Best Drill Bits for Metal: What CNC Machinists Actually Use

In manufacturing, CNC machinists use many drill bits to machine CNC parts. Choosing the right drill bit for the metal isn’t just about cutting through hard materials. In CNC machining and metalworking, the right drill bit directly affects hole accuracy, surface finish, tool life, machining cycle, and overall part quality. This article will tell you the correct drill bit selection to ensure your every machining operation is accurate and error-free.

Types of Drill Bits for Metal

First of all, let me introduce to you the common types of drill bits in the manufacturing industry. Each of them has its own characteristics and uses.

Twist Drill Bits

This is the most common type of drill bit and is well-suited for both CNC and hand drills. The standard point angle of the twist drill is 118°, which is suitable for soft metals (such as aluminum and copper), while 135° is suitable for hard metals (such as stainless steel and tool steel). Although the helix angle of twist drills is typically 28°–30°, I recommend using a larger helix angle (35°–40°) when machining aluminum. This is done to ensure smoother chip evacuation.

Additionally, when using a twist drill on your CNC, I also recommend using a spot drill for initial positioning to prevent walking.

Indexable Insert Drills

This is a CNC-specific drill bit, with a diameter range typically 16mm or more.  When the cutting edge of this type of drill bit wears out, it can be replaced immediately, thereby reducing downtime. In addition, indexable insert drills are well suited for high-volume production and offer low cost per hole. Its only disadvantage is the high initial investment.

Solid Carbide Drill Bits

Solid carbide drill Bits are mainly used for CNC high-speed machining. The hardness of this type of drill bit is much higher than HSS, allowing for higher spindle speeds and feed rates, but its price is 5-10 times that of HSS.

Additionally, solid carbide drill bits are brittle, requiring high machine tool rigidity and clamping accuracy. If you need to batch process stainless steel, titanium alloy, and cast iron, this type of drill bit is a suitable choice.

Center Drill / Spot Drill

When you need to drill holes in workpieces, these drill bits are definitely needed, and their function is for positioning. Center drills have a 60° angle, while spot drills have a 90° or 120° angle.

For modern CNC machines, I recommend using spot drills because they have better rigidity and more accurate positioning. Moreover, when you are positioning, the depth only needs to be 0.5–1mm.

Gun Drill

Gun drills are intended for deep hole machining with L/D greater than 10:1. The drills are single-edged, and their internal coolant channels deliver cutting fluid directly to the cutting edge.

However, this type of drill requires extremely low feed rates and high spindle speeds, with coolant pressure of 8–12 bar or higher. Additionally, gun drills can only be used with specialized deep hole drilling machines, and are not suitable for ordinary machining centers.

Step Drill

Step drill is very suitable for thin sheet metal with thickness <3mm, one drill bit can drill multiple diameters. These drill bits are typically made of high-speed steel (HSS) or cobalt steel, and those with a TiN coating offer a longer service life. However, these drill bits are not suitable for CNC mass production and is mainly used for manual tools.

Key Materials & Coatings Explained

In fact, an excellent drill bit mainly depends on its material and coating, and next you will learn about the specific types of materials and coatings.

Materials

HSS

HSS can be said to be the most basic drill bit material, containing tungsten and molybdenum alloys. It can operate at temperatures as high as 600 degrees Celsius.  The material is low-priced and can be reground, making it suitable for low-volume parts machining.

Cobalt Steel M35 / M42

There are two grades of cobalt steel: M35, which contains 5% cobalt, and M42, which contains 8% cobalt. The maximum operating temperature for this material is approximately 700–750°C, and its hardness and heat resistance are superior to those of standard high-speed steel (HSS). In addition, drill bits made from this material are well-suited for machining stainless steel and high-temperature alloys.

Solid Carbide

Solid carbide is primarily composed of tungsten carbide (WC) and a cobalt (Co) binder. Its hardness reaches HRA 92–94, far exceeding HSS. The maximum operating temperature for this type of drill bit is over 900°C.

