Large-Scale CNC Processing Services in China
This guide is for engineers and sourcing managers who need big machined parts, not small brackets. It covers what to check before you send a drawing: machine travel, 5-axis setup, achievable tolerance, certifications and MOQ. Read it and you can tell whether a Chinese supplier can actually cut your part or only quote it.
In this article
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Key takeaways
Large-scale CNC processing services in China: what to check first
Use the left column as your question list. The right column is what a capable supplier should be able to answer without going away to check.
| Check | What good looks like | Why it matters |
|---|---|---|
| Machine travel | 4,000 mm on the long axis | A part that overhangs the stroke needs a second setup |
| Axis count | 16 simultaneous 5-axis centers | Fewer setups means tighter position between faces |
| Tolerance | ±0.005 mm on stable features | Thin walls and deep pockets drift past this |
| Surface finish | Ra 0.8–1.6 μm as standard | Fine finish to Ra 0.2–0.8 μm needs extra passes |
| Certifications | ISO 9001, IATF 16949, ISO 13485, ISO 27001 | Shows which regulated industries the shop already serves |
| Inspection | 100% inspection before shipment | One report per batch, not per part, hides outliers |
| MOQ | No minimum order quantity | Prototype and production use the same setup logic |
| Quote turnaround | DFM feedback within 12 hours | Slow DFM usually means the part was never reviewed |
The short version
If the part fits the travel, needs three or more faces machined, and weighs more than two people can lift, plan for five-axis in China and check the certificate scope before you check the price.
What large-scale means in machine travel
Large-scale is not a marketing word. It is a number on a spec sheet. On our largest frame the travel is 4,000 × 400 × 150 mm, and that shape is unusual: a very long X, a shallow Y, and a short Z. It suits long beams, rails, structural plates and extruded profiles. If your part is 900 mm tall and 400 mm wide, it does not fit, no matter how long the machine is.
The next frame down runs 750 × 1,150 × 550 mm and 600 × 600 × 600 mm. Those are the sizes that cover most large brackets, housings and manifolds. Compact frames run 500 × 500 × 450 mm and 500 × 310 × 200 mm, with a Ø400 mm rotary table for round work. Send the bounding box and the heaviest single feature and you will get an honest yes or no.
Weight matters as much as size. A 4,000 mm steel beam can be lifted and clamped, but a 4,000 mm thin-wall aluminium extrusion will deflect under its own weight between supports. Tell the supplier where the part can be supported. If it cannot be supported anywhere, the tolerance on the far end will not hold.
Ask one more question: how many setups does this take? A part that fits the stroke in one setup is a different job from a part that needs three. Each extra setup adds a datum transfer, and datum transfer is where ±0.005 mm quietly becomes ±0.05 mm.
- 1Send the bounding boxLength, width, height in millimeters, plus part weight.
- 2Name the critical featureThe one dimension that decides whether the part works.
- 3Say where it can be clampedFree areas and forbidden areas, marked on the drawing.
Five-axis setup on parts that are hard to move
On a large part, the expensive minutes are not cutting time. They are the time spent moving the part, re-indicating it and hoping the second face lines up with the first. A 300 kg housing does not swing back onto the table easily. Every re-clamp is a chance to lose position.
Simultaneous 5-axis machining solves this by tilting the tool instead of the part. The machine reaches five faces in one setup, and the relationship between those faces is set by the machine, not by the operator. For large parts with bores on several faces, or pockets that meet at an angle, that is the difference between a part that assembles and a part that needs rework.
Five-axis is not automatically better. A flat plate with holes on one face is faster on a three-axis machine, and cheaper. A part with a single angled face can often be done on a four-axis mill with a tilting head. The rule we use: if the part needs three or more faces machined and weighs more than a person can lift, plan for five-axis.
One more limit. Five-axis work needs clearance for the head and the tool holder. Deep cavities with narrow openings can block the spindle before the tool reaches the bottom. Check the tool length needed against the cavity depth, and expect the shop to shorten the tool and reduce feed rather than risk a crash.
