Titanium is the material that separates experienced deep hole drilling shops from the rest. I have drilled more titanium holes than I can count — here is what I have learned about making them consistently.
Every titanium alloy behaves differently. Get the parameters wrong on one alloy and you lose the tool, the part, or both. Get them right across the board and titanium becomes predictable.
I cover the broader aerospace deep hole drilling landscape in another article. This one is specifically about titanium parameters, tool life, and coolant — the three things that matter most when the material is titanium.
Alloy Differences: Ti-6Al-4V vs Ti-6Al-2Sn-4Zr-2Mo vs CP Titanium
I work with three main titanium alloys regularly. They are not interchangeable from a drilling standpoint.
Ti-6Al-4V (Grade 5) is the standard. It accounts for roughly 50% of all titanium used worldwide. It cuts relatively cleanly for a titanium alloy — the chips are short and break well at the right feed. I start at 35-45 m/min for gun drilling and adjust from there.
Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) is a different animal. This is a high-temperature alloy used in turbine engine components. It is stronger and tougher than Ti-6Al-4V at elevated temperatures. What that means at the tool tip is higher cutting forces and faster edge breakdown. I drop cutting speed by 20-25% compared to Ti-6Al-4V. The tool life hit is real — I get about half the hole count before regrind.
CP Titanium (Grade 2) is the easiest to drill of the three. It is commercially pure, softer, and more ductile. The problem is not tool wear — it is chip control. CP titanium produces long, stringy chips that want to wrap around the tool. I run higher feed rates to break the chips, even if it means surface finish takes a small hit.
Here is the comparison table I reference when quoting titanium jobs:
| Alloy | Cutting Speed (m/min) | Feed (mm/rev) | Coolant Pressure (psi) | Expected Tool Life (m) |
|---|---|---|---|---|
| Ti-6Al-4V | 35-50 | 0.025-0.045 | 1200-1800 | 8-15 |
| Ti-6Al-2Sn-4Zr-2Mo | 25-35 | 0.020-0.035 | 1500-2000 | 3-7 |
| CP Titanium (Grade 2) | 45-60 | 0.040-0.065 | 800-1200 | 15-25 |
Tool life in that table is total drilled meters on a 10mm gun drill before regrind, assuming a depth ratio of 30:1. Going deeper drops those numbers fast — at 80:1 I see roughly 40% less life on the same tool.
Cutting Parameters by Diameter
Diameter changes everything in titanium. Small diameters are fragile — the tool can snap from chip packing alone. Large diameters need more coolant flow and higher machine torque than you might expect.
| Diameter (mm) | Cutting Speed (m/min) | RPM | Feed (mm/rev) | Penetration Rate (mm/min) | Coolant Pressure (psi) |
|---|---|---|---|---|---|
| 6 | 30-40 | 1600-2100 | 0.015-0.025 | 24-53 | 1500-2000 |
| 10 | 35-45 | 1100-1450 | 0.025-0.040 | 28-58 | 1200-1800 |
| 15 | 35-50 | 750-1050 | 0.030-0.045 | 23-47 | 1200-1600 |
| 20+ | 35-50 | 550-800 | 0.040-0.055 | 22-44 | 1000-1500 |
For 6mm diameters, coolant pressure matters more than anything else. You cannot clear chips through a 4mm coolant hole in the drill without enough pressure. I run 6mm tools at 1800 psi minimum and check the flow meter every hour.
For 20mm and larger, the challenge shifts to flow. I need at least 80 L/min through a 20mm gun drill to get the chips out. If the pump cannot deliver that volume at 1200 psi, I drop back to a larger drill tube or switch to BTA drilling.
Coolant Pressure — Why Titanium Needs More Than Steel
The short answer is heat. Steel conducts heat away from the cutting edge at roughly seven times the rate of titanium. In steel, the coolant mostly needs to lubricate and flush chips. In titanium, the coolant is the primary heat removal mechanism.
I have run the numbers on my own machines. At 1000 psi in steel, the coolant removes roughly 40% of the heat generated at the cut. In titanium at the same pressure, the tool tip runs 150-200 degrees Celsius hotter because less heat goes into the chip. At 1500 psi, the temperature drops back into a safe range for the carbide edge. There is a direct relationship between coolant pressure and edge temperature in titanium.
I covered the coolant pressure fundamentals in more detail here, but the key point for titanium is this: if your machine tops out at 800 psi, you cannot drill titanium reliably. The minimum viable pressure for production titanium work is 1200 psi at the tool. I prefer 1500-1800 psi for overhead margin.
The other factor is chip evacuation. Titanium produces chips that are thin and ribbon-like. At low pressure, these chips pack in the flute and weld together. Once that happens, the coolant cannot reach the cutting edge and the tool fails in seconds. High pressure keeps chips moving through and out of the hole.
