Material Selection for Drill Bits: When to Upgrade from a Generic Set

Walk into most job shops running 1 to 3 machines and you'll find a mix of drill bits that accumulated over years: some name-brand HSS in a roll pouch, a few cobalt bits someone bought for a stainless job, a broken set of TiN-coated bits from a home improvement store, and a handful of odds and ends. Nobody sat down and made a tooling strategy. Bits got bought when something stopped working.

This post is for shops that want to actually think through it — not to build a dissertation on metallurgy, but to have a clear, usable decision process.

Start Here: Standard HSS Is Good Enough More Often Than You Think

Plain high-speed steel — M2 or equivalent — is the correct answer for a large percentage of drilling work. If you're drilling mild steel (1018, 1020, A36), aluminum, soft cast iron, wood, or plastic at moderate speeds with good cutting fluid, a quality HSS jobber drill is not holding you back. Don't over-complicate it.

The key word is "quality." There's an enormous difference between name-brand American or German HSS and the import drills that come in 115-piece sets for $19. Both are labeled HSS. They are not the same thing. The cheap imports are often undertempered, ground inconsistently, and wear out several times faster. If your current experience with HSS is frustrating, the answer might not be cobalt — it might be buying Precision Twist, Norseman, Cleveland, or Chicago-Latrobe instead of whatever came in a plastic case.

Buy quality HSS first. Run it correctly. That fixes most problems.

When to Step Up to M42 Cobalt

Cobalt HSS — M42 grade, which is 8% cobalt — is the right upgrade for specific situations. The cobalt content raises the red hardness of the steel, meaning it holds its edge better at elevated temperatures. That matters in materials that generate a lot of heat or work-harden at the cutting zone.

Upgrade to cobalt when you're regularly drilling:

• Stainless steel (300 series especially). 304 and 316 work-harden rapidly. A standard HSS bit dulls faster in stainless than almost anything else. Cobalt handles it.
• Tool steel or hardened material under 45 Rc. Above 45 Rc you're generally looking at carbide, but in the 35–45 range, cobalt gives you a meaningful advantage.
• Inconel, Hastelloy, or other high-temp alloys. These are nasty on tooling. Cobalt is the minimum — some shops use carbide for production quantities.
• Any situation where you're consistently burning through HSS drills faster than expected. Cobalt pays for itself quickly if you're going through HSS bits at an unusual rate.

Cobalt costs roughly 2–3x what quality HSS costs for the same size. In the applications above, that's easily justified by the extended tool life. In mild steel and aluminum, you won't notice the difference — don't spend extra for it there.

On Coatings: TiN, TiAlN, and the Rest

Coatings are often oversold to job shops. Here's the practical reality:

TiN (Titanium Nitride) — the gold-colored coating you see on consumer drill sets — does add some surface hardness and reduces friction. On name-brand HSS, it extends tool life modestly in mild steel applications. On cheap HSS, it doesn't fix the underlying problem. If you see TiN on a $25 drill set, the coating is marketing, not an engineering upgrade.

TiAlN (Titanium Aluminum Nitride) — the darker, more purplish coating — is a real performance upgrade for high-speed, dry cutting applications. It has much better thermal stability than TiN and works well in hardened materials at elevated speeds. This is a production coating for production conditions. If you're running a CNC at full speed through hardened die steel without flood coolant, TiAlN matters. For general job shop work with coolant, it's usually not the bottleneck.

Black oxide — not really a coating, more of a surface treatment — provides mild corrosion resistance and slight lubricity. Fine on HSS, but don't confuse it with an actual performance coating.

The practical rule: coatings matter when heat and surface speed are the limiting factor. If you're drilling in a knee mill with flood coolant at moderate speeds, you're not at the limit where coatings change outcomes. If you're drilling dry at high surface footage in a CNC spindle, coatings start to pay off.

The Decision Tree

For a 1–3 operator job shop, here's how to actually make the call:

Step 1. Is the current tooling quality name-brand HSS? If no, fix that first before upgrading material.

Step 2. What material are you drilling? Mild steel, aluminum, soft cast iron, plastic → quality HSS is correct. Stainless, tool steel 35–45 Rc, high-temp alloys → go to cobalt.

Step 3. Are you running dry at high speeds in hardened material? → Consider TiAlN coated cobalt. Running with flood coolant at conventional speeds? → Skip the coating, it won't change outcomes meaningfully.

Step 4. Is this production volume (hundreds of holes per week in the same material) or job shop variety (different materials daily)? Production → optimize for that specific material. Variety → quality HSS, cobalt for stainless, keep inventory simple.

The Maintenance Factor

None of this matters if you're running worn drills. A worn M42 cobalt bit drills worse than a fresh M2 HSS bit. The biggest lever in any shop's drill tooling performance is consistently resharpening bits before they're completely shot — not buying increasingly exotic tooling to compensate for running things dull.

If you're not currently resharpening your HSS and cobalt drills, start there. It's the highest-ROI change most shops can make to their tooling costs.