Surface finish Ra 0.8 on stainless 316 turning — insert geometry or feeds?

Question

Customer drawing requires Ra 0.8 µm on a Ø25 mm 316 stainless shaft, 120 mm long. I'm getting Ra 1.4–1.6 consistently. Insert: CNMG 120408, PVD coated for stainless Vc 180 m/min, feed 0.15 mm/rev, DoC 0.5 mm finish pass Flood coolant Do I need a wiper insert or is 316 just gummy enough that I should be looking at polishing?

Elif Kaya · Accepted Answer

Switch to a wiper geometry insert CNMG WF or similar — that alone usually halves Ra at the same feed. Then: Increase Vc to 200–220 m/min; 316 smears built up edge at lower speeds and that shows as roughness. Keep feed at 0.15 with a wiper; 0.8 nose radius is fine. Make sure the finish pass is a single continuous pass with no dwell — any stop marks the surface. Ra 0.8 is very achievable on 316 without polishing.

Mehmet Arslan · Answer

Tailstock support matters too at 120 mm length on Ø25. If the part deflects even slightly you get periodic roughness that no insert fixes.

Surface finish Ra 0.8 on stainless 316 turning — insert geometry or feeds?

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