Twist Drill: Definition, Nomenclature, Type, Advantages, Application [Notes & PDF]

What is a Twist Drill Bit?

A Twist drill bit is a cutting tool used with a drill machine to create cylindrical holes in various materials, such as wood, metal, or plastic. It is typically a cylindrical or conical-shaped metal piece with spiral grooves called flutes along its length. The flutes help to remove debris and chips from the hole as the drill bit rotates.

Must Read: Types of Drill Bits

twist drill nomenclature

Here is an expanded description of each part of a twist drill bit, doubling the number of words:

Twist drill nomenclature

1. Body: The primary and central cylindrical portion of the drill bit that extends from the shank to the drilling end. It provides structural integrity and stability to the overall design of the drill bit, ensuring precise and controlled drilling.

2. Shank: The non-cutting end of the drill bit, usually a cylindrical section with a specific diameter, that is inserted into the drill chuck. It acts as a secure connection point between the drill bit and the drilling machine, allowing for efficient power transmission during drilling operations.

3. Dead Center: The meticulously positioned central point located at the drilling end of the twist drill bit, serving as the axis or center of rotation for the drill bit. It ensures proper alignment and minimizes wobbling during drilling, resulting in accurate hole creation.

4. Point: The sharpened and tapering tip of the drill bit that initiates the drilling action by piercing the material being drilled. It features a carefully crafted geometry to facilitate easy penetration and reduce the amount of force required for drilling.

5. Lips: The precise and keen cutting edges formed by the intersection of the two flutes at the drilling end of the drill bit. These edges exhibit exceptional sharpness and hardness to effectively shear and remove material during the drilling process.

6. Body Clearance: The strategically relieved area situated behind the cutting edges or lips. It offers ample space for efficient chip removal, preventing chip congestion and ensuring the drill bit operates smoothly, reducing heat buildup and prolonging the bit’s lifespan.

7. Chisel Edge: The straight and refined edge formed at the center of the drill bit where the two lips meet. It aids in the initial guidance and stability of the drill bit during the early stages of drilling, facilitating precise hole placement.

8. Chisel Edge Corner: The sharply defined corner formed at the intersection of the chisel edges at the center of the drill bit. It assists in accurate positioning and centering of the drill bit, enhancing drilling precision and minimising the risk of wandering.

9. Face: The flat and meticulously machined surface located behind the lips, extending from the dead center to the chisel edge. It provides consistent support to the lips and plays a crucial role in facilitating efficient chip evacuation and maintaining cutting performance.

10. Flank: The smoothly contoured and structurally integral surface of the drill bit that connects the face to the body. It ensures stability and strength during drilling operations, minimizing vibration and deflection for enhanced drilling accuracy.

11. Flutes: The precisely formed and carefully spaced spiral or helical grooves that extend along the length of the drill bit. These flutes act as pathways for the swift and effective removal of chips and debris, preventing clogging and promoting efficient chip evacuation.

12. Heel: The terminating end of the drill bit situated behind the cutting edges and flutes. It contributes to the overall robustness and stability of the drill bit, maintaining alignment and preventing unnecessary deflection during drilling.

13. Neck: The skill-fully tapered or reduced diameter section connecting the body to the shank. It serves as a transition zone, smoothly blending the larger body to the narrower shank, optimizing strength and reducing the risk of breakage during demanding drilling tasks.

14. Tang: A specifically designed flat or tapered section located on the shank of certain drill bits. The tang provides a reliable means of securely gripping the drill bit in compatible drill chucks, ensuring firm attachment and minimizsng any potential slippage during drilling operations.

Understanding the intricate details and functions of each part of a twist drill bit is crucial for utilizing it effectively in various drilling applications.

Type of Twist Drill

The various types of Twist Drill are follows:

  1. Taper-shank Drills
  2. Cobalt Highspeed Steel
  3. Straight shank drills, taper length
  4. Straight shank drills, jobber’s length
  5. Heavy-duty drills
  6. Cotter pin drills
  7. Straight fluted drill
  8. Half-round drills
  9. Multi-cut drill
  10. Deep Hole Drill
  11. Shell-type core drill and
  12. Carbide Drills

Here are the various types of twist drill bits:

1. Taper-shank Drills: These drill bits have a tapering shank that is designed to fit into a tapered drill chuck. They are commonly used in larger drilling machines for heavy-duty applications.

