What is the angle of a twist drill bit

A twist drill bit is one of the most widely used cutting tools in industrial machining, construction, woodworking, metal fabrication, and engineering applications. The geometry of a twist drill is not random; instead, it is a carefully engineered combination of angles, clearances, rake profiles, and helix designs that collectively determine the efficiency, stability, accuracy, and smoothness of the drilling process. Among all the design parameters, the drill point angle—commonly referred to as the drill bit angle—is one of the most crucial because it directly affects penetration rate, heat generation, chip removal efficiency, burr formation, hole roundness, and overall tool life. Understanding this angle is essential not only for machinists and engineers but also for industrial buyers who must select the appropriate drill bit for specific materials such as mild steel, stainless steel, hardened alloy steel, aluminum, copper, brass, plastics, composite sheets, ceramics, or wood. By mastering the concept of twist drill bit angles and studying the various brands and models available on the global market, users can dramatically improve drilling performance while reducing tool wear, energy consumption, and production waste.

In precision engineering, the angle of a twist drill bit primarily refers to the point angle, a geometric feature formed at the cutting end of the drill where the two main cutting edges meet. For general-purpose twist drills, the most common angles are 118 degrees and 135 degrees, but specialized bits may use angles ranging from 80 degrees to 150 degrees, depending on the target application. The correct drill angle ensures that cutting forces remain balanced, the bit does not wander, the chips are safely evacuated, and the cutting temperature stays within an optimal range. Therefore, the choice of drill angle should always be aligned with the hardness of the workpiece material, the drilling speed, the coolant system, and the desired surface finish. Below we will explore the significance, function, structure, measurement method, and practical selection guidelines for twist drill angles, along with detailed examples of global brands and models that incorporate specialized geometries.

Understanding the Point Angle of a Twist Drill Bit

The point angle of a twist drill bit is the angle formed at the tip between the two cutting lips. It determines how aggressively the drill engages with the material. A smaller angle results in a sharper cutting action but increased point fragility, while a larger angle provides strength and stability but requires more thrust force to penetrate the workpiece. The classic point angle of 118° is designed for general-purpose drilling in mild steel, soft metals, and wood. The sharper 118-degree angle reduces heat and provides a smooth entry, but it may dull more rapidly when used on harder metals such as stainless steel or titanium alloys. On the other hand, the 135° split-point angle is engineered for harder materials, providing superior centering ability and minimizing bit walking.

Drills for plastics may use point angles as low as 80° to 90°, producing extremely sharp cutting edges that prevent melting or micro-fracturing. Similarly, drills for soft aluminum and copper may use angles around 100° to 110°, while specialized drills for hardened tool steels can use angles of 135° to 140° for durability and reduced chipping. Industrial cobalt drills and carbide drills for aerospace engineering sometimes employ reinforced angles as high as 145–150°, enabling them to withstand drilling operations in superalloy materials such as Inconel, Hastelloy, Waspaloy, titanium Ti-6Al-4V, and aerospace-grade stainless steels.

Overview of Common Twist Drill Bit Angles

A wide spectrum of twist drill angles exists, each optimized for specific applications. Below are the most common ranges:

118-Degree Angle

This is the standard geometry for traditional HSS twist drills. The 118° point angle is ideal for softer materials and general-purpose drilling tasks. It provides balanced performance between penetration speed and edge durability. This angle works effectively in mild steel, cast iron, softwood, and numerous plastics. In woodworking, the 118° angle helps maintain cleaner hole edges by reducing tear-out.

135-Degree Angle

This is a common split-point angle used in high-performance drills, particularly cobalt and carbide varieties. The 135° angle reduces walking, which makes it perfect for drilling into metals that require precise hole placement without the need for a center punch. It also reduces axial thrust, making it suitable for hard steel, stainless steel, and hardened alloys.

90–100 Degree Angles

These sharper angles are seen in drilling applications for plastics and composite materials, where a gentle cutting action is necessary to prevent surface burning or cracking. Low-angle points are also used in PCB drill bits, micro drills, and specialized polymer drills.

