Deep Hole Drilling Titanium Ti-6Al-4V: Parameters, Tooling, and Best Practices

Deep Hole Drilling Titanium: The Rules Are Different

I’ve machined a lot of difficult materials over the years, but titanium is the one that demands the most respect in deep hole drilling.

Not because it’s the hardest material — it isn’t. But because it combines three properties that punish mistakes without warning: it work-hardens instantly when the tool rubs instead of cuts, it traps heat at the cutting edge because its thermal conductivity is a fifth of steel’s, and its chips are chemically reactive and prone to welding themselves to the tool if coolant pressure drops.

I’ve seen a deep hole job in Ti-6Al-4V go from running smoothly to a snapped drill in less than a second — no squeal, no warning signs. That’s titanium.

This guide covers what I’ve learned from my own work and from manufacturer technical data by Sandvik, Guhring, Allied Machine, and ISCAR, plus discussions with engineers who drill titanium for a living — primarily in aerospace and medical.

What Makes Titanium Hard to Deep-Hole Drill

Low Thermal Conductivity

Titanium’s thermal conductivity is about 6.7 W/m·K — roughly 1/5 that of steel and 1/25 that of aluminum. Nearly all the heat generated at the cutting edge stays there. The tool tip can reach 1000°C even when the bulk material feels cool to the touch.

This heat concentration softens the cutting edge, accelerates flank wear, and promotes chemical reaction between the titanium and the tool material.

Work Hardening

Titanium work-hardens aggressively. If the feed rate drops below the critical minimum chip thickness, the tool stops cutting and starts rubbing. The rubbing work-hardens a thin surface layer. The next pass must cut through that hardened layer, generating even more heat. This feedback loop destroys tools fast.

The critical minimum feed is approximately 0.05 mm/tooth (0.002“ IPT). Below this, you’re rubbing, not cutting.

Chemical Reactivity

Titanium is chemically reactive with many tool materials at cutting temperatures. It welds to uncoated carbide through diffusion wear — titanium atoms migrate into the carbide structure, weakening the cutting edge. This is why tool coating selection matters more for titanium than for almost any other material.

Saw-Tooth Chip Formation

Ti-6Al-4V produces segmented (saw-tooth) chips through adiabatic shear banding. The chip forms in two stages: material plastically deforms ahead of the tool until a critical strain, then catastrophic shear occurs along a narrow band. This generates cyclic force fluctuations that can drive high-frequency vibration (Journal of Materials Processing Technology, 2024).

The chip compression ratio directly correlates with surface roughness — tighter chips produce better finishes.

Reading the Chips: Titanium Edition

Recommended Cutting Parameters

Gun Drilling (1 — 20 mm diameter)

Notes:

• Use the lower half of the feed range for diameters under 3 mm
• TiAlN or AlTiN coated carbide gun drills required — uncoated carbide fails rapidly through diffusion wear
• Academic research on Ti-6Al-4V gun drilling tested cutting speeds of 20 — 50 m/min and feeds of 0.01 — 0.06 mm/rev at coolant pressures of 1 — 5 MPa, confirming that higher pressure directly improves chip evacuation and surface finish (Nanjing University of Aeronautics and Astronautics, 2024)

Feed Rate by Drill Diameter (Gun Drilling, Ti-6Al-4V)

Depth-to-Diameter Ratio Correction

Titanium requires more aggressive derating than stainless or aluminum because heat buildup accelerates exponentially with depth. I’ve seen shops ignore this and wonder why their tool life drops by 60% between 10:1 and 20:1 depth ratios.

BTA Drilling (12 — 65 mm diameter)

Guhring’s RT 100 T series (TiAlN-coated, 135° point angle) lists 130 SFM (≈40 m/min) for titanium alloys at ≤250 BHN, with feed rates by diameter: 0.004 IPR (0.10 mm/rev) for 3.17 mm, 0.006 IPR (0.15 mm/rev) for 6.35 mm, and 0.007 IPR (0.18 mm/rev) for 9.52 mm and 12.7 mm drills (Guhring RT 100 T technical documentation, 2024).

Trepanning (Large Diameter, > 40 mm)

For large-diameter deep holes in titanium — common in aerospace landing gear components — trepanning is more efficient than solid BTA drilling because it produces a usable core.

