Key takeaways
- If you’ve ever tried drilling into steel with a standard black oxide bit meant for wood, you know the result: a lot of heat, a screeching noise, and a hole that either doesn’t happen or ends up oversized and ragged.…
What's inside
If you’ve ever tried drilling into steel with a standard black oxide bit meant for wood, you know the result: a lot of heat, a screeching noise, and a hole that either doesn’t happen or ends up oversized and ragged. Metal needs a bit designed for the job, and which one depends more on what metal you’re cutting and how often you do it than on brand loyalty.
Bit materials: what actually matters
The material a drill bit is made from determines how much heat it can handle before it goes soft and dull. Heat is the enemy with metal drilling, not the metal itself.
High-speed steel (HSS) is the baseline for metalworking bits. It holds an edge at higher temperatures than carbon steel and resists the kind of rapid dulling you get from friction. A basic HSS bit set will get through mild steel, aluminum, brass, and sheet metal without drama, as long as you keep speeds reasonable and use a little cutting oil.
Cobalt bits (M35 or M42 grade, usually 5-8% cobalt content) are HSS with cobalt mixed in, which raises the heat tolerance further. These are the ones to reach for with stainless steel, cast iron, or anything hardened. They cost noticeably more than plain HSS, but they last longer in tough material and don’t anneal (soften) as easily if you push them a bit too hard.
Titanium-coated bits are HSS underneath with a thin titanium nitride coating. The coating reduces friction and adds surface hardness, which helps the bit stay sharp longer in general use. But the coating is only skin deep. Once you drill through it, which happens fast if you’re resharpening or working abrasive material, you’re back to bare HSS performance. Treat the coating as a bonus on a budget set, not a reason to pick a bit for stainless steel work.
Carbide bits are the extreme end: very hard, very heat resistant, and very brittle. They’re the right call for hardened steel or masonry-adjacent jobs, but they chip or snap if you flex them sideways or hit the material at an angle. Not a great fit for handheld drilling unless you’re experienced and the setup is rigid.
Quick comparison
| Bit type | Best for | Typical cost | Weak point |
|---|---|---|---|
| Black oxide / carbon steel | Wood, light plastic, occasional soft metal | Low | Dulls fast in metal, overheats quickly |
| High-speed steel (HSS) | Mild steel, aluminum, brass, general shop use | Low-Medium | Softens under sustained heat in hard alloys |
| Cobalt (M35/M42) | Stainless steel, cast iron, harder alloys | Medium-High | More brittle than plain HSS, costs more |
| Titanium-coated HSS | General use, slightly longer life than bare HSS | Low-Medium | Coating wears off, then it’s just HSS |
| Carbide | Hardened steel, masonry-adjacent material | High | Brittle, chips or snaps if flexed |
What to actually buy
For most home shops and DIY projects, a quality HSS drill bit set covers the vast majority of jobs: brackets, hinges, mild steel sheet, aluminum stock, the occasional bolt hole in a car part. These sets usually run from 1/16″ up to 1/2″ or so, which is the range you’ll use 95% of the time. There’s no need to spend extra on cobalt or carbide if you’re drilling mild steel a few times a year.
If stainless steel is a regular part of your work, cobalt is worth the upgrade. Stainless work-hardens as you cut it, meaning the material gets harder right at the point of contact if you hesitate or run too slow. A cobalt bit set handles that better and won’t dull after three holes the way a cheap HSS bit might.
For sheet metal specifically, a step bit (sometimes called a unibit) is worth having separately. It’s a cone-shaped bit with stepped diameters that drills clean, burr-free holes in thin material without grabbing and spinning the sheet. Standard twist bits tend to catch and tear thin stock, especially past 18 gauge.
Technique matters more than the bit
A good bit used wrong will still fail. A few things that cause more problems than people expect:
Speed: slower is almost always right for metal. A 1/2″ bit in steel should run at a few hundred RPM, not full trigger. High speed generates heat, and heat is what actually kills bits, not the hole count. If you see the tip glowing or the bit discoloring, you’re running too fast or pushing too hard without lubrication.
Cutting oil: a few drops of cutting oil (or even plain motor oil for home jobs) on the bit tip when drilling steel extends bit life dramatically and keeps the hole cleaner. Skip it on aluminum, which gums up with oil; a bit of WD-40 or going dry works better there.
Pilot holes: for anything over 1/4″ in steel, drill a smaller pilot hole first. It reduces the load on the bigger bit’s cutting edges and makes centering easier, since large bits wander on a flat surface without a starting point.
Pressure: push firmly and steadily, not in short hard bursts. Bits that chatter or bounce are usually underloaded (not enough downward pressure) rather than overloaded, which is the opposite of what people assume.
If you’re set up with the right bit, correct speed, and some lubrication, a basic corded drill will outdrill a cordless unit on tough metal jobs too, since it won’t bog down under sustained load the way battery torque can on long cuts.