Coatings

Engineer’s suggestion:  

• Aluminum alloy machining: DLC-coated or uncoated polished drill bits are the preferred choice; TiN-coated bits are prone to sticking to aluminum.
• Stainless steel machining: TiAlN is the most cost-effective choice.
• High-speed dry cutting: AlTiN has the strongest thermal stability.

Best Drill Bits by Metal Type

After introducing the basic types of drill bits, if you still don’t know which drill bit should be used for the materials you need, then the following content will directly tell you the answer. We’ll help you choose the most suitable drill bit based on the material.

Low Carbon Steel / Mild steel

There are many drill bit options for this material. If you’re on a tight budget, an HSS drill bit will suffice. But if you also pursue the service life of the drill bit, then you need to use drill bits made of cobalt steel.

• Small-volume production: Guhring RT 100 U. This drill offers wide tolerance parameters and is suitable for a variety of materials.
• High-volume CNC machining: Kennametal KSEM indexable drill. The inserts on this drill can be replaced without stopping the machine, which helps reduce the cost per hole.

Stainless Steel

The most common issue encountered when machining stainless steel is work hardening. This means that as soon as the machine tool stops cutting, the workpiece surface hardens, which can cause the tool to chip during subsequent machining operations. So for stainless steel machining, the core logic of your choice of drill bits is that the drill bit can continue cutting, has good heat dissipation, and is hard enough.

• Precision holes: For parts requiring precision holes in CNC machining, I recommend the Sandvik CoroDrill 860. This is because this drill offers high centering accuracy and direct internal cooling to the drill tip.
• CNC mass production: The OSG EX-SUS series. The geometric angle of this drill is optimized for stainless steel, and its tolerance can be stably controlled within H7.

Aluminum Alloy

As you know, aluminum is the most widely used material due to its excellent machinability. However, in aluminum machining, aluminum has one drawback: it tends to stick to the tool. Therefore, when selecting drill bits for aluminum, you should follow two key principles: 1. Efficient chip removal 2. No tool sticking.

• CNC high-speed machining: Nachi Aqua Drill EX Flat. This drill bit offers the best anti-gluing performance.
• CNC mass production: Kennametal B041A. This drill bit ensures smooth chip evacuation at high speeds and produces a smooth hole surface.

Cast Iron

Because cast iron is brittle, the chips produced are powdery. Cast iron CNC machining usually does not require chip evacuation design, but drills need to be wear-resistant.

• Standard holes: Guhring RT 100 U. This drill offers excellent thermal stability during dry cutting.
• Large-diameter holes: Kennametal KSEM indexable drills. These drills are the preferred choice forhigh-volume manufacturing of cast iron parts.

Hardened Steel

For hardened steel, you should only use solid carbide drill bits. For materials with a hardness of HRC 60 or higher, I recommend you directly use EDM machining.

CNC Machining:

• HRC 45–55: Sandvik CoroDrill 860-PM. This drill bit has internal cooling and is optimized for hard steel.
• HRC 55–60: OSG EX-HO-GDR. This drill is essentially designed for die steel, with geometry optimized for high hardness.
• Precision mold holes: Guhring Speedmax. This drill bit can maintain good dimensional stability when machining high-hardness materials.

Titanium Alloy

Titanium alloys have extremely poor thermal conductivity, so heat tends to accumulate at the cutting edge. If you use the wrong drill bit, the cutting edge could burn out in a matter of seconds. Therefore, when selecting the correct cutting head for titanium alloy, the principle you should follow is heat dissipation.

• Aerospace precision holes:: Sandvik CoroDrill 860-MM
• High-Volume hole machining: Guhring RT 100 T
• High-Pressure cooling applications: Kennametal KSSM

Copper / Brass

Copper is soft but tough. If you use a standard twist drill to drill holes, the hole diameter of the copper parts will be inaccurate. In copper CNC machining, the key consideration when selecting a drill bit is that it must have a zero or negative rake angle.

• Precision hole: Nachi SG-ESS. The hole wall has high smoothness and stable dimensions.

What are The Best Drill Bits for Metal?  (2026)

Below, I will recommend you the latest and most useful drill bits. You can choose to use them according to your own needs.

Manual level

Here are several common types of drill bits.

