Nothing replaces walking the floor
I have audited dozens of CNC shops in China, and I can tell you this: a video call, a gallery of website photos, and even a third-party audit report do not tell you what your own two eyes will tell you when you walk onto a shop floor. How the machines are arranged, how parts are staged between operations, how inspection records are kept, how the coolant smells - these things tell you more about a supplier than any certificate.
You do not need to be a CNC expert to run an effective audit. You need a checklist, a set of questions, and the willingness to walk slowly and ask why when something looks off. Here is the framework I use every time.
Before you go: preparation
A good audit starts before you get on the plane.
- Request documents ahead of time: Ask for ISO 9001 certificate, equipment list (brand, model, year), sample CMM and FAI reports, and quality manual - review before the visit.
- Schedule the visit formally but consider an unscheduled follow-up: The first visit is always prepared. A second at short notice - a day early or en route to another supplier - shows the factory as it normally runs.
- Bring a checklist and a camera: Take photos of everything - machines, inspection equipment, work in progress, calibration stickers, quality records. You will forget details within hours of leaving.
- Bring a sample part or drawing: If you have a representative part you will be sourcing, bring it or a detailed drawing. Walk the floor with it and ask how they would make it, which machines they would use, how they would inspect it.
The floor walk: what to look for
The production floor is where you see whether a supplier actually does what they claim.
| Area | What to check | Green flag | Red flag |
|---|---|---|---|
| Machine shop | Count and identify machines: brands, models, age, number of axes, maintenance condition | Modern CNC equipment (DMG MORI, Mazak, Haas, Doosan, FANUC) in clean, well-maintained condition; evidence of regular maintenance logs | Most machines are old or manual; idle machines during what should be a production day; fluid leaks, excessive chip buildup, broken or missing gauges |
| Work in progress | How parts are staged between operations; how WIP is identified and tracked | Parts are labeled with work order numbers, operations are tracked on travelers or digital systems, parts are stored in clean bins between ops | Piles of unmarked parts on the floor, no visible work order tracking, parts mixed together without identification |
| Tooling setup | How tools are set up, stored, and managed; presetting equipment | Tool presetters in use, tools stored in organized racks, setup sheets visible at machines | Loose tools scattered on surfaces, no setup documentation, operators using hand-measured tools without presetting |
| Finishing area | If they do in-house finishing (deburring, polishing, blasting): organization and process control | Dedicated finishing area with consistent processes, parts protected after finishing | Parts thrown together after machining, visible damage from poor handling, no separation between rough and finished parts |
The quality room deep dive
The inspection and metrology area tells you whether a shop can actually verify the tolerances they quote.
- CMM: Is there a CMM (coordinate measuring machine)? What brand (Zeiss, Hexagon, Mitutoyo are strong)? Is it in a temperature-controlled room? When was it last calibrated (check the calibration sticker and certificate)?
- Hand inspection tools: Look for micrometers, calipers, height gauges, bore gauges. Are they clean, calibrated, and stored properly? Check calibration dates on random tools.
- Surface roughness testers, hardness testers, optical comparators: Not every shop needs these in-house, but they should have access (in-house or via subcontractor) if your parts require them.
- Sample inspection records: Ask to see recent CMM reports, FAI reports, and non-conformance records. Good record-keepers show them without hesitation; a shop that cannot produce them is not doing real QC.
- Calibration system: Ask how they manage calibration of inspection equipment. There should be a calibration schedule, traceable calibration standards, and records for every instrument.
The management conversation
After the floor walk, sit down with the owner or general manager and ask questions that go beyond pricing:
- Ownership structure: Is this a family shop, a privately held company, or a subsidiary? Who makes final decisions on capacity investment and quality issues?
- Export experience: How long have they been exporting to US/EU customers? Can they provide references you can contact directly?
- Capacity and utilization: Current utilization? At 95% they cannot take rush orders; at 30% there may be financial stability issues.
- Subcontracting policy: Which processes do they outsource (heat treat, plating, anodizing)? Which subcontractors do they use? How do they qualify and audit subcontractors? This matters for quality and IP control.
- Quality staff: How many dedicated quality inspectors do they have? What training and certification do quality personnel have?
- Lead time commitments: Ask about typical lead times - 5-7 working days for prototypes is a reasonable benchmark - and for production runs.
Bottom line: trust your eyes
A factory audit is not a bureaucratic exercise. It is the most reliable way to verify that a supplier can actually do what they claim. The best shops are proud to show you their floor, their quality room, and their records. The worst steer you to a conference room, impressing you with certificates while avoiding the floor. If something feels wrong - dirty floor, idle machines, missing records, evasive answers - trust that feeling. The right supplier will welcome your scrutiny.
Frequently Asked Questions
Do I need to visit China personally to audit a supplier?
For initial qualification of a supplier who will produce critical parts, yes - a personal visit is worth the investment. For lower-value parts or re-orders, you can use video walkthroughs, third-party inspection services, or trusted local representatives. But there is no substitute for your own eyes on the floor for a first-time qualification.
What does a typical factory audit trip to China cost?
A three-to-five day trip to visit 3-5 suppliers in a major CNC cluster typically costs a few thousand dollars including flights, hotel, translation, and local transportation. Compared to the cost of a bad production run or a quality failure, it is one of the best investments in sourcing.
How long should a factory audit take?
Plan for 2-4 hours per supplier for a thorough first audit. This gives you time for a slow floor walk (45-90 minutes), quality room inspection (30-45 minutes), document review (15-30 minutes), and a management conversation (30-60 minutes). Rushing through in under an hour means you will miss things.
Can I hire a third-party audit service instead of going myself?
Yes, third-party audit firms (SGS, Bureau Veritas, and specialized China-based QC firms) can perform supplier audits on your behalf. These are useful for preliminary screening or for regular repeat audits, but for a critical first-time supplier qualification, I recommend combining a third-party report with your own visit.
What should I do if an audit reveals red flags?
It depends on the flag. Missing or expired calibration on a CMM is a problem that can be fixed - give the supplier a corrective action request and re-audit. A shop that cannot produce any quality records, has mostly idle machines, or lies about their equipment list is a walk-away situation. Not every red flag disqualifies a supplier, but dishonesty always does.