Tool Coating Selection — Why AlCrN Works Best
I have tested most coatings on titanium. The results are not subtle.
TiN (titanium nitride) — useless in titanium. The coating breaks down around 600 degrees Celsius, and titanium pushes edge temperatures well past that. I see coating failure within the first meter.
TiAlN (titanium aluminum nitride) — better. The aluminum oxide layer that forms during cutting provides some thermal barrier. Good for about 4-8 meters on Ti-6Al-4V depending on parameters.
AlCrN (aluminum chromium nitride) — the best I have found for titanium. The chromium adds oxidation resistance that holds up above 900 degrees Celsius. In my testing, AlCrN-coated gun drills last 40-60% longer than TiAlN on Ti-6Al-4V under identical parameters. On Ti-6242, the gap is even wider — AlCrN gives nearly double the tool life.
The coating works best when applied to a micrograin carbide substrate with 10-12% cobalt binder. The combination handles the thermal cycling and mechanical shock of deep hole drilling in titanium. I recommend AlCrN as the standard for any titanium job and only switch to uncoated tools when regrinding frequency is low enough that coating cost does not justify itself.
Surface Finish Achievable
Gun drilling in titanium produces a better surface finish than most people expect. With stable parameters and sharp tooling, I hold Ra 0.6-1.2 microns consistently.
The finish is not uniform along the hole. The entry section (first 10-20 diameters) typically shows the roughest surface because the drill is still stabilizing. After that, the finish stabilizes at around Ra 0.8 microns until the last few diameters before breakthrough.
If I need better than Ra 0.6 microns, I follow with a ball burnishing pass. That compresses the surface to Ra 0.2-0.4 microns and improves fatigue performance — important for aerospace titanium parts. Skiving and roller burnishing works well on larger diameters.
The straightness I hold on titanium is typically 0.05-0.08 mm per 100 mm of depth. Titanium has a lower elastic modulus than steel, so the drill deflects more. Using a closely fitted guide bushing at the entry is essential.
Common Problems
I have dealt with all of these in production. Here is what they look like and how I fix them.
Notch wear — This shows as a groove at the outer corner of the cutting edge. It happens when the cutting speed is too high for the alloy. The outer corner of the drill travels the longest path and sees the highest temperature. If I see notch wear developing before 3 meters of drilling, I drop the speed by 10% and check coolant alignment. Misaligned coolant jets accelerate notch wear significantly.
Work hardening — Titanium work-hardens when feed drops below 0.015 mm/rev or when the tool dwells. The hardened layer creates a new surface that is harder than the bulk material. If I need to stop the feed mid-hole, I back the tool out of the cut completely rather than leaving it stationary against the workpiece. The restart must use a feed ramp-up that passes through the hardened zone quickly.
Chip packing — The most common cause of tool breakage in titanium. Chips pack in the flute, coolant stops flowing to the edge, and the tool overheats and breaks. I watch the coolant pressure gauge. If I see a pressure spike of 200 psi or more, chips are packing. I increase feed rate to break chips shorter or increase pressure to push them through. On small diameters (under 8mm), chip packing is the primary failure mode.
Tool Life Expectations
Tool life in titanium is lower than any common material except Inconel. Here are my real numbers from production runs.
On Ti-6Al-4V with AlCrN-coated gun drills at 40 m/min and 0.03 mm/rev, I expect 8-12 meters of total drilled length before the first regrind. Subsequent regrinds each remove 0.3-0.5 mm of carbide from the OD, so the tool diameter drops by that amount. A 10mm gun drill can typically be reground 4-6 times over its life, giving roughly 40-70 total meters drilled.
On Ti-6242, tool life is roughly half that. I budget for 3-6 meters per grind and plan more frequent tool changes.
On CP titanium, tool life is excellent — 15-25 meters per grind. The failure mode there is edge rounding rather than notch wear. I can usually push the tool longer before the surface finish degrades.
The largest variable is depth ratio. At 20:1 depth ratio, I get 100% of those numbers. At 50:1, I see roughly 60-70%. At 80:1, tool life drops to 35-50% of the baseline. The added torque from the longer flute creates more heat, and chip evacuation becomes harder.
Key Takeaways
- Ti-6242 needs 20-25% lower speed than Ti-6Al-4V and tool life is roughly half — factor this into quoting.
- AlCrN coating outperforms TiAlN by 40-60% in titanium. Do not use TiN at all.
- Minimum viable coolant pressure for titanium is 1200 psi at the tool. 1500-1800 psi is preferred for margin.
- Reduce cutting speed by 10% if notch wear appears before 3 meters of drilling.
- Never let feed drop below 0.015 mm/rev — titanium work-hardens instantly.
- Tool life at 80:1 depth ratio is roughly half what it is at 20:1. Plan tool changes accordingly.
- For chip packing, watch the coolant pressure gauge. A 200 psi spike means chips are jamming the flute.