135°. On the one hand, drill bits with an 118° drill pint angle are suitable for soft materials like mild steel and aluminum. On the other hand, drill bits with a 135° drill pint angle are suitable for drilling hard materials.
-Helix Angle/ Spiral Angle
There are many helix angles used in drilling, with the common ones being 10-29, 19-49, and 27-45 degrees.
- Drills 19 to 49° helix angle is the general one suitable for a major application.
- Drills with 10 to 29° helix angles are suitable for hard materials made from aluminum and have better chip evacuation, fracture resistance, and edge strength.
- Drills with 27 to 45° helix angles are suitable for the hardest materials, such as stainless steel, which requires low torque and has cutting resistance.
Sizes of Drill Bits
There are different drill bit standard sizes, such as the Fractional Inch, Wire Gauge and Letter, and the metric drill bit size. Use a proper drill bit size chart to get the proper size and dimension of the drill bit.
What drill bit stays sharp the longest?
Titanium drill bits are sharp and stay sharp better than other drill bits. However, sharpening them requires re-coating, which is a huge disadvantage of the drill bits.
Which is better for hard material, cobalt or carbide?
Carbide drilling bits are the hardest and most brittle. Consequently, they are suitable for hard materials.
Which drill bit is best for metal?
Cobalt drill bits are the most suitable for metals such as stainless steel, aluminum, etc. However, consider other factors, such as size and length, when choosing.
What is the strongest drill bit?
Polycrystalline diamond (PCD) drill bits are the strongest. They are considered the hardest drill bits, making them suitable for the toughest materials, such as glass and ceramic.
