Supplier selection guide

CNC machining in SA: 7 proven checks before you commit

This guide is for engineers and sourcing staff comparing CNC machining in SA against offshore capacity. It covers tolerance, lead time, order quantity, certification and how to read a quotation. Use it to screen a shop in one call, and to spot the RFQ that looks cheap but will cost you a rework loop.

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CNC machining in SA supplier check on 5-axis machined engine parts

On this page

1
Key takeaways
2
What to compare before you send an RFQ
3
Tolerance and size: the two filters that cut the list fastest
4
Lead time and order quantity: where quotes quietly diverge
5
Certification, materials and the paperwork that protects you
6
7 steps to qualify a supplier in one working day

Start here

Key takeaways

Tolerance first, then priceA ±0.05 mm shop cannot hold ±0.005 mm on a bearing bore, no matter the rate.

Ask for the travel envelopePart size decides the machine class before anything else is discussed.

Order quantity is a cost leverFrom one prototype to 10,000+ parts changes fixturing, not just unit price.

Certification narrows the listIATF 16949 or ISO 13485 remove shops that cannot support your industry.

Confirm the data trailWhich dimensions are inspected, and does the report ship with the parts?

Screening table

What to compare before you send an RFQ

Two columns of hard numbers, one column of what actually decides the award.

Check	What a serious shop shows	Why it decides the award
Tolerance capability	±0.005 mm on critical features, stated per feature	A blanket claim is not a process capability
Machine travel	4,000 mm maximum processing size, listed per machine	Oversize parts mean a second setup or a lost quote
Order quantity	No minimum order quantity, 1 to 10,000+ parts	Prototype and production pricing diverge fast
Certification	ISO 9001:2015, IATF 16949:2016, ISO 13485:2016	Regulated industries audit the certificate, not the pitch
Quotation turnaround	Quote and free DFM analysis within 12 hours	Slow quoting hides a slow engineering team
First article	100% inspection before shipment, reports on request	Tells you who owns the scrap
Data handling	Secure uploads, NDA available on request	Your drawings are your product

Check 1–2

Tolerance and size: the two filters that cut the list fastest

Start with the tightest tolerance on the drawing, not the title block default. If a bearing bore or a seal groove carries ±0.005 mm, the shop needs temperature-stable spindles, a probe, and a metrology plan that matches. A general ±0.1 mm shop can still be a good fit for brackets and covers, but it should never quote the bore.

Size is the second filter. Ask for the travel envelope of the specific machine that will run your part, not the shop's largest machine. A 4,000 × 400 × 150 mm envelope suits long extrusions and rails. A 750 × 1,150 × 550 mm or 600 × 600 × 600 mm envelope covers most housings. Compact 500 × 500 × 450 mm and 500 × 310 × 200 mm machines handle small, high-volume work with fast chip-to-chip times.

Be direct about the mismatch. A part that needs 5-axis work on five faces at ±0.01 mm true position should not be split across three 3-axis setups to save money. Each re-clamp adds stack-up error you cannot inspect away.

Surface finish follows the same logic. Ra 0.8–1.6 μm is a normal machined finish. Ra 0.2–0.8 μm needs a finer strategy and often a separate finishing pass. Ra 1.6–3.2 μm is as-machined and is fine for non-sealing surfaces. Put the finish callout only where it matters, or the price climbs for no reason.

1
Tight featuresName the feature and the tolerance, not a single global number.
2
Setup countEach extra setup adds positional error and handling risk.
3
Finish zonesCall out sealing and sliding surfaces only.

Check 3–4

Lead time and order quantity: where quotes quietly diverge

Lead time promises are easy to make and hard to verify. Ask what happens between PO and first chip. A shop that can start production within 24 hours usually has material on the shelf and a released program. A shop that needs two weeks to source aluminium is quoting from a catalog, not a schedule.

Order quantity changes the whole manufacturing method. One prototype may be machined from a billet with soft jaws. A 10,000-part run justifies a fixture, a first article, and possibly a different process route. Ask both prices at the same time so you can see the crossover point.

