What is stainless steel CNC machining?
Stainless steel CNC machining is the production of parts from corrosion-resistant stainless grades by milling and turning. Stainless steel is the choice for food machinery, medical devices, chemical and pharmaceutical equipment, marine and outdoor applications.
See our Stainless steel page for material properties and our CNC machining page for all CNC options.
Stainless steel grades
| Grade | Key property | Machinability | Typical use |
|---|---|---|---|
| 303 | Sulphur-added, the easiest stainless to machine | Very good | Shafts, bushings, fasteners |
| 304 | The most common grade, good corrosion resistance | Moderate | Food equipment, general parts |
| 316L | Contains molybdenum, resistant to chlorides and chemicals | Moderate | Marine, chemical, medical |
| 17-4 PH | Precipitation hardening, high strength | Moderate | Aerospace, pump and valve parts |
| 420 / 410 | Hardenable by heat treatment | Moderate | Cutting and wear parts |
303 is easy to machine but not suitable for welding, and its corrosion resistance is lower than 304. If you need welding or high corrosion resistance, choose 304 or 316L.
Why is stainless steel hard to machine?
| Property | Effect | What the manufacturer does |
|---|---|---|
| Work hardening | The surface hardens during cutting | Sharp tools, continuous and stable cuts |
| Low thermal conductivity | Heat builds up in the tool | Suitable cutting speeds and coolant |
| High toughness | Chips do not break easily | Tools with chip breakers |
For these reasons stainless steel machines noticeably slower than aluminum and the part price is higher.
Tolerances and surface finish
| Feature | Standard | On request |
|---|---|---|
| General tolerance | ISO 2768-m | ISO 2768-f |
| Critical dimensions | ±0.05 mm | ±0.01–0.02 mm |
| Surface roughness | Ra 1.6–3.2 µm | Ra 0.8 µm, polishing |
In food and medical applications, low roughness and a design without sharp corners matter for cleanability.
Surface finishes
| Finish | What it provides |
|---|---|
| Passivation | Removes free iron, improves corrosion resistance |
| Electropolishing | Smooth, bright, easy-to-clean surface |
| Bead blasting | Uniform matte surface |
| Brushing (satin) | Decorative finish |
| Polishing | Mirror finish |
Design guidelines
- Avoid deep, narrow pockets; tool wear is high in stainless.
- In food and medical parts, avoid sharp internal corners and narrow gaps that can trap dirt.
- Keep thread depth only as deep as the function requires.
- For welded parts, choose 304 or 316L instead of 303.
- State the grade and, if needed, the material certificate (EN 10204 3.1) on the drawing.
What drives the price
- Grade: 316L and 17-4 PH cost more than 304.
- Machining time: stainless machines slower than aluminum.
- Finishing: electropolishing and polishing add labour.
- Tolerances, quantity and certification requirements.
What we need for a quote
- 3D model in STEP format and PDF drawing
- Stainless grade (303, 304, 316L, 17-4 PH, etc.)
- Quantity and surface finish
- Material certificate requirement
- Whether the part is for food or medical use
Frequently asked questions
Should I choose 304 or 316L?
304 is sufficient for general-purpose applications. For seawater, chloride environments, chemicals or medical applications, molybdenum-bearing 316L is more suitable.
Which stainless steel is easiest to machine?
Grade 303 is the easiest to machine thanks to its sulphur content. However, it is not suitable for welding and its corrosion resistance is lower than 304.
Do stainless steel parts rust?
With the right grade and finish they are very durable. Passivation after machining removes free iron from the surface and improves corrosion resistance.
Why is stainless CNC machining more expensive than aluminum?
Stainless steel work-hardens and conducts heat poorly, so it is machined at lower speeds with higher tool wear.