Achieving Ra 0.4 Micron Surface Finish in Stainless Steel 304 Turning
Consistently hitting bearing-grade Ra 0.4 micron surface roughness in CNC turned 304 stainless steel without post-grinding requires wiper insert technology, positive chip control, and stable G96 constant surface speed.
Engineering Specifications & Parameters
Insert Grade
PVD TiAlN / TiSiN coated micro-grain carbide
Insert Geometry
WNMG / CNMG with WQ/WM Wiper Technology
Cutting Speed (G96)
130 - 170 m/min
Finishing Feed Rate
0.10 - 0.16 mm/rev
Grinding Elimination
Eliminates secondary cylindrical grinding for O-ring and seal journals
Achievable Surface Roughness
Ra 0.35 - 0.45 microns (16 microinches)
Eliminating Secondary Grinding on Stainless Shafts
Standard ISO inserts produce feed grooves that limit turned surface finish on 304 stainless steel to Ra 0.8–1.6 μm. Utilizing Wiper insert geometry enables direct Ra 0.4 μm (16 μin) finishes.
Wiper Insert Cutting Mechanics
Wiper inserts feature a flat smoothing facet tangential to the nose radius that smooths out peak-to-valley feed marks on every spindle revolution.
Turning Parameters for Ra 0.4 μm
Cutting Speed (G96 CSS): 130 to 170 m/min. Constant surface speed is mandatory across facing transitions.
Feed Rate: 0.10 to 0.16 mm/rev (Wiper inserts deliver Ra 0.4 at 2x higher feed than conventional inserts).
Depth of Cut (ap): 0.25 to 0.50 mm. The finishing cut must exceed the insert nose hone to ensure clean shear and prevent work-hardened rubbing.
