Swiss Turning Titanium
What shops actually deal with when running titanium on Swiss lathes — and what engineers need to specify.
Titanium grades for Swiss turning
Grade 2 (CP titanium): The workhorse for medical implants, dental components, and corrosion-resistant fasteners. Yield strength 275 MPa, excellent biocompatibility. Machines easier than Ti-6Al-4V but is gummier — produces long, stringy chips that wrap around tooling. Most Swiss shops run Grade 2 at 150–250 SFM with carbide.
Grade 5 (Ti-6Al-4V): The aerospace standard. Yield strength 880 MPa, significantly harder to machine. Alpha-beta alloy with a tendency to work-harden and gall. Swiss shops run this at 80–150 SFM. The ELI (Extra Low Interstitial) variant is used for medical implants — same machinability, tighter chemistry controls.
Grade 23 (Ti-6Al-4V ELI): Medical-grade version of Grade 5. Lower oxygen and iron content improves fatigue life and fracture toughness. Identical machining parameters to Grade 5. Used for bone screws, spinal implants, and trauma plates.
Beta alloys (Ti-3Al-8V-6Cr-4Mo-4Zr, Ti-15-3): Occasionally seen in aerospace Swiss work. Higher strength than alpha-beta alloys, but more difficult to machine. Reduce speeds by 20–30% compared to Ti-6Al-4V.
Guide bushing considerations
Titanium bar stock requires carbide guide bushings — not brass or steel. Titanium galls against soft metals under the pressure and heat of the guide bushing contact. A brass bushing will seize within minutes. Carbide bushings cost 3–5x more ($200–500 vs $50–100) but are required for reliable production.
Bar stock straightness matters more with titanium than with steel or brass. Titanium bar that's even 0.002" out of straight will chatter in the guide bushing and produce out-of-tolerance parts. Specify centerless-ground bar stock for critical work — the premium ($2–5/lb over standard drawn bar) is cheaper than scrap parts.
Bushingless Swiss machines (Citizen L-series cincom, Star SR-J) can run titanium without the guide bushing for parts with L:D ratios under 3:1. This eliminates the galling risk but reduces support for longer parts. For L:D above 4:1, the guide bushing is non-negotiable.
Turning parameters
Grade 2 CP titanium: 200–280 SFM, 0.003–0.008" IPR, 0.010–0.040" DOC. Use sharp, positive-rake inserts with polished rake faces. Uncoated C2/C3 carbide or PVD TiAlN-coated inserts. The polished rake face reduces built-up edge (BUE) — titanium's tendency to weld itself to the cutting edge.
Grade 5 Ti-6Al-4V: 100–180 SFM, 0.002–0.006" IPR, 0.010–0.030" DOC. Same insert geometry but slower speeds. The higher hardness produces shorter chips — which is actually easier to manage in the Swiss machine's tight tooling envelope. Kennametal KC5010, Sandvik GC1115, and Iscar IC806 are proven grades.
Thread whirling (bone screws): 250–400 SFM peripheral speed on the whirling ring, 0.010–0.020" feed per revolution of the spindle. Thread whirling is the standard process for medical bone screw threads in titanium — it produces the thread profile in a single pass with no burrs. Cycle times of 15–30 seconds per bone screw thread are typical.
Live tooling operations
Cross-drilling titanium on Swiss requires through-tool coolant on the live tool spindle. Without it, the drill binds and breaks — titanium's low thermal conductivity traps heat at the drill tip. Use 135° split-point carbide drills with TiAlN coating. Peck cycle with 0.5–1.0D peck depth to clear chips.
Cross-milling: 80–120 SFM, 0.001–0.003" IPT, maximum 0.015" DOC per pass. Small-diameter end mills (0.020–0.125") on Swiss live tool spindles have limited rigidity — take light passes and let the tool cut, don't push it.
Hex and Torx drive machining: program as interpolated milling, not broaching. Broaching titanium on Swiss produces excessive force and insert wear. Interpolated milling takes longer but gives better tool life and dimensional control.
Coolant
Titanium is one of the few Swiss turning materials where high-pressure coolant makes a dramatic difference. Standard Swiss machines run oil coolant at 50–150 PSI. Upgrading to 500–1,000 PSI through-tool on the main spindle tooling extends tool life 2–3x on titanium.
Oil-based coolant (Swiss oil) is standard and preferred. Water-soluble coolant works but increases the risk of hydrogen embrittlement on titanium — hydrogen absorption into the cut surface during machining can cause delayed cracking in fatigue-loaded parts. For medical and aerospace titanium work, oil coolant is the conservative choice.
Coolant concentration for oil: 100% (Swiss machines run straight cutting oil, not emulsions). For shops running water-soluble on Swiss, maintain 10–12% concentration with a pH monitor — titanium is sensitive to alkaline conditions.
Achievable tolerances
OD turning: ±0.0005" is routine on Swiss with carbide guide bushings. ±0.0002" is achievable with in-process gauging and thermal stabilization (let the machine warm up for 30+ minutes before running critical parts).
Thread tolerance: Class 2A fit is standard. Class 3A is achievable with thread whirling or single-point threading with sharp inserts. Medical bone screw threads (buttress, HA-type) are typically specified to thread form tolerance, not class — the shop verifies with optical comparators or thread gauges.
Concentricity: 0.0005" TIR is routine between main spindle and sub-spindle operations. 0.0002" TIR requires collet runout verification and bar stock selection.
Surface finish: Ra 16–32 µin is standard with sharp carbide tooling. Ra 8–16 µin is achievable with diamond-tipped inserts on Grade 2 (not recommended for Grade 5 — diamond reacts with titanium above 750°F). Burnishing as a secondary operation achieves Ra 4–8 µin for medical implant surfaces.
Cost factors
Titanium Swiss work costs 3–4x more than equivalent parts in 303 stainless. The drivers:
Material: Ti-6Al-4V bar stock in Swiss diameters (0.125–1.250") runs $25–60/lb. Grade 2 is $15–30/lb. Compare to $2–4/lb for 303SS. On a bone screw that uses 0.3 oz of material, the titanium cost is $0.50–1.00 per part — small. On a larger aerospace pin using 2 oz, it's $3–7 per part.
Cycle time: Running at half the speed of stainless doubles the machine time. A 45-second cycle in 303SS becomes 80–120 seconds in Ti-6Al-4V.
Tooling: Insert life on titanium is 30–50% of stainless steel. Where an insert cuts 500 parts in 303SS, it might cut 150–250 in titanium. Carbide guide bushing replacement adds $200–500 every 50,000–100,000 parts.
Scrap rate: First-article setup on titanium takes longer and wastes more bar stock. Budget 10–20 parts of setup scrap on a new job vs 3–5 parts for stainless. At $25–60/lb, that scrap cost is real.