2. Cobalt High-Speed Steel: These drill bits are made of high-speed steel alloyed with cobalt, which enhances their heat resistance and durability. They are suitable for drilling hard materials such as stainless steel and cast iron.

3. Straight Shank Drills, Taper Length: These drill bits have a straight shank with a longer length compared to standard jobber’s length drills. They are often used in machining operations that require deeper holes.

4. Half-Round Drills: Half-round drills have a semi-circular cross-section, with one flat side and one rounded side. They are used for drilling holes with a flat-bottomed recess, such as for installing dowels.

5. Carbide Drills: Carbide drills are made of carbide material, known for its hardness and heat resistance. These drills are suitable for drilling in tough materials such as hardened steel and abrasive composites.

These various types of twist drill bits offer specialised features and characteristics to cater to specific drilling requirements in different industries and applications.


Drill bits are made from a variety of materials, each chosen for its specific properties and suitability for different drilling applications. Here are some common materials used for drill bits:

  1. High-Speed Steel (HSS): High-speed steel is a popular choice for drill bits due to its excellent balance of hardness, toughness, and heat resistance. It is an alloy of steel with elements like tungsten, molybdenum, chromium, and vanadium. HSS drill bits are versatile and can effectively drill in materials such as wood, metal, plastic, and composites.
  2. Cobalt Steel: Cobalt steel drill bits are made by alloying high-speed steel with cobalt. The addition of cobalt enhances the hardness, heat resistance, and durability of the drill bit. Cobalt drill bits are particularly well-suited for drilling in hard materials like stainless steel, cast iron, and high-temperature alloys.
  3. Carbide-Tipped: Carbide-tipped drill bits feature a cutting edge made of carbide, which is a very hard and wear-resistant material. The carbide tip is brazed or welded onto a steel body. Carbide-tipped bits are known for their ability to drill in tough materials, including concrete, masonry, and ceramics.
  4. Solid Carbide: Solid carbide drill bits are made entirely of carbide material. Carbide is extremely hard and can withstand high temperatures, making these bits highly suitable for drilling in hard and abrasive materials like hardened steel, cast iron, and composites. Solid carbide bits are commonly used in machining and high-precision drilling applications.
  5. Diamond-Coated: Diamond-coated drill bits have a thin layer of diamond particles deposited onto the cutting edge. Diamond is the hardest known material, making these bits exceptionally effective for drilling in very hard materials like glass, ceramics, and stone.
  6. Titanium Nitride (TiN) Coated: TiN-coated drill bits have a thin layer of titanium nitride applied to the surface. The coating enhances the hardness, lubricity, and wear resistance of the drill bit. TiN-coated bits are commonly used in metalworking applications, providing extended tool life and reduced friction during drilling.
  7. Black Oxide Coated: Black oxide-coated drill bits undergo a surface treatment that provides corrosion resistance and improved lubricity. The black oxide coating helps reduce friction and heat during drilling. These bits are commonly used for general-purpose drilling in materials like wood, metal, and plastic.

The choice of drill bit material depends on factors such as the type of material being drilled, the desired hole size and quality, and the specific requirements of the drilling application. Selecting the appropriate drill bit material ensures optimal performance and longevity of the tool.

twist drill angle

The twist drill angle refers to the angle formed by the cutting lips of a twist drill bit. The two primary angles associated with a twist drill are the point angle and the helix angle:

  1. Point Angle: The point angle is the angle formed between the cutting edges at the tip of the drill bit. It determines the aggressiveness and efficiency of the cutting action. The most common point angle for twist drills is 118 degrees or 135 degrees. The 118-degree angle is commonly used for general-purpose drilling in materials like wood, metal, and plastic. The 135-degree angle is often preferred for drilling in harder materials such as stainless steel and cast iron.
  2. Helix Angle: The helix angle refers to the angle formed between the leading edge of the flute and a plane perpendicular to the drill axis. It determines the rate at which the drill bit advances into the material and affects chip evacuation. The helix angle can vary depending on the application and material being drilled. Typically, twist drills have helix angles ranging from 20 degrees to 40 degrees. Steeper helix angles are used for softer materials, while shallower angles are used for harder materials.