Irwin Tools Cobalt M-42

• Material: cobalt steel
• Suitable for: stainless steel, hard steel, cast iron
• Features: 135° split top angle, accurate positioning, no need for center drilling
• Price range: set approximately $30–$50

DEWALT DW1269 Pilot Point

• Material: HSS, TiN coating
• Suitable for: ordinary carbon steel, aluminum
• Price range: set approximately $20–$35

Bosch CO14B Cobalt

• Material: cobalt steel
• Suitable for: stainless steel, hard metals
• Features: 135° point angle, stable quality German brand
• Price range: individual piece approximately $8–$15

CNC Professional Level

Here are the main types of professional-grade drill bits used for CNC drilling services.

Sandvik Coromant CoroDrill 860

• Type: Solid carbide, internal cooling
• Suitable for: Stainless steel, titanium alloys
• Features: Patented point angle design, high centering accuracy, extremely long tool life
• Typical applications: Aerospace, medical devices

Kennametal KSEM Modular Drill

• Type: Indexable modular drill bit
• Suitable for: Carbon steel, alloy steel, cast iron high-volume production
• Features: Replaceable cutter head, no need for regrinding, reduces single hole cost
• Diameter range: 14–80mm

Guhring RT 100 U

• Type: solid carbide, general type
• Suitable for: steel, stainless steel, cast iron
• Features: high cost-performance ratio, large tolerance parameters, suitable for multi-variety small batch CNC machining

OSG A-Brand / EX series 

• Japanese brand, stable quality
• Suitable for: precision hole machining, tolerance within H7
• Features: high dimensional accuracy, uniform coating

Iscar Sumocham

• Type: Indexable carbide drill bit
• Features: The tool head can be replaced quickly, no tool calibration is required, and it is suitable for high-tempo production lines.

CNC Machining — Drill Bit Selection & Parameters

I’m sure many of you are eager to know the reasons for recommending the drill bits mentioned above. This brings us to the most important part of this article, which I’ll explain in detail below.

CNC vs. Hand Drilling

There is a big difference in the logic of selecting drill bits for CNC and hand drills. CNC machine tools have high spindle rigidity, precise rotational speed, and the feed of the drill bit can also be programmed, so you can use more radical parameters. Hand drills have problems with vibration and unstable axial force. In order to solve these problems, a more forgiving drill bit design is required.

In addition, CNC drill bits are generally made of solid carbide, but hand drills are not. And CNC has very high requirements for clamping accuracy.

In CNC machining, the setting of cutting speed and feed rate is very critical. You can use the following formulas to calculate the corresponding data.

Cutting Speed Formula:

$$v_c = \frac{\pi \cdot d \cdot n}{1000}$$

• V_c​= Cutting speed (m/min)
• D = Drill bit diameter (mm)
• n = Spindle speed (RPM)

Calculating RPM from Cutting Speed:

$$n = \frac{v_c \cdot 1000}{\pi \cdot d}$$

Large Hole Solutions

When it comes to machining large holes with a diameter of 25 mm or more, it can be said to be an independent technical field. In this size range, ordinary drill bits have extremely low efficiency and torque requirements surge dramatically, so you must use specialized solutions.

Indexable Insert Drill

• Diameter range: 16–80mm
• Representative products: Sandvik CoroDrill 880, Kennametal KSEM, Iscar Sumocham
• Suitable for: CNC mass production, carbon steel, alloy steel, cast iron with large holes

Spade Drill 

• Diameter range: 25–150mm+
• Representative products: Kennametal Spade Drill, Iscar Spade series
• Suitable for: Rough machining of large holes, subsequent boring or reaming finishing is required

Core Drill

• Diameter range: 12–150mm
• Representative products: Hougen Rotabroach, Milwaukee Big Hawg, Fein Slugger
• Suitable for: on-site drilling of steel structures, manual processing of thick plates, and one-time large holes

Key Parameter for Large Hole Machining

The larger the diameter, the lower the rotational speed. When setting the rotational speed, you should not rely on personal experience. And you should calculate the RPM using the cutting speed formula.

