Buyer's guide

Shanghai CNC Machining: What to Verify Before You Order

This guide is for engineers and sourcing teams comparing shanghai CNC machining quotes for prototype and production parts. It lists the checks that actually change part quality, cost and schedule, and the ones that only look good on a brochure. Read it and you can judge a supplier from four documents and one sample part.

Get Instant Quote Talk to an Engineer

±0.005 mm toleranceNo MOQISO 9001 / IATF 169493–5 day shipping

On this page

1
Key takeaways
2
What to compare before you send a PO
3
Tolerance: match the number to the feature
4
Lead time: find out when the clock starts
5
MOQ, setup cost and how the price is built
6
Certificates: read the scope, not the logo
7
Materials, finishes and what the shop actually runs
8
Seven steps from first email to approved supplier

Short version

Key takeaways

Tolerance needs a size±0.005 mm is a claim. On which feature, over what length? Ask before you compare prices.

No MOQ is commonGood shops run one prototype and 10,000+ parts on the same line. Ask how setup is priced.

Certificates are not qualityISO 9001 tells you there is a system. The inspection report tells you about your parts.

12 hours is the quote testA quote without DFM notes is a price list. DFM feedback is what saves money.

One sample beats five catalogsOrder one part with a hard feature, then measure it yourself.

Judging criteria

What to compare before you send a PO

Columns map to the five checks explained below.

Check	Weak answer	Strong answer
Tolerance	±0.005 mm, no feature list	±0.005 mm with datum and feature callouts
Lead time	3–5 days, no start date	Clock starts at PO and DFM sign-off
MOQ	50 pieces minimum	One prototype to 10,000+ runs
Certification	ISO 9001 mentioned in email	Copy of certificate, scope, expiry date
Quote content	Price and total only	Price, setup, DFM notes, inspection plan
Material trace	'Aluminum'	6061-T6 with mill cert on request
Finish spec	'Anodized'	Hardcoat, 25 μm, masked threads listed
Rework policy	Not stated	Free rework, written in the quote

Check 1

Tolerance: match the number to the feature

Every shanghai CNC machining quote says something about accuracy. The useful question is where that number applies. ±0.005 mm across a 20 mm bore is routine on a 5-axis center. The same number over a 4,000 mm part is a different problem, because thermal drift and fixturing start to dominate.

Ask the supplier to mark which features carry the tight tolerance. If the drawing has three critical bores and everything else is loose, say so. A shop that machines the whole part to the tight number will charge you for time you do not need. A shop that ignores the note will ship parts that fail at assembly.

Datum structure matters as much as the number. If your drawing references A-B-C and the shop clamps on a raw casting face, the inspection result will drift even when the machine is capable. Send the GD&T with the model, not after the first article fails.

1
Send a marked printHighlight the three or four features that matter.
2
State the datumInspection follows the datum, not the vise.
3
Check the CMM reportNumbers on paper, not a green checkmark.

Check 2

Lead time: find out when the clock starts

'Parts ship in 3–5 days' is a real number for many shops, but only after tooling, material and the DFM review are settled. If the clock starts when the PO lands and the material is not in stock, the same shop can take two weeks.

A useful quote states three dates: quote turnaround, production start, and shipment. A shop that can return a quote and a free DFM analysis within 12 hours and start production within 24 hours is telling you its front office is not the bottleneck.

Late delivery is not random. It usually traces back to a material order placed after the PO, or a fixture built after the first article. Ask which operations are subcontracted. Heat treat and anodizing are the two that break schedules most often.

1
Ask for three datesQuote, production start, shipment.
2
Ask what is outsourcedHeat treat and plating are common delays.
3
Keep a bufferOne week on a first article is cheap insurance.

Check 3

MOQ, setup cost and how the price is built

No minimum order quantity sounds generous, but it does not mean the first part is cheap. Setup, programming and fixturing are fixed costs. On a one-off part they dominate the price. On a 10,000-part run they nearly disappear.

So ask for the quote broken into setup, material, machining time and finish. A supplier that quotes one lump sum is not hiding anything illegal, but you cannot tell whether a design change will cost 40 dollars or 400. Once the breakdown is on the table, you can also see whether a small design change removes a second setup.

For prototypes, run the numbers on two or three quantities. The step from one part to five often costs very little, because the fixture already exists. The step from five to fifty is where per-part price starts to fall.

1
Split the quoteSetup, material, machine time, finish.
2
Price two quantitiesOne and five, or five and fifty.
3
Look for setup trapsUndercuts and deep pockets add operations.

