Expert Buyer’s Guide: 5 Key Checks for the Best Drill Bit Set for Metal

Abstract

Selecting an appropriate drill bit set for metalworking is a determination grounded in material science and mechanical engineering principles, not mere preference. This analysis examines the constituent factors that define the efficacy and longevity of drill bits when applied to various metals. The investigation focuses on five pivotal areas: the fundamental material composition of the bit, the application and type of surface coatings, the geometry of the drill point and flutes, the comprehensiveness and organization of the set itself, and the alignment of these technical specifications with the intended application. It evaluates the properties of High-Speed Steel (HSS), cobalt alloys (M35, M42), and solid carbide, contrasting their performance characteristics. Furthermore, it deciphers the functional benefits of coatings such as Titanium Nitride (TiN) and Titanium Aluminum Nitride (TiAlN). The objective is to provide a clear framework for professionals and enthusiasts, enabling an informed selection process that optimizes cutting performance, precision, and tool life, thereby moving beyond superficial assessments to a deeper, more functional understanding of the tool's capabilities.

Key Takeaways

• Match the bit material to the metal; cobalt is for hardened steel, HSS for softer metals.
• Coatings like TiN or TiAlN significantly extend tool life and improve cutting efficiency.
• A 135-degree split point prevents "walking" and is superior for starting holes on hard surfaces.
• Choose the best drill bit set for metal with a comprehensive size index to avoid work interruptions.
• Proper speed, pressure, and lubrication are as vital as the bit itself for clean results.
• A quality, well-organized case protects your investment and improves workflow efficiency.

Table of Contents

• Check 1: Scrutinizing the Core Material Composition
• Check 2: Decoding Surface Treatments and Coatings
• Check 3: Understanding Drill Point and Flute Geometry
• Check 4: Evaluating the Set's Configuration and Case
• Check 5: Aligning Your Choice with Application and Technique
• Frequently Asked Questions (FAQ)
• Conclusion
• References

Check 1: Scrutinizing the Core Material Composition

The journey toward selecting the ideal drill bit begins not at the cutting edge, but deep within the atomic structure of the tool itself. The material from which a drill bit is forged dictates its fundamental capabilities—its hardness, its ability to withstand the intense heat generated by friction, and its resilience against the torsional stresses of drilling. To choose a set without first understanding its material DNA is akin to selecting a vehicle without considering its engine. The metal you intend to drill presents a unique challenge, and the drill bit must possess the intrinsic properties to meet that challenge head-on. A material perfectly suited for drilling into soft aluminum would lamentably fail, perhaps catastrophically, when faced with the unyielding nature of stainless or hardened steel. Our exploration, therefore, commences with a deep examination of the primary materials used in modern drill bit manufacturing, moving from the foundational to the highly specialized.

High-Speed Steel (HSS): The Foundational Choice

High-Speed Steel represents the bedrock of modern metal drilling technology. Its name is not a marketing flourish; it is a direct descriptor of its capability. HSS was developed to cut metal at higher speeds than the high-carbon steels that preceded it, a revolutionary step that dramatically increased manufacturing productivity in the early 20th century. What gives HSS its character is a complex alloying process. At its core, it is a steel, an alloy of iron and carbon, but it is enriched with other elements, most notably tungsten and/or molybdenum. These elements form intensely hard carbide particles within the steel's matrix.

Imagine a concrete wall. The concrete itself is strong, but embedding steel rebar within it makes it vastly stronger. In HSS, the steel matrix is the concrete, and the tungsten or molybdenum carbides are the rebar. This structure gives HSS its signature property: "hot hardness." As a drill bit cuts through metal, the friction generates immense heat, often reaching several hundred degrees Celsius at the cutting tip. A simple carbon steel tool would soften at these temperatures, its cutting edge would dull almost instantly, and it would cease to function. HSS, because of its alloyed carbides, retains its hardness and sharp cutting edge even when red-hot. This allows it to continue cutting effectively where lesser steels fail. The most common grade for drill bits is M2 HSS, a molybdenum-based steel that offers a balanced combination of hardness, wear resistance, and toughness, making it a reliable and cost-effective choice for general-purpose drilling in non-ferrous metals like aluminum and copper, as well as mild steels and plastics.

