Titanium alloys — Ti-6Al-4V being the most common, along with CP titanium, Ti-3Al-2.5V, and specialty grades — share a set of properties that make them challenging to machine with any cutting tool. Understanding the specific mechanisms helps explain every rule that follows.
Low thermal conductivity. Titanium conducts heat poorly compared to steel or aluminum. Heat generated at the cutting interface doesn't dissipate into the workpiece or the chip — it concentrates at the cutting edge. This is the root cause of most titanium drilling failure. The edge simply gets hot and softens faster than it would in any other common metal.
High work-hardening rate. Titanium work-hardens rapidly under compressive stress — including the pressure from a chisel edge pushing and rubbing rather than cutting. A thick web, a dull drill, or a rubbing flank all harden the surface ahead of the cutting edge, creating progressively harder material with each pass. This accelerates wear in a self-reinforcing cycle.
Chemical affinity for tool materials. Titanium is chemically reactive at elevated temperatures and has a tendency to form alloys with HSS and carbide at cutting temperatures. This causes galling — material from the workpiece welds to the cutting edge — which disrupts geometry and accelerates failure. This is also why titanium drilling requires sharp edges and positive cutting action rather than rubbing.
Solid carbide is theoretically superior to HSS in titanium — harder, more heat-resistant, and capable of higher speeds. But solid carbide doesn't tolerate the real-world conditions of job shop titanium drilling: fixturing that deflects slightly, parts that aren't perfectly secure, drills that occasionally catch on a burr or a hardened surface spot.
M42 cobalt HSS has roughly 8% cobalt content, which improves red hardness — the ability to maintain hardness at elevated temperatures. It reaches around 66 HRC vs. standard M2 HSS at 63 HRC. In titanium drilling at correct SFM, M42 cobalt outlasts standard HSS by a significant margin and handles the occasional overload that would fracture carbide.
For job shops doing occasional or moderate titanium work — not dedicated production runs — M42 cobalt is the practical tool. It's resharpable, forgiving of imperfect setup, and available at reasonable cost compared to solid carbide.
Titanium drilling geometry differs from steel in several ways:
135° point angle. The flatter geometry reduces chisel pressure on the work-hardening surface. In titanium specifically, minimizing the time and pressure the chisel edge spends compressing material before the cutting lips engage is critical.
Split-point or heavily thinned web. Same reason — split-point geometry nearly eliminates the chisel edge. This is particularly valuable in titanium because even a short chisel rubbing period on the surface causes hardening that the cutting lips then have to fight through.
Higher relief angle. Titanium springs back after cutting — the elastic recovery is higher than steel. A standard relief angle can allow the flank to rub the freshly cut surface, which generates heat and work-hardens the newly exposed material. Increased relief (2–4° above standard) keeps the flank clear.
Sharp cutting edges — no edge prep. Unlike carbide in titanium, which sometimes benefits from a slight honed edge to prevent chipping, HSS in titanium requires the sharpest possible edge. Any rounding of the cutting lip increases the rubbing component and accelerates heat buildup. Drill quality and sharpness matter more in titanium than in almost any other material.
Speed discipline is the single most important variable in titanium drilling survival.
Surface speed: 15–30 SFM for Ti-6Al-4V with HSS cobalt. This is dramatically lower than mild steel (70–100 SFM) or even stainless (30–50 SFM). The low speed is not optional — it's what keeps the tool-interface temperature below the point where HSS softens and galling begins. Running faster feels productive until the drill fails at hole 3 instead of hole 20.
Consistent feed. Titanium punishes rubbing. The drill must feed at a rate that keeps positive chip formation — actual cutting rather than burnishing. If you can't see chip curls or hear the characteristic cutting sound, you're rubbing. Increase feed before decreasing speed. Many titanium drilling failures come from too-light feed at too-low speed, not from aggressive parameters.
Flood coolant or cutting oil. Coolant in titanium serves two purposes: temperature reduction and lubrication to reduce galling. Sulfurized cutting oil or a high-quality sulfochlorinated cutting fluid works better than water-soluble coolant in titanium because of its film strength — it prevents the metal-to-metal contact that leads to galling better than emulsions do. If you're using water-soluble coolant, use high concentration (10:1 minimum) and apply consistently. Intermittent coolant application causes thermal shock and accelerates edge failure.
Peck drilling above about ¾" depth. In titanium, chips need to evacuate reliably. Packed chips in the flute create heat and can weld to the flute surface. Peck drilling — retracting the drill periodically to clear chips — is standard practice for anything deeper than 1.5× diameter in titanium alloys.
Titanium drilling demands sharper geometry than any other common material, which means the resharpen threshold comes sooner. Signs a titanium drill needs resharpening: increased thrust force, surface finish degrading on the bore wall, any squealing or rubbing sound during cutting, or visible edge rounding under 10x magnification.
When sending titanium drills for resharpening, specify the material. A resharpener who knows the application will grind appropriately high relief, specify split-point or aggressive web thinning, and ensure the cutting edge is polished rather than left with grinding marks that become stress risers. Geometry optimized for titanium — versus a generic steel-focused regrind — extends tool life significantly in subsequent use.
Also note web thickness on worn drills. Cobalt drills that have been through multiple resharpens in titanium work will have thickened webs that need thinning. Requesting web thinning along with the titanium material specification produces a drill that's better suited for the next run than a standard regrind would.
Mark titanium drills separately from general-use drills. Even a single titanium drilling job leaves edge wear patterns that differ from steel work, and mixing them back into the general pool means they'll get resharpened to steel geometry instead of titanium geometry.
Pilot holes in titanium are valuable for larger diameters. Above ⅜", a ¼" pilot reduces the contact area the final drill pushes through and cuts the total axial thrust required. The pilot also reduces the chance of drill wander, which is common in titanium without a center-punched start.
After any break or extended pause in the cut — retract fully, clear chips, re-apply coolant, and re-engage slowly. Re-entering a partial hole in titanium is one of the highest-risk moments in the operation. The drill is entering already-compressed material with whatever hardening the previous pass left behind.
Specify the material when you mail them in — we'll grind 135° split-point with high relief on the WinsloMatic, optimized for your next Ti run.
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