140–150 Degree Angles

These are reinforced angles used in aerospace-grade carbide drills. They deliver high strength, reduced vibration, and superior heat resistance. Such angles are essential when drilling superalloys, carbon fiber reinforced polymers (CFRP), and titanium alloys.

Special Angles

Manufacturers may offer proprietary geometries, such as parabolic flute profiles, multi-facet points, four-facet points, and S-shaped points. These designs change the effective cutting angle and improve performance in high-precision CNC machining environments.

Why the Drill Angle Matters in Engineering and Industrial Machining

Although inexperienced users may overlook drill point angles, they are fundamental to drilling success in both manual and automated machining environments. An incorrect angle can result in excessive heat generation, premature tool failure, inaccurate hole diameters, poor chip evacuation, and even machine tool overload.

A correctly selected drill angle ensures:

• Reduced Heat Buildup

• Lower Cutting Forces

• Accurate Hole Positioning

• Smooth Chip Removal

• Less Work Hardening of Metal

• Longer Tool Lifespan

• Improved Drilling Speed

• Better Hole Surface Quality

For example, drilling stainless steel with a 118° drill would cause faster blunting because stainless steel work-hardens easily. A 135° cobalt drill is preferred in such scenarios. Meanwhile, drilling acrylic with a 135° carbide drill risks cracking; instead, an 85–90° acrylic bit is ideal.

Brands and Models of Twist Drill Bits with Specific Angles

Below is a detailed list of brands and models known for manufacturing high-precision twist drill bits with specific angles.

DeWalt (USA)

DeWalt is a global leader in power tools and industrial accessories, offering numerous twist drill models engineered with specific angles for various materials.

Notable Models:

• DeWalt DW1354 Titanium Drill Bit Set (135° Split Point)

• DeWalt DW1177 Black Oxide Twist Drill Set (118° Standard Point)

• DeWalt DWA1189 Titanium Pilot Point Drill Bits (118° / Pilot Point Geometry)

DeWalt’s 135° split-point design minimizes walking, making it easier to start clean holes in metal and reducing heat buildup. Their titanium-coated DW1354 model is particularly popular for drilling into hardwoods, sheet metal, and stainless steel.

Makita (Japan)

Makita is highly regarded for producing precision-machined industrial drill bits suitable for contractors and metal fabrication professionals.

Notable Models:

• Makita T-01725 Contractor-Grade Bit Set (118°)

• Makita B-65399 Black Oxide Drill Set (118° Standard Angle)

• Makita D-65484 High-Speed Steel Metal Drill (135° Split Point)

Makita’s 118° bits are ideal for general-purpose construction tasks, while their 135° split-point bits excel in high-torque drilling applications.

Bosch (Germany)

Bosch produces some of the most precise and durable twist drill bits in the world, especially engineered for CNC machining and automotive manufacturing.

Notable Models:

• Bosch CO14B Cobalt Drill Bit (135° Split Point)

• Bosch BL21A Black Oxide Bit Set (118° Angle)

• Bosch Daredevil Multipurpose Drill Bits (Variable Point Geometry)

Bosch’s cobalt series employs 135° angles that enhance stability in high-temperature drilling environments.

Milwaukee (USA)

Milwaukee specializes in professional contractor-grade drill bits suitable for metal, carbide applications, and heavy-duty fabrication.

Notable Models:

• Milwaukee 48-89-4631 Red Helix Cobalt Drill (135° Split Point)

• Milwaukee Thunderbolt Black Oxide Bits (118°)

• Milwaukee Shockwave Impact Drill Bits (Optimized Point Angle ~135°)

Their Red Helix series features a variable helix and reinforced 135° angle for rapid penetration into steel.

Irwin (USA)

Irwin Tools is a traditional manufacturer known for high-quality drill bits for mechanics and machinists.