Cobalt Alloys (M35 & M42): The Endurance Champions

When the challenge escalates from mild steel to formidable materials like stainless steel, cast iron, or titanium alloys, HSS begins to reach its thermal limits. This is where cobalt enters the narrative. Cobalt drill bits are not made of cobalt; they are HSS bits to which a significant percentage of cobalt has been added to the steel alloy itself. The two most prevalent grades are M35, which contains 5% cobalt, and M42, which contains 8% cobalt.

The inclusion of cobalt has a profound effect on the steel's metallurgy. Cobalt does not form carbides itself. Instead, it integrates into the steel matrix, fundamentally increasing the material's "red hardness" or "hot hardness" to a level significantly beyond that of standard HSS. It acts as a binding agent that helps the steel matrix resist softening at even higher temperatures. Think of it as upgrading the concrete in our earlier analogy. While the rebar (carbides) is the same, the concrete (matrix) is now a high-performance mix that can withstand far greater stress before showing signs of failure.

This superior heat resistance is not just an abstract quality; it has direct, practical consequences. When drilling a hard material like stainless steel, which is a poor thermal conductor, heat builds up rapidly at the drill tip. A standard HSS bit would quickly overheat, anneal (soften), and become useless. An M35 or M42 cobalt bit, however, can endure this intense thermal punishment, maintaining its sharp cutting edge for a much longer period. This results in a longer tool life, the ability to drill through tougher materials, and the capacity to operate at higher speeds compared to HSS. The trade-off is a slight increase in brittleness—they are less forgiving of bending or flexing than HSS—and a higher cost. Yet, for anyone regularly working with hardened metals, the investment in a cobalt drill bit set is an investment in efficiency and capability.

Solid Carbide: The Pinnacle of Hardness

At the apex of the material hierarchy sits solid carbide. Unlike HSS or cobalt bits, which are steel alloys, solid carbide bits are typically composed of tungsten carbide (WC) particles sintered together with a metallic binder, usually cobalt. The result is a material of extraordinary hardness, approaching that of a diamond. On the Mohs scale of hardness, where diamond is a 10, tungsten carbide registers around 9. This extreme hardness allows solid carbide bits to cut the most difficult and abrasive materials with remarkable ease, including hardened steels above 50 HRC, high-temperature superalloys, and abrasive composite materials like carbon fiber.

Because they are so hard, carbide bits exhibit exceptional wear resistance. The cutting edge remains sharp for an incredibly long time, even in high-volume production settings. This makes them the ultimate choice for CNC machining and other industrial applications where precision and tool longevity are paramount. However, this extreme hardness comes with a significant compromise: brittleness. Solid carbide is very rigid and has poor tensile strength. It cannot tolerate much bending or vibration. A carbide bit that is handled improperly, dropped, or used in a wobbly, unstable hand drill is likely to chip or shatter. They demand a rigid setup, such as a drill press or milling machine, and precise control over speeds and feeds. Their cost is also substantially higher than HSS or cobalt bits, placing them in the realm of specialized or professional-grade tools where performance justifies the expense. For a general-purpose workshop, a full set of carbide bits is often overkill, but having specific sizes for particularly challenging jobs can be invaluable.

A Comparative Analysis: Material vs. Application

To make a rational choice, one must weigh the properties of each material against the demands of the job and the constraints of the budget. The following table provides a structured comparison to aid in this decision-making process.

This table clarifies the functional trade-offs. HSS offers versatility and toughness at a low cost, making it the workhorse for softer materials. Cobalt provides the necessary heat resistance for tougher metals, representing a significant step up in performance for a moderate increase in price. Solid carbide delivers the ultimate in hardness and wear resistance for the most demanding industrial applications, but requires a rigid setup and a larger budget. Understanding this hierarchy is the first and most vital check in selecting the best drill bit set for metal.

Check 2: Decoding Surface Treatments and Coatings

If the core material of a drill bit is its heart, the coating is its skin—a thin but profoundly important layer that mediates every interaction with the workpiece. Coatings are not merely for aesthetics; they are a sophisticated application of material science designed to enhance a bit's performance in specific ways. They can increase surface hardness, reduce friction, improve chip flow, and act as a thermal barrier. A coated bit can often outperform an uncoated bit of a superior base material, demonstrating that the surface is as significant as the substrate. Ignoring the coating is to ignore a key dimension of the tool's intended function. Let us examine the most common treatments and coatings, from the basic to the advanced, to understand the value they add.