The twist drill angle plays a significant role in the cutting performance, chip evacuation, and overall efficiency of the drill bit. It is essential to select the appropriate drill bit with the correct twist drill angle for the specific drilling application and material to achieve optimal results.

twist drill geometry

The geometry of a twist drill refers to the various parameters and characteristics that define its shape, structure, and cutting properties. Some important aspects of twist drill geometry include:

  1. Point Angle: The point angle is the angle formed between the cutting edges at the tip of the drill bit. It determines the aggressiveness and efficiency of the cutting action. Common point angles for twist drills are 118 degrees or 135 degrees, although other angles may be used for specific applications.
  2. Lip Relief Angle: The lip relief angle is the angle between the cutting edge and a line perpendicular to the drill axis. It helps in reducing friction and heat buildup during drilling by providing clearance for the cutting edges.
  3. Helix Angle: The helix angle is the angle formed by the spiral or helical flutes of the drill bit. It determines the rate at which the drill bit advances into the material and affects chip evacuation. The helix angle can vary depending on the application and material being drilled.
  4. Flute Shape and Width: The flute shape and width influence chip evacuation and material removal during drilling. Flutes may have various shapes, such as parabolic, straight, or twisted, and their width can vary to optimize chip flow and prevent clogging.
  5. Web Thickness: The web thickness is the central portion of the drill bit between the flutes. It provides structural support to the cutting edges and prevents excessive deflection during drilling.
  6. Margin: The margin is the land area between the cutting edges and the outer diameter of the drill bit. It helps center the drill bit during drilling and provides stability.
  7. Overall Length and Diameter: The overall length and diameter of the drill bit determine the drilling depth and the size of the hole being drilled. Twist drills come in various lengths and diameters to accommodate different drilling requirements.
  8. Coatings: Many twist drills feature coatings such as titanium nitride (TiN), black oxide, or diamond coatings. These coatings enhance wear resistance, reduce friction, and improve the overall performance and lifespan of the drill bit.

By carefully considering and optimising the various aspects of twist drill geometry, manufacturers can create drill bits that are efficient, durable, and suited for specific drilling applications and materials.

Applications of twist Drill

Twist drill bits have a wide range of applications across various industries and for different materials. Some of the common applications of twist drill bits include:

  1. Metalworking: Twist drill bits are extensively used in metalworking applications. They can drill holes in materials like steel, aluminum, brass, and other metals. Whether it’s for general fabrication, construction, automotive, or aerospace industries, twist drill bits are essential tools for creating holes in metal components.
  2. Woodworking: Twist drill bits are also commonly used in woodworking applications. They can drill holes in wooden materials, including solid wood, plywood, and MDF (Medium-Density Fiberboard). Woodworkers use twist drill bits for tasks such as creating dowel holes, pilot holes for screws, and general hole drilling in woodworking projects.
  3. Plastic and Composite Materials: Twist drill bits are suitable for drilling holes in various plastic materials, such as acrylic, PVC, and ABS. They are also used for drilling holes in composite materials like fiberglass, carbon fiber, and laminates.
  4. DIY and Home Improvement: Twist drill bits are widely used in DIY projects and home improvement tasks. Whether it’s drilling holes to install shelves, hooks, or assembling furniture, twist drill bits are essential tools for many household applications.
  5. Electrical and Plumbing: Electricians and plumbers often use twist drill bits to create holes for running wires, cables, and pipes through walls, floors, or ceilings. Twist drill bits allow them to efficiently and accurately drill holes in different materials encountered in electrical and plumbing installations.
  6. Metal Fabrication: In metal fabrication processes such as machining, drilling precise holes is a common requirement. Twist drill bits are used in milling machines, lathes, and other machining equipment to create holes for bolts, dowels, and other fasteners.

