Engineering · Machining guide
How to machine 316L stainless.
316L is the molybdenum-bearing austenitic stainless that handles pharmaceutical CIP/SIP, marine seawater, and surgical implant applications. The machining problem is work-hardening — stop the tool, restart the tool, and the next pass cuts harder material than the first. The fix is keep the chip moving, use sharp tools, and run flood coolant.
01 · Why 316L is harder than it looks
Work-hardening, gummy chips, low conductivity.
316L isn’t hard — annealed Brinell is ~165 HBW. But it work-hardens aggressively under cutting pressure, which means a dull tool or a stalled cycle creates a hardened layer the next cut has to chew through. Thermal conductivity is also poor (16 W/m·K, ~1/3 of carbon steel), so heat concentrates at the cutting edge.
The molybdenum that gives 316L its corrosion resistance also makes the chips gummy. Chip control is harder than in 304. Use chip-breaker insert geometry and high-pressure coolant where possible.
02 · Tool selection
Sub-micron carbide, sharp edges.
- Coated carbide (PVD AlTiN)
Sub-micron grain. AlTiN coating handles the heat better than TiN. Sharp edges with positive rake — dull edges in 316L start work-hardening immediately.
- Honed cutting edges (0.0004–0.0008″)
Sharp enough to cut clean, robust enough not to chip. Negative rake or heavy hone creates more cutting pressure and accelerates work-hardening.
- Solid carbide end mills, 4-flute
Standard for milling. Variable-helix or chatter-resistant geometry helps in deep slot work. Avoid HSS — work-hardens too fast.
- Cermet or CBN for finishing on volume
For high-volume surgical and pharma work, cermet inserts give cleaner surface finish and longer tool life — and the cleaner surface helps electropolish yield. (PCD is for non-ferrous only — diamond dissolves into iron at cutting temperature.)
03 · Cutting parameters
Maintain chip load — don’t reduce when in doubt.
| Operation | Tool | SFM | IPT / IPR |
|---|---|---|---|
| Roughing turn | Coated carbide | 300–450 | 0.010–0.018 IPR |
| Finishing turn | Coated carbide | 400–550 | 0.005–0.010 IPR |
| Finishing turn | Cermet | 500–700 | 0.003–0.006 IPR |
| End mill (rough) | Solid carbide | 200–300 | 0.003–0.005 IPT |
| End mill (finish) | Solid carbide | 300–400 | 0.002–0.003 IPT |
| Drilling | Solid carbide | 60–100 | 0.003–0.006 IPR |
| Tapping | Spiral-flute carbide | 20–35 | — |
04 · Practical notes
Surface chemistry matters here.
- Coolant: sulfur-free water-soluble flood at 8–10% concentration. Sulfur additives can cause stress-corrosion cracking concerns on austenitic stainless. Through-tool coolant ideal for deep features.
- No iron contamination from grinding: if grinding is required, use silicon carbide or CBN wheels — aluminum-oxide wheels transfer iron particles that pit during electropolish.
- Don’t reduce feed if you’re struggling: counterintuitive for 316L. Reducing feed lets the tool dwell and work-harden the surface. Maintain proper chip load even when surface finish needs improving — fix surface finish with a sharper tool, not slower feed.
- Citric passivation: per AMS 2700 Method 2 for finished surfaces. See citric vs nitric passivation.
- Process order for electropolished surfaces: machine → citric wash → electropolish → final passivation. The intermediate citric wash removes embedded iron before electropolish exposes it.
Keep exploring
Related tools & references
Mechanical properties, UNS, AMS specs, and machinability at a glance.
Convert these SFM and IPT figures into spindle RPM and feed rate.
Recommended chip load by tool diameter for stainless.
316L stainless density for part weight and stock estimates.
Citric per AMS 2700 Method 2 for finished 316L surfaces.
Technically reviewed by the True Precision Machining engineering team · Last reviewed June 2026
Standards referenced: AMS 5653, AMS 2700
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Send your drawing — 316L stainless is a material we run regularly. Aerospace, medical, and defense work welcome.
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