Supplier selection guide

Collaborative CNC Machining Services: 7 Proven Checks

This guide is for engineers and sourcing teams choosing a collaborative CNC machining services partner. It covers the checks that actually predict part quality: tolerance capability, material and finishing coverage, quote transparency, MOQ, certifications and confidentiality. Read it once and you can score any supplier on the same sheet.

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±0.005 mm tolerance4,000 mm max part sizeNo MOQISO 9001 / IATF 16949

On this page

1
Key takeaways
2
What to check, what a good answer looks like
3
Tolerance and DFM: where collaborative CNC machining starts
4
Materials, finishes and who owns the process
5
Lead time, MOQ and the real cost of a slow quote
6
Certifications, inspection and confidentiality
7
Seven steps to qualify a collaborative partner

Short version

Key takeaways

Tie the tolerance to a featureA ±0.005 mm claim means little until it is tied to a feature size and a sampling plan.

Quote speed reflects drawing reviewA supplier that returns DFM notes with the price usually catches problems before cutting metal.

MOQ decides if prototyping is practicalWith no minimum order quantity you can run one part, inspect, revise, then scale to 10,000+.

Certifications are scope questionsISO 9001, IATF 16949, ISO 13485 and ISO 27001 each cover a different risk.

Check capacity against your part envelopeMachine count and travels matter more than a list of equipment names.

Decision table

What to check, what a good answer looks like

Use this as a scoring sheet during supplier review.

Check	Weak answer	Strong answer
Tolerance	"High precision" with no number	±0.005 mm tied to named features
DFM feedback	Price only, no comments	Quote plus DFM notes in 12 hours
MOQ	500 pieces minimum	No minimum, one piece up to 10,000+
Certifications	One ISO 9001 copy	ISO 9001, IATF 16949, ISO 13485, ISO 27001
Capacity	"Many machines"	127 CNC machines, 16 five-axis centers
Part envelope	Not stated	Up to 4,000 mm, Ø400 mm rotary table
Finishing	Outsourced, no control	In-house anodizing, plating, laser marking
Inspection	Certificate of conformance only	100% inspection, reports on request

Check 1-2

Tolerance and DFM: where collaborative CNC machining starts

Most supplier problems start before the first cut. A shop that quotes from a STEP file without opening the drawing will miss tight callouts, thin walls and datums that cannot be reached in one setup. When you evaluate collaborative CNC machining services, ask what the shop does in the first 24 hours. GreatLight returns a quotation and a free DFM analysis within 12 hours, and production can start within 24 hours of approval.

Tolerance is the second half of that check. ±0.005 mm (±0.0002 in) is achievable, but only on features the process can actually hold. A 200 mm long bore and a 6 mm diameter pin do not behave the same way. Send the two or three features that carry function and ask the shop to confirm each one. If the answer is a single blanket number, keep asking.

Surface finish follows the same logic. Ra 0.2–0.8 μm is a fine finish, Ra 0.8–1.6 μm is the usual high-quality band, and Ra 1.6–3.2 μm is as-machined. Specify the finish only where it matters: sealing faces, sliding surfaces, optical seats. Polishing every face adds cost and can round edges you wanted sharp.

A simple test: ask for the inspection method behind the tolerance. Calipers cannot verify ±0.005 mm. A shop that names its CMM and its sampling plan is telling you it has done this before.

1
Give the functional featuresMark 2-3 critical dimensions instead of tolerancing the whole drawing.
2
Ask for the setup countFewer setups usually mean better position tolerance.
3
Match finish to functionRa 0.8–1.6 μm covers most mating surfaces.

Check 3-4

Materials, finishes and who owns the process

Material coverage is easy to claim and harder to prove. The useful question is which grades the shop machines every week, because that is where the feeds, speeds and tooling are already dialed in. A shop that runs 6061-T6, 7075, 304 and 316L daily will hold tolerance on those alloys far more consistently than one learning them on your job.

GreatLight machines aluminium grades including 6061, 2024, 5052, 6063, 6082, 7075 and ADC12; stainless 303, 304, 316, 316L, 17-4PH and 440C; steels such as 1018, 1045, 4130, 4140 and 4340; copper and brass including C36000 and beryllium copper; titanium TA2 and TC4 (Ti-6Al-4V); Inconel; magnesium; and plastics from POM and PEEK to carbon fibre.

Finishing is where schedules slip. If the machine shop sends parts out for anodizing, you inherit a second queue and a second set of tolerances. In-house finishing keeps the part under one quality system. Anodizing, electroless nickel, zinc, silver and gold plating, powder coating, black oxide, bead blasting, tumbling, brushing, polishing, and laser marking with a minimum character height of 1.5 mm can all sit in the same production plan.

For prototype runs, rapid processes matter too. Vacuum casting, sheet metal fabrication, die casting and 3D printing through SLM, SLA and SLS let you test form and fit before committing to a machining program.

1
Ask which alloys run weeklyRoutine work holds tolerance better than occasional work.
2
Keep finishing in-house when possibleOne vendor, one inspection record, fewer handoffs.
3
Check marking limitsLaser marking needs at least 1.5 mm character height.