For a 50 mm hole, I recommend a cutting speed of 80 m/min, which corresponds to a spindle speed of only about 509 RPM:

$$n = \frac{1000 \times 80}{\pi \times 50} \approx 509RPM$$

In addition, you should pay attention to a few points:

1. The feed of the drill bit must be sufficient. If the feed of the drill bit for large holes is too small, the blade wear will increase.
2. The coolant flow rate should be increased
3. When drilling holes with a diameter exceeding 40 mm, you should first check the machine tool’s torque curve to confirm that the torque is sufficient at low speeds.

Sharpest Drill Bits for Clean Metal Cutting

Drill bits have specific geometric parameters and performance specifications. Often, CNC machinists select the appropriate drill bit based on the specific application and also assess the sharpness of each type of drill bit.

Core Factors

Point Angle 

• 118°: Standard angle. Drill bits with this angle are suitable for soft metals and provide good initial penetration, but they do not center well on hard materials.
• 135°: Split Point. This is the first choice for hard metals. It is self-centering, does not require drilling locating holes, and the cutting force is more evenly distributed.
• 140°: Used in some high-performance carbide drill bits to further reduce axial cutting force.

Helix Angle

The larger the helix angle, the faster the chip removal and the lighter the cutting, but the rigidity decreases.

• Aluminum alloy: 35°–40°helix angle.
• Steel: 28°–30°helix angle.
• Hardened steel: 20°–25°helix angle.

Cutting Edge Treatment 

The edge radius of the sharp drill is controlled at 2–5 μm. 

• Honing Treatment: The cutting edge radius is 10–20 μ.
• Polished Flutes: It can reduce chip removal friction.

 Accuracy

• Runout: <0.005 mm
• Edge length symmetry: If the length difference between the two blades exceeds 0.05mm, the hole diameter will be too large.

Recommended Drill Point Angle by Metal Type

Recommended Sharpest Drill Bits

General-Purpose Metal Drill Bits

• Precision Twist Drill (PTD) Red Band Cobalt: The drill bit has high edge grinding accuracy and has a split top angle of 135°.
• Regal Cutting Tools Cobalt: Industrial grade precision.

 CNC Solid Carbide Drills Bits 

• Sandvik CoroDrill Delta-C: Four-flute design. Extremely low cutting force.
• Guhring Driltex: 5-axis CNC grinding.

Sheet Metal Drills Bits

• Greenlee Slug-Splitter Step Drill: Clean cut without burrs.
• Irwin Unibit Step Drill: Single-edged spiral design.

Solid Carbide vs. Tipped

How to Extend Drill Bit Life in CNC Operations

The service life of drill bits has always been a topic of concern for you. Next, I’ll offer some practical advice.

Initial Test Cut

When drilling the first hole with a new drill bit, start by using only 70% of the normal settings. Once you confirm that the drilling results are satisfactory, you can adjust the settings to normal levels.

Monitor Drill Bit Wear

Once the wear on the rear face of the tool (VB) exceeds 0.3 mm, you should replace the tool.

Signs of Tool Breakage

If any of the following conditions occur, you should stop the machine and inspect it.

• The cutting noise becomes deeper
• The chips turn darker (bluish)
• The spindle load increases

Regrind Judgment

Solid carbide drill bits can be reground 2–3 times. However, since the diameter decreases by approximately 0.1–0.3mm after each regrinding, you need to reconfirm the tolerances.

Storage

You definitely know that drill bits must not come into contact with one another. Therefore, you must store various drill bits in separate compartments, especially those made of carbide.

Clamping Inspection

After each clamping, you must use a dial indicator to check the runout. If it exceeds 0.02 mm, the drill bit must be re-clamped.

Cutting Fluid Concentration

The concentration of water-soluble cutting fluid is generally maintained at 8–12%. If the concentration is too low, the cooling effect will not be good.

Conclusion

Well, that’s all about the best drill bits for metal. I believe you will gain a lot after reading this. As a professional CNC machining manufacturer, we also select the best machining solutions based on customer drawings, including drill bits, materials, processes, and so on. We have been providing high-quality precision machining services and contract CNC machining to customers from all over the world, and have received unanimous praise from them for our excellent part quality. Welcome to contact us if you have any needs.

