Titanium sits at around 36 HRC in typical aerospace alloys — softer than hardened steel by a wide margin. And yet it chews through HSS drill bits at a rate that surprises machinists who are used to working steel. If you have ever run a production job in Ti-6Al-4V and watched a freshly sharpened bit go dull in under fifty holes, you know the frustration. The problem is not hardness. It is a combination of properties that HSS tooling handles poorly, and understanding the mechanism is the first step to managing it.
Work Hardening: The Core Problem
Titanium work-hardens aggressively when it is machined poorly. Run too slow, let the tool rub instead of cut, or let the feed drop for even a second, and the material directly under the cutting edge densifies and hardens. On the next revolution the edge is attacking a harder surface than it was a moment ago. That layer compounds. The practical result is that a titanium hole that starts easy gets progressively harder to drill if your parameters are drifting or your edge is degrading.
This is the failure mode most machinists do not see clearly. They think the bit went dull from normal abrasion. In some cases it did. But in titanium, a degrading edge creates the conditions for faster degradation. A bit that is 70% sharp in titanium does not perform at 70% — it performs worse, and it deteriorates faster than a fully sharp bit would.
The fix is to keep your edges sharp and your feeds consistent. A dull bit in titanium is not just a slower bit — it is a bit that is actively making itself worse.
Heat: Where HSS Loses
Titanium has low thermal conductivity — roughly one-sixth that of steel. In steel, heat generated at the cutting zone moves into the chip and into the workpiece. Titanium holds the heat at the tip. The cutting edge of your HSS drill is sitting in a hot zone that does not dissipate well, and HSS loses its hardness above about 600°C. Once that edge softens even slightly, wear accelerates rapidly.
This is why carbide is the preferred choice for high-volume titanium work. But carbide is not always the right answer for every shop. Small diameter drills in carbide are fragile and expensive. Job shops running occasional titanium parts have legitimate reasons to use HSS. The key is managing heat through process, not just through tooling upgrades.
Speeds, Feeds, and Coolant — The Actual Numbers
For HSS in titanium, surface speed should be conservative: 15 to 25 SFM depending on alloy and diameter. Ti-6Al-4V runs at the lower end of that range. Smaller diameters can push toward the upper end because the absolute heat input is lower. Do the RPM math for your diameter — do not guess.
Feed rate matters more in titanium than in most materials. You need the edge to be cutting, not rubbing. A common mistake is running feeds that are too light, thinking that will protect the bit. In titanium it does the opposite. Use a feed rate that produces a real chip. For a 3/8" HSS bit in Ti-6Al-4V, something in the 0.004 to 0.006 IPR range is a reasonable starting point. Dial it in from there based on chip color and sound.
Coolant is not optional. Flood coolant directed at the cutting zone is the baseline. Soluble oil works. Straight cutting oil is better if your setup allows it. The goal is not just cooling — it is also lubrication to reduce the tendency of titanium to gall and weld itself to the cutting edge. Titanium has a strong affinity for HSS tool steel at elevated temperatures. Built-up edge from titanium welding to your drill is a real failure mode, and it looks like edge wear when you examine the bit later.
Peck Drilling — Do Not Skip It
Peck drilling in titanium is not optional for anything beyond shallow holes. The chip in titanium is stringy and tough. It does not break on its own the way steel chips do. If you let that chip pack in the flute, you get friction heat, chip welding, and in small diameters, bit breakage.
Peck depth depends on diameter, but a general rule is one diameter per peck, retracting fully to clear chips on each cycle. For deep holes — anything over 4x diameter — go more aggressive with the peck frequency. The time lost to peck cycling is always less than the time lost to a broken bit or a ruined hole.
Knowing When to Resharpen vs. Replace
In titanium, the resharpen window is shorter than in steel. A bit that is noticeably dull — the kind of dull you would push through another hundred holes in mild steel — is already causing problems in titanium. Cutting force is up, heat is up, and work hardening of the workpiece surface is happening. Sharpen earlier than you think you need to.
The signs to watch in titanium: chip color going gold or blue (heat), thrust load increasing noticeably, squealing or chatter that was not there at the start of the job, holes starting to run slightly oversized. Any one of these is a signal. In titanium, do not wait for the full constellation of symptoms.
Whether a bit is worth resharpening depends on web thickness. Titanium wear concentrates at the cutting lips and at the outer corners. If you have good lip length remaining and the web has not been thinned too many times, a fresh grind will restore full performance. A properly resharpened HSS bit with a split-point or web-thinned geometry cuts significantly better in titanium than a worn-out factory bit — the split point reduces thrust and the tendency for the chisel edge to rub and harden the material surface.
If you are running regular titanium jobs and going through bits at a rate that hurts, batch resharpening is worth looking at seriously. MachinistPost's mail-in resharpening service is a workable option for shops that do not want to invest in grinding equipment — send a batch, get consistent geometry back. The math on regrind cost vs. new bit cost in titanium almost always favors resharpening unless the bit is physically too short to run safely.
Bottom Line
Titanium drilling is a process discipline problem more than a tooling problem. Sharp edges, consistent feeds, real coolant, and peck cycling cover most of the failure modes. The shops that chew through bits in titanium are usually missing at least one of those four. Get all four right and your HSS bit life in titanium becomes predictable and manageable.