China's Major CNC Processing Experts: What Large High-Precision Work Really Takes

A large part with features on several faces is not a three-axis job in practice. Every repositioning of a heavy workpiece adds setup error, and the fixture itself starts to bend under load. On a 4,000 mm long frame, a tenth of a millimetre of fixture deflection shows up directly in the bore positions.

Simultaneous five-axis work cuts the number of setups. The tool reaches the feature at the correct angle instead of the operator tilting the part by hand, so hole-to-hole and face-to-face relationships stay inside one datum scheme. GreatLight runs 16 simultaneous five-axis machining centers for this reason, alongside 12 four-axis mills and 27 three-axis machines for simpler geometry.

Five-axis is not automatically the right answer. A flat plate with holes on one face machines faster and cheaper on a three-axis mill with a rigid tombstone. The judgment call is the number of distinct tool approach directions and how tightly those directions must relate to each other.

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  Use five-axis whenFeatures sit on 3+ faces and must share one datum, or the part is too heavy to reposition accurately.
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  Stay on three-axis whenWork is single-face, flat, and setup error can be absorbed by the tolerance.
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  Watch fixture stiffnessOn long parts, support spacing matters more than spindle power.

GreatLight works to ±0.005 mm (±0.0002 in) on critical features. That number only means something when it is attached to a feature and a measurement method. A bore diameter held to ±0.005 mm is routine on a good five-axis center with thermal compensation. The same callout on a 3,000 mm span between two bores is a different problem, because thermal growth of the part and the machine now dominate.

Surface finish ranges from Ra 0.2–0.8 μm on fine-finished sealing faces to Ra 1.6–3.2 μm on as-machined surfaces. Finer finishes usually mean slower passes and more tool changes, so specify the coarsest finish that still functions. Engineers often over-specify here and pay for it in cycle time.

Inspection is the other half of the tolerance story. A shop that reports ±0.005 mm without telling you which instrument, at what temperature, and against which datum is not giving you usable data. We run raw material checks, in-process monitoring and final inspection on 100% of parts, with reports on request.

Aluminium grades like 6061-T6, 7075 and 6082 cut fast and hold tolerance well, which makes them the default for large structural parts. 7075 machines cleanly but moves more after roughing, so we leave stock and take a stress-relief pass before finishing. On a 2,000 mm plate, that step is the difference between a flat part and a banana.

Stainless 304 and 316L work-harden quickly. Heavy roughing with a light finishing pass tends to fail; the tool has to stay engaged and the coolant has to reach the cut. 17-4PH is common in aerospace and medical work and behaves better after heat treatment, so the sequence matters as much as the grade.

Titanium TC4 (Ti-6Al-4V) and Inconel sit at the difficult end. Low thermal conductivity pushes heat into the tool, so speeds drop and cycle times rise. Magnesium AZ31B and AZ91D cut easily but need careful chip handling because fine magnesium swarf is a fire risk. We machine all of these on the same floor, which is why the quote depends on the geometry, not just the material name.

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  Aluminium 6061-T6General structural work, good stability, fast cycles.
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  Stainless 316LCorrosion resistance, but keep the cutter engaged.
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  Titanium TC4Aerospace and medical, slow speeds, rigid setup.
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  InconelHigh-temperature parts, short tool life, plan for it.

Ask for the machine list with travels, not a machine count. A shop with 50 small three-axis mills cannot make a 3,000 mm rail no matter how many machines it owns. Travel figures tell you what is physically possible.

Then ask how they hold a datum across setups. The good answers sound boring: a probing routine, a documented setup sheet, a specific fixture. Vague answers about experience are a warning sign on large parts.

Certification is a floor, not a ceiling. GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. Those cover quality systems, automotive, medical devices and information security respectively. They tell you the process is documented and auditable, which matters when a part fails and you need to trace why.

Finally, check the post-machining path. A part that needs anodizing, bead blasting and laser marking should not travel between three vendors, because every handoff is a chance to lose a dimension or damage a finished face. Keeping finishing in-house is one of the few real advantages a large Chinese supplier can offer.

Quotation and a free DFM analysis come back within 12 hours. Production can start within 24 hours of an approved drawing and material availability. Parts typically ship in 3–5 days for standard work, though large multi-setup parts and difficult alloys run longer. Our historical late-delivery probability is below 2%.

There is no minimum order quantity. One prototype and a 10,000+ part run go through the same floor, which matters for engineers who need to validate a design before committing tooling. Uploads are handled as confidential, and an NDA is available on request.

For large precision parts, the honest answer on schedule depends on three things: how much material has to come off, how many setups the geometry needs, and whether heat treatment or surface finishing is in the route. Send those three answers with the drawing and the quote will be accurate rather than optimistic.