The Uncoated Truth: Black Oxide and Bright Finish

Before we delve into advanced coatings, we must understand the baseline. A "bright finish" drill bit is exactly what it sounds like—it has no coating at all. The bit is simply ground from the base material (usually HSS) and polished. This finish is perfectly acceptable for drilling into soft materials like aluminum or magnesium. In these cases, the material being drilled has a tendency to stick to the cutting edge, a phenomenon known as a "built-up edge." A smooth, uncoated flute can sometimes help prevent this material adhesion better than a coated one. However, bright finish bits offer no additional wear resistance and minimal corrosion protection.

A step above the bright finish is the black oxide coating. This is not a layer of paint but a chemical conversion process that treats the surface of the HSS bit. The process creates a layer of black iron oxide (magnetite) on the tool. This layer offers several modest benefits. It provides a degree of corrosion resistance, which is useful for storage. It also helps to retain cutting fluid on the tool's surface, improving lubricity during the drilling operation. The most notable benefit, however, is that the tempering and stress-relieving process that accompanies the black oxide treatment can reduce grinding stress in the tool, slightly increasing its durability. Black oxide is a common, economical finish that offers a slight performance upgrade over a bright finish, making it a popular choice for general-purpose HSS drill bit sets. It does not, however, increase the hot hardness or intrinsic wear resistance of the cutting edge.

Titanium Nitride (TiN): The Golden Standard

The appearance of the iconic gold-colored drill bit marked a significant leap forward in cutting tool technology. This color comes from a Titanium Nitride (TiN) coating, applied through a process called Physical Vapor Deposition (PVD). In a vacuum chamber, a high-voltage arc vaporizes a solid titanium source. This titanium vapor reacts with nitrogen gas present in the chamber and deposits onto the drill bits as a very hard, thin ceramic layer.

The TiN coating is much harder than the HSS substrate it covers. This immediately provides a significant increase in abrasion resistance, meaning the cutting edge stays sharp for much longer. A TiN-coated HSS bit can have a lifespan three to five times longer than an uncoated HSS bit under the right conditions. Beyond hardness, TiN has a low coefficient of friction. This "slipperiness" is incredibly valuable. It reduces the energy needed to push the drill through the material and, more importantly, it helps chips flow more smoothly up the flutes and out of the hole. Better chip evacuation prevents the flutes from clogging, reduces heat buildup, and results in a cleaner hole. TiN is an excellent all-around coating, well-suited for increasing the performance and life of HSS bits when drilling iron, mild steel, and other ferrous materials. Its main limitation is its thermal stability; it begins to break down at temperatures around 600°C, making it less suitable for the extreme heat generated when drilling stainless or other very hard steels.

Titanium Carbonitride (TiCN) and Titanium Aluminum Nitride (TiAlN): Advanced Performance

For applications that push beyond the limits of TiN, more advanced coatings have been developed. Titanium Carbonitride (TiCN) is one such example. Recognized by its violet-gray hue, TiCN is created by introducing carbon (in the form of methane) into the PVD process along with titanium and nitrogen. The resulting ceramic layer is significantly harder than TiN and possesses a lower coefficient of friction. This makes it exceptionally effective at resisting abrasive wear. TiCN is an excellent choice for drilling hard and tough materials like cast iron and stainless steels, where the combination of hardness and lubricity helps to protect the cutting edge and efficiently clear chips.

Perhaps the most versatile high-performance coating is Titanium Aluminum Nitride (TiAlN). Its distinctive dark purple to black appearance signals its advanced capabilities. During the PVD process, aluminum is added to the titanium-nitrogen reaction. This is where the magic happens. When the TiAlN-coated tip heats up during cutting (above 800°C), the aluminum in the coating oxidizes, forming a microscopic layer of aluminum oxide (Al₂O₃) right at the cutting interface. This layer is chemically stable, extremely hard, and an excellent thermal insulator. In essence, the bit creates its own protective ceramic barrier in response to the heat of the cut. This allows TiAlN-coated bits, especially those on a cobalt substrate, to excel in high-heat applications like drilling hardened steel, titanium alloys, and nickel-based superalloys. It is particularly well-suited for high-speed machining and even dry drilling (without coolant), as the heat is what activates its protective mechanism.

The Impact of Coatings on Tool Life and Performance

It is crucial to conceptualize a coating not as a passive layer but as an active component of the cutting system. The choice of coating should be as deliberate as the choice of base material. A high-quality coating on a standard HSS bit can enable it to perform tasks typically reserved for a more expensive, uncoated cobalt bit. The following table illustrates the hierarchy of common coatings and their ideal uses.

