Stainless steel CNC machining

We machine all four stainless families by CNC milling and CNC turning. Stainless sheet parts are cut and bent through our sheet metal services. The exact grade is confirmed in your quote.

Stainless grades are grouped by their metallurgical structure, and the structure decides whether a grade is magnetic and whether it can be hardened (SSINA).

The 300 series gives the best all-round corrosion resistance, the 400 series is magnetic and partly hardenable, and the PH grades reach high strength by aging (SSINA). The 200 series uses less nickel and more manganese than the 300 series (BSSA).

Example grades are labels, not a list of what we stock. The mill certificate that ships with your parts gives the composition and properties for the batch you receive. Grades 303 and 416 are the free-machining versions of 304 and 410 (Nickel Institute), and they trade some corrosion resistance and weldability for easier cutting.

Stainless steel work hardens: the surface under the tool gets harder as it is cut. Work hardening is one of the main features that set stainless machinability (Nickel Institute). Grades 304 and 316 machine at about half the rate of free-cutting carbon steel (SASSDA).

What that means for your part:

• Cycle time. Stainless parts take longer to cut than the same part in aluminum or mild steel, so the material choice shows up in the quote.
• Small holes and fine threads. Deep small holes and fine threads take more care in work-hardening grades. Use the largest thread and hole size the design allows.
• Free-machining grades. If the part has many turned features and won’t be welded, 303 or 416 can cut cost. Ask in your quote.
• Austenitic grades and magnetism. 300-series parts can become slightly magnetic where they are cold worked (SASSDA). Say so on the drawing if the part must be non-magnetic.

17-4 PH is supplied solution treated, called Condition A, and reaches its strength by aging at a set temperature (BSSA). The aged conditions are named with an H and a number, such as H900 or H1150. Different conditions trade strength against toughness.

Write the condition you need next to the grade, for example “17-4 PH, H1150” (an example callout). Tell us the condition the finished part must be in, and the quote confirms how the part will be made and treated.

Passivation is the finish most often specified for machined stainless parts. It removes free iron left on the surface by cutting and helps the protective chromium oxide layer re-form, using a nitric or citric acid treatment (BSSA). ASTM A967 and ASTM A380 are the standards most drawings cite (ASTM International).

Not every stainless grade suits acid passivation; some high-carbon martensitic grades need care (BSSA). We confirm the treatment for your grade in the quote.

Our full list of finishes:

• As-machined
• Bead blasting
• Anodizing Type II
• Anodizing Type III (hard anodizing)
• Powder coating
• Brushing
• Passivation
• Electroplating (nickel, chrome, zinc)
• Painting

Write the grade, the condition if it matters, and the product standard if one applies. For example (an example callout, not a recommendation): “Stainless steel 316, bar to ASTM A276, passivate to ASTM A967”. Other product standards seen on drawings include ASTM A479, A582 for free-machining bar and A564 for PH bar (ASTM International).

What to put on the drawing or in your message:

1. Grade, such as 304, 316 or 17-4 PH. “Stainless steel” alone isn’t enough to quote.
2. Condition, for PH and martensitic grades.
3. Finish, with the passivation standard and any surfaces to mask.
4. Equivalents, if you’d accept another grade, such as 303 in place of 304.

Every order comes with a mill certificate that traces the metal to its batch, along with QC inspection and ISO 9001 documentation.

• Standard QC inspection
• Material certification (mill certs)
• ISO 9001 documentation