Online CNC Processing Service Guide
This online CNC processing service guide is for design engineers and sourcing staff who upload CAD files and buy machined parts without visiting the shop floor. It covers the checks that separate a supplier you can build around from one that costs you a week. Read it and you can judge a quote, a tolerance claim and a lead time before you place the first order.
In this article
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Key takeaways
Online CNC processing service comparison checklist
Use this table to score two or three suppliers against the same job.
| Check | What good looks like | Warning sign |
|---|---|---|
| Quote turnaround | Engineer-reviewed quote and DFM notes within 12 hours | Instant number with no file comments |
| Tolerance capability | ±0.005 mm stated per feature, with an inspection method | One global tolerance printed on the quote |
| Lead time | Production starts within 24 hours, parts ship in 3–5 days | Two-week window before the first cut |
| MOQ | No minimum order quantity, one part accepted | Tooling or setup fee for a prototype |
| Certifications | ISO 9001, IATF 16949, ISO 13485, ISO 27001 on record | Certificates offered only after payment |
| Inspection | 100% inspection before shipment, reports on request | Sample-only inspection by eye |
| File security | Secure uploads, NDA available on request | Files sent as plain email attachments |
| Materials | Aluminium, stainless, steel, titanium, plastics in stock | Limited to one or two alloys |
Pick the supplier that answers the engineering questions
If a supplier cannot tell you how they will hold ±0.005 mm, which machine will run the part and when inspection happens, the price is the least useful number on the quote.
What an online CNC processing service guide should tell you first
An online CNC processing service removes the phone calls, the faxed drawings and the site visit. You upload a 3D model, get a price, and the part arrives. That is the promise. The engineering question is what happens between the upload and the shipping box, because that is where tolerances drift, finishes get skipped and lead times slip.
The first thing to check is who reads your file. A real service has a manufacturing engineer pull the model into CAM, look at the wall thickness, the tool reach and the datum scheme, then send back notes with the quote. At GreatLight that analysis comes back within 12 hours and it is free. If the quote arrives with no comments at all, nobody looked.
The second check is scope. Some platforms only mill. Others handle turning, sheet metal, die casting, vacuum casting and surface finishing under one roof. For a part that needs machining plus anodizing, one supplier removes the shipping step between operations and the argument about who scratched it.
Keep your own copy of the original model. The supplier's CAM file is not a deliverable, and revisions should always trace back to a file you control.
Tolerance, finish and machine travel: the numbers to verify
Tolerance claims are easy to print and hard to hold. A useful online CNC processing service guide gives you the conditions, not just the number. ±0.005 mm (±0.0002 in) is realistic on a rigid setup with a ground fixture, stable material and a finishing pass. It is not realistic on a 0.8 mm free-standing fin or on a part clamped only by a vise on one end.
Surface finish works the same way. Ra 0.8–1.6 μm is a normal machined finish. Ra 0.2–0.8 μm needs a dedicated finishing pass and usually a different tool. Ra 1.6–3.2 μm is as-machined and perfectly fine for brackets, housings and most internal parts. Specify finish only where a seal, a bearing or a sliding surface needs it.
Size drives machine choice. GreatLight runs 127 high-precision CNC machines, including 16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers. Maximum processing size reaches 4,000 mm, with a 4,000 × 400 × 150 mm travel on the large frame and a Ø400 mm rotary table for round work.
Material also sets the limit. Aluminium 6061-T6 and 7075 cut cleanly and hold tight tolerances. 17-4PH stainless and Ti-6Al-4V move more under heat, so plan roughing and finishing as separate operations. Thin-wall Inconel parts need more passes and more patience, not a tighter tolerance callout.
- 1Tight tolerance, simple geometry
- 2Undercuts and angled holes
- 3Long, slender parts
- 4Cosmetic surfaces
MOQ, lead time and certification: what to check before you commit
Minimum order quantity is the quiet cost driver. A platform that accepts one part lets you validate a design before you spend on a run, and GreatLight carries no minimum order quantity from a single prototype to 10,000+ part runs. If a supplier quotes a setup charge on a prototype, you are paying for their scheduling, not for your part.
