Sample Approval With Chinese Factories: A Process

Sample Approval With Chinese Factories: A Process

Short answer: Sample approval with a Chinese factory is a staged gate process, not a single "send me a sample" email. The workable sequence is: freeze the drawing and revision, approve T1 samples against a dimensional report, run a first article inspection (FAI) on production tooling or production programs, sign a golden sample, then release pre-production quantities. Budget 2-4 weeks for CNC and spring samples, 4-8 weeks where new stamping dies are involved, and never approve a sample without a numbered report tied to a specific drawing revision. At BQUQ, quotes for this work go out in 12 working hours.

Most sourcing failures we see are not manufacturing failures. They are approval failures — a sample was approved, but nobody wrote down what "approved" meant, against which drawing revision, on which machine, with which material lot. Six months later the production parts are dimensionally different and there is no document to argue with.

This article lays out the approval process we use with overseas buyers, in the order it actually happens. It is written for engineers and sourcing managers who need a repeatable gate structure rather than a vague handshake.

Why does sample approval need a formal process at all?

Because a sample is evidence, and evidence is only useful if it is traceable. A part that fits in your hand proves the geometry is achievable once. It does not prove the process can repeat that geometry across 50,000 pieces, across three tooling cavities, across a material lot change, or across a night shift.

Three specific risks drive the need for structure:

Revision drift. Your CAD file is rev C. The supplier's programmer works from a PDF exported at rev B. The sample looks right, the drawing it was made to was wrong, and the error only surfaces at assembly.

Sample-to-production gap. A CNC sample is often cut on a 3-axis machine with generous fixturing and slow feeds. Production runs on a different machine, or on a die, with different workholding. The sample was not a lie — it was just not representative.

Silent concessions. A supplier finds a feature is hard to hold, adjusts it slightly, and ships. Nobody mentions it because the part "looks fine." Two months later the deviation matters.

A formal approval process closes all three. It also protects the supplier: when the buyer has signed a golden sample and an FAI report, disputes about "what was agreed" become document lookups rather than negotiations.

Stage 0: Freeze the specification before you ask for a sample

Nothing wastes more time in China sourcing than sampling against a moving drawing. Before any sample request goes out, lock these items:

• Drawing revision and format. Native 3D (STEP) plus a controlled 2D drawing with GD&T or, at minimum, explicit tolerances and datums.
• Material specification. Not "stainless steel" but grade, condition, and finish — e.g. SUS304, 1/2 hard, per a named standard.
• Critical-to-function dimensions. Mark them. A 20-dimension drawing where all 20 are treated as equally critical is a drawing where nothing is critical.
• Surface and cosmetic requirements. Especially for visible stamped brackets, heat sinks, and finished CNC parts. "No scratches" is not a specification.
• Packaging and labelling. Sample-stage packaging decisions become production packaging decisions by default.

If your drawing has an unresolved tolerance stack, resolve it now. A ±0.005 mm CNC process is achievable at BQUQ, but only when the drawing says which features carry that tolerance and which do not.

Stage 1: T1 samples — prove the geometry

T1 is the first physical iteration. For CNC machining, T1 is usually cut from solid stock on production-intent equipment. For custom metal stamping, T1 may be laser-cut or wire-cut rather than die-formed, because the die does not exist yet — and that distinction must be stated explicitly on the report.

What you should receive with T1 samples:

The dimensional report is the heart of it. A report that lists "OK" against each dimension is nearly worthless. You want numbers, and you want to see which dimensions are running near the tolerance limit — those are the ones that will drift in production.

Reading a T1 report properly

Two habits separate experienced buyers from everyone else.

First, look at capability, not just conformance. A dimension at nominal ±0.001 mm on a ±0.005 mm tolerance is comfortable. A dimension sitting at 90% of the tolerance band on a sample is a production risk, even though it passes.

Second, look for the dimensions that were not reported. If a report covers 12 of 20 ballooned dimensions, ask why. Usually it is because the supplier lacks the gauge — which is itself important information about their inspection capability.

Stage 2: First Article Inspection (FAI)

FAI is where the process, not the part, gets approved. The distinction matters: T1 answers "can you make this shape?" FAI answers "can your production process make this shape repeatedly, and can you prove it?"

FAI should be run on production tooling or production programs, using production material, with production workholding. For a stamping project this means the die is built and running. For CNC it means the production CAM program and the production fixture. For compression springs it means the production coiler setup with the final wire lot.

A practical FAI package for a Chinese supplier relationship:

Full PPAP is rarely appropriate for low-volume or custom industrial parts, and demanding it can push a supplier into paperwork theatre. A "PPAP-lite" — dimensional report, material cert, golden sample, deviation list, packaging trial — covers the risk for most buyers of custom CNC, stamping, spring, and heat sink parts.

The golden sample

The golden sample is the single most useful artefact in the entire process and the one most often skipped. It is a physical part, signed and dated by both parties, marked with the drawing revision and the FAI report number, and retained in a controlled location on both sides.

When a dispute arises eighteen months later, the golden sample ends it in five minutes. Without one, the dispute becomes a comparison of two parts and two opinions.

