China CNC Machine Service: What Engineers Should Check Before Sending a Drawing

A good China CNC machine service is only as good as the machine it puts your part on. The first question is not how cheap the quote is but which spindle will cut the geometry. A bracket with holes on five faces needs a different setup than a shaft with a single turned diameter, and the two should not be quoted against each other.

GreatLight runs 127 high-precision CNC machines across three wholly-owned plants in Dongguan and a factory in Singapore. That includes 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Travels range from 500 × 500 × 450 mm up to 4,000 × 400 × 150 mm, with a Ø400 mm rotary table for round work.

The practical effect is fewer setups. One 5-axis cycle can finish five faces of a housing and hold position between them, which removes the stacked error that comes from re-clamping on a three-axis machine. For a long extrusion or a frame rail, the 4,000 mm travel matters more than the axis count.

What does not fit: parts under roughly 20 mm with thin walls below 0.5 mm, deep bores with an aspect ratio past 8:1, and features smaller than the cutter can reach. Those need EDM or a different process, and a supplier who says yes to everything is telling you they did not read the drawing.

Every supplier page quotes a tolerance number. The useful question is which features on your drawing that number covers and how it is verified. Our general machining tolerance is ±0.005 mm (±0.0002 in) on critical dimensions, measured with calibrated instruments and reported on request.

Tolerance is not free. Holding ±0.005 mm on a 300 mm aluminium plate means temperature control, fixturing and slower passes. If half the drawing sits at ±0.1 mm, say so, and the quote drops. Engineers who mark only the functional dimensions get better prices than engineers who tolerance everything.

Surface finish matters just as much. As-machined surfaces land at Ra 1.6–3.2 μm, a high-finish pass reaches Ra 0.8–1.6 μm, and fine finishing gets to Ra 0.2–0.8 μm. A sealing face and a clearance slot should not share the same callout.

Material changes the answer. Aluminium 6061 and 7075 cut cleanly and hold tight numbers. Stainless 316L and 17-4PH work-harden, so light passes and sharp tooling are required. Titanium TC4 and Inconel move more under heat, which means the finishing cut has to be planned from the start.

The workflow starts with a drawing and a 3D model. Within 12 hours we return a quotation plus a free DFM analysis that flags thin walls, unreachable corners, toleranced holes that should be reamed, and features that would be cheaper as a separate part. Production can start within 24 hours of approval.

Materials come from stocked or qualified sources. We hold aluminium 6061-T6, 7075, 2024 and ADC12; stainless 303, 304, 316L, 440C and 17-4PH; steels including 4140, 4340 and A36; copper and brass grades such as C36000; titanium TA2 and TC4; and plastics from POM and PEEK to carbon fibre.

Finishing is handled in house or by qualified partners: anodizing in clear, colour, hardcoat and conductive types, electroless nickel and zinc plating, powder coating, black oxide, bead blasting, brushing and polishing. Laser marking is available down to 1.5 mm character height.

Inspection is 100% before shipment, with raw material checks, in-process monitoring and a final inspection. Reports are issued on request. Our historical late-delivery probability sits below 2%, and parts normally ship in 3–5 days once production is running.

Certificates only help if the auditor understands your industry. We hold ISO 9001:2015 for general quality management, IATF 16949:2016 for automotive and EV work, ISO 13485:2016 for medical devices, and ISO 27001:2022 for information security.

That last one matters more than buyers expect. Your CAD files, BOMs and volumes are commercially sensitive. Uploads stay confidential, and a non-disclosure agreement is available on request before any file changes hands.

If your product is a prototype for aerospace, robotics, electronics, new energy or industrial machinery, the same process discipline applies. The difference is which clauses of the standard get audited and which inspection records you will be asked to keep for traceability.

No minimum order quantity applies. We run single prototypes and production runs past 10,000 parts on the same equipment, so the process you approve at prototype stage is the process that ships in volume.

Offshore machining pays off when your part is machinable, the drawing is stable, and you have time for one shipment cycle. It is a poor fit when the design is still moving weekly, when a fit issue needs a same-day physical fix, or when the part is so simple that a local shop can beat the logistics.

It is also a poor fit when the part is enormous and heavy. A 4,000 mm frame is possible, but freight and handling can outweigh the machining saving. Similarly, high-volume castings and stampings belong in those processes, not in a mill.

Ask for the process plan, not just the price. Which machine, how many setups, which datum, how the critical dimension is measured. A supplier who can answer that in writing on the first reply is usually the one who will answer it on the last shipment.

Then check capacity against your ramp. Three plants and 150 technicians absorb a sudden increase better than a single-floor shop, and a Singapore site can shorten logistics for Southeast Asia assembly lines.