CNC Programming

Turning Surface Roughness Calculator

Geometric ideal (tool marks) • Ra / Rz / Rt

Feed per rev (f)

mm/rev in/rev

Tool nose radius (R)

mm inch

Process preset (optional) — None (custom) — Roughing (f ≈ 0.35 mm/rev, R = 0.8 mm) Semi-finish (f ≈ 0.20 mm/rev, R = 0.8 mm) Finish (f ≈ 0.10 mm/rev, R = 0.4 mm) Fine finish (f ≈ 0.05 mm/rev, R = 0.4 mm)

Reality factor (optional)

1.00× (ideal geometry) 1.20× (light wear / small vibrations) 1.50× (typical production allowance) 2.00× (difficult material/setup)

Tip: set the preset closest to your cut, then fine-tune feed and radius.

Arithmetic mean roughness (Ra)

—

Ideal geometric estimate

Ten-point roughness (Rz)

—

≈ 4 × Ra (rule-of-thumb)

Total height (Rt ≈ Rmax)

—

Theoretical cusp height

Show formulas & unit handling

Ra (mm) ≈ f² / (32·R)   →   Ra (µm) = 1000 · f² / (32·R)
Rt (mm) ≈ f² / (8·R)   →   Rt (µm) = 1000 · f² / (8·R)
Rz (µm) ≈ 4 · Ra (µm) (typical turning rule-of-thumb)

f = feed per revolution, R = tool nose radius. Use consistent units internally (we convert in/rev & inch to mm first). Results are geometric ideals; real surfaces often measure higher due to tool wear, material, chatter, coolant, etc. Use the “Reality factor” to apply a practical allowance.

© Turning Roughness Estimator • Designed for quick what-if checks on lathes (Fanuc/Siemens/Okuma, etc.)