Mark it clearly. A scribed or laser-marked ID on a non-functional surface, plus a tag, plus a photo in the report. Do not rely on "the one in the blue box."

Stage 3: Pre-production and pilot quantities

Sample approval is not production approval. The next gate is a pilot run — typically a few hundred to a few thousand pieces — that tests the things a sample cannot test: tooling wear over a run, fixture repeatability, operator-to-operator variation, in-process inspection cadence, and packaging at volume.

This is also where you learn the supplier's real communication rhythm. How fast do they flag a problem? Do they send a photo and a question, or do they ship and hope? If you are running a pilot, the guide on pilot production with Chinese suppliers covers the quantities and checkpoints that make it worthwhile.

For a broader view of how this fits into supplier selection, see the China supplier vetting checklist.

How long does sample approval actually take?

Timelines vary enormously by process. The table below shows typical, indicative ranges for a well-prepared buyer with a frozen drawing — not commitments.

The single biggest variable is not the factory. It is how long the buyer takes to return comments. We have seen a 3-week stamping FAI cycle stretch to 9 weeks because drawing clarification emails sat unanswered for days at a time. Assign one engineer as the single approval authority and give them authority to decide.

Common sample approval mistakes

Approving from photos. Photos are useful for confirming the part exists. They cannot confirm a 0.02 mm feature.

Approving without a revision number. Always cite the drawing revision on the approval email. "Approved" with no revision is an invitation to ambiguity.

Skipping the deviation list. If a supplier cannot hold a feature, you want it written down and signed, not silently absorbed. An approved deviation is a managed risk. An unapproved one is a defect.

Treating the golden sample as a formality. It is the contract's physical annex.

Letting the sample sit on a desk. Samples that are not measured and reported are souvenirs. If you lack in-house metrology, ask the supplier for a full dimensional report and spot-check the critical dimensions with a trusted third party.

Not comparing quotes before sampling. Sampling is expensive in time. The China quote comparison guide explains how to shortlist before you commit to a sample cycle.

How BQUQ handles sample approval

BQUQ runs four production lines — CNC machining, metal stamping, custom springs, and heat sink production — in one ISO9001 factory in Dongguan. That matters for approval because multi-process parts do not need to be shipped between vendors mid-approval, and the FAI report covers every operation under one document set.

Our standard practice:

• Quotes returned within 12 working hours, with the sample plan and inspection method stated up front.
• CNC tolerances to ±0.005 mm where the drawing specifies them.
• Flexible MOQ, so a pilot run is a realistic option rather than a theoretical one.
• Dimensional reports issued with T1 and FAI samples, ballooned against your drawing revision.
• Golden samples signed, dated, and retained by both parties.

Send drawings and a target quantity to sc@bquq.com and you will get a quote plus a proposed approval sequence, not just a price.

Frequently Asked Questions

Q: How many samples should I approve before production?

A: Three to ten pieces from a single production setup is the practical range for most custom parts. Fewer than three gives you no view of repeatability. More than ten adds cost without adding much information, unless the tooling is multi-cavity or multi-slide, in which case you want at least one part from every cavity or station.

Q: Is a first article inspection the same as PPAP?

A: No. FAI is a dimensional and material verification of parts from production tooling. PPAP is a broader automotive-oriented submission including capability studies, control plans, and process flow documents. For custom industrial CNC, stamping, and spring parts, an FAI package plus a golden sample and deviation list usually manages the risk adequately without the full PPAP overhead.

Q: What should I do if the sample is close but not conforming?

A: Get the deviation written down before you decide. Ask for the measured value, the nominal, the tolerance, and the supplier's proposed fix. If the deviation is functionally irrelevant, approve it formally as a concession tied to a drawing revision. If it is functional, reject it and require a new T1 — do not accept "we will fix it in production."

Q: Do I need to visit the factory to approve samples?

A: Not for most parts. A dimensional report, material certificate, photo set, and a shipped sample cover the technical verification. A visit is valuable for new stamping dies, complex assemblies, or when you want to assess inspection capability and shop discipline directly. Many buyers combine a first-article approval with a factory audit on the same trip.

Q: How long is a golden sample valid?

A: Until the drawing, material, process, or tooling changes — whichever comes first. Any of those triggers a new FAI and a new golden sample. Practically, review golden samples annually even if nothing has changed, and always re-sign when a die is refurbished or a CNC program is re-posted.

Related Resources

• About BQUQ and our Dongguan factory: /about/
• CNC machining services: /cnc-machining/
• Custom metal stamping services: /custom-metal-stamping/
• Compression spring manufacturing: /compression-springs/
• Industry trends and sourcing context: /industry-dynamics/
• Technical articles library: /bquq-blog/
• Frequently asked questions: /faq/
• Case studies: /case/
• Contact the engineering team: /contact/

Authored by the BQUQ Engineering Team. BQUQ (Dongguan) runs CNC machining (±0.005 mm), metal stamping, custom springs, and heat sink production in one ISO9001 factory. Source-direct from Dongguan, China — quote in 12 hours: sc@bquq.com | WhatsApp +86 13713157787 | www.bquq.com