Ultimately, the coating serves to protect the integrity of the cutting edge. By reducing friction, it lowers the heat generated. By acting as a thermal barrier, it prevents the heat that is generated from softening the substrate material. By providing a harder surface, it resists the abrasive wear that dulls the edge. A well-chosen coating on a quality bit from a manufacturer of professional power tools leads to faster cutting, longer tool life, better hole quality, and lower overall cost per hole—a cascade of benefits originating from a layer often only a few microns thick.

Check 3: Understanding Drill Point and Flute Geometry

Beyond the material and its coating lies the drill bit's form—its geometry. The specific shape of the cutting tip and the design of its spiral flutes are not arbitrary; they are the result of over a century of engineering refinement aimed at solving specific physical problems encountered during drilling. How a bit initiates a hole, how it shears material, and how it ejects that material are all dictated by its geometry. Two bits made of the same M42 cobalt with the same TiAlN coating can perform dramatically differently if one has a 118-degree point and the other has a 135-degree split point. To ignore geometry is to overlook the very features that translate the material's potential into practical performance.

The Significance of the Point Angle: 118° vs. 135°

The most prominent feature of a drill bit's tip is its point angle. This is the angle formed by the two primary cutting edges at the very tip of the bit. The two most common angles found in any workshop are 118 degrees and 135 degrees, and each is tailored for different tasks.

A 118-degree point is the traditional, more acute angle. Think of it as a sharper, more pointed cone. This shape is ideal for drilling into softer materials like aluminum, copper, mild steel, and wood. The sharp point engages the material aggressively and centers relatively well on its own. The longer cutting edge, a consequence of the acute angle, helps to distribute the cutting load, which is effective in materials that are easily sheared.

A 135-degree point, by contrast, is a flatter, more obtuse angle. This geometry is the standard for drilling into harder and tougher materials, such as stainless steel, hardened steel, and other high-strength alloys. Why the flatter angle? The primary reason is to reduce the "walking" or "wandering" of the drill bit as it starts a hole. On a hard, smooth surface, a sharp 118-degree point can easily skate out of position before it bites into the material. The flatter 135-degree point has more surface contact at the initiation of the cut, which provides greater stability and helps keep the hole precisely where it was intended. Additionally, the shorter cutting edge of a 135-degree point concentrates the drilling pressure over a smaller area. This increases the force per unit area, which is necessary to form a chip in hard, difficult-to-machine materials.

The Split Point Advantage: Self-Centering Precision

If you look closely at the very tip of a drill bit, you will see a small, non-cutting edge that connects the two main cutting lips. This is called the "chisel edge." On a conventional point bit, this chisel edge acts more like a wedge than a cutting tool; it has to push material out of the way before the main cutting lips can engage. This is the primary cause of a drill bit "walking" and is why using a center punch to create a starting dimple is often necessary for accurate hole placement.

The split point is an elegant solution to this problem. A split point bit has additional grinding on the tip that "splits" the chisel edge, creating a secondary cutting edge at the very center of the bit. In essence, it eliminates the non-cutting chisel edge and replaces it with a sharp, active cutting point. The effect is immediate and profound. A split point bit is "self-centering." It will not wander when starting a hole, even on a hard, curved, or irregular surface. It begins cutting the moment it touches the material, eliminating the need for a center punch in most applications. This not only improves accuracy but also reduces the amount of axial force, or "push," required to start the drill. While a split point can be found on both 118-degree and 135-degree bits, it is most commonly and most valuably paired with the 135-degree point, as it directly counteracts the walking tendency of the flatter angle on hard materials. For anyone seeking precision, especially when using a hand drill, a set with a 135-degree split point is a superior choice.

Flute Design: The Unsung Hero of Chip Evacuation

The spiral grooves that run up the body of a drill bit are called flutes. While their most obvious function is to provide the cutting edges, they serve an equally vital purpose: to act as a channel for chip evacuation. As the bit cuts, it creates chips of metal that must be transported up and out of the hole. If this process is inefficient, the flutes can become packed with chips—a condition known as "clogging." A clogged flute prevents the bit from cutting effectively, generates excessive heat, and can lead to bit breakage or a poorly finished hole.

