China's large scale CNC: what engineers should check before quoting

A 200 mm bracket and a 3,000 mm structural beam can use the same cutting tools and the same CAM software. What changes is everything around them. Thermal drift over a long part, fixture stiffness, and how the machine holds position at the far end of travel all start to matter more than spindle speed.

In practice, we treat large-scale work as parts that need more than 1,000 mm of travel on at least one axis, or parts heavy enough that lifting and re-clamping becomes a handling risk. That covers a lot of ground: aerospace structural members, EV battery tray sections, robotics gantries, pump housings and long mold inserts.

The reason is simple. A 0.01 mm error at the spindle becomes a 0.1 mm gap when the tool reaches 2,000 mm from the datum, if the setup is not stable. Large parts do not forgive loose fixturing.

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  Travel over 1,000 mmUsually means a gantry or a long-bed bridge machine.
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  Part mass over 200 kgHandling and clamping dominate the setup plan.
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  Many features on one faceFive-axis access can remove two or three re-clampings.

GreatLight runs 127 high-precision CNC machines across three wholly-owned plants covering 7,600 m² in Dongguan, plus a factory in Singapore. The largest travel is 4,000 × 400 × 150 mm on a long-bed machine, which suits long extrusions, rails and beams. Medium frames run 750 × 1,150 × 550 mm and 600 × 600 × 600 mm, and the compact cells handle 500 × 500 × 450 mm and 500 × 310 × 200 mm.

Sixteen simultaneous 5-axis machining centers do the complex work. Twelve four-axis mills and 27 three-axis machines cover the simpler geometry, and 16 mill-turn centers take parts that need turning and milling in one setup. A Ø400 mm rotary table is available for round or index features.

The selection question is not "which machine is best". It is which machine removes the most setups while still holding tolerance. A part that fits a 3-axis machine with two setups is often cheaper and faster there than on a 5-axis center.

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  Long and thinLong-bed machine, support the middle to stop chatter.
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  Box-shaped, 5 facesSimultaneous 5-axis in one setup.
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  Round with cross holesMill-turn, avoids a second fixture.

Aluminium is the easiest large-part material. Grades 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082 and 7075 all machine cleanly, and 7075 gives the best strength-to-weight for structural work. The catch is stress. A long aluminium beam machined from plate can move 0.2 mm or more after the skin is removed, so rough, stress-relieve, then finish.

Stainless 303, 304, 316, 316L, 420, 430, 431, 440C and 17-4PH (SUS630) hold up better dimensionally but cut slower and work-harden. Steel grades 1018, 1045, 4130, 4140, 4340, A36 and tool steel are common for structural and mold work. Titanium TA1, TA2, TC4 (Ti-6Al-4V), Inconel and magnesium AZ31B / AZ91D are available, though titanium and Inconel long parts need slower feeds and more tool changes.

Copper and brass grades C101, C103, C110, beryllium copper, C27400, C28000 and C36000 machine fast and hold tolerance well. Plastics such as ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE and carbon fibre are usually fine for large panels, but PEEK and carbon fibre need sharp tooling and good extraction.

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  Aluminium plateRough, stress-relieve, finish. Plan for movement.
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  Stainless and steelSlower cutting, better dimensional stability.
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  Titanium and InconelBudget tool wear into the cycle time.

Five-axis machining is not automatically better. If a part has one flat face with holes and a few pockets, a 3-axis machine with a good fixture will beat a 5-axis center on cost and often on lead time. The 5-axis advantage appears when the part has features on multiple faces at compound angles, or when a single setup removes a real alignment risk.

Long parts also have practical limits. A 4,000 mm beam with a tight flatness callout may need the part supported at multiple points and checked in stages. If the drawing demands ±0.005 mm across the full 4,000 mm, we will say so before quoting, and we may suggest splitting the part or relaxing the datum.

Very thin walls are another case. Below about 1.5 mm on a large aluminium part, chatter and distortion become the limiting factor, not the machine. Sometimes the honest answer is a different process, such as casting or sheet metal fabrication.

We quote from the drawing, not from a catalog. If the geometry does not suit large-scale CNC, we say that too.

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  One flat face onlyThree-axis with a solid fixture is usually cheaper.
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  Full-length tight toleranceAsk about datum strategy before committing.
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  Thin walls under 1.5 mmConsider casting or sheet metal instead.

Every part gets 100% inspection before shipment, covering raw material check, in-process monitoring and final inspection. Reports are available on request. For a large part, we usually inspect in stages, because a 3,000 mm part cannot be fully verified after it leaves the machine if the fixture was released.

Quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours of approval, and parts ship in 3–5 days for standard work. Historical late-delivery probability is below 2%. Those numbers depend on part complexity and material availability, so they are confirmed with the quote.

There is no minimum order quantity. We run one prototype or 10,000+ part runs. Uploads are secure and confidential, and an NDA is available on request. Certifications held are ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. Finishes include anodizing, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing, polishing and laser marking.

For large work, send the 3D model and a 2D drawing with datums, plus the flatness and parallelism callouts. Those are the two documents that decide whether the part is a good fit for China's large scale CNC capacity.