CNC machining 304 stainless steel covers a wide range of parts that need corrosion resistance, weldability and a clean appearance. 304 is the most widely used austenitic stainless, and its low-carbon version, 304L, is the standard when parts will be welded after machining. Wexmar turns, mills and Swiss-machines 304 and 304L at our shop in Canastota, New York, for food equipment hardware, fluid handling components, brackets and general industrial parts.
304 Stainless Machinability
304 has an approximate machinability rating of about 45 on the scale where AISI 1212 steel is 100. That is a little over half the rate of 303 stainless, which is the free-machining version of the same basic chemistry. The difference comes from what 304 does under the tool: it is tough, ductile and work hardens quickly, so it produces long, stringy chips, generates heat at the tool tip and punishes dull or rubbing tools.
Tolerances and Surface Finish
Typical production tolerances for precision 304 stainless turned parts are plus or minus 0.001 in. on diameters, with plus or minus 0.0005 in. achievable on short Swiss-turned features. Milled features typically hold plus or minus 0.002 in. on location. Typical finishes are 32 Ra on turned diameters and 63 Ra on milled faces, with 16 Ra possible on selected surfaces. These are typical figures, not guarantees. Long, slender parts and thin walls tend to deflect and move as internal stress is released.
Work Hardening, Heat and Chip Control
- Never let the tool dwell. Rubbing, pausing in a cut or taking very light passes hardens a skin on the surface that dulls the next tool. We program constant, positive feeds and finishing passes deep enough to cut beneath any hardened layer.
- Tool geometry. Sharp, positive-rake carbide with a stainless-specific chipbreaker and PVD coating works well. Variable-pitch end mills reduce chatter on the horizontal mills.
- Heat management. 304 conducts heat poorly, so heat concentrates at the tool tip. High-pressure coolant on the lathes and flood coolant on the mills keep edges cool and flush chips away.
- Stringy chips. Chips can wrap tools and mark finished surfaces. Chip-break cycles, correct chipbreaker selection and coolant aimed at the cut zone keep them under control.
- Tough burrs. 304 burrs are hard and tenacious, especially at cross holes. Deburr tooling is programmed into the cycle rather than left to hand work.
- Distortion. Heavy stock removal can release stress. Roughing, releasing and then finishing keeps flatness and roundness in check.
Finishing and Heat Treat Options
304 cannot be hardened by heat treatment; only cold work raises its strength. Finishing and thermal processes are coordinated through qualified outside processors:
- Passivation to remove free iron and restore the passive surface
- Electropolishing for smooth, easy-to-clean surfaces
- Black oxide for low-glare stainless hardware
- Solution annealing or stress relief after heavy cold work or welding
- Welding of machined subassemblies, typically in 304L
Common 304 Parts and Processes
- Food and beverage equipment hardware
- Pipe fittings, flanges and adapters
- Shafts, rollers and pins
- Brackets, mounting plates and enclosure hardware
- Pump and valve components
Turned 304 parts run on our Mazak and Doosan lathes with live tooling and Y-axis, so cross holes and flats are finished in one setup; see CNC turning. Flanges, brackets and blocks go to the Mazak horizontal machining centers, where pallet changers and 4-axis indexing handle multiple faces. Small-diameter 304 parts up to 32 mm run on Maier Swiss machines.
Cost Index: 304 Compared With Other Materials
| Material | Approx. machinability (1212 = 100) | Cost index vs 6061 | Notes |
|---|---|---|---|
| 304 / 304L stainless | ~45 | 2.2 | Weldable, work hardens |
| 303 stainless | ~78 | 1.8 | Free-machining, not weldable |
| 316 stainless | ~36 | 2.5 | Better chloride resistance |
| 17-4 PH stainless (Cond A) | ~40 | 2.8 | Precipitation hardening |
| 410 stainless (annealed) | ~55 | 2.0 | Hardenable, less corrosion resistant |
| 6061-T6 aluminum | ~180 | 1.0 | Baseline |
Values are typical and illustrative for a comparable part; actual quotes depend on geometry, quantity, tolerances and mill pricing.
Industries and Applications
A 304 stainless machine shop sees work from many directions. At Wexmar, 304 and 304L parts go to food and beverage equipment builders, pump and fluid power OEMs, instrumentation makers, electrical hardware suppliers and defense build-to-print programs. Our industries page has more on each sector. Material certs, heat-lot traceability and CMM reports are available on request.
Getting a quote
For 304 or 304L parts, upload a drawing for an instant estimate in PDF or STEP format, or call (315) 400-2654 during shop hours. A human estimator confirms every quote and will check grade, finish and passivation requirements before release.