Lead time has two halves. The quote and DFM analysis should come back within 12 hours. Production can start within 24 hours of approval, and parts ship in 3–5 days. Ask what the clock starts on: purchase order, drawing approval or material arrival. The answers differ, and the difference is often a week.
Certifications should match the industry you sell into. ISO 9001:2015 covers general quality systems. IATF 16949:2016 is what automotive and EV programs expect. ISO 13485:2016 applies to medical devices. ISO 27001:2022 covers information security, which matters when you upload proprietary CAD. Ask for the certificate scope, not just the logo.
Inspection is the last gate. GreatLight inspects 100% of parts before shipment, with raw material checks, in-process monitoring and final inspection, and reports on request. If your drawing has a true position callout, say so at quote time so the inspection plan includes it.
File formats, quoting inputs and data security
Send a STEP or IGES solid for machining. Those formats carry the functional geometry a CAM programmer needs. DXF and DWG 2D drawings are useful as a companion when you have specific notes, datums or thread callouts, but a 2D file alone forces the supplier to guess the third dimension.
The model should be the master. Put tolerances on the drawing, not in a separate email, and state the critical features explicitly. If every dimension is ±0.005 mm, the part becomes expensive for no reason. Mark the three or four features that actually matter.
Uploads are secure and confidential, and an NDA is available on request. For defense, medical or unreleased consumer work, sign the NDA before the first upload rather than after. It costs nothing and removes a later argument.
Expect DFM notes on the first pass. Common ones: a pocket too deep for the tool diameter, a thread too close to a wall, a sharp internal corner that needs a corner radius, or a finish callout on a surface that will be gripped in the vise.
How to place and track an online CNC order
Seven steps from CAD file to inspected parts.
- 1Prepare the model and drawingExport STEP or IGES, add a 2D drawing with datums and critical tolerances. Remove construction geometry and hide unused bodies before export.
- 2Upload and describe the jobState material grade, quantity, finish and any inspection requirement. Aluminium 6061-T6, 20 pieces, clear anodize, first-article report is enough detail.
- 3Read the DFM notesExpect feedback within 12 hours. Check wall thickness, tool reach and corner radii against your design intent before you approve anything.
- 4Confirm material and finishMatch the alloy to the function. 6061 for general work, 7075 where strength matters, 316L for corrosion, PEEK for high temperature. Confirm the finish spec in words, not just a color.
- 5Approve and release to productionProduction can start within 24 hours of approval. Ask for the first-article plan on tight-tolerance features before the run begins.
- 6Check the inspection packageRequest dimensional reports for critical features. 100% inspection happens before shipment; reports come on request, so ask early.
- 7Receive and verifyParts ship in 3–5 days. Measure the critical features on arrival against your drawing, not against the supplier's report alone.
Online CNC processing service questions
Can I order just one part?
Yes. There is no minimum order quantity, so a single prototype goes through the same process as a production run.
The per-part cost is higher because setup is spread over one piece, but you get a real part to test instead of a guess.
What tolerance can I actually expect?
±0.005 mm (±0.0002 in) is achievable on rigid setups with stable material and a finishing pass.
Thin walls, long unsupported features and some titanium alloys will not hold that. Tell us which features are critical and the tolerance can be applied where it matters.
Which file format should I upload?
STEP or IGES for the 3D geometry, with DXF or DWG as a companion for 2D notes.
A 2D drawing alone is workable but slower, because the programmer has to interpret the third dimension.
How fast is the quote and the delivery?
Quotation and free DFM analysis come back within 12 hours. Production can start within 24 hours of approval.
Parts ship in 3–5 days. The clock depends on when material is released and the drawing is frozen.
Are my drawings kept confidential?
Uploads are secure and confidential, and an NDA is available on request.
For unreleased products, sign the NDA before the first upload so the terms cover the files from day one.
Do you handle machining plus finishing?
Yes. Anodizing, plating, powder coating, black oxide, bead blasting, polishing and laser marking are all available.
Laser marking has a minimum character height of 1.5 mm, so keep part numbers above that size.
Send a model, get an engineer-reviewed quote
Upload your STEP file and receive a quote with DFM notes within 12 hours. No minimum order quantity, 100% inspection before shipment.
12-hour quoteProduction in 24 hoursNo MOQ100% inspection
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