The efficiency of chip evacuation is largely determined by the "helix angle" of the flute—the angle of the spiral relative to the axis of the bit. A standard drill bit typically has a helix angle around 30 degrees. This is a good compromise that works well for a variety of materials, including most steels. However, for certain materials, a specialized flute design is better. When drilling soft, gummy materials like aluminum or copper, which tend to produce long, stringy chips, a "fast" spiral with a higher helix angle (e.g., 40 degrees) is more effective. The steeper angle acts like an auger, pulling the chips out of the hole more aggressively. Conversely, when drilling very hard, brittle materials like cast iron or high-alloy steels that produce small, broken chips, a "slow" spiral with a lower helix angle is sometimes used. This provides more cross-sectional strength to the bit and a larger channel for the smaller chips. While most general-purpose sets will feature a standard 30-degree helix, being aware of its function helps diagnose drilling problems related to chip evacuation.

Web Thickness and Its Role in Strength

Running through the center of the drill bit, between the flutes, is a column of metal known as the "web." The web is the backbone of the drill bit. Its thickness is a critical design parameter that balances strength against cutting efficiency. A thicker web makes for a stronger, more rigid drill bit. This increased rigidity is essential for heavy-duty drilling applications where high feed rates are used, and it makes the bit much more resistant to breaking under high torque loads. Many heavy-duty cobalt and carbide bits feature a thickened web for this reason.

However, there is a trade-off. As the web gets thicker toward the shank of the bit, the chisel edge at the tip also becomes wider. As we discussed, a wide chisel edge does not cut efficiently and requires more thrust force to penetrate the workpiece. To counteract this, bits with a thick or "heavy-duty" web are almost always designed with a split point. The split point negates the negative effect of the wide chisel edge, allowing the bit to benefit from the strength of a thick web while still being self-centering and requiring less force to start. This combination of a thick web and a split point is a hallmark of a high-performance, professional-grade drill bit designed for demanding work.

Check 4: Evaluating the Set's Configuration and Case

A drill bit is rarely a solitary tool; its utility is magnified when it is part of a well-conceived set. The selection of a drill bit set involves an assessment not just of the individual bits but of the collection as a whole. Does the set provide a logical and useful range of sizes? Is it organized in a way that facilitates workflow and protects the tools? These are not secondary considerations. A set with significant gaps in its size range can bring a project to a halt, while a flimsy, poorly marked case can lead to lost time, frustration, and damaged bits. A truly great set is a functional system, and evaluating that system is a crucial step in the purchasing process.

Fractional vs. Numbered vs. Lettered Sizes: A Complete Toolkit

In the world of drilling, precision often demands more than just "small, medium, and large." Drill bit sizes are standardized across several systems, and a comprehensive toolkit will often include more than one.

The most common system, particularly in North America, is the fractional inch system. These sets typically range from 1/16" up to 1/2" or larger, in increments of 1/64". A standard 29-piece fractional set (1/16" to 1/2" by 64ths) is the cornerstone of many workshops, covering the vast majority of general fabrication and repair needs for clearance holes and basic fastening.

For tasks requiring greater precision, especially for tapping holes to create threads, the numbered gauge and lettered gauge systems are indispensable. Numbered drill bits range from size 80 (the smallest, at 0.0135 inches) to size 1 (the largest, at 0.2280 inches). Lettered bits continue where the numbered bits leave off, running from size A (0.2340 inches) to size Z (0.4130 inches). These systems provide the very specific, non-obvious diameters required to drill the correct size hole before using a tap to cut threads for a given screw size (e.g., a #10-32 tap requires a #21 drill). Without these specific sizes, tapping is a frustrating exercise in broken taps and stripped threads. While a master set containing all three systems can be large and expensive, a good starting point is a robust fractional set, supplemented by a smaller number/letter index if threading is a common task. The best drill bit set for metal for a serious fabricator is often a combination of these systems.

The Merits of a Comprehensive Index

The "index" refers to the collection of sizes included in the set. The primary virtue of a good drill bit set is that it has the size you need, when you need it. A common frustration with smaller, budget-oriented sets is that they have large gaps between sizes. You might have a 1/4" bit and a 5/16" bit, but the 9/32" or 17/64" bit required for a specific dowel or fastener is missing. This forces compromises—drilling an oversized hole that results in a sloppy fit, or spending time searching for a single bit.

A comprehensive index, such as the aforementioned 29-piece fractional set, is a significant quality-of-life improvement. It ensures that the correct size is almost always at hand, saving time and improving the quality of the work. For professionals, even larger sets are available. A 115-piece set, for example, would typically include a full fractional range from 1/16" to 1/2" by 64ths, a full numbered range from #1 to #60, and a full lettered range from A to Z. While this may seem excessive for a hobbyist, for a machine shop or dedicated metalworker, this completeness is the definition of efficiency. When evaluating a set, do not just look at the largest and smallest bit; examine the increments between them. Are there gaps? A well-planned index is a sign of a manufacturer, like YDS Tools, that understands the real-world needs of its users.

