Chinese CNC Processing Expert: How to Judge One Before You Send a PO

Most suppliers in Dongguan and Shenzhen run three-axis vertical mills. That covers flat plates, brackets, and simple housings, and it is cheap. The moment a part needs features on five faces, or a true position callout across two datums, three-axis work means multiple setups. Each setup adds a re-fixture, a new origin, and stack-up error.

A Chinese CNC processing expert should be able to tell you which machine will run your part and why. We have 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, and 16 mill-turn centers. Maximum processing size is 4,000 mm. Common travels are 4,000 × 400 × 150 mm, 750 × 1,150 × 550 mm, and 600 × 600 × 600 mm.

Mill-turn matters more than buyers expect. A shaft with a milled flat, a cross hole, and a thread can leave one machine complete. That removes a second op and the concentricity drift that comes with it. Ask any Chinese CNC processing expert whether the turning and milling happen on the same spindle. The answer tells you a lot about their process planning.

• 1
  Five-axisOne setup for features on five faces; use it for contoured pockets and angled holes.
• 2
  Mill-turnCombines turning and milling; good for shafts with cross features.
• 3
  Large travelUp to 4,000 mm; long rails and beams fit without segmenting.
• 4
  Rotary tableØ400 mm; suits round parts that need indexed milling.

A ±0.005 mm tolerance is achievable on aluminum and on 17-4PH stainless when the geometry cooperates. It is not achievable on a thin wall, a long unsupported bore, or a part that moves after heat treat. That is why we ask for the drawing before quoting. A number without the feature list behind it means nothing.

Surface finish follows the same logic. Ra 0.8–1.6 μm comes off the machine with a correct cutter and feed. Ra 0.2–0.8 μm usually needs a finishing pass or a secondary operation, which changes cost and lead time. Tell us the finish on the functional face only. Polishing a non-sealing surface is money spent for nothing.

Some parts should not go to a Chinese CNC processing expert at all. A single plastic cover, a part with a 6-week schedule, or a design that is still changing every week is better served locally. Air freight and revision churn will eat the labor savings. Say so early; we would rather lose the order than ship scrap.

Aluminum 6061-T6 is the default for prototypes and most enclosures. It cuts fast, holds ±0.005 mm on moderate features, and anodizes cleanly. 7075 gives higher strength but machines slower and is harder to anodize to a uniform color. 2024 is strong and light, though it needs a protective finish or it will corrode.

Stainless is where quotes diverge most. 303 machines freely and suits shafts and fittings. 304 and 316 work-harden, so tool paths and feeds need care. 17-4PH (SUS630) holds tight tolerance after aging, which is why medical and aerospace parts use it. The alloy drives cycle time more than the part shape does.

Titanium TC4 (Ti-6Al-4V) and Inconel cut slowly and wear tools. Magnesium AZ31B and AZ91D cut fast but need chip control because fines are flammable. Plastics are a different problem: PEEK and POM move with temperature, so a ±0.005 mm callout on a long PEEK part is often unrealistic. Ask for the material first, then the tolerance.

Inspection is the part of the quote that buyers underweight. We check raw material on receipt, monitor in process, and inspect 100% before shipment. Reports come on request. Historical qualification rate is 99.99%. If a supplier cannot show you a first-article report, dimensional data, or a material cert, the tolerance claim is a guess.

Certificates have scope, and scope matters. ISO 9001:2015 covers general quality management. IATF 16949:2016 is the automotive standard and applies to production part approval. ISO 13485:2016 covers medical device manufacturing. ISO 27001:2022 covers information security, which is the one buyers forget. Ask which certificate applies to your part, not how many they hold.

For defense and medical work, confidentiality is a separate conversation. Uploads stay secure, and we sign an NDA on request before drawings change hands. If your compliance team needs the NDA signed first, send that request before the RFQ. It saves a week.

Send a STEP file and a 2D drawing with tolerances and finish. We return a quotation and a free DFM analysis within 12 hours. The DFM note flags features that will be hard to hold, thin walls that will chatter, and tolerances tighter than the process supports. That feedback is usually worth more than a small price difference.

Production can start within 24 hours of approval. Standard parts ship in 3–5 days. Historical late-delivery probability sits below 2%. There is no minimum order quantity, so one prototype and a 10,000-part run go through the same quoting path.

Post-processing covers anodizing (clear, color, hardcoat, conductive), electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, brushing, and polishing. Laser marking holds a minimum character height of 1.5 mm. Keep that in mind when you place a part number on a small face.