The twist drill bit is a versatile and commonly used type of cutting tool that serves as the go-to choice for a wide range of drilling applications, including wood, plastic, and even metal materials. As a standard and widely available drill bit option, the twist drill bit is the preferred tool for general-purpose drilling tasks across various industries and DIY applications, such as home repairs, maintenance, and building projects with metal, wood, or ceramics.
Its helical (twisted) flute design facilitates the removal of debris from the hole being drilled and reduces friction, making it suitable for a wide range of materials and applications. Its ability to effectively and efficiently create holes in a diverse range of materials makes the twist drill bit an essential component in the toolbox of both professionals and hobbyists alike. But what exactly is a twist drill bit? Let’s take a look at the ins and outs of twist drill bits and we’ll explain to you the materials they are made of, flute designs, point angles, coatings, and their applications.
What is a Twist Drill Bit?
A twist drill bit, also referred to as a fluted bit, is suitable for general-purpose drilling in materials such as wood, plastic, metal, ceramic, and masonry. It’s the most common type of drill bit and has a helical (twisted) flute design that helps to remove debris from the hole being drilled. The term “twist” refers to the helical or spiral shape of the flutes or grooves that run along the length of the drill bit.
The modern twist drill bits were invented by Sir Joseph Whitworth in 1860, and later subsequent enhancements were made by Steven A. Morse of East Bridgewater, Massachusetts, who experimented with the pitch of the twist to improve performance. Initially, manufacturing involved cutting two grooves on opposite sides of a round bar and then twisting the bar to create the helical flutes. Contemporary manufacturing, however, typically involves rotating the bar while passing it by a grinding wheel, cutting the flutes in a similar manner to cutting helical gears.
Components of a Twist Drill Bit
Point (tip): The leading end of the drill bit that contacts the material to be drilled. At the top, the angle is measured between the two major cutting edges. Centering the twist drill in the material requires a point angle. The point is typically ground to a specific angle tailored to the material, with common angles being 118 degrees and 135 degrees for general-purpose use. For very soft materials, a point angle of 118 degrees is the best choice, while 135 degrees is more appropriate for drilling tougher materials. These bits may require a starter hole but resist binding and premature wear if used with the correct feed rate.
Flutes: The flutes are the spiral-shaped grooves that run along the drill bit’s length. Flutes have multiple functions, such as facilitating chip removal, providing a path for cooling the bit during operation, and guiding the cutting edges.
Cutting edges: The sharp edges along the point's sides where the actual drilling action occurs. Each cutting edge is responsible for cutting into the material as the bit rotates.
Shank: The end of the drill bit opposite the point. It is the part inserted into the chuck of a drill or drilling device. Shanks can be straight which fits standard drill chucks or tapered which are used for heavy-duty drilling applications, depending on the drill bit's size and application.
Helix angle (spiral angle): The angle formed by the helical shape of the flutes. The helix angle affects chip removal and is a critical factor in the drill bit's design. Common helix angles range from 12 to 45 degrees, with higher angles used for softer materials and higher helix angles suited for softer materials.
Web: The central portion that connects the two flutes is called the web. The web's thickness influences the drill bit's rigidity and strength. A thicker web provides more strength but can make the bit harder to sharpen.
Chisel edge: The edge formed by the intersection of the point and the flute and has no cutting effect. Nonetheless, because it joins the two primary cutting edges, it’s necessary for its construction. It helps guide the drill bit into the material and contributes to the cutting action.
Types of Twist Drill Bits
Twist drill bits come in a variety of material compositions and coatings, including high-speed steel (HSS), cobalt steel, and carbide, each designed to optimize performance for specific applications.
Material composition
High-Speed Steel (HSS)
HSS is the most commonly used material for twist drill bits due to its affordability and versatility. HSS bits are known for their durability, improved wear resistance, and ability to maintain hardness at high temperatures, making them suitable for a wide range of general-purpose drilling applications, including wood, plastic, and soft metals like aluminum and brass.
Cobalt Steel
Cobalt drill bits are made from an alloy that typically includes around 5-8% cobalt, enhancing the bit's performance. The addition of cobalt increases the bit's heat resistance and hardness to the steel, allowing it to withstand very high drilling temperatures and resist wear. They are ideal for drilling through very hard, abrasive materials such as treated stainless steel, titanium, and cast iron.
Carbon
Carbon drill bits are composed of tungsten carbide, a material known for its extreme hardness and heat resistance. These bits maintain their sharpness and structural integrity under intense heat and wear conditions, although they can be brittle and prone to chipping if misused. They are suitable for industrial applications involving hard and abrasive materials like ceramics, hardened steel, and composites. They are also commonly used in CNC machining and other precision environments. Although Carbon drill bits are the most expensive option, they provide the highest performance and lifespan, making them the preferred choice for industrial and heavy-duty applications.
Coatings
In addition to the material composition, twist drill bits can also be coated with various materials to enhance their durability and performance.
Titanium Nitride (TiN)
TiN is a more expensive coating applied to HSS bits, giving them a distinctive gold color. This coating significantly increases surface hardness, enhances corrosion resistance, and reduces friction between the bit and the workpiece. TiN-coated bits can last up to six times longer than standard HSS bits, commonly used for drilling metals, including stainless steel, cast iron, aluminum, magnesium, etc.
Titanium Aluminum Nitride (TiAlN)
TiAlN is a more advanced coating that offers better wear resistance and heat resistance compared to TiN. It provides superior heat resistance and hardness, allowing the bit to withstand higher cutting speeds and temperatures without losing its sharpness. TiAlN-coated drill bits are suitable for high-speed drilling in harder and abrasive materials such as hardened steels and ceramics and production environments where long tool life and high efficiency are critical.
Black Oxide
Black oxide is a heat treatment applied to HSS bits, resulting in a black finish. This treatment reduces friction between the bit and the workpiece, resulting in a 50% longer service life compared to standard HSS bits. This coating also provides mild corrosion resistance and is an affordable option with increased lifespan and reduced friction, suitable for a wide range of general-purpose drilling applications.
How to Select the Right Twist Drill Bit for Your Need?
Choosing the right twist drill bit involves considering the desired hole size, the material to be drilled, the specific requirements of the task, and the type of drilling equipment available. For general household and light industrial applications, HSS bits provide a cost-effective and versatile option. When drilling through harder materials, cobalt bits offer enhanced performance due to their superior heat resistance and hardness. For the most demanding applications, such as drilling through extremely hard or abrasive materials, carbide bits are the preferred choice due to their exceptional durability and reduced downtime.
Coatings like TiN, TiAlN, and black oxide further enhance the performance and lifespan of drill bits. TiN-coated bits and TiAlN-coated bits, with their high surface hardness and reduced friction, are ideal for high-speed drilling and demanding tasks. Black oxide-coated bits provide an affordable option with increased lifespan and reduced friction, suitable for a wide range of general-purpose drilling applications.
Findbuytool offers industrial-grade twist drill bits ideal for drilling wood, metal, plastics, and aluminum. We offer two types of affordable twist drill bits: HSS twist drill bits and Cobalt twist drill bits. Our HSS twist drill bits are made from high-quality high-speed steel, with a point angle of 118 degrees. Our cobalt twist drill bits are made of HSS-CO 5% (M35) for superior durability and long-lasting high performance. Designed for heavy-duty work, each drill bit meets exacting tolerances and can perfectly drill 1-13 mm-sized holes in all materials, including but not limited to wood, stainless steel, and masonry.
