You're about to send your CAD files to a Chinese CNC shop. You've got a quote. The price is right. The timeline works. The communication is smooth.

But you don't know if they can actually make your part. Not "they say they can." Actually make it. Within tolerance. Batch after batch. On time.

Here's the system I use to qualify CNC suppliers. It takes about 48 hours. It works without a technical degree. And it catches the suppliers who talk a good game but can't deliver.

Check 1: The Machine List

Ask the supplier for a list of their CNC machines. Not "we have 20 machines." An actual list: brand, model, age, control system.

The answer you want to see: DMG MORI, Mazak, Okuma, Haas, or other major brands. The age should be under 10 years. If the supplier has a mix, that's fine. If the supplier has all Taiwanese or domestic brands, that's also fine. The point is that they can give you the list.

The red flag is "we have many machines" without specifics.

Pass/fail: Pass if they provide the list. Fail if they cannot.

Check 2: The CAM Software

Ask: "What CAM software do you use for programming?"

The answer you want: Mastercam, Hypermill, NX, PowerMill, or other industry-standard. The answer you do not want: "we have our own system" or "the operator does it manually."

The software quality affects the toolpath quality. The modern software generates better toolpaths than older software. The operator still matters. But the software is a proxy for the shop's investment in technology.

Pass/fail: Pass if they use a recognized CAM system. Fail if they cannot name one.

Check 3: The Material Test Certificate

Ask: "Do you provide material test certificates with your shipments?"

The answer you want: yes, we provide MTCs from the mill. The answer you do not want: "we can if you ask." That means it's not standard. That means they may skip it if you forget.

For critical parts, the MTC is non-negotiable. It proves the material is what they say it is. The supplier who provides it without asking is the supplier who takes quality seriously.

Pass/fail: Pass if MTCs are standard. Fail if they are optional.

Check 4: The CMM and Inspection Equipment

Ask: "Do you have a CMM in-house, and when was it last calibrated?"

The answer you want: yes, we have a CMM, calibrated in the last 12 months. The answer you do not want: "we use handheld gauges" or "we send parts to an outside lab."

The CMM is the gold standard for dimensional inspection. The supplier who has one is investing in quality. The supplier who does not is checking parts manually, which is slower and less reliable.

Pass/fail: Pass if they have a CMM and it's calibrated. Fail if they do not.

Check 5: The Surface Roughness Tester

Ask: "Do you have a surface roughness tester? What model?"

This is a small but important detail. The surface roughness tester is a common and inexpensive piece of equipment. If the supplier does not have one, they are not measuring surface finish. That means they do not know whether they are hitting the spec.

Pass/fail: Pass if they have one and can name the model. Fail if they do not.

Check 6: The Quality Lab

Ask: "Can you show me a photo of your quality lab?"

The answer you want: a photo of a clean room with a CMM, a surface tester, and possibly a hardness tester. The answer you do not want: "our quality is checked on the shop floor."

The quality lab does not need to be large. It needs to be real. A supplier who has a dedicated quality space is a supplier who takes quality seriously.

Pass/fail: Pass if they provide a photo. Fail if they cannot.

Check 7: The Training Program

Ask: "How do you train your operators?"

The answer you want: a structured program with a defined time period (e.g., 3 months of training before an operator works independently). The answer you do not want: "on the job."

The machine operator is the human factor in precision machining. The best machines can be operated poorly. The structured training program is the differentiator.

Pass/fail: Pass if the training is structured. Fail if it is informal.

Check 8: The First Article Inspection Process

Ask: "Tell me about your first article inspection process."

The answer you want: a clear description: sample parts are pulled from the first production run, measured on the CMM, compared to the drawing, and documented. The report is sent to the buyer for approval before the batch is released.

The answer you do not want: "we check the first piece and then run the batch."

The difference between these two answers is the difference between a quality system and a casual process.

Pass/fail: Pass if the FAI is documented. Fail if it is informal.

Check 9: The In-Process Gauging

Ask: "Do you measure parts during the production run, or only at the beginning and end?"

The answer you want: "we measure during the run." The supplier who measures during the run is the supplier who catches errors before they become scrap. The supplier who measures only at the beginning and end is the supplier who gambles with your quality.

The specific method can vary. In-process gauging can be manual (operator checks every 5th part) or automated (in-machine probe). Both are acceptable. The point is that there is a defined interval.

Pass/fail: Pass if there is an in-process check. Fail if there is not.

Check 10: The Machine Maintenance

Ask: "What is your machine maintenance schedule?"

The answer you want: a defined schedule (e.g., "we service the spindle every 2,000 hours"). The answer you do not want: "when the machine breaks, we fix it."

The machine that is maintained is a machine that holds tolerance. The machine that is not maintained is a machine that drifts.

Pass/fail: Pass if the schedule is defined. Fail if it is "when it breaks."

The Decision Framework

Now you have ten checks. Here's how to use them.

The Rule of Ten: If a supplier fails one check, they may still be acceptable. If they fail two checks, be careful. If they fail three checks or more, they are not a serious supplier.

What to Do with the Results

If the supplier passes at least eight of ten checks, they are likely a competent machining partner. The missing checks should be addressed in the contract. For example, if they pass all but "MTC as standard," add a clause requiring MTCs with every shipment.

If the supplier passes five to seven checks, they may be acceptable for simple parts. They are not acceptable for tight-tolerance parts. The risk is too high.

If the supplier passes four or fewer checks, walk away. The cost of the project will exceed the price savings.

The 48-Hour Process

Here is the timeline for qualifying a CNC supplier using this checklist.

• Hour 0: Send the 10-question email to the supplier.

• Hour 1-24: Wait for the supplier to respond. The speed of the response is itself a signal. A supplier who responds within 4 hours is hungry. A supplier who takes 24 hours is not.

• Hour 24-48: Evaluate the responses. Assign pass/fail marks. Note any gaps.

• Hour 48: Decide if the supplier qualifies. If they do, send the CAD files. If they do not, move to the next candidate.

This process works for any CNC supplier in any location. It works with established factories and with new ones. It catches the good ones early. It filters out the bad ones quickly.

Your Takeaway

You do not need to understand the physics of CNC machining to qualify a supplier. You need to ask the right ten questions and evaluate the answers.

The supplier who passes the checklist is the supplier who is organized, invested in quality, and capable of delivering consistent results. The supplier who fails the checklist is a gamble.

I have used this checklist on hundreds of suppliers. It works. It catches the bad ones before they waste your time. It identifies the good ones early.

If you have a supplier you're evaluating and want to run them through the checklist, send me their answers. I will tell you what I see.

A Simple, Step-by-Step Framework for Separating Real Machining Capability from Sales Talk

Ten checks. One pass/fail system. No engineering degree required. Here's how to qualify a CNC supplier in 48 hours – without leaving your desk.

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