FAQ:

Q1: What are the toughest drill bits for metal? 

A: Solid Carbide. Its hardness can reach HRA 92 or above, and its heat resistance exceeds 1000°C.

Q2: Can standard drill bits be used on CNC machines?

A: Yes, they can, but it is not recommended. HSS drill bits wear out extremely quickly under the high speeds and feed rates of CNC machines, and they are not as precise as carbide drill bits.

Q3: What speed should be used when drilling stainless steel? 

A: For hand drills using cobalt steel drill bits, use approximately 300–500 RPM for a 10mm diameter. For CNC machines using carbide drill bits, use approximately 1200–2000 RPM for a 10mm diameter.

Q4: Can hardened steel be drilled with a standard drill bit?

A: Cobalt steel can barely be used below HRC 45, but the tool life is very short. Above HRC 45, only solid carbide is recommended.

Q5: How to prevent the drill bit from slipping on metal and failing to locate?

A: You can use a center drill or spot drill to drill a locating hole with a depth of 0.5–1mm, and then switch to a drill bit to drill the hole.

Q6: Are titanium or cobalt drill bits better?

A: Cobalt drill bits have excellent hardness and heat resistance, making them more suitable for hard metal machining. While titanium-coated drill bits are only suitable for soft metal machining, they are more appropriate for light-duty use.

Q7: Which drill bit is harder, carbide or cobalt?

A: Carbide is much harder than cobalt steel. The hardness of cobalt steel M42 is about HRC 67–70, while the hardness of solid carbide can reach HRA 92–94.

Q8: What are the disadvantages of cobalt drill bits?

A: 1. The price is expensive. Cobalt steel drill bits are 2–4 times more expensive than regular HSS drill bits. 2. Cobalt steel is more brittle than standard HSS. 3. Regrinding is more difficult. 4. Cobalt steel drill bits are difficult to drill high-hardness materials above HRC 45.

Q9: What’s better, black oxide or cobalt drill bits?

A: Black oxide treatment is the most basic surface treatment process. Its function is to slightly reduce the friction of the drill bit and prevent rust. Cobalt steel drill bits, on the other hand, offer excellent hardness and heat resistance, as well as a long service life, so they are definitely the better choice.

Q10: What are common mistakes when drilling hardened steel?

A: First, using the wrong tool or incorrect settings. Second, the rotation speed is too high, which will accelerate the wear of the drill bit. Third, the machine tool cuts intermittently.. Fourth, no cooling or insufficient cooling.

Q11: What are the best drill bits for metal drilling?

A: This mainly depends on your equipment and materials. For manual drilling of ordinary steel, it is recommended to use M35 or M42 cobalt-containing high-speed steel. I recommend Irwin Cobalt and Bosch’s CO series. For CNC machining of hard metals, solid carbide should be used. Sandvik, Guhring and OSG are all commonly used brands in the industry.

Q12: What types of drill bits are recommended for stainless steel?

A: The minimum standard is cobalt steel M42. And if you still need to pursue accuracy and service life, you need to choose solid carbide.

Q13: Which drill bit brands are top-rated for metalwork?

A: There are the following brands：

• Industrial/CNC Grade: Sandvik Coromant, Guhring, OSG, Kennametal, Mitsubishi Materials
• Hand Drill/Professional Grade: Irwin, Bosch Professional, Precision Twist Drill (PTD), Regal Cutting Tools
• Cost-effective options: YG-1, Nachi

Q14: What are the advantages of carbide-tipped drill bits for metal?

A: Carbide-tipped drill bits have a higher cutting edge hardness and greater heat resistance, and they are capable of machining hard materials such as cast iron.

Q15: Can you recommend durable drill bits for heavy metal projects?

A: You only need to remember the following three points: solid carbide drills are used for CNC precision holes; indexable insert drills are used for large-diameter batch holes; an annular cutter with a magnetic drill press is used for on-site hole making in thick steel plates.

Q16: Which is harder, HSS or carbide?

A: Carbide is much harder than HSS. The hardness of HSS is about HRC 62–65, and the hardness of solid carbide is HRA92–94, which converts to approximately HRC 75–80.

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