China Large CNC Machining Service Factory: How to Judge One
This page is for engineers and sourcing teams who need large machined parts, roughly 1 m to 4,000 mm, and want to separate real capability from a website claim. It covers machine travels, workholding, metrology, material behavior, and what to ask before you send a drawing.
What makes large machining a different problem
The part is bigger than the machine's sweet spot, so every decision about setup, heat, and measurement gets harder.
Machine travels and configurations that actually matter
A large part is not just a small part scaled up. On a 1,500 mm housing, the spindle may sit 800 mm from the column, and that overhang changes everything about rigidity. Thermal growth over a six-hour cycle can move the tool a few hundredths of a millimeter. A factory that lists 4,000 mm travel but only has one machine at that size will struggle with schedule. You want redundancy at the top end of the size range.
GreatLight runs 127 high-precision CNC machines across three wholly-owned plants, with a 4,000 mm maximum processing size. The largest travel is 4,000 × 400 × 150 mm. That shape suits long, narrow parts like structural rails, spars, and base plates. Medium travels of 750 × 1,150 × 550 mm and 600 × 600 × 600 mm handle gearbox housings, manifolds, and fixture plates. Compact travels of 500 × 500 × 450 mm and 500 × 310 × 200 mm cover brackets and small enclosures.
The machine mix matters as much as the envelope. Sixteen simultaneous 5-axis machining centers cut angled faces and compound bores in one setup, which removes the stack-up error that comes from flipping a large part four times. Twelve four-axis mills and 27 three-axis machines handle the bulk of prismatic work. Sixteen mill-turn centers cut shafts and ring parts in one cycle. A Ø400 mm rotary table adds fourth-axis work on parts that would otherwise need a custom fixture.
- 1Ask for the travel, not the part sizeA 4,000 mm machine can cut a 4,000 mm part only if the fixture and tool clearance fit inside the same envelope.
- 2Count machines at the top sizeOne large machine means a single spindle failure stops your order.
- 3Check the 5-axis countFewer setups on a large part means less re-datuming error.
Workholding and setup strategy for parts over 1 m
A 2 m weldment will sag under its own weight if you support it at four points. The fixture has to hold the part in a defined state, not just clamp it. For weldments, that often means stress-relieving before finish cuts and roughing with extra stock. For a 7075 aluminum spar, it may mean vacuum fixturing or a custom tombstone to avoid clamping distortion on thin walls.
Every additional setup adds a datum shift. A part cut in three setups accumulates three alignment errors on top of the machine's own positioning error. Five-axis work helps here. So does designing the fixture and the part together, which is why a DFM review before cutting matters more on large parts than on small ones. We return a DFM analysis with the quote, usually within 12 hours.
Handling is part of setup. A 200 kg part needs a crane, and the crane needs a path. A factory that moves large parts with a forklift and wooden blocks will hold different tolerances than one with a gantry and a granite surface plate. It is worth asking how parts move between operations.
Large-part capability at a glance
Numbers below come from our current machine list and inspection records.
| Item | Specification | Typical use |
|---|---|---|
| Maximum processing size | 4,000 mm | Rails, spars, base plates |
| Largest travel | 4,000 × 400 × 150 mm | Long, low-profile parts |
| Medium travel | 750 × 1,150 × 550 mm | Gearbox housings, manifolds |
| Medium travel | 600 × 600 × 600 mm | Fixture plates, frames |
| Compact travel | 500 × 500 × 450 mm | Brackets, small enclosures |
| Rotary table | Ø400 mm | Ring parts, 4th-axis work |
| Tolerance | ±0.005 mm | Bores, fits, mating faces |
| Finish | Ra 0.8–1.6 μm | Sealing and sliding surfaces |
| Finish | Ra 1.6–3.2 μm | General machined faces |
How you verify a large part after machining
Measuring a 3 m part is harder than cutting it. A caliper and a height gauge will not cover a 4,000 mm envelope. You need a large-travel CMM, a laser tracker for volumetric accuracy over long distances, or a portable measuring arm for features that cannot be moved to a granite plate. If the factory cannot measure the part, it cannot prove the tolerance.
Ask what the inspection report contains. A useful report ties each critical dimension to a drawing callout, states the instrument used, and shows the measured value against the nominal. Reports that only say "passed" do not let you do anything with the data. We inspect 100% before shipment, covering raw material check, in-process monitoring, and final inspection, with reports on request.
