We turn 303, 304, 316L, 420 and 17-4PH bar into shafts, fittings and valve bodies. Tolerances to ±0.005 mm, finishes down to Ra 0.2 μm, and every batch inspected before it ships.
Four failures we see on incoming drawings every week.
Austenitic grades work-harden fast. A tool that rubs instead of cuts tears the surface, and 304 threads pick up on the mating part. We run sharp inserts, higher feed and a sulfur-bearing grade such as 303 when the part does not need corrosion resistance.
Long slender shafts and thin-wall tubes deflect under cutting force. Turn the OD first and the bore comes back oval by 0.02 mm or more. We sequence roughing and finishing in separate passes and check roundness on the machine before the part comes off.
316L is gummy. Light finishing passes smear rather than shear, leaving Ra above 1.6 μm and visible chatter marks on a sealing face. We push feed rate and depth of cut instead of dropping them, then verify with a profilometer.
Stainless moves after machining as residual stress releases. A part that measures in tolerance on the lathe can go out of tolerance two days later. We rough, stress-relieve when the drawing allows, then finish and measure at 20 °C.
Grade selection, tooling and inspection sequence decided before the first chip.
Most stainless turning problems are material problems wearing a machining costume. 303 machines cleanly and holds a fine finish, but its sulfur content limits weldability and slightly lowers corrosion resistance. 304 is the general-purpose choice and work-hardens readily. 316L adds molybdenum for chloride environments and turns gummier than either.
For high-strength parts we use 17-4PH (SUS630), which reaches roughly 1,100 MPa after aging. 420 and 440C cover wear surfaces such as shafts and valve stems. We recommend a grade from the drawing's function, not from what is already on the shelf.
Stainless bar arrives with residual stress from rolling or drawing. Cut a lot of material off one side and the part bends toward the relieved side. On a Ø30 mm shaft with an 8 mm flat, that movement can exceed the ±0.005 mm drawing tolerance before the part ever reaches inspection.
We rough with stock left on, let the part equalize, then take the finishing pass. For parts with tight concentricity we turn the critical diameters in one clamping on a mill-turn center instead of moving the part between operations. That removes the re-chucking error entirely.
Machinability is rated against 303 as the baseline.
| Grade | Typical use | Machinability |
|---|---|---|
| 303 | Shafts, fittings, no welding | Best, reference grade |
| 304 | General parts, food equipment | Good, work-hardens |
| 316 / 316L | Marine, chemical, medical | Fair, gummy, needs sharp tools |
| 17-4PH (SUS630) | High-strength shafts, aerospace | Fair, age to ~1,100 MPa |
| 420 / 431 | Valve stems, pump parts | Good, harden to 50 HRC |
| 440C | Bearings, wear surfaces | Hard to turn, 58 HRC max |
One shop covers the turned part and everything that happens to it after.
16 mill-turn centers and 127 machines total handle bar work from Ø2 mm up to 4,000 mm, with live tooling for cross-holes and flats in the same setup.
16 simultaneous 5-axis centers cut angled ports, impeller passages and complex contours that a lathe alone cannot reach.
Turned prototypes ship in 3–5 days so the design can be tested on the bench before tooling is committed.
Passivation, bead blasting, polishing, electroless nickel and laser marking, with character height down to 1.5 mm.
Enclosures, brackets and die-cast housings for the assembly your turned part sits inside.
Raw material certificates, in-process checks and final dimensional reports on request, with 100% inspection before shipment.
Numbers are for the Dongguan plant unless noted.
| Item | Range |
|---|---|
| Turning tolerance | ±0.005 mm (±0.0002 in) |
| Fine finish | Ra 0.2–0.8 μm |
| Standard finish | Ra 0.8–1.6 μm |
| As-machined finish | Ra 1.6–3.2 μm |
| Rotary table | Ø400 mm |
| Maximum part size | 4,000 mm |
| Order quantity | One prototype to 10,000+ parts |
| Quote turnaround | 12 hours with free DFM analysis |
Six things that decide whether the turned parts fit the first time.
Not just in the sample. Process capability is monitored on every batch, and 99.99% of parts meet the drawing at final inspection.
We flag thin walls, sharp internal corners and tolerances that will cost you money before you place the order.
Once the drawing and material are confirmed, the first operation can be on a machine the next working day.
Founded in 2011, three wholly-owned plants and 150 technicians working mainly in stainless, steel and aluminum.
ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022 cover quality, automotive, medical and data handling.
One prototype or a 10,000-part run goes through the same inspection process and the same report format.
Sensor housings and fluid fittings turned from 303 and 316L, then passivated and laser marked.
316L and titanium shaft components with fine finishes for instrument assemblies.
Valve stems and drive shafts in 420 and 431, heat treated and ground where the drawing calls for it.
17-4PH actuator pins and joint hardware turned to tight concentricity in one clamping.
Start from the service environment. Chlorides or washdown means 316L. If the part only needs strength and finish, 303 turns faster and cheaper. Welded assemblies rule out 303 because of its sulfur content.
When the drawing calls for high strength, 17-4PH is the usual answer. It machines in the annealed condition and ages to roughly 1,100 MPa without the distortion of a quench-and-temper cycle.
Yes, within limits. Diameter and concentricity on a rigid part are routine. Length over 300 mm is where thermal growth and deflection start to matter, and we may need to turn between centers or add a steady rest.
If a feature is genuinely beyond that, we will say so in the DFM report rather than quote a number we cannot hold.
Cutting force is the enemy. We take lighter radial passes, support the wall with a fixture or expanding mandrel, and finish in a separate operation after the part has cooled.
Walls below 0.8 mm get a design note, because at that thickness the clamping pressure alone can leave a mark.
Standard turning gives Ra 1.6–3.2 μm. A controlled finishing pass reaches Ra 0.8–1.6 μm, and polishing or lapping takes it to Ra 0.2–0.8 μm.
Tell us the seal type and the finish requirement together. A face that is too smooth can fail to hold a static seal as well as one with the specified roughness.
Yes. Passivation removes free iron left by tooling and restores the chromium oxide layer on 304, 316L and 17-4PH. It matters most on parts headed for chemical, marine or medical service.
Bead blasting, tumbling and brushing are also available when the drawing calls for a cosmetic finish instead.
A STEP or IGES file, a 2D drawing with tolerances and finish callouts, the grade, and the quantity. Material certificates and inspection reports are quoted on request.
Missing a dimension is common. We flag it in the DFM analysis instead of guessing, and you get the quote and the notes together within 12 hours.
No. One prototype and a 10,000-part run both go through the same process. The difference is in the fixturing and the inspection sampling plan, not in whether we will take the job.
Prototypes typically ship in 3–5 days once production starts.
We sign your NDA or provide ours. Uploads are handled as confidential, access is limited to the engineers and machinists on the job, and ISO 27001:2022 covers our information handling.
Ask for the NDA before you send files if your process requires it.
Upload your file and we will return pricing, lead time and a DFM note within 12 hours. No minimum order quantity, and 100% inspection before anything ships.
12-hour quote100% inspectionNo minimum order quantityNDA on request
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CNC Metals 13 grades
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