Notable Models:

• Irwin 3018002 Cobalt M-35 Bit (135° Split Point)

• Irwin 91128 Black Oxide Bit (118° Angle)

• Irwin Hanson Metal Index Bits (135°)

Irwin’s cobalt bits are popularly used in automotive repair, metalworking shops, and industrial maintenance.

Guhring (Germany)

Guhring is one of the world’s top manufacturers of CNC-grade drill bits and cutting tools.

Notable Models:

• Guhring Series 5521 Solid Carbide Twist Drill (140° Angle)

• Guhring Series 5514 HSS Jobber Drill (118°)

• Guhring Firex® Coated High-Performance Drills (135° Multi-Facet)

Guhring’s 140° carbide drills are ideal for aerospace alloys and deep rigid drilling environments.

Dormer Pramet (Sweden / Czech Republic)

Dormer Pramet is a premium brand widely used in CNC machining centers and industrial steel manufacturing.

Notable Models:

• Dormer A110 HSS Drill (118° Angle)

• Dormer A147 Carbide Drill (140° Angle)

• Dormer MPX Series Multi-Purpose Drills (135°)

Their 140-degree carbide models are engineered for ultra-hard materials and precision drilling.

Yamawa (Japan)

Known primarily for taps, Yamawa also produces high-precision drills for metal cutting.

Notable Models:

• Yamawa Hard Material Drill HDR Series (140°)

• Yamawa General Purpose Drill GD Series (118°)

Yamawa’s 140° drills provide excellent chip evacuation in difficult-to-cut materials.

Hikoki / Hitachi (Japan)

Hitachi (now Hikoki) manufactures industrial-grade drill bits used globally in manufacturing plants.

Notable Models:

• Hitachi 728065 Bit Set (118°)

• Hikoki Cobalt Industrial Drills (135°)

These bits are known for long-life performance in metal fabrication.

Chinese Brands (Muwei, WORKPRO, Mulinsen, TASP, JELLAS, etc.)

China produces a vast range of drill bits at competitive pricing.

Representative Models:

• WORKPRO W124086A HSS Drill Bit (118°)

• JELLAS Titanium Drill Set (135°)

• Mulinsen High-Speed Steel Bits (118°/135° depending on model)

These brands offer cost-effective solutions for general workshop and home use.

How to Select the Correct Drill Angle for Different Materials

Choosing the right drill angle is not guesswork but a systematic process that involves evaluating material hardness, heat sensitivity, tool rigidity, and drilling speed.

Steel and Mild Steel

Use 118° or 135°. For general steel, 118° works well. For harder alloy steel, 135° cobalt drills are recommended.

Stainless Steel

Always use 135° cobalt or carbide bits to prevent work-hardening.

Aluminum and Copper

Use 100°–110° where possible, though 118° also works. Lower angles prevent chatter.

Plastics (Acrylic, Nylon, Polycarbonate)

Use 80°–90° to prevent melting and cracking.

Wood

Use 118° standard point angles or brad-point geometries.

Titanium and Superalloys

Use 135–150° carbide drills with coolant.

Cast Iron

Use 118°, as the brittle structure cuts easily.

Understanding Other Critical Angles in Twist Drill Geometry

Besides the point angle, other angles define drill performance:

• Lip Relief Angle

• Chisel Edge Angle

• Helix Angle

• Rake Angle

• Clearance Angle

Each contributes to reduced friction, controlled chip flow, and enhanced cutting efficiency.

Conclusion

The angle of a twist drill bit is far more than just a numerical value; it is a foundational parameter that influences every aspect of drilling performance. By understanding the full range of available drill angles—from 80° for plastics to 150° for aerospace-grade materials—and by selecting the correct angle based on workpiece hardness, mechanical properties, and drill type, users can achieve superior results in both manual and CNC machining environments. Major global brands such as DeWalt, Bosch, Makita, Milwaukee, Guhring, Dormer Pramet, Hikoki, and many Chinese manufacturers offer specialized drill bit models with precise geometries optimized for different industrial needs. The correct choice can extend tool life, reduce production costs, and significantly improve drilling accuracy, making it an essential aspect of engineering knowledge.