Guides / Materials
5-Axis Machining Stainless Steel: Grades, Tolerances and Cost
September 26, 2026
Stainless steel covers a wide range of machinability, from grades that cut almost as easily as mild steel to grades that punish a tool the way titanium does. Which one is on your drawing changes the tolerance a shop can hold, how long the part takes and what it costs.
The common grades, in order of difficulty
303 is a free-machining grade, with added sulfur that breaks chips cleanly and lets tools run faster. 304 is tougher and gummier, prone to work hardening if the tool dwells or runs too slow. 316 machines similarly to 304 but adds molybdenum for corrosion resistance, at a similar machining difficulty. 17-4PH, a precipitation-hardening grade, machines easier in its solution-annealed state and considerably harder once heat treated to full hardness.
Work hardening is the main challenge
Austenitic grades like 304 and 316 harden under the tool if it rubs instead of cutting cleanly, which then makes the next pass harder still. This is why speeds and feeds matter more on stainless than on most materials: a tool run too slow or too light creates the exact problem it was meant to avoid. Shops that run stainless regularly use sharp, coated tools and consistent chip load to keep the cut clean.
Tolerance and finish
±0.025 mm is a reasonable target on 304 or 316 for critical features, similar to titanium, since finishing passes have to manage work hardening and heat rather than run at aluminum speeds. 303 can hold slightly tighter tolerance more easily due to its cleaner cut. 17-4PH after heat treatment machines more like a hardened tool steel, and tolerance expectations should follow that, not the softer annealed condition.
Typical parts
- Medical and food-contact components, usually 316
- Fasteners and fittings, often 303
- Structural and marine hardware, usually 304 or 316
- High strength brackets and pins, often 17-4PH
Cost versus other materials
Stainless generally costs more to machine than aluminum and less than titanium or Inconel, sitting in the middle of the difficulty range. Raw material cost is moderate, but slower cutting speeds and faster tool wear than aluminum add up on both cycle time and tooling. 17-4PH after heat treatment pushes cost closer to a hardened alloy steel.
What to confirm on your RFQ
State the exact grade and condition, annealed or heat treated for 17-4PH specifically, since the difference changes machining difficulty substantially. If corrosion resistance is not a hard requirement, ask whether a cheaper grade would meet the application, since defaulting to 316 out of habit adds cost without always adding benefit.
The short version
Not all stainless is equally hard to machine. 303 cuts easily, 304 and 316 need care to avoid work hardening and 17-4PH depends heavily on heat treat condition. Naming the exact grade and condition on your RFQ gets you a more accurate quote than “stainless steel” alone.
See also: 5-axis material selection matrix.
Frequently asked questions
Which stainless grade machines the easiest?
303 is the easiest common grade, since it contains sulfur specifically to improve machinability. 304 and 316 cut harder and slower, and 17-4PH harder still, especially after heat treatment.
Do I need 316 instead of 304 for a medical or food part?
Often yes for corrosion resistance in those environments, but confirm with your specification rather than defaulting to 316. It costs more and machines slower than 304 for no benefit if the application does not need it.
Does stainless cost more to machine than aluminum on a 5-axis job?
Yes, usually. It cuts slower, work hardens more than aluminum if the tool dwells and wears tools faster, so cycle time and tooling cost both run higher for a similar part.
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