Critical note on speed limits: For TC10 at feed rates above 0.15 mm/rev or cutting speeds above 27 m/min, violent vibrations cause micro-cracking and tool tipping that cannot be repaired by resharpening (SAGE Journals, 2022). Stay within these bounds for tool stability.

At optimal parameters (63.3 m/min, 0.18 mm/rev, 4 MPa), spiral and fragmented chips are produced — these evacuate most reliably. Achievable accuracy: IT8—IT10, surface roughness Ra 3.2 — 6.3 µm (MDPI Processes, 2025).

Tool Selection

Gun Drilling

Why not PCD: Titanium reacts chemically with the cobalt binder in PCD tools at cutting temperatures, causing rapid edge breakdown. Stick to AlTiN or AlCrN-coated carbide.

Guhring’s RT 100 T series (Series 6513) is a general-purpose deep hole carbide drill with TiAlN coating and 135° point angle, designed for depths up to 30×D. It requires a pilot hole of 1.5×D to 3×D depth with m7 tolerance, and needs minimum 40 bar coolant pressure (Guhring, 2024).

Sandvik’s CoroDrill 860 with -SM geometry is optimized specifically for ISO S materials including titanium, with TiAlSiN coating for enhanced heat resistance (Sandvik Coromant, 2024).

BTA Drilling

Single-tooth BTA tools are preferred over multi-tooth for titanium — multi-tooth designs generate more vibration that accelerates tool wear in this material. Recommended tool geometry:

Allied Machine’s APX drill with replaceable inserts has been successfully used on Timetal 17 at 82 SFM (0.0035 IPR) and 131 SFM (0.0055 IPR), with the higher feed producing better chip formation (Allied Machine, 2024).

Coolant: The Critical Variable

In titanium deep hole drilling, coolant is not optional — it is the most important variable you control.

Pressure Requirements

UNISIG’s gun drilling machines for medical and aerospace titanium applications run coolant systems rated at 3,000 PSI (207 bar) (UNISIG, 2024). This is the level where coolant stops being just coolant and becomes a high-pressure chip evacuation system.

Case study: A Ti-6Al-4V gun drilling operation running at 30 bar coolant pressure experienced regular tool breakage. Increasing pressure to 70 bar eliminated tool breakage completely and improved surface finish by one Ra grade (Practical Machinist case discussion, 2024).

Oil-Based vs Water-Based Coolant

My recommendation for most deep hole titanium jobs: Use a chlorine-free, low-viscosity EP cutting oil (such as Multicut Ultra 7 or COOLCUT NEO 3724 N) for gun drilling diameters under 10 mm. Use water-soluble emulsion at 8 — 12% concentration for larger diameters and BTA drilling where heat removal is the priority.

CHLORINE-FREE is essential for titanium. Chlorinated coolants can cause stress corrosion cracking in titanium components, which is unacceptable in aerospace applications.

Surface Finish and Tolerance Expectations

Titanium’s low thermal conductivity means that achieving the lower end of these ranges requires careful coolant management. If the tool overheats, thermal expansion of the workpiece can push hole size out of tolerance before you realize there’s a problem.

Common Problems and Fixes

Problem 1: Drill Breakage Without Warning

Cause: Titanium’s segmented chip formation generates cyclic force fluctuations. When chatter hits the resonant frequency of the tool/workpiece system, the carbide tip fractures.

Fixes:

• Change cutting speed by 10 — 15% to shift the chatter frequency
• Ensure the tool overhang is as short as possible
• Verify coolant pressure at the tool tip, not just at the pump gauge
• Increase feed rate to produce thicker chips that dampen vibration

Problem 2: Rapid Tool Wear — Short Tool Life

Cause: Diffusion wear — titanium atoms migrate into the carbide structure at cutting temperatures above 500°C.

Fixes:

• Switch to AlTiN or AlCrN coating (better thermal barrier than TiAlN)
• Reduce cutting speed to stay below the diffusion temperature threshold
• Increase coolant pressure to remove heat from the cutting edge
• Check coolant concentration — too low accelerates wear

Problem 3: Built-Up Edge and Chip Welding

Cause: Titanium’s chemical reactivity causes it to weld to the cutting edge when coolant fails to maintain a fluid barrier.

