Stainless Steel CNC Machining
We machine stainless steel every day — 303, 304, 316, 17-4PH, 15-5PH, 416 — across medical, aerospace, marine, and food-grade applications. ±0.005mm standard tolerance. Full material certification with every order.
Which Stainless Grade Should You Choose?
The most common mistake we see is people specifying 316 when 304 would work perfectly fine, or specifying 17-4PH when a cheaper grade with post-machining heat treatment would do the job. Here's a practical breakdown based on what we've actually machined over the years.
| Grade | Machinability | Strength | Corrosion | Relative Cost | Our Recommendation |
|---|---|---|---|---|---|
| 303 | Excellent | 586 MPa | Good | $ | Fittings, fasteners, shafts, connectors |
| 304 | Good | 586 MPa | Very Good | $$ | General purpose: enclosures, brackets, food equipment |
| 316 | Good | 586 MPa | Excellent (marine) | $$$ | Marine hardware, medical, chemical processing |
| 17-4PH | Good (annealed) | 1,172 MPa | Very Good | $$$ | Aerospace structural, high-strength medical |
| 15-5PH | Good (annealed) | 1,103 MPa | Very Good | $$$$ | Aerospace, defence, high-performance shafts |
| 416 | Excellent | 517 MPa | Moderate | $$ | High-volume turned parts, threaded components |
Cost indication: $ = least expensive, $$$$ = premium grade. Prices vary with market conditions.
Real Talk: Machining Stainless Steel
Stainless steel gets a reputation for being hard to machine. It's not hard — it's just different from mild steel. The problems come from three things: work hardening, built-up edge, and chip control.
Work hardening. If your cutting tool rubs instead of cutting, the surface layer of stainless hardens instantly. Then the next pass tries to cut through hardened material, and you get tool chatter, poor finish, and eventually a scrapped part. The fix is simple: maintain constant chip load. Never let the tool dwell. Always climb mill.
Built-up edge. Stainless has a tendency to weld itself to the cutting edge under heat and pressure. This is why you see so much variation in surface finish — the BUE builds up, breaks off, and leaves a rough patch. We manage this with polished-flute carbide tooling, higher coolant pressure (40 bar minimum, 70 bar preferred), and running at the recommended speed for each specific grade — not a one-size-fits-all feeds and speeds chart.
Chip control. 304 stainless produces long, stringy chips that tangle around the tool, the spindle, and the part. If chips wrap around the tool during a critical finishing pass, the surface is scrap. Our machines have high-pressure through-spindle coolant that breaks chips into manageable segments, and chip conveyors with coolant filtration that remove them from the cutting zone.
These aren't problems you solve with a magic tool coating. They're process problems. And they're the reason an experienced shop with the right setup delivers consistent results on stainless, while a generalist shop struggles.
Our Stainless Steel Capabilities
Standard Tolerance
±0.005 mm
303, 304, 416 hold well. 17-4PH requires annealed state.
Precision Tolerance
±0.002 mm
Achievable on 303, 416 with CMM. Premium cost.
Surface (Turned)
Ra 0.4 µm
Standard for 303, 304. 316 needs polished pass.
Surface (Ground)
Ra 0.2 µm
All grades with cylindrical grinding.
Applications by Grade
Medical Instruments
Grades: 316L, 17-4PH
Surgical handles, implant trials, orthopaedic instruments
Learn more →Aerospace Hardware
Grades: 15-5PH, 17-4PH
Structural brackets, actuator housings, landing gear pins
Learn more →Marine Components
Grades: 316
Boat fittings, propeller shafts, underwater housings
Food Processing
Grades: 304, 316
Conveyor components, mixing blades, valve bodies
Chemical Processing
Grades: 316, 317
Pump housings, impellers, pipe fittings
Machining Stainless Steel?
We work with stainless daily — 304, 316, 17-4PH, 15-5PH. Send us your print and we'll give you an engineer-reviewed quote.