It’s worth noting that the specific drill bit size, type, and coating may vary depending on the application and material being drilled. Using the right twist drill bit and employing proper drilling techniques can ensure accurate and efficient hole creation in various applications.

Advantages of twist drill

Twist drill bits offer several advantages that make them widely used and versatile tools for drilling. Here are some of the key advantages of twist drill bits:

  1. Versatility: Twist drill bits are highly versatile and can be used for drilling holes in a wide range of materials, including metal, wood, plastic, and composites. This versatility makes them suitable for various industries and applications.
  2. Wide Range of Sizes: Twist drill bits are available in a wide range of sizes, from small diameters for precise holes to larger diameters for more significant drilling tasks. This variety allows for flexibility in choosing the appropriate size for specific applications and hole requirements.
  3. Efficient Chip Removal: The spiral or helical flutes on twist drill bits serve an essential function of efficient chip removal. As the drill bit rotates, the flutes help to lift and remove the chips and debris from the hole, preventing clogging and ensuring smooth drilling progress.
  4. High Drilling Speed: Twist drill bits, when used correctly, can achieve high drilling speeds, allowing for efficient and time-saving operations. The design of the twist drill bit with its cutting edges and flutes facilitates smooth and swift material removal during drilling.
  5. Precise Hole Placement: Twist drill bits are designed to create accurate and precise holes. With their sharp cutting edges and point, they allow for precise hole placement, enabling accurate alignment and assembly of components.
  6. Ease of Use: Twist drill bits are user-friendly and easy to use. They can be inserted into a drill chuck quickly, and drilling can be initiated with minimal effort. Their widespread availability and compatibility with various drilling machines make them convenient tools for both professionals and DIY enthusiasts.
  7. Cost-Effective: Twist drill bits are generally cost-effective compared to other specialized drill bits. They are readily available and come in a range of affordable options, making them a practical choice for many drilling applications.

Overall, the advantages of twist drill bits, such as versatility, efficient chip removal, high drilling speed, precise hole placement, ease of use, and cost-effectiveness, contribute to their popularity and widespread use in various industries and applications.

disadvantages of twist drill

While twist drill bits offer many advantages, there are a few potential disadvantages to be aware of:

  1. Limited Hole Shape: Twist drill bits are primarily designed for drilling round cylindrical holes. If you require non-cylindrical or specialized hole shapes, such as square, rectangular, or slotted holes, twist drill bits may not be suitable. Specialized drill bits or other tools may be needed for such applications.
  2. Limited Material Compatibility: Although twist drill bits are versatile, they may not be ideal for certain materials. For example, when drilling hard materials like hardened steel or ceramics, twist drill bits may struggle to maintain their cutting efficiency and durability. In such cases, specialized drill bits designed for those materials may be more appropriate.
  3. Risk of Wandering: Twist drill bits have a pointed tip, which can sometimes cause the bit to wander or deviate from the desired drilling path, especially when starting a hole. This can result in inaccurately positioned or angled holes. Proper center punching or using pilot holes can help minimize this issue.
  4. Heat Generation: During prolonged drilling or when drilling hard materials, twist drill bits can generate heat due to friction. Excessive heat can affect the cutting efficiency and lifespan of the drill bit, as well as potentially damage the material being drilled. Proper cooling or lubrication techniques, such as using cutting fluid or coolant, can help mitigate this issue.
  5. Wear and Dullness: Over time and with extensive use, twist drill bits can become dull or worn out. Dull drill bits can lead to decreased cutting efficiency, increased drilling time, and a higher risk of overheating. Regular maintenance, such as sharpening or replacing worn-out drill bits, is necessary to maintain optimal performance.
  6. Limited Depth Control: Twist drill bits may have limitations when it comes to precise depth control. While drill bits with depth stop collars can help achieve consistent hole depths, they may not provide the same level of accuracy as specialized drilling tools designed for precise depth control.

It’s important to note that many of these potential disadvantages can be overcome or mitigated by using appropriate drilling techniques, selecting the right drill bit for the material and application, and employing proper maintenance and care for the drill bits.

Reference : Merriam-Webster

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