Drilling into metal looks straightforward, but the results depend heavily on using the right drill bit. Metal behaves very differently from wood or plastic, and the wrong bit can overheat, dull quickly, or wander off target before it ever breaks through. For most DIY users, understanding the basics of metal drill bits prevents frustration and avoids damaging both tools and materials.
This guide explains which drill bit to use for metal, how sizing works, and what changes based on material type. It also covers common mistakes and practical questions that come up during real-world projects, from drilling thin sheet metal to thicker steel brackets.
Quick Answer
For most DIY metal drilling, a high-speed steel (HSS) drill bit is the standard choice. Cobalt HSS bits are preferred for harder metals, while titanium-coated bits improve durability for repeated use. Standard twist drill bits with a 118-degree tip angle work for most household metal projects.
This rule changes when working with very hard metals, thin sheet metal, or precision holes. Stainless steel, hardened steel, and cast iron often require cobalt bits and slower drilling speeds. Thin metal benefits from step bits or pilot holes to reduce grabbing and distortion.
How Drill Bit Size Works
Drill bit size refers to the diameter of the hole it creates, and accuracy matters more with metal than softer materials. Metal does not compress around the bit, so the hole size is determined almost entirely by the bit’s actual diameter and how steadily it’s drilled. Fractional, metric, and numbered drill bits are all commonly used for metal work, depending on the application.
For most DIY projects, fractional sizes are sufficient, especially when drilling holes for bolts, screws, or rivets. Metric bits are often required for imported hardware or machinery components, where tolerances are tighter. Numbered bits fall between fractional sizes and are typically used when precise hole sizing is important, such as tapping threads.
A common approach when drilling metal is to start with a smaller pilot hole, then enlarge it to the final size. This reduces stress on the bit, improves accuracy, and helps prevent the bit from wandering across the surface. Pilot holes are especially useful when drilling larger diameters or working with harder metals.
Best Drill Bit Type for This Job
High-speed steel drill bits are the baseline option for drilling metal. They are affordable, widely available, and capable of handling aluminum, mild steel, brass, and copper. For occasional metal drilling, a quality HSS bit set is usually sufficient and offers good balance between cost and performance.
Cobalt drill bits are a step up and are designed for tougher materials. They contain a higher percentage of cobalt alloyed throughout the bit, not just coated on the surface. This allows them to maintain hardness at higher temperatures, which is important when drilling stainless steel or thicker steel stock.
Titanium-coated drill bits are another common option, though they are often misunderstood. The titanium nitride coating reduces friction and extends edge life, but once the coating wears off, the bit performs like standard HSS. For light to moderate DIY use, they offer longer life than plain HSS but are not a replacement for cobalt when drilling hard metals.
Material Considerations
Different metals require different approaches, even when using the correct drill bit. Aluminum is soft and easy to drill but tends to grab the bit if speed is too high or pressure is uneven. Using moderate speed and steady pressure produces clean holes and prevents clogging.
Mild steel is one of the most common materials DIY users drill into. It requires slower speeds than aluminum and benefits from cutting oil to manage heat. Without lubrication, bits dull quickly and may discolor from overheating, which shortens their usable life.
Stainless steel and hardened steel demand more care. These materials work-harden if drilled incorrectly, meaning the surface becomes harder as it heats up. Slow speeds, firm pressure, and cobalt bits help prevent this issue. Cast iron is brittle and usually drilled dry, producing powdery chips rather than long shavings, but it still benefits from controlled speed and pressure.
Common Mistakes to Avoid
One frequent mistake is drilling metal at the same speed used for wood. High speeds generate excess heat, dull bits quickly, and can cause the bit to lose its temper. Slowing the drill and letting the bit cut steadily produces better results and extends tool life.
Another common issue is failing to secure the workpiece. Metal can spin dangerously if the bit catches, especially with thin stock. Clamping the material prevents movement and improves hole accuracy, while also reducing the risk of injury.
Using dull or damaged bits is also a problem. Metal exposes weaknesses in cutting edges quickly, and a bit that struggles to cut should be replaced or sharpened. Forcing a dull bit leads to poor holes, excessive heat, and unnecessary wear on the drill itself.
Frequently Asked Questions
Can wood drill bits be used on metal?
Wood drill bits are not designed for metal and typically have a brad point that prevents proper cutting. In practice, they dull quickly and perform poorly, even on thin metal. Standard twist drill bits are a better choice.
Do I need cutting oil when drilling metal?
Cutting oil is recommended for most metals, especially steel and stainless steel. It reduces heat, improves chip removal, and extends bit life. Aluminum may require less lubrication, but oil still improves results.
Why does my drill bit squeal or smoke?
Squealing or smoke usually indicates excessive speed or lack of lubrication. Slowing down and applying cutting oil typically resolves the issue. Continued drilling under these conditions can permanently damage the bit.
What tip angle works best for metal?
A 118-degree tip angle is standard for general metal drilling and works well for most DIY projects. Harder metals may benefit from a 135-degree split point, which reduces walking and requires less pressure.
Should I drill metal in reverse first to mark the spot?
Running the bit briefly in reverse can help mark the surface and reduce wandering on smooth metal. However, center punching the location is a more reliable method for accurate hole placement.
Final Thoughts
Choosing the right drill bit for metal comes down to matching the bit material and technique to the type of metal being drilled. High-speed steel bits handle most household projects, while cobalt bits are better suited for harder materials and repeated use. With proper speed, lubrication, and preparation, drilling metal becomes a controlled and predictable task rather than a frustrating one.