Engineering · Machining guide
How to machine 304 stainless.
304 is the general-purpose austenitic stainless — food-service, architectural, hardware, fasteners, fabricated weldments. Slightly easier to machine than 316L (no molybdenum, less gummy chips) but the same work-hardening discipline applies. This guide covers parameters, tooling, and the practical differences from 316L.
01 · 304 vs 316L
Same family, slightly easier.
304 and 316L are both austenitic stainless steels — same crystal structure, similar mechanical properties, similar work-hardening behavior. The differences that matter for machining:
- No molybdenum in 304 — chips break a bit cleaner, slightly less gummy than 316L.
- Slightly higher SFM tolerated — typically 10–20% faster than 316L on the same operation.
- 304L vs 304: 304L has lower carbon (≤0.03%) for weldability without sensitization. Same machining — the difference doesn’t affect cutting parameters.
- Free-machining variants: 303 (sulfur-bearing) and 304L-F have substantially better machinability (~85/100) but lose corrosion resistance and weldability.
02 · Cutting parameters
Numbers that work.
| Operation | Tool | SFM | IPT / IPR |
|---|---|---|---|
| Roughing turn | Coated carbide | 350–500 | 0.010–0.020 IPR |
| Finishing turn | Coated carbide | 450–600 | 0.005–0.010 IPR |
| End mill (rough) | Solid carbide | 250–350 | 0.003–0.006 IPT |
| End mill (finish) | Solid carbide | 350–450 | 0.002–0.003 IPT |
| Drilling | Solid carbide | 70–110 | 0.003–0.006 IPR |
| Tapping | Spiral-flute | 25–40 | — |
| Reaming | Coated carbide | 40–80 | 0.001–0.002 IPR |
IPT (chip-load) values assume roughly ½–1″ end mills; scale down for smaller tools — see the chip-load chart.
03 · Practical notes
Same discipline as 316L.
- Coolant: water-soluble flood at 8–10% concentration. Sulfur-bearing EP coolant is fine on 304. Chloride, not sulfur, is the stress-corrosion concern on austenitic stainless: if chlorinated additives are used, clean parts thoroughly before any heating, welding or passivation.
- Climb mill, don’t conventional: conventional milling re-cuts chips and work-hardens the surface. Climb milling lifts chips away. Always climb in 304.
- Don’t dwell: stopping the spindle while engaged work-hardens the surface — same problem as 316L. Avoid pauses mid-cut.
- Sharp tools always: a dull tool in 304 work-hardens the workpiece in front of it, accelerating its own demise. Replace edges on schedule, not after they fail.
- Passivation: per ASTM A967 / AMS 2700. Citric (Method 2) or nitric (Method 1) both work fine on 304 — see our passivation comparison.
- For free-machining work: consider 303 if corrosion isn’t critical. ~30% faster cycle times and dramatically less work-hardening, but unweldable and lower corrosion resistance.
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.
304 stainless density for part weight and stock estimates.
Both methods work on 304 per ASTM A967 / AMS 2700.
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