Surface Finish Calculator

Inputs

Solve for

Choose whether you know the feed (and want the finish) or the target Ra (and want the largest feed that meets it).

Feed per revolution (f)

Feed per revolution (the distance the tool advances each turn of the work).

Nose radius (r)

Tool nose (corner) radius of the insert.

Default result

Surface roughness Ra(Ra)

1.603µm

Also computed

Roughness Rz (≈ Rmax)(Rz)6.25µm

Peak-to-valley height of the scallop.

Feed per revolution(f)0.2mm

The feed used for these results.

Method notes 4 notes

This is the THEORETICAL (ideal) finish — the geometric scallop a perfect round-nose tool leaves: Ra ≈ f²/(31.2·r), Rz ≈ f²/(8·r), with f and r in the same units.
Halving the feed quarters the roughness; doubling the nose radius halves it.
Real Ra is always higher than this ideal — built-up edge, tool wear, vibration, deflection and an unstable setup all add roughness. Treat the result as a best-case starting point, not a guarantee.
Geometry only: it assumes a true round nose, f < the straight-edge length of the nose, and ignores the cutting-edge condition and material.