For CNC machining in SA buyers, shipping and customs time often dominates the total. That makes quoting speed more valuable than a small unit-price edge. Get the quote, the DFM notes and the material lead time in one document so you can compare apples to apples.

Watch for a quotation that lists only a unit price. It should state material grade, finish, inspection level, packing and the Incoterm. Missing scope is where change orders are born.

1
24-hour startPossible when material and program are already released.
2
Quantity breakAsk for 1, 100 and 10,000 piece pricing together.
3
Quote scopeMaterial, finish, inspection, packing, Incoterm.

Check 5–7

Certification, materials and the paperwork that protects you

Certification is a filter, not a badge. ISO 9001:2015 covers general quality management. IATF 16949:2016 is what automotive programs expect. ISO 13485:2016 applies to medical device work. If your industry is regulated, ask for the certificate number and the scope statement. A shop certified for one process is not automatically certified for another.

Material traceability matters more than the alloy list. Most shops stock 6061, 304, 316L and 7075. Fewer hold 17-4PH, Ti-6Al-4V, Inconel or beryllium copper with mill certificates on file. Ask for the certificate with the quote when the part is safety-related.

Inspection is the last place to save money. 100% inspection before shipment, with raw material check, in-process monitoring and a final report, is the baseline for anything that fits into an assembly you cannot afford to rework. Reports on request should be a yes, not a negotiation.

Confidentiality is a real selection criterion. Uploads should be secure, and an NDA should be available on request before you send production drawings. If a supplier hesitates on that, treat it as a signal about how they handle everything else.

1
Scope checkMatch the certificate scope to your process and industry.
2
Mill certsAsk for them with exotic alloys, not after delivery.
3
NDA firstSign before drawings leave your server.

How to run the screen

7 steps to qualify a supplier in one working day

Work through these in order. Stop at the first step the supplier cannot answer with a number or a document.

1
Send a drawing with real tolerancesInclude the tightest feature, the material grade and the finish zones. Vague drawings attract vague quotes.
2
Ask for the machine classRequest the travel envelope and axis count of the machine that will run the part. Compare against 4,000 mm maximum processing size and 5-axis capability.
3
Request a quote and DFM notesA 12-hour turnaround with written DFM feedback shows the engineering team actually read the file.
4
Price three quantitiesAsk for 1, 100 and 10,000+ parts. Identify where fixturing starts to pay off.
5
Ask for the certificate scopeISO 9001:2015, IATF 16949:2016, ISO 13485:2016, ISO 27001:2022. Note which one covers your process.
6
Confirm the inspection planWhich dimensions are checked, with what instrument, and does the report ship with the parts?
7
Sign the NDA and release the POKeep the DFM notes, the quote scope and the inspection plan in one folder for the first article review.

FAQs

Questions buyers ask before awarding the job

How tight a tolerance can a typical shop hold?

On critical features, ±0.005 mm (±0.0002 in) is achievable with temperature control, probing and a matching metrology plan.

On general features, ±0.05 mm is normal and cheaper. Put the tight number only where the function needs it.

What order quantity makes sense for a first run?

Start with one prototype to prove the geometry and the finish, then move to a small batch. There is no minimum order quantity at a shop set up for both.

Above roughly 1,000 parts, ask whether a fixture and a dedicated process route reduce the unit price.

Do I need IATF 16949 or is ISO 9001 enough?

ISO 9001:2015 is enough for industrial machinery, robotics and general electronics work.

Automotive and EV programs usually require IATF 16949:2016. Medical device work points to ISO 13485:2016. Check the scope statement, not just the logo.

How do I compare a local quote with an offshore one?

Compare landed cost, not unit price. Add freight, duty, packing and the cost of your own time on follow-up.

Then compare the quote scope line by line: material grade, finish, inspection level and Incoterm. If one quote is missing scope, it is not cheaper.

What should be in the first article report?

The report should list the dimensions checked, the instrument used, the nominal and actual values, and the pass or fail result.

Ask for it on the first run. If the supplier cannot produce one, the inspection process is probably visual.

Can I keep my design confidential during quoting?

Yes. Send only what the quote needs, and sign an NDA before releasing production drawings.

Secure uploads and an NDA available on request are reasonable baseline expectations, not favors.