1. What machines will my part run on?
Ask for make, model and axis count. A shop that cannot name the specific machine does not have its own floor. A real factory will tell you "your 7075 housing will run on our DMG MORI 5-axis" without hesitation.
Red flag: "we have many machines" without specifics.
2. What tolerance can you hold on my critical features - without special process?
A precise answer: "On bearing bores we hold ±0.005 mm routinely; ±0.002 mm needs grinding after CNC." A vague answer: "we are very accurate."
The shop that knows its own capability limits will not over-promise.
3. Do you have in-house CMM inspection?
Ask for a sample CMM report from a recent job. Shops that outsource inspection will delay results by 3–5 days and cannot react in real time to dimensional drift.
4. What is your on-time delivery rate over the last 12 months?
A real number (e.g., "96% on-time over the last 12 months") tells you more than any marketing claim. Vague answers mean they do not track it.
5. What materials do you stock?
Shops that stock 6061-T6, 7075-T6, 304/316 stainless, Delrin and PEEK cut lead time by days. Shops that order every material per job add 5–10 days and material minimums.
6. Can you provide First Article Inspection (FAI)?
FAI packages with dimensional reports, material certs and photos are standard for automotive and aerospace customers. If the shop has never done one, they are not ready for production work.
7. What certifications do you hold?
ISO 9001 is baseline. IATF 16949 for automotive, ISO 13485 for medical, AS9100 for aerospace. Ask to see the certificate (not just a claim on a website).
8. How do you handle DFM feedback?
A good shop reviews your STEP file before quoting and flags thin walls, deep pockets, over-toleranced features and sharp internal corners. A bad shop quotes immediately and blames your design when the part fails.
Red flag: instant quotes with no engineering review on complex parts.
9. What is your standard lead time - and your expedited option?
Ask for both. A shop that offers 7-day prototype, 15-day standard, and 5-day expedited shows it controls its own schedule. A shop that says "2–3 weeks" for everything has no scheduling system.
10. Who will I talk to during production?
Ask for a named contact (sales engineer + project manager), not a generic info@ inbox. CNC problems come up - material substitutions, tolerance challenges, finish questions - and you need a human who knows your project.
11. Can you scale with me from prototype to 10,000 pieces?
Some shops are great at prototypes but cannot repeat quality at volume. Ask: "What changes when I move from 10 pieces to 1,000 per month?" The answer should mention locked programs, dedicated fixtures, and CMM sampling plans.
12. What is your reorder process?
When you reorder, do they re-run the same program? Do they hold your fixture? Is the price the same? Shops that keep your tooling and program history give you stable repeat pricing and lead times.
The cheapest quote is usually the wrong one
Quotes for the same part can vary 30–50% between shops. Here is how to read it:
Quotes within 10% of each other: normal variance in machine time and margin.
Quote 30% below median: they missed a tolerance, an operation, or are quoting a smaller machine that will struggle.
Quote 30% above median: they lack the right equipment and are pricing in extra setups or outsourcing.
What a good partner looks like
After working with a good CNC shop for 6 months, you should have:
A named engineer who knows your parts
Stable lead times within ±2 days
Parts that pass your incoming inspection without firefighting
DFM suggestions that save you money on the next revision
No surprises on invoice
FAQ
Q: Q: How many quotes should I get?
A: At least 3. Use the spread to identify outliers. A good middle-quote shop with engineering responsiveness beats a cheap quote with no communication.
Q: Q: Should I choose the cheapest supplier?
A: No. The cheapest quote usually means a feature was missed or the shop will outsource your work. Choose the quote that understands your requirements and answers the 12 questions above precisely.
Q: Q: How important are certifications?
A: For prototypes, less. For production in automotive, medical or aerospace, absolutely required. Ask what certifications your industry needs.
Q: Q: What if I need a shop near me vs overseas?
A: For urgent parts, local shops are faster. For cost-sensitive production, a Shenzhen factory like JCTOP delivers at 30–50% less with 7–12 day air-freight lead times.
Q: Q: How do I protect my design?
A: Sign an NDA before sending STEP files. Use a shop willing to sign. Avoid sending the full assembly - send individual part files.
Ask us the 12 questions. We will answer in writing, show you our floor, and send a sample CMM report. Contact Bella at yaqingliang277@gmail.com or WhatsApp 8614775540498.
