Stainless Steel Turned Parts
303 / 304 / 316L / 17-4PH · Ø1–20 mm · passivation · ±0.005 mm
CHX Metal machines stainless steel turned parts in 303, 304, 316L and 17-4PH on 70 Tsugami Swiss-type lathes, bar Ø1–20 mm at ±0.005 mm, with passivation and electropolishing in 3–7 days. Monthly capacity is 5 million pieces; quotes return in 24 hours.
Stainless is where turned-part quotes diverge most. Two suppliers quote the same drawing and the numbers differ by 40% — not because one is greedy, but because one selected 303 and the other assumed 316L, and one accounted for work hardening while the other did not. Sorting out the grade first saves the whole conversation.
Pick the grade before you pick the supplier
| Specification | Capability |
|---|---|
| 303 (1.4305) | Free-machining sulphur grade. Fastest and cheapest to turn; lower corrosion resistance, not for welded assemblies |
| 304 / 304L (1.4301) | General purpose. Tougher to machine than 303, work-hardens, welds well |
| 316 / 316L (1.4404) | Molybdenum addition for chloride and marine exposure; medical and food-contact default |
| 17-4PH (1.4542) | Precipitation hardening, high strength after ageing; used for shafts and valve parts |
| 430F (1.4104) | Magnetic free-machining ferritic; sensors and solenoid cores |
If the environment has chlorides, 303 will pit and the failure will be blamed on the machining. If the part is welded after turning, sulphur in 303 embrittles the weld. Neither problem is visible in a sample inspection, and both are decided at the material-selection step.
Work hardening: the single biggest cost driver
Austenitic stainless work-hardens — the surface gets harder as it is cut. A light finishing pass on a hardened layer cuts through abrasive material, destroys the insert and leaves a smeared finish. The correct approach is a feed rate high enough to cut under the hardened layer and a depth of cut that stays below it.
This is why a supplier that quotes stainless with the same parameters as brass will either lose money or deliver a poor surface. It is also why the DFM note should state the intended cutting strategy before the price is final.
Tolerances and the thermal problem
Stainless conducts heat poorly, so the part and the gauge both warm up. Measuring immediately after machining reads oversize; measuring after cooling reads true. A ±0.005 mm call on a Ø8 mm stainless shaft is achievable, but only if the measurement happens at a controlled temperature with a record of it.
For parts that combine a tight bore and a thin wall, the sequence matters more than the tolerance: rough, stress-relieve, then finish. Skipping the intermediate step is the usual cause of a bore that goes oval after the part leaves the machine.
Passivation and electropolishing
- Passivation (ASTM A967) removes free iron from the surface after machining and restores the chromium oxide layer. It is not a coating, so it cannot chip.
- Electropolishing removes a controlled layer and improves Ra; specified where cleanability or a burr-free edge matters.
- Pickling is for heat-affected zones after welding, not a substitute for passivation on a machined part.
- Turnaround for either process is 3 to 7 days, and both should be followed by a cleanliness check if the part is for medical or food contact.
Parts we run in stainless
Sensor and transducer housings, medical instrument shafts and pins, valve stems and seats, food-processing fittings, marine hardware, chemical pump components, fastener and insert families, and robot joint pins. Typical diameter range is Ø1–20 mm on the Swiss cell, up to Ø300 mm on the lathes.
Related capabilities
CNC turned parts manufacturer · Steel CNC machining · Brass turned parts · Aluminium turned parts · Surface treatment · Medical device parts · CNC machining China
Request a quote
Send drawing (STEP / PDF / DXF) with material, tolerance and annual volume to mc@chxmetal.com. DFM feedback and a price within 24 hours, NDA on request.
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Frequently asked questions
Which stainless grade should I specify for turned parts?
303 if machinability and cost dominate and there is no welding or chloride exposure. 304 for general use, 316L for chlorides, marine or medical contact, 17-4PH where strength after ageing is needed.
Why is stainless more expensive to machine than brass or aluminium?
Austenitic grades work-harden, conduct heat poorly and wear tooling faster. Cutting parameters must be set to cut under the hardened layer, which reduces speed and increases tool consumption.
Can you hold ±0.005 mm on a stainless shaft?
Yes on critical diameters, measured at controlled temperature with in-process SPC. A part measured warm reads oversize, so the inspection record states the temperature at measurement.
Do you offer passivation and electropolishing?
Yes, passivation to ASTM A967 and electropolishing, both in 3 to 7 days. Both are finishing operations, not coatings, so they do not change the part dimension beyond the controlled removal.
What is the lead time and MOQ?
MOQ is one piece. Prototypes in 3 to 7 days, production in 7 to 15 days after drawing approval, finishing adds 3 to 7 days.