- 1Count the facesThree or more machined faces on a heavy part points to five-axis.
- 2Check head clearanceDeep narrow cavities can stop the spindle before the tool reaches depth.
- 3Watch tool stick-outA long tool deflects. Expect lighter passes and slower feed.
Tolerance and finish you can actually hold
±0.005 mm is a real number in our shop, and it is also a number with conditions. It applies to features that are rigid, accessible and measured at a stable temperature. A 20 mm bore in a 40 mm steel block will hold it. The same tolerance across 3,000 mm of unsupported aluminium will not, because the part moves more than the tolerance while it is being cut.
The practical split is this. Critical fits, bearing bores and mating faces get ±0.005 mm. General dimensions on large parts sit comfortably at ±0.05 mm, and pushing them tighter adds cost without adding function. Tell us which dimensions are functional and which are reference. That single decision usually removes more cost than any negotiation on hourly rate.
Surface finish follows the same logic. Ra 1.6–3.2 μm is as-machined and fine for most structural faces. Ra 0.8–1.6 μm is our standard for sealing faces and sliding surfaces. Ra 0.2–0.8 μm needs slower passes, a fresh tool and sometimes a finishing operation after heat treatment. On a large part, fine finish over a big area is a time cost, not a skill problem.
Heat treatment and coating change dimensions. Anodizing builds a few micrometres; hardcoat builds more. If a bore is anodized after machining, the bore shrinks. Say so on the drawing, and the bore can be cut oversize before coating.
- 1Mark functional dimensionsTighten only the fits that carry load or seal.
- 2Allow ±0.05 mm elsewhereGeneral dimensions on large parts rarely need more.
- 3Flag post-processingAnodizing and plating change bore sizes.
Certifications and audit trail
Certifications are a shortcut to knowing which industries a supplier already serves. ISO 9001:2015 covers general quality management. IATF 16949:2016 is the automotive and EV standard, and it means the shop already lives with traceability and change control. ISO 13485:2016 is for medical devices, where process validation and records are routine. ISO 27001:2022 covers information security, which matters when your drawings are the product.
Read the scope on the certificate, not just the logo. A certificate that covers machining of aluminium parts may not cover heat treatment or coating done by a subcontractor. Ask who does the outside operations and whether those suppliers are on the same quality system.
For regulated work, ask what the inspection record contains. Ours covers raw material check, in-process monitoring and final inspection, with reports on request. For large parts, the important record is often dimensional: which features were measured, on what instrument, at what temperature.
If your drawings are sensitive, an NDA is available on request, and uploads are handled as confidential. That is a document question, not a machining question, but it decides whether a supplier can be used at all.
- 1Check the certificate scopeMake sure subcontract operations are covered.
- 2Ask for the inspection record formatKnow what you will receive before you order.
- 3Settle the NDA earlyIt is faster before drawings are released.
Lead time, MOQ and how quotes are built
On a large part, lead time is dominated by material, not by cutting. A standard aluminium plate is on the shelf. A 4,000 mm 4140 forging may not be. Ask whether the material is in stock at the quoted size, and whether the quote assumes a sawn blank or a near-net shape. That one question explains most lead-time surprises.
Our standard flow is a quotation with free DFM analysis within 12 hours, production starting within 24 hours, and parts shipping in 3–5 days for repeat work with material on hand. First-off large parts take longer because of fixturing and first-article inspection. Historical late-delivery probability is below 2%, which is a record, not a promise for your specific part.
MOQ is not the constraint you might expect. There is no minimum order quantity, from one prototype to a 10,000-part run. What varies is setup: a one-off large part carries the full fixturing cost, while a repeat run spreads it. If you expect volume later, say so at quote stage and the fixture can be designed for both.
Quotes should be broken down enough to compare. Ask for material, machining, finishing and inspection as separate lines. If a quote is a single number, you cannot tell whether the supplier understood the part or just estimated by weight.
