Choosing the right drill bits for metal means matching the bit material to the metal you are cutting. The same steel that drills mild steel with ease can struggle in hardened stainless, so a little knowledge goes a long way.
Know Your Bit Materials
Three bit materials cover almost all metal drilling. High-speed steel (HSS) is the affordable all-rounder for mild steel, aluminium and brass. Cobalt steel adds heat resistance that lets it cut tough, hard and abrasive metals like stainless. Solid carbide is the hardest and holds an edge at the highest temperatures, ideal for hardened steel and production work where longevity matters most. Our materials and applications guide goes deeper on each.
Match the Bit to the Metal
- Mild steel: Quality HSS or cobalt with cutting oil.
- Stainless steel: Cobalt is the go-to for its heat resistance; drill slow with firm pressure.
- Aluminium: HSS cuts freely; use lubricant to stop the bit clogging.
- Cast iron: HSS or carbide, drilled dry since cast iron is self-lubricating.
- Hardened steel: Solid carbide or specialty bits designed for the hardness.
Speed and Feed Basics
The harder or thicker the metal, the slower the speed. Large bits and tough metals want low RPM and steady feed, while smaller bits in soft metal can run faster. The goal is a continuous chip curling off the cutting edge; dust and squealing mean you are rubbing, generating heat, and dulling the bit. Firm pressure keeps the edge cutting.
Lubrication and Heat
Heat is the enemy of any metal bit. Cutting oil on steel and stainless carries heat away and improves finish and bit life. Aluminium benefits from a lighter lubricant, while cast iron is best drilled dry. Peck drilling deeper holes, pulling out to clear chips, prevents heat buildup and binding.
Why Bit Quality Matters
Cheap bits lose their edge fast in metal, wander off centre and overheat. A precisely ground, American-made HSS, cobalt or carbide bit starts on the mark, cuts cleaner, and lasts far longer, which makes it cheaper per hole in the end.