CNC Online Processing in China: How the Upload-to-Part Flow Works

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  What CNC Online Processing in China Actually Automates
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  Files, Tolerances and Surface Finish: Where Online Quotes Drift
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  DFM Feedback: The Part of the Process That Changes Your Design
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  Materials, Quantity and What an Online Route Handles Well
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  Inspection, Certification and Shipping Out of Dongguan
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  When Online CNC Processing Fits and When It Does Not

The word online covers two different things, and mixing them causes most of the confusion. The first is quoting: geometry in, price and lead time out. The second is machining: chips on the floor. Only the first is automated end to end. A script reads your solid model, extracts the bounding box, volume, hole count and tool reach, then returns a number.

That number is an estimate built from feature recognition, not from a machinist reading your drawing. It is usually right for simple prismatic parts and usually wrong for anything with deep pockets, thin walls or tight true-position callouts. This is why an online quote on a bracket is trustworthy and an online quote on a manifold is a starting point for a conversation.

Machining itself is not automated in the same way. A programmer still picks workholding, sets the datum, chooses tools and writes or verifies the toolpath. At GreatLight that step happens with human review before a spindle turns. The online layer removes travel and email delay; it does not remove engineering judgment.

The practical consequence: treat an instant quote as a fast first data point. Send the file, get the number, then ask for DFM feedback before you commit to a run of 500.

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  AutomatedGeometry parsing, material cost, machine time estimate, quote generation.
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  ManualWorkholding choice, datum strategy, toolpath verification, first-article check.

Send STEP or Parasolid for anything with 3D surfaces. Send DXF for flat sheet parts. STL is a mesh, so the quote engine guesses at cylinders from triangles and can misread hole diameters by 0.05–0.1 mm. If you only have an STL, expect to confirm critical dimensions by email.

Default tolerances matter more than most engineers expect. General machining holds ±0.1 mm comfortably. Tightening a single bore to ±0.005 mm is achievable on our 5-axis centers, but it changes inspection time and sometimes the process plan. Mark only the features that need it. A drawing where every dimension is ±0.01 mm costs more and slows the job.

Surface finish follows the same logic. As-machined runs Ra 1.6–3.2 μm. A Ra 0.8–1.6 μm finish is a normal fine-machining pass. Below Ra 0.8 μm you are into lapping or polishing territory, which is a separate operation and a separate line on the quote.

One habit that saves money: put tolerance and finish notes in the 3D file as annotations, not only on a separate PDF. When the model and the drawing disagree, the shop has to stop and ask, and that email round trip is where your two-day advantage disappears.

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  Best uploadSTEP AP214 with annotations, or Parasolid.
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  Avoid for quotingSTL meshes and screen-capture screenshots.

DFM feedback is where an online order earns its keep. A tool can quote a 0.8 mm internal corner, but a 6 mm end mill cannot cut it without wire EDM or a sinker. Standard practice is to relieve internal corners to a radius at least one third of the pocket depth, and to keep floor radii larger than the tool nose.

Deep pockets are the other common issue. A pocket deeper than four times its width needs a long-reach tool, which deflects and chatters. If you can open the pocket width or split the part, the quote drops and the finish improves. Our engineers flag this within 12 hours of upload, together with the free DFM analysis.

Threads, reamed holes and tight bores should be called out explicitly. An online engine counts holes; it does not know that a Ø6 H7 reamed bore is different from a Ø6 clearance hole. State it in the model or the note field and the process plan will include the reamer.

None of this is exotic. It is the same conversation a machinist would have with you across a bench, just moved into the first reply instead of the first phone call.

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  Corner radiusAt least one third of pocket depth for internal corners.
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  Pocket depthKeep under 4× width to avoid long-reach tooling.
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  Reamed holesCall out H7 or press-fit bores as separate features.

Aluminium dominates online CNC work for good reason. 6061-T6 machines fast, holds tolerance and anodizes cleanly. 7075 gives higher strength at the cost of tool wear. 2024 is strong but corrosion-sensitive, so it usually needs a coating. Stainless 303 and 304 machine predictably; 316L is gummier and slower, and 17-4PH needs a heat-treat step that changes lead time.

Titanium TC4 (Ti-6Al-4V) and Inconel are machinable here but they are not cheap-and-fast parts. Tool life drops, cycle times rise, and the quote reflects it. If a part is titanium only because the last project was titanium, question that before uploading.

Quantity is where online processing in China beats most local shops. There is no minimum order quantity, so a single prototype and a 10,000-part run both go through the same quote flow. For one-offs, the setup dominates the price. For volume, the setup amortizes and the per-part cost drops, but only if the design has already survived a DFM pass.

Plastics are worth mentioning because engineers forget them. POM, PEEK, PA and ABS all machine on the same centers. PEEK is expensive and abrasive; POM cuts clean but moves with temperature. Both need sharp tooling and light finishing passes.

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  Fast and predictable6061-T6, 303 stainless, 1045 steel, POM.
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  Slow and costlyTi-6Al-4V, Inconel, 316L, PEEK.

Every part is inspected before shipment, not sampled. That means raw material check on receipt, in-process monitoring at the machine, and a final inspection before packing. Reports are available on request. For most parts a first-article layout plus dimensional report is enough; for regulated work you will want the full documentation pack.

Certifications are worth stating plainly because engineers get asked about them in audits. GreatLight holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The first covers general quality, the second automotive, the third medical devices, and the fourth information security, which matters when you are uploading proprietary CAD.

On the shop floor we run 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Maximum processing size is 4,000 mm. That range matters for long extrusion-style parts and for small high-feature count components alike.

Uploads are treated as confidential, and an NDA is available on request. If your drawing is under an existing NDA with another supplier, say so before uploading so we can paper the file transfer the same way.

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  Inspection100% before shipment, reports on request.
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  CertificationsISO 9001, IATF 16949, ISO 13485, ISO 27001.
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  Capacity127 machines, 16 five-axis centers, 4,000 mm max size.