Guide to China Precision CNC Processing Factory Selection

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  Key takeaways
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  What to check on a China precision cnc processing factory
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  Start with the part, not the country
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  Machine list and the travel envelope
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  Tolerance, finish and what the report proves
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  Materials a precision factory should handle
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  Certifications, confidentiality and MOQ
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  Lead time, quote quality and total cost
• 9
  How to audit a China precision cnc processing factory

Most sourcing problems start before the RFQ. A buyer sends a drawing to ten China precision cnc processing factory contacts and compares price, but the drawing itself already decides which shops can quote. Feature count, wall thickness, datum structure and material drive the process plan more than the country does.

Write down four numbers before you email anyone: the tightest tolerance on the drawing, the largest outside dimension, the annual quantity, and the surface finish callout. Those four decide whether you need a 5-axis center, a mill-turn machine or a simple 3-axis mill. A shop with the wrong machine will still quote, and the price will look fine until the first article fails.

Also note which dimensions are functional and which are reference. A ±0.005 mm callout on a cosmetic edge costs money for no reason. Engineers who mark true functional tolerances get faster quotes and fewer arguments at inspection. This is the single biggest cost lever you control before the PO.

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  Tightest toleranceDrives machine choice and inspection method.
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  Largest dimensionMust fit inside the machine travel envelope.
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  Annual quantityDecides fixture design and whether tooling is worth it.
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  Finish calloutRa 0.2–0.8 μm needs different tooling than as-machined.

A real precision shop publishes its machine mix because the mix explains what it can and cannot do. GreatLight runs 127 high-precision CNC machines across 3 wholly-owned plants in Dongguan and Singapore, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. A Ø400 mm rotary table handles round work that would otherwise need a second setup.

Travel matters more than the model name. The large platform covers 4,000 × 400 × 150 mm. Medium platforms run 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Compact cells sit at 500 × 500 × 450 mm and 500 × 310 × 200 mm. If your part is 900 mm long, the compact cell is not a scheduling problem, it is a hard stop.

Five-axis work pays off when a part has undercuts, deep pockets on angled faces, or five faces that must share one datum. One setup removes the stack-up error that comes from flipping a part four times. For a flat bracket with two holes, three-axis is cheaper and just as accurate. Match the machine to the geometry, not to the brochure.

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  5-axisAngled faces, undercuts, one-datum parts.
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  Mill-turnShafts and housings with turned and milled features.
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  3-axisPrismatic parts with open faces.
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  Rotary tableØ400 mm round parts, indexed holes.

A tolerance claim is only as good as the measurement behind it. ±0.005 mm (±0.0002 in) is achievable on a rigid setup with the right tooling, but it depends on feature type, material and thermal control. A 200 mm aluminium plate behaves differently from a 20 mm stainless boss. Ask which features the shop will guarantee at that level and which will run looser.

Surface finish follows the same logic. Ra 0.2–0.8 μm is a fine finish that usually needs a dedicated finishing pass or a secondary operation. Ra 0.8–1.6 μm is common for sealing faces and bearing seats. Ra 1.6–3.2 μm is as-machined and fine for brackets. Over-specifying finish adds cycle time on every part, forever.

Inspection is the proof. A shop running 100% inspection before shipment should describe three stages: raw material check, in-process monitoring, and final inspection. Reports come on request. For medical and automotive work, the paper trail matters as much as the part. If a supplier cannot show an inspection plan, the tolerance claim is marketing.

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  Ra 0.2–0.8 μmFine finish, sealing faces, optical parts.
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  Ra 0.8–1.6 μmBearing seats and mating surfaces.
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  Ra 1.6–3.2 μmAs-machined, structural parts.
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  First articleCMM report before the full run.

Material range tells you how many process windows the shop has already tuned. Aluminium 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12 cover most brackets and housings. Stainless 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH cover food, medical and marine parts. Steels 1018, 1045, 4130, 4140, 4340 and A36 cover structural and tooling work.

The hard materials separate shops. Titanium TA1, TA2 and TC4 (Ti-6Al-4V) plus Inconel need low cutting speeds, rigid tooling and heat control. Not every factory will quote them, and the ones that do will ask about the drawing tolerance before giving a number. That question is a good sign.

Copper and brass grades C101, C103, C110, beryllium copper, C27400, C28000 and C36000 come up in electronics and RF work. On the plastic side, ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre all machine differently. PEEK and carbon fibre are abrasive and need carbide or diamond tooling. Send the grade, not just the word "plastic".

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  Aluminium6061, 7075, 2024, 6082 and more.
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  Stainless303, 304, 316L, 17-4PH, 440C.
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  Titanium and InconelTC4, TA2, Inconel, magnesium.
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  PlasticsPOM, PEEK, PC, PA, carbon fibre.

Certifications are industry keys, not trophies. ISO 9001:2015 is the baseline quality system. IATF 16949:2016 is what automotive and EV buyers ask for first. ISO 13485:2016 covers medical devices. ISO 27001:2022 covers information security, which matters when you upload CAD files that are not public. Check the scope on the certificate, not just the logo.

Confidentiality should be a process, not a promise. Uploads are treated as secure and confidential, and an NDA is available on request. If your part is pre-launch, sign the NDA before you send the full drawing package. Send a simplified model first if the geometry is sensitive.

MOQ is the fastest way to read a factory. GreatLight has no minimum order quantity and runs from one prototype to 10,000+ part runs. A shop that only wants high volume will price a prototype high on purpose. A shop that only does prototypes cannot hold process control across a 5,000-part lot. You want both paths under one roof, because the fixture built for the prototype is the one that should carry into production.

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  ISO 9001:2015Baseline quality management.
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  IATF 16949:2016Automotive and EV programs.
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  ISO 13485:2016Medical device components.
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  ISO 27001:2022Data and file security.

Lead time claims are easy to make and easy to check. A quotation and free DFM analysis within 12 hours is a reasonable benchmark for a shop with an engineering desk. Production can start within 24 hours once the drawing and material are confirmed. Parts ship in 3–5 days for standard work. Historic late-delivery probability sits below 2%, which is the number to ask about, not the best week the sales team remembers.

Read the DFM notes, not just the price. A good quote flags a 0.5 mm wall that will deflect, a sharp internal corner that needs a smaller cutter, or a tolerance that forces a second operation. Those notes save money in the run. If the quote is a bare price with no comments, the CAM team may not have opened your file.

Total cost includes finishing and freight. Anodizing, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing, polishing and laser marking all add steps. Laser marking has a minimum character height of 1.5 mm, so plan part numbers accordingly. A cheap machining price plus a badly planned finish schedule is not cheap.

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  Quote in 12 hoursWith free DFM analysis.
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  Start in 24 hoursAfter drawing and material confirmation.
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  Ship in 3–5 daysStandard production lots.
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  FinishingAnodizing, plating, coating, laser marking.