Fixes:

• Increase coolant pressure and direct it precisely at the cutting edge
• Use oil-based coolant for better lubricity
• Increase feed rate to produce thicker chips that carry heat away
• Avoid PCD tooling — it reacts chemically with titanium

Problem 4: Work Hardening at Hole Entry

Cause: The drill rubs instead of cutting during entry, hardening the surface before the cut begins.

Fixes:

• Always use a pilot hole at least 1.5×D deep
• Enter the pilot hole with the spindle stopped, feed into position, then start the spindle
• Use a single-point bored guide bushing within 0.0005“ clearance for the first inch

Problem 5: Chip Clogging in Deep Holes

Cause: Titanium’s saw-tooth chips are abrasive and difficult to evacuate through long chip flutes.

Fixes:

• Increase coolant pressure — this is the single most effective fix
• Check that the chip flute cross-section is adequate for the hole diameter
• For gun drilling, verify the V-groove clearance angle is correct for titanium
• Consider pecking for depths beyond 50:1, with very shallow pecks (0.3 — 0.5 mm)

Critical Do’s and Don’ts

DO:

• Use TiAlN, AlTiN, or AlCrN coated carbide — never uncoated
• Maintain minimum 40 bar coolant pressure, 70+ bar preferred
• Use a pilot hole with a shorter, more rigid drill
• Keep feed rate high enough to cut — minimum 0.05 mm/rev for gun drilling
• Change cutting parameters one variable at a time when troubleshooting
• Monitor chips — tight silver segments mean correct parameters

DON’T:

• Use PCD tooling — chemical reaction with titanium destroys it
• Peck deeply — 0.5“ pecks cause work hardening at the hole bottom
• Let the tool dwell — even 0.5 seconds of rubbing hardens the surface
• Reduce feed as depth increases — maintain constant feed, reduce speed only
• Use chlorinated coolants on titanium destined for aerospace

Starting Points Summary

New titanium deep hole drilling job — gun drilling, Ti-6Al-4V, 6 mm diameter, 30:1 depth ratio:

• Speed: 25 m/min (≈ 1,325 RPM)
• Feed: 0.015 mm/rev
• Coolant: 80 bar, chlorine-free EP oil
• Tool: TiAlN-coated solid carbide gun drill
• Pilot hole: 1.5×D deep, m7 tolerance

For BTA drilling, Ti-6Al-4V, 25 mm diameter, 20:1 depth:

• Speed: 35 m/min (≈ 445 RPM)
• Feed: 0.12 mm/rev
• Coolant: 50 bar, water-soluble emulsion 10%
• Tool: Single-tooth BTA head, AlTiN-coated inserts

For trepanning, Ti-6Al-6V-2Sn, >40 mm diameter:

• Speed: 22 m/min
• Feed: 0.13 mm/rev
• Coolant: Oil-based, high flow (250 L/min)
• Tool: Single-tooth cemented carbide, rake 7°, relief 12°

References

• Guhring. RT 100 T — Deep Hole Carbide Drill (Series 6513). Titanium Cutting Data Table, 2024.
• Guhring. RT 100 T Drilling Procedure — Pilot Hole and Feed Guidelines. Technical Documentation, 2024.
• Sandvik Coromant. CoroDrill 860 with -SM Geometry for ISO S Materials. Technical Data, 2024.
• Sandvik Coromant. ISO S Holemaking — Titanium and Superalloys. Industry Solutions, 2024.
• Allied Machine. Catching ‘22’: Beat the Challenges of Titanium. Technical Article, 2024.
• Allied Machine. Deep Hole Drilling Guidelines — T-A, GEN3SYS, APX Systems. 2024.
• UNISIG. UNE6 Small-Diameter Gundrilling Machine for Medical and Aerospace. Product Specifications, 2024.
• Nanjing University of Aeronautics and Astronautics. Research on Chip Formation Mechanism in Gun Drilling of Ti6Al4V. Journal of Aeronautics, 2024.
• SAGE Journals. The Effect of Trepanning Parameters on Wear of Tool and Surface Quality of Titanium Alloy. Vol. 14, 2022.
• MDPI Processes. Optimization of Chip Morphology in Deep Hole Trepanning of Titanium Alloy. Vol. 13, 2025.
• Practical Machinist Forum. “Deep Drilling in Titanium” and “Titanium Drilling Help” discussions, 2024.
• Journal of Materials Processing Technology. Chip Formation Mechanics in Ti-6Al-4V Drilling. 2024.