Case Quality: Protecting Your Investment

The case, or index box, is far more than packaging. It is an integral part of the tool system. A quality set of cobalt or carbide bits is a significant investment, and the case is the first line of defense in protecting that investment.

A durable case prevents bits from being lost or damaged. Bits rattling around loose in a toolbox drawer will have their cutting edges chipped and dulled long before they ever touch metal. A good case holds each bit securely in its own designated spot. Look for robust materials. While many cases are plastic, a high-quality, impact-resistant polymer is far superior to thin, brittle plastic that will crack if dropped. Metal cases offer excellent durability but can be prone to rusting if not cared for. The hinge is another critical point of failure; a sturdy, full-length piano hinge is vastly superior to two small plastic flex hinges that are destined to break.

Organization is the other key function of the case. Each position should be clearly and permanently marked with the corresponding bit size. Faintly printed or stick-on labels that will wear off are a sign of a low-quality set. The markings should be molded, stamped, or engraved into the case itself. This allows for quick identification of the correct bit and ensures that bits are returned to their proper place, maintaining the order of the set. A well-designed case will often have multiple layers or fold-out panels that present the bits for easy access. Spending a little extra for a set with a robust, well-marked case pays dividends in saved time and preserved tool life.

Left-Handed Drill Bits: The Specialty Tool for Extraction

While not typically included in standard sets, it is worth mentioning a specialty tool that every mechanic and fabricator should be aware of: the left-handed drill bit. These bits are identical to standard bits in every way except one—the flutes are ground in the opposite direction, and they are designed to cut when the drill is running in reverse.

Their primary and most celebrated use is for extracting broken bolts and screws. When a bolt snaps off flush with a surface, the first step in removal is to drill a hole in its center for a screw extractor. By using a left-handed drill bit for this task, the cutting action itself applies a counter-clockwise (loosening) torque to the broken fastener. In many cases, as the bit begins to bite, this torque is enough to catch the broken piece and back it out of the hole, eliminating the need for an extractor altogether. Having a small set of left-handed bits on hand can turn a frustrating, time-consuming repair into a quick and simple fix. They are a problem-solver of the highest order and a worthy addition to any comprehensive drilling toolkit.

Check 5: Aligning Your Choice with Application and Technique

The final and most practical check involves synthesizing all prior knowledge—material, coating, and geometry—and applying it to the specific task at hand. A drill bit is only "best" in the context of a particular job. The most advanced solid carbide bit is the wrong choice for drilling wood, and a basic HSS bit is destined for failure against hardened tool steel. Success in metal drilling is a triad of the right tool, the right material, and the right technique. This section will bridge the gap between tool selection and practical application, providing guidance on how to approach different metals and emphasizing the critical role of speed, feed pressure, and lubrication.

Drilling Soft Metals: Aluminum, Copper, and Brass

Soft, non-ferrous metals like aluminum, copper, and brass present their own unique challenges. They are not hard, so they do not require extreme heat resistance from the bit. A standard, uncoated HSS bit is often the ideal choice. In fact, some very slick coatings can be a disadvantage here. The primary difficulty with these materials is their "gummy" nature. They tend to produce long, continuous chips that can clog flutes, and the material can weld itself to the cutting edge, forming a "built-up edge" that ruins the hole's finish and accuracy.

Technique is paramount. A fast spiral drill bit (with a high helix angle) can be beneficial for aggressively pulling the stringy chips out of the hole. The most important consideration, however, is speed and lubrication. These metals should be drilled at relatively high speeds compared to steel. A proper cutting fluid is also highly recommended. For aluminum, a specialized lubricant like kerosene or a dedicated aluminum cutting fluid is best, as it prevents the material from sticking to the bit. For brass, which produces small, brittle chips, drilling can often be done dry, but a lubricant will always improve the surface finish. A light touch is needed; forcing the drill can cause the bit to "grab" and jam, especially as it breaks through the other side of the workpiece.