Check 5-6

Lead time, MOQ and the real cost of a slow quote

Lead time is a system output, not a promise. It depends on machine availability, material stock and how fast drawings get reviewed. Ask for three numbers: quote turnaround, production start, and ship time for a typical part. GreatLight quotes within 12 hours, can start production within 24 hours, and ships parts in 3–5 days. The historical late-delivery probability is below 2%.

MOQ is the check that decides whether a supplier fits your program. A 500-piece minimum kills a prototype loop, because you need one part to test before you need five hundred. No minimum order quantity means you can run a single piece, measure it, change the design, and only then commit to a 10,000+ part run with the same supplier and the same process history.

Capacity belongs in the same conversation. Machine count sets the ceiling on how much work the shop can absorb without pushing your job to the back. GreatLight runs 127 high-precision CNC machines across three wholly-owned plants, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines and 16 mill-turn centers.

Part size is the other half. Travels of 4,000 × 400 × 150 mm handle long structural parts, 750 × 1,150 × 550 mm and 600 × 600 × 600 mm cover mid-size housings, and 500 × 500 × 450 mm or 500 × 310 × 200 mm suit compact work. A Ø400 mm rotary table supports cylindrical and angled features in one setup.

1
Ask for three datesQuote, production start, ship. Vague answers hide queue time.
2
Test MOQ with a single partOne good part proves more than a signed quality manual.
3
Match travels to your partA part that needs two setups costs more than one that fits.

Check 7

Certifications, inspection and confidentiality

Certifications are scope statements, not decorations. ISO 9001:2015 covers general quality management. IATF 16949:2016 applies to automotive production and its change-control discipline. ISO 13485:2016 speaks to medical device manufacturing. ISO 27001:2022 covers information security, which matters when your drawings and CAD files leave your network.

Ask which certificate applies to the process that will run your parts, and ask to see the scope. A certificate for a different site or a different product family does not cover your job.

Inspection is the practical side of the same question. 100% inspection before shipment, with raw material checks, in-process monitoring and final inspection, is a workable baseline. Reports are available on request. For a first article, ask for dimensional data on the critical callouts rather than a generic conformance sheet.

Confidentiality needs a process, not a promise. Uploads should be secure and confidential, and a mutual NDA should be available on request. If your program involves defense, medical or unreleased consumer products, settle the NDA before you send the STEP file. It costs a day and prevents a harder conversation later.

1
Match certificate to processIATF for automotive, ISO 13485 for medical, ISO 27001 for data.
2
Request dimensional dataAsk for numbers on the critical features, not a generic sheet.
3
Sign the NDA firstDo it before the first file upload.

How to run the review

Seven steps to qualify a collaborative partner

Run these in order. Each step can eliminate a supplier before you spend engineering time.

1
Send a real drawing, not a catalog partUse a part you have already made. Include material, critical dimensions and finish. A real drawing exposes how the shop reads GD&T.
2
Set the tolerance per featureMark 2-3 functional features at ±0.005 mm and leave the rest at general tolerance. See whether the shop pushes back with a reason.
3
Ask for DFM notes with the priceA quote without comments is a price, not an engineering review. Expect feedback within 12 hours.
4
Confirm material and finish in one planAsk which alloy grade they will buy and which finishing steps stay in-house. Watch for outsourced anodizing.
5
Test the MOQ with one pieceOrder a single part. Measure it yourself. Then decide whether to scale to the full run.
6
Check capacity against your envelopeConfirm the machine travels cover your largest part, and ask about the Ø400 mm rotary table for angled features.
7
Settle inspection and NDA termsAgree on 100% inspection, report format, and a mutual NDA before the first upload.

FAQs

Questions engineers ask before committing

What does collaborative mean in practice?

It means the shop reviews your design before quoting and tells you what will be hard to machine. You get DFM notes with the price, not after the first part fails inspection.

The workflow stays open: you approve the process plan, then production starts, usually within 24 hours.

Can one supplier handle both prototype and production volumes?

Yes, if there is no minimum order quantity. You can start with one part and scale to 10,000+ on the same machines and fixtures.

Keeping both stages with one supplier also means the process knowledge from the prototype carries into production.

How do I know the tolerance will hold in a batch?

Ask for the sampling plan and the inspection method, not just the tolerance number. Calipers cannot confirm ±0.005 mm.

A shop with 100% inspection before shipment and in-process monitoring gives you a traceable record for each batch.

What certification do I need for automotive or medical parts?

Automotive production usually calls for IATF 16949:2016. Medical device work points to ISO 13485:2016. General quality management is covered by ISO 9001:2015.

If your files are sensitive, ISO 27001:2022 covers information security. Check that the certificate scope matches the site doing your work.

How large a part can be machined?

Travels of 4,000 × 400 × 150 mm cover long parts. Mid-size work fits 750 × 1,150 × 550 mm or 600 × 600 × 600 mm.

Compact parts run on 500 × 500 × 450 mm and 500 × 310 × 200 mm machines. A Ø400 mm rotary table handles angled and cylindrical features in one setup.

What finishes are available after machining?

Anodizing in clear, colour, hardcoat and conductive types; electroless nickel, zinc, silver and gold plating; powder coating and black oxide; bead blasting, tumbling, brushing and polishing.

Laser marking and engraving are also available, with a minimum character height of 1.5 mm.