- 1Ask about material stockPlate on the shelf cuts weeks off large-part lead time.
- 2Separate the quote linesMaterial, machining, finishing and inspection should be visible.
- 3Mention future volumeFixture design can serve the prototype and the run.
Step by step: how to qualify a supplier for a large part
Run these in order. Each step is designed to kill a bad fit early, before you spend engineering time.
- 1Send the bounding box and weightLength × width × height in millimeters plus part weight. Ask directly whether it fits the machine travel, and ask for the travel figure in millimeters, not a photo of the machine.
- 2Mark functional dimensions onlyPut ±0.005 mm on fits and mating faces. Leave general dimensions at ±0.05 mm. Add a note saying which faces are datums for inspection.
- 3Ask how many setupsIf the answer is three or more on a part over 200 kg, ask whether five-axis can bring it to one. Request the fixture concept as a sketch, not a promise.
- 4Request DFM feedback in writingA capable shop returns notes on wall thickness, tool access, thread depth and corner radii, usually within 12 hours. Vague feedback means the part was not reviewed.
- 5Confirm material and blank formAsk if the material is in stock at the quoted size. Confirm whether the price assumes sawn plate, near-net forging or cast blank.
- 6Check certificate scope and NDAVerify that ISO 9001, IATF 16949, ISO 13485 or ISO 27001 coverage includes the operations you are buying. Sign the NDA before releasing sensitive drawings.
- 7Agree the inspection recordDecide which features are measured, on what instrument, and what report you receive. 100% inspection before shipment is the baseline.
- 8Run a first article before the full runMeasure the first part against the drawing, including the datums. Fix the process on one part rather than on fifty.
Questions engineers ask before ordering
Can you machine a part longer than 4,000 mm?
Not in one setup. The largest travel we run is 4,000 × 400 × 150 mm. Longer parts are usually split into sections that bolt or weld together, with the joint designed as a datum.
Sometimes a part longer than the stroke can be repositioned mid-cycle on the same table, but the second position is a second setup. We will tell you which dimensions survive that and which do not.
Is ±0.005 mm realistic on a 2,000 mm aluminium part?
On rigid features, yes. On long unsupported sections, no. Aluminium moves with temperature and with the material removed during cutting, so a 2,000 mm span can shift more than 0.005 mm on its own.
The usual approach is to hold ±0.005 mm on the critical bore or fit, and let the long general dimensions sit at ±0.05 mm. Finish machining after a stress-relief step also helps.
Do you charge for DFM analysis?
No. Quotation and DFM analysis come back within 12 hours at no cost. You get the notes whether or not you place the order.
The notes usually cover wall thickness, tool access, thread depth, corner radii and any feature that will need a second setup.
What is the minimum order quantity for large parts?
There is no minimum order quantity. We run from one prototype to 10,000+ part runs on the same equipment.
For a single large part, the fixture cost is carried by that part. If volume may follow, tell us at quote stage so the fixture can be designed to serve both.
Which materials do you machine at this size?
Aluminium grades including 6061, 6061-T6, 2024, 5052, 5083, 6063, 6082, 7075 and ADC12. Stainless including 303, 304, 316, 316L, 17-4PH. Steel including 1018, 1045, 4130, 4140, 4340 and A36.
We also machine titanium TA1, TA2 and TC4 (Ti-6Al-4V), Inconel, magnesium AZ31B and AZ91D, copper and brass grades, and engineering plastics such as POM, PEEK and PC.
How do you protect our drawings?
Uploads are handled as secure and confidential, and an NDA is available on request. ISO 27001:2022 covers our information security management.
If your part is export-controlled or under a customer NDA, tell us before releasing files so the right agreement is in place first.
Send the bounding box, get a real answer
Quotation and DFM analysis within 12 hours. Tell us the length, width, height and weight, and we will say whether it fits the machine.
12-hour quote100% inspectionNDA on request
More from the shop floor
We publish setup notes, tooling trials and inspection data from the factory floor.