Tackling Mild Steel and Structural Steel

Mild steel and structural steel are the most common materials in general fabrication. They represent a step up in hardness from aluminum but are still well within the capabilities of standard tooling. A good quality HSS bit will perform adequately, especially for occasional use. However, for anyone doing a significant amount of steel drilling, this is where coatings begin to show their true value. A TiN-coated HSS bit will last significantly longer and cut more smoothly than its uncoated counterpart. For more demanding work or for longer tool life, an M35 cobalt bit is an excellent investment.

Heat management is the key to success when drilling steel. Steel is a tougher material and a poorer thermal conductor than aluminum, meaning heat builds up at the drill tip more quickly. This necessitates a reduction in drilling speed. A common mistake is to run the drill too fast, which generates excessive heat, rapidly dulls the cutting edge (visible as the corners of the cutting lips rounding over), and can even burn the bit, turning it blue or black. Always use a cutting fluid or oil. The fluid serves two purposes: it cools the bit and the workpiece, and it lubricates the cutting action, reducing friction and aiding in chip removal. Consistent pressure and a steady feed rate will produce a clean, continuous chip, which is a sign of an efficient cutting operation.

Conquering Hardened Steel and Stainless Steel

This is where professional-grade tooling becomes a necessity, not a luxury. Materials like stainless steel, tool steel, and other hardened alloys are defined by their toughness and abrasion resistance. Stainless steel, in particular, has a nasty habit of "work hardening." As you drill it, the material at the point of the cut becomes harder in response to the heat and pressure. If your drill bit stops cutting and starts rubbing, even for a moment, it can create a hardened layer that is nearly impossible for the bit to re-engage and cut through.

To combat these challenges, you need a bit with exceptional hot hardness and abrasion resistance. An M35 (5% cobalt) bit is the minimum requirement, but an M42 (8% cobalt) bit is the superior choice. The cobalt alloy allows the cutting edge to remain hard even when glowing red-hot. For the utmost performance, a cobalt bit with a TiAlN coating is the state-of-the-art solution. The TiAlN coating forms a protective aluminum oxide layer that thrives in the high-heat environment created by drilling these materials.

Technique is absolutely non-negotiable here. Slow speed and high pressure are the rules. You must run the drill at a fraction of the speed you would use for mild steel. The goal is to create a thick, continuous chip, which indicates that you are shearing the metal, not just creating frictional heat. The high pressure is needed to keep the cutting edge engaged and prevent it from rubbing, which would cause work hardening. A steady, uninterrupted feed is vital. Do not "peck" at the hole unless it is very deep and you need to clear chips. And, of course, use a high-quality, sulfurized cutting oil generously and continuously to cool the operation and flush away chips. Drilling hardened steel is a deliberate, methodical process, and the right bit is only half the battle.

The Role of Speed, Feed, and Lubrication

It is impossible to overstate the importance of the relationship between rotational speed (RPM), feed rate (how fast you push the drill), and lubrication. Many more drill bits are destroyed by improper technique than by simple wear and tear. The fundamental principle is this: the harder the material, the slower the speed.

Think of it as a budget of energy. At a high RPM, you are putting a lot of energy into the cut very quickly. For a soft material that shears easily, this is efficient. For a hard material, this rapid energy input manifests almost entirely as heat, because the material resists being sheared. This heat is the enemy; it softens the bit's cutting edge and leads to failure. By slowing the speed, you give the cutting edge time to do its job—to get under the material and lift a chip, carrying heat away with it.

The feed rate must be matched to the speed. Too little pressure causes the bit to rub instead of cut. Too much pressure can overwhelm the cutting edge and cause the bit to chip or break. The goal is to apply enough firm, consistent pressure to produce a good chip. The sound and feel of the drill are your best guides. A smooth cutting sound and the production of two continuous, curling chips (from the two cutting lips) is the sign of a healthy cut. A high-pitched squeal is a sign of excessive speed and rubbing.

Lubrication, or cutting fluid, is the third part of this equation. It is not optional when drilling most metals. It dramatically reduces friction, which in turn reduces the heat generated. It cools the cutting edge, preserving its hardness. It also acts as a flushing agent, helping to wash chips out of the flutes and away from the cutting zone. The right choice of fluid—from light oil to heavy sulfurized oil to specialized waxes—can make a dramatic difference in tool life and hole quality. Mastering the interplay of speed, feed, and fluid is what separates the novice from the expert and is the final key to unlocking the full potential of the best drill bit set for metal. Knowing the history and mission of a tool company, such as the one detailed on this about us page, can also provide confidence in the quality and engineering behind the products.

