- Ppk ≥ 1.67 initial on key characteristics, ≥ 1.33 on general — with a documented Cpk = 1.851 (one characteristic on one part, not a blanket capability claim) on a representative length feature.
- In-house Hexagon CMMs, profilometer, XRF spectrometer, hardness and coating testers.
- Three verifiable certificates — ISO 9001, IATF 16949 and ISO 14001, with numbers you can check.
- Full APQP/PPAP capability — process flow, control plan, SPC, PFMEA and environmental procedures.
Read the tolerance band before you read the index. Cpk is a ratio of the tolerance band to the process spread, not an absolute measure of accuracy. The figure above was recorded on a length characteristic with a 0.4 mm band (76.1–76.5 mm) — wide by design. Hold the same process spread against a ±0.005 mm feature and it fails outright. Ask for the band, the subgroup count and the sampling window on every capability number a supplier quotes.
What does "quality" actually mean in CNC machining?
In machining, quality has a precise, boring definition: the part measures within the tolerance on the drawing, in the alloy you specified, with the surface finish you called out — every time, not once. Everything else — the adjectives, the mission statements, the "we care about quality" paragraphs — is noise unless it is backed by a measured value.
That definition matters because it is the only one that is falsifiable. A part either measures 10.0013 mm or it does not; the alloy either matches the mill certificate or it does not; the finish either meets the Ra callout or it does not. A supplier that can show you measured values on every one of those dimensions is running a quality system. A supplier that shows you a logo and a slogan is not. The rest of this page is about which measurements to ask for, and how to read them.
There is a second-order reason the definition has to be boring. Quality is what makes a supplier's other claims — tolerance, capacity, lead time — repeatable. A factory that holds a tolerance once is a coincidence; a factory that holds it across ten thousand parts is a quality system. When you audit quality, you are not asking whether a shop can make your part, but whether it can make your part the same way, every time, so that the supplier you approve is the supplier that actually ships.
Which metrology equipment does the lab actually own?
In precision work, what is not measured is not guaranteed, and the measurement has to happen in the supplier's own building, not at a lab you never see. The machines make the parts; the lab makes the guarantee. A quality CNC machining operation owns these instruments and uses them on every batch.
| Instrument | What it verifies |
|---|---|
| Hexagon GLOBAL S CMMs (2) | Dimensional verification — the core of the inspection report |
| Gear measuring center (ZD20) | Gear geometry, module and profile |
| Vision measuring machines | 2D profile and feature measurement |
| KEYENCE VK-X3000 laser microscope | Surface micro-topography |
| SURFCOM 1800D profilometer | Surface roughness (Ra) and profile |
| XRF spectrometer (iCHEQ) | Material composition against the mill certificate |
| HVS-1000A micro-Vickers | Hardness verification |
| Fischer coating thickness gauge | Plating and coating thickness |
| Salt spray and tensile testers | Corrosion resistance and mechanical strength |
A shop that outsources its metrology is outsourcing the one thing you are paying it to guarantee. Ask whether the CMM is in-house, and whether the dimensional report ships with every batch — the answer separates a quality operation from a reseller.