For very large parts, some dimensions are better proven at the assembly stage. A laser tracker can align two sub-assemblies in place. That is often more useful than a single CMM report, because it reflects how the parts will actually fit together.
Material behavior changes the cutting strategy
Cutting a 200 kg block of 7075 aluminum is a different job from cutting a 4340 steel weldment. Aluminum moves heat into the chip and cuts fast, but it also moves under clamping and can distort after material removal. Steel weldments carry residual stress from welding, so roughing, stress relief, and finishing are usually separate operations with time between them.
Titanium and Inconel sit at the other end. TC4 (Ti-6Al-4V) and Inconel generate high cutting temperatures, work-harden quickly, and wear tools fast. Speeds and feeds drop, cycle times rise, and coolant strategy becomes a real decision rather than a default. A shop that quotes titanium at aluminum parameters is either guessing or planning to scrap the part.
We machine 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075, and ADC12 in aluminum; 303, 304, 316, 316L, 420, 430, 431, 440C, and 17-4PH in stainless; 1018, 1045, 4130, 4140, 4340, A36, and tool steel; copper and brass grades from C101 to C36000; and TA1, TA2, TC4, Inconel, and magnesium AZ31B / AZ91D. Plastics include ABS, PC, PMMA, POM, PA, PEEK, PP, HDPE, and carbon fibre.
Material choice also drives finishing. Anodizing and hardcoat change dimensions slightly. Electroless nickel adds a uniform layer that can tighten a bore. Laser marking needs a minimum character height of 1.5 mm to stay legible. Plan the finish before you set the final dimensions.
What to check before you place a large-part order
Certifications tell you the factory runs a documented process. GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022. The first two cover general and automotive quality systems. The third matters if your part touches a medical device. ISO 27001 covers information security, which is relevant when you send drawings and CAD files across borders.
Lead time is a capability question, not a promise. We return a quotation and free DFM analysis within 12 hours, and production can start within 24 hours. Parts ship in 3–5 days on standard work. Our historical late-delivery probability is below 2%. There is no minimum order quantity, so a single prototype and a 10,000+ part run go through the same process.
Confidentiality is usually the first concern for a new overseas supplier. Uploads are handled as secure and confidential, and an NDA is available on request. If your drawing package includes a fixture design or a proprietary geometry, sign the NDA before you send files.
One practical test: send a drawing with one tight bore, one long datum, and one thin wall, and ask for a DFM note with the quote. The quality of that note tells you more about the factory than any brochure.
- 1Match certificates to your industryISO 9001 for general work, IATF 16949 for automotive, ISO 13485 for medical.
- 2Ask for the inspection planWhich dimensions, which instrument, which report format.
- 3Confirm handling and fixturingHow the part is supported and moved between operations.
- 4Check the communication loopWho answers engineering questions, and how fast.
Common questions
How large a part can you machine in one setup?
Our largest travel is 4,000 × 400 × 150 mm, and the maximum processing size is 4,000 mm. That envelope suits long, low-profile parts.
Larger or taller parts may need multiple setups. We will tell you during the DFM review if a single setup is not realistic.
Can you hold ±0.005 mm on a part over 2 m?
The tolerance is achievable on specific features, such as a bore or a mating face, when the setup supports it and the material is stable.
Long spans accumulate thermal and clamping error. We usually agree on which dimensions are critical and inspect those against the drawing callout.
What inspection equipment do you use for large parts?
We use large-travel CMMs, laser trackers for volumetric accuracy, and portable measuring arms for features that cannot move to a plate.
Every part is inspected 100% before shipment, with reports on request.
Do you machine weldments as well as solid billet?
Yes. Weldments usually need stress relief between roughing and finishing, and extra stock on the finish cuts.
We will flag this in the DFM note because it changes both cost and lead time.
Is there a minimum order quantity?
No. We run from one prototype to 10,000+ part runs on the same process.
For large parts, the setup cost dominates at low volume, so the per-part price drops sharply once the fixture exists.
How do you handle confidentiality?
Uploads are secure and confidential, and we hold ISO 27001:2022 for information security.
An NDA is available on request if your package includes proprietary geometry or fixture designs.
Send a drawing and get a DFM note with the price
Quotation and free DFM analysis within 12 hours. No minimum order quantity.
12-hour quote100% inspectionNDA on request
