Exotic alloys are where machinists earn their pay. Titanium, Inconel, and hardened steel are all in widespread use — aerospace, defense, oil and gas, medical equipment — and all three are genuinely difficult to drill compared to mild steel or aluminum. But "difficult" doesn't mean "impossible with HSS." It means the margin for error is narrow and the technique has to be right.
Titanium has very low thermal conductivity. In steel and aluminum, heat generated at the cutting edge conducts away into the workpiece and the chip. In titanium, it doesn't — it stays concentrated at the tool tip. This heats the cutting edge above its tempering point fast, especially at normal drilling speeds. Titanium also has a strong tendency to weld to cutting tools (built-up edge), which ruins geometry instantly. Chips are often long and stringy, creating chip evacuation problems in deep holes.
Inconel and nickel superalloys work-harden rapidly. The act of cutting Inconel causes the freshly-cut surface to harden. This means a dull tool — or a tool spinning too fast and rubbing instead of cutting — is cutting into a harder material than it started with. The combination of work-hardening and high cutting forces is what makes Inconel the reputation it has.
Hardened steel (above ~45 HRC) is hard in the conventional sense. Anything above 55 HRC is approaching the hardness of HSS itself, which makes conventional drilling essentially impossible. Between 45 and 55 HRC, HSS can still cut but only with very low speeds, sharp geometry, and good cooling.
Yes, with significant conditions. HSS is a slower, more forgiving tool than carbide, which is both its weakness and its advantage in some exotic material applications. Carbide is brittle — it wants rigid setups, consistent cutting conditions, and good chip evacuation. HSS bends before it breaks, which can be an advantage on light machines or when setup rigidity is questionable.
Slow down. A lot. 15–25 SFM in titanium is a common starting point. For Inconel, 15–20 SFM. For hardened steel (45–50 HRC), 10–15 SFM. These speeds feel uncomfortably slow on a drill press — that's intentional.
Keep consistent feed pressure. In work-hardening materials especially, stopping the feed — even momentarily — allows the drill point to rub instead of cut. Maintain forward feed pressure. Don't let the bit dwell.
Sharp geometry, always. A worn drill is a heat generator. In exotic materials, heat is already the enemy. A dull drill in Inconel isn't just inefficient — it'll be scrap in seconds. Inspect cutting edges before every hole in difficult material.
In mild steel, cutting fluid is helpful. In exotic materials, it's the difference between cutting and destroying. Cutting fluid does three things: reduces heat at the cutting zone, lubricates the chip-edge interface to reduce built-up edge (critical in titanium), and helps flush chips before they re-cut.
For titanium: sulfurized cutting oil, neat oil, or a quality soluble oil at high concentration. Flood coolant is better than brush application — you need volume, not just a film.
For Inconel: sulfurized oil or EP (extreme pressure) cutting fluid. More pressure than titanium requires. Flood coolant if available.
For hardened steel: sulfurized cutting oil, applied generously and continuously. Do not use water-soluble cutting fluid at low concentration in these materials. Go full-strength oil or high-concentration soluble.
All three materials benefit from peck drilling — titanium and Inconel especially. For titanium: full peck cycles, 0.5x diameter increments or less. Retract fully, brush or drip fresh cutting oil into the hole, re-enter slowly. For Inconel: same approach. Short increments, full retract, fresh fluid on each cycle. In Inconel, a packed chip that gets re-cut is a disaster — it work-hardens on contact. For hardened steel: peck to manage heat buildup. Short increments, retract fully, let the part and bit cool slightly between cycles.
For titanium: a 135° split-point geometry is preferred over a 118° conventional point. The split point reduces thrust load at entry and improves centering.
For Inconel: same preference for 135° split point. Some machinists prefer a slightly lower relief angle (8–10° rather than standard 12–15°) to give the edge more support under high cutting forces.
For hardened steel: standard 118° geometry can work at very low speeds. TiAlN-coated HSS or cobalt HSS handles the heat better than uncoated standard HSS.
Switch to carbide when: material hardness is above 50 HRC (HSS is fighting a losing battle), you have rigid CNC setup with flood coolant, production volume justifies carbide's higher upfront cost, or you've burned through multiple HSS drills on the same job and the holes still aren't acceptable.
HSS is the right call when: you have a light manual machine where carbide's brittleness is a liability, you need a handful of holes in a difficult material and don't have carbide on hand, or setup rigidity is questionable (a rigid setup is mandatory for carbide).
In exotic materials, drill bit wear is fast. Watch for: increased feed force for the same material and depth, squealing or chatter (clearance faces rubbing), color change in chips (in titanium especially, blue-gray chips mean the cutting zone is getting too hot), chip character change (chips getting shorter and more granular), and slight oversize on hole diameter.
When you see any of these, stop. A dull drill in exotic material doesn't slowly get worse — it fails suddenly. Better to pull the bit and inspect than to snap it off in a titanium aerospace part.
If you've been running exotic materials and your HSS drills are looking rough, send them in. We regrind the lips to correct geometry with proper clearance angles, and return them sharp. A sharp, correctly-ground drill performs better in difficult materials than a dull one, every time.
SEND US YOUR DRILLS →