Drill Bits for Metal: What Actually Works
Metal drilling advice has gotten complicated with all the coatings, materials, and conflicting guidance flying around. As someone who started drilling metal with whatever wood bits were in the drawer, ruined several bits and a few workpieces in the process, and then actually learned the material science behind why certain bits work on certain metals, I learned everything there is to know about drill bits for metal. Today, I will share it all with you.
Why Metal Drilling Is Different
Wood drilling and metal drilling look similar but the physics are different in ways that matter. Wood is soft enough that moderate heat from the cutting edge doesn’t affect the bit’s hardness. Metal — especially steel — transfers heat into the bit rapidly and if the cutting edge gets hot enough it loses its temper, meaning the hardness that allows it to cut is permanently reduced. You can’t resharpen your way back from a bit that’s been overheated past its tempering temperature. That’s why bits marketed for wood drilling fail quickly on metal — they’re not formulated to handle the heat generated at the cutting edge against metal.
Twist Drill Bits: HSS vs. Cobalt
High-Speed Steel (HSS) twist bits are the baseline for metal drilling. HSS is formulated to retain hardness at temperatures that would soften ordinary steel, which is why it’s the standard for metal-working applications. For aluminum, brass, and mild steel — the metals most woodworkers and DIYers encounter — quality HSS bits work well when used correctly. The operative word is quality. Cheap import HSS bits are often poorly heat-treated and dull quickly; a set of Irwin or Bosch HSS bits costs more and lasts dramatically longer.
Cobalt drill bits are HSS with 5-8% cobalt added to the alloy, which raises the hot hardness significantly — the bit maintains its cutting edge at higher temperatures than standard HSS. That makes cobalt the right choice for harder metals: stainless steel, hardened steel, cast iron, and heat-resistant alloys. Cobalt bits are more brittle than standard HSS, which means they’re more prone to breaking if the drill catches or if you apply lateral pressure during drilling. Use a drill press rather than a hand drill when you can, and let the bit cut at its own rate rather than forcing it. That’s what makes cobalt bits endearing to machinists — they’re purpose-built for hard material and genuinely outperform everything else in that application.
Titanium Coating: What It Actually Does
Titanium-coated drill bits are standard HSS with a titanium nitride (TiN) coating applied to the surface. The coating reduces friction and increases surface hardness, which extends bit life compared to uncoated HSS. The limitation is that the benefit is in the coating, not the substrate — once the coating wears through from resharpening or extended use, you’re back to standard HSS performance. Titanium bits are the right choice if you’re buying a general-purpose set for occasional metal drilling and want longer service life without the cost of cobalt. For production metal work or drilling hard metals, cobalt is the better investment. Probably should have led with this: the titanium marketing is real but modest — it’s a meaningful improvement over bare HSS, not a replacement for cobalt.
Carbide-Tipped Bits
Solid carbide and carbide-tipped drill bits are the top tier for hardness and heat resistance. They cut harder materials than cobalt, last longer in production applications, and produce cleaner holes in abrasive materials. The trade-offs are significant: carbide is brittle — vibration or lateral force that a cobalt bit would survive will snap a carbide bit. They require a rigid, vibration-controlled setup (drill press or CNC, not a hand drill) and sharp, consistent technique. The cost is also much higher. For most shop metalwork, cobalt handles everything you’ll encounter. Carbide bits earn their place in specific production or machining contexts.
Point Geometry and Drill Bit Angles
The standard 118-degree point angle on general-purpose twist bits works for soft metals and most DIY applications. A 135-degree split point — flatter, with a secondary ground at the very tip — cuts its own starting point without center punching, reduces walking on smooth metal, and applies less thrust force during drilling. For drilling in a drill press with good workholding, either works. For hand drilling where maintaining position at the start of the hole is harder, the split point 135-degree geometry is noticeably better. I’m apparently someone who drilled many off-center holes before I understood why the 135-degree bits were worth the small premium, and they work for me while standard 118-degree bits never started as cleanly on smooth steel.
Lubrication: Not Optional
Cutting fluid or cutting oil during metal drilling isn’t optional — it’s what prevents the bit from overheating and extends bit life by a factor of several times. Apply cutting fluid to the drill point before starting and periodically during the cut. Tap Magic for steel and stainless, WD-40 for aluminum (aluminum-specific cutting fluid is better but WD-40 works acceptably). The cutting fluid does two things: it cools the cutting edge by absorbing and carrying away heat, and it lubricates the chip clearance in the flutes so chips evacuate cleanly rather than packing and adding friction. On blind holes especially, pull the bit out periodically to clear chips. Packed chips in a blind hole are a frequent cause of bit breakage and work-hardening of the hole wall.
Tips for Drilling Metal Effectively
Center punch before drilling — the divot keeps the bit from walking across smooth metal at the start of the cut. Start at lower speed and increase for softer metals; hard metals and larger diameters require lower speeds throughout. For holes larger than 3/8 inch, step drill from a smaller pilot size rather than trying to plunge a large bit directly — the required thrust force overloads most hand drills and the bit is more prone to walking and chattering. Secure the workpiece solidly; an unsecured metal workpiece that grabs the bit and spins is a serious safety hazard. Apply steady, moderate pressure — not aggressive force that generates heat, not so light that the bit rubs rather than cuts.