Check 4

Certificates: read the scope, not the logo

ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022 mean different things. ISO 9001 is a general quality system. IATF 16949 is for automotive production. ISO 13485 covers medical devices. ISO 27001 covers information security, which matters when you upload drawings of an unreleased product.

Ask for the certificate copy, the issuing body and the expiry date. Then ask a harder question: which site is certified? A group with three plants can hold a certificate at one address and run your parts at another. If the certificate does not name the plant that will machine your part, treat it as marketing.

Certification does not measure your part. The inspection record does. For a first order, request dimensional reports for the critical features, material certificates for the lot, and a finish thickness reading if the drawing calls for hardcoat or plating.

1
Match the standard to the industryIATF for auto, 13485 for medical.
2
Confirm the certified siteThe address on the certificate must match.
3
Ask for the inspection recordRaw material, in-process, final.

Check 5

Materials, finishes and what the shop actually runs

A shop that lists every material usually runs a few of them well. Ask what it machines most weeks. Aluminum 6061, 7075 and 6082 are everyday work. Titanium Ti-6Al-4V and Inconel are not, and they behave differently: tool wear climbs, feeds drop, and a job quoted like aluminum will run late.

Stainless has its own traps. 303 machines freely, 316L work-hardens, and 17-4PH in the H900 condition will fight a light finishing pass. If your part is 17-4PH and the quote is close to the 303 price, ask which condition the material is in.

Finishing is where drawings get vague. 'Anodized' can mean clear, colored, hardcoat or conductive, and masking threads and bores is a separate operation. Laser marking has a minimum character height around 1.5 mm; smaller text fills in. Put the finish spec, color code and mask list on the drawing.

1
Name the alloy and temper6061-T6, not 'aluminum'.
2
Say the finish typeHardcoat, 25 μm, mask M6 threads.
3
Flag exotic alloys earlyTitanium and Inconel need their own quote.

How to run the evaluation

Seven steps from first email to approved supplier

1
Send a real drawing, not a sketchUse a STEP file plus a 2D print with GD&T, material, finish and quantities. A rough sketch gets a rough price. Note any cosmetic surfaces.
2
Ask for a quote and DFM notes in one replyYou want price, setup breakdown, lead time and comments on features that are hard to machine. Feedback on a thin wall or a deep pocket is worth more than a small discount.
3
Compare tolerance against the feature listPrint the four tolerance claims side by side. If one quote claims ±0.005 mm on everything and another lists features, the second one read your drawing.
4
Confirm the certified site and the inspection planAsk which plant will run the job, which certificate covers it, and what will be measured before shipment. 100% inspection before shipment is the baseline.
5
Order one part with a hard featurePick the tightest bore, the thinnest wall or the deepest pocket. A part that skips the difficult feature proves nothing.
6
Measure the sample yourselfUse your own CMM or gauge. Check the finish thickness if the drawing calls for it. Compare against the inspection report that came with the part.
7
Scale up in two stepsRun a small batch of five to ten before a full production order. Watch the first-article time and whether the quoted lead time holds.

FAQs

Questions buyers ask before the first PO

How do I compare quotes when the drawings are the same?

Put the four numbers side by side: per-part price, setup, quoted lead time, and what is included in inspection. The lowest per-part price often hides a setup fee or excludes finishing.

Then check the DFM notes. If one supplier flagged a feature and another did not mention it, the second quote may change after the first article.

Is a lower price a warning sign?

Not by itself. Small shops with low overhead can beat large ones on simple parts. The warning sign is a price that is far below the others with no explanation in the quote.

Ask how the job will be set up. If the answer is vague, the price is a guess and it will move once machining starts.

What should I do when my part has one tight feature?

Say so on the drawing and mark it. Most of the part can run at a general tolerance, and only that feature needs the tight number and a CMM check.

This usually lowers the price, because the shop can use faster passes everywhere else and still hold the critical dimension.

Do I need an NDA before uploading CAD files?

If the design is unreleased, yes. An NDA costs nothing and takes a day to sign. Check whether the supplier holds ISO 27001:2022, which covers information security management rather than part quality.

Uploads should be treated as confidential by default. Confirm who inside the shop can open the files and whether they are deleted after the job.

What lead time should I expect for a first article?

For a machined part with material in stock, production can start within 24 hours and parts can ship in 3–5 days. Add time for finishing, heat treat or an outside process.

The first article is slower than repeat orders because of programming and fixturing. Ask for the date the fixture will be ready, not just the ship date.

How many parts should I order for a pilot run?

Five to ten is a good pilot. It is enough to see whether the process repeats, and small enough to absorb a design change.

Check the spread between parts. If the first part is in tolerance and the tenth is drifting, the fixture or the tool is moving.