Below is a practical, technical checklist for buying a lathe intended for ultra-precision hard turning (~58–60 HRC steels).

1) Target capability (define up front)

• Geometry & finish goals: e.g., roundness ≤ 2 µm, cylindricity ≤ 3 µm, size Cpk≥1.33, surface finish Ra 0.05–0.2 µm on bearing seats/lands.
• Allowable cycle & DOC: finishing DOC often 0.02–0.10 mm, feeds 0.02–0.08 mm/rev; confirm machine’s stability at these chip loads with CBN.
• Work envelope & workholding style: collet vs. diaphragm/air chuck, tailstock/steady rest, sub-spindle needs.

2) Base, ways, and mechanical stiffness

• Structure: slant-bed or box-type cast iron with high damping; premium machines use hydrostatic ways for near-zero stick–slip and sub-micron contouring.
• Thermal symmetry: mirrored bed/spindle centerlines; isolated ballscrew/linear-motor heat; ribbed casting; verified warm-up drift < 2–3 µm.
• Axes: preloaded ballscrews with dual-nut or linear motors; direct-drive turrets (BMT/HSK/Capto) to avoid indexing error.
• Feedback: glass scales on X/Z with 0.05–0.1 µm resolution; ISO 230 ball-bar/laser accuracy & repeatability reports supplied.

3) Spindle system

• Runout & stiffness: certified radial/axial ≤ 1 µm at gauge; high-precision angular-contact or hydrostatic spindle.
• Thermal control: chiller with oil/air-oil lubrication, thermal mapping & real-time compensation in the CNC.
• Speed/torque: finishing often at 120–300 m/min with PCBN; ensure torque is stable at low DOC to avoid “size push-off”.

4) Workholding and part support

• Concentricity: diaphragm/air chucks or collets with ≤ 2 µm TIR; fine-adjust masters; quick-change soft jaws.
• Axial control: true dead-length clamping to prevent length growth; draw-tube stiffness checked.
• Support: programmable tailstock or hydrostatic/roller steady rest for long slender parts.

5) Tooling & process for 60 HRC

• Inserts: PCBN (wiper geometry, honed/negative rake for interrupted cuts; sharp positive for continuous light finishing).
• Nose radius: typically 0.2–0.4 mm for fine form without chatter.
• Coolant strategy: dry/MQL or filtered oil; if wet, use fine filtration (≤ 5 µm) and temperature-controlled coolant.
• Balance: shrink-fit or precision collet toolholders; tool length kept minimal; turret face runout ≤ 2 µm.

6) CNC control features (ultra-precision)

• High-resolution interpolation (nano-interpolation), look-ahead, and spline/NURBS support for form turning.
• Thermal error comp, pitch-error maps, straightness & squareness comp, and volumetric compensation loaded from factory.
• In-process gauging: spindle probe or post-process closed-loop size control with automatic wear comp.

7) Environment & installation

• Temperature control: hold shop at 20 °C ±1 °C; machine has fully enclosed guarding and laminar airflow (avoid drafts).
• Foundation: leveled on specified points; consider isolation pads; verify ball-bar immediately after install and after 24-h soak.
• Cleanliness: mist extraction; magnetic/.paper filtration to protect slides & scales.

8) Automation & peripherals

• Bar feeder / parts catcher sized to bar quality & straightness; measure bar whip limits at your rpm.
• HP coolant, through-tool oil, chip conveyor, and part washing if required for bearing surfaces.

9) Documentation, proof, and support

• Run-off on your parts meeting your print (size, form, finish) with a signed capability study.
• Factory certs: ISO-230 accuracy charts, spindle runout cert, scale resolution, turret index repeatability.
• Service: availability of CBN application engineers, spindle/chiller service, spare parts lead time, training.

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Quick buyer’s checklist

• Flatness/stability of base and hydrostatic/box-way option
• Glass scales on X/Z, 0.1 µm or better; compensation tables loaded
• Spindle runout ≤ 1 µm, active thermal control
• Workholding TIR ≤ 2 µm; dead-length clamping
• Proven PCBN process window on 58–60 HRC with your material
• Environment controlled to ±1 °C; fine coolant filtration ≤ 5 µm
• Signed run-off hitting roundness/cylindricity/finish targets