Frequently Asked Questions (FAQ)

What is the difference between M35 and M42 cobalt?

M35 cobalt bits contain 5% cobalt in the HSS alloy, while M42 bits contain 8%. The higher cobalt content in M42 makes it harder and provides superior "hot hardness," meaning it retains its strength at higher temperatures. This makes M42 the preferred choice for extremely hard or abrasive materials like tool steel or Inconel, while M35 is an excellent, more cost-effective choice for general stainless steel and other tough alloy drilling.

Can I sharpen cobalt or titanium-coated drill bits?

Cobalt bits can be sharpened, as the cobalt is part of the entire steel alloy. However, it requires a specialized grinding wheel (such as a silicon carbide or CBN wheel) and a jig to correctly replicate the point angle and split point geometry. Sharpening a coated bit (like TiN) will remove the coating from the cutting edge, and with it, the benefits of increased hardness and lubricity. The bit will still function as a standard bit of its base material (e.g., HSS) after sharpening.

Is it necessary to use cutting fluid when drilling metal?

For almost all metal drilling, yes. Cutting fluid, or oil, serves three critical functions: it lubricates the cut to reduce friction, it cools the drill bit to prevent it from losing its hardness, and it helps flush chips out of the hole. The only common exception is cast iron, which is often drilled dry as its graphite content acts as a natural lubricant. Using the wrong speed is the fastest way to ruin a bit, but neglecting to use fluid is a close second.

Why do my drill bits break when drilling hard metal?

Breakage in hard metal is usually due to a few factors. It can be caused by using a bit that is too brittle for the application (like using a carbide bit in a wobbly hand drill), excessive feed pressure that overloads the bit, or a bit jamming due to inefficient chip evacuation. Another common cause is work hardening—if you let the bit spin without cutting, it hardens the surface of the metal, and when you reapply pressure, the shock can fracture the bit. Use slow speeds, firm and steady pressure, and lots of cutting fluid.

What does "HSS" stand for and is it good enough for metal?

HSS stands for High-Speed Steel. It is an alloy specifically designed to cut materials at high speeds by resisting the softening effect of the heat generated by friction. HSS is absolutely good enough for many metals and is the standard for general-purpose drilling in materials like aluminum, copper, brass, and mild steel. It is only when you move to harder materials like stainless steel or hardened alloys that superior materials like cobalt become necessary.

How can I tell if a drill bit is dull?

There are several signs. A dull bit will require significantly more force to cut. Instead of producing clean, curling chips, it will create dust or small, flaky chips. The drill may squeal loudly as the bit rubs instead of shearing the material. Visually inspect the cutting lips at the tip; if the sharp corners appear rounded over or you can see small, shiny flat spots along the edge, the bit is dull and needs to be replaced or sharpened.

What is the best drill bit set for metal for a beginner?

A beginner should start with a quality HSS set that includes a TiN (Titanium Nitride) coating. A 29-piece fractional set (1/16" to 1/2" by 64ths) with a 135-degree split point offers tremendous versatility. This combination provides good durability, covers a vast range of common sizes, and the split point makes it much easier to start holes accurately without the bit "walking." This type of set is cost-effective and capable of handling everything from wood and plastic to aluminum and mild steel, allowing a beginner to learn proper technique before investing in more specialized cobalt sets.

Conclusion

The pursuit of the best drill bit set for metal concludes not with a single product recommendation, but with the cultivation of a discerning capability. We have journeyed through the foundational structure of the tools, from the atomic makeup of their core materials—HSS, cobalt, and carbide—to the functional elegance of their surface coatings. We have examined the critical influence of geometry, appreciating how a 135-degree split point can ensure precision and how flute design dictates the efficiency of the cut. The inquiry extended to the practical considerations of the set as a system, weighing the merits of a comprehensive index against the protective necessity of a durable case.

Ultimately, the selection process is an act of aligning these technical attributes with the specific demands of the task. The challenge presented by a sheet of aluminum is fundamentally different from that of a plate of hardened steel, and our choice of tool must reflect an understanding of that difference. The principles of proper technique—the methodical application of correct speeds, feeds, and lubrication—emerge not as afterthoughts, but as co-equal partners to the hardware itself. A craftsman armed with this knowledge no longer sees a wall of assorted drill bits but a palette of specific solutions. The choice ceases to be a guess and becomes a deliberate, informed decision, ensuring that every hole drilled is not just a void in a piece of metal, but a small testament to precision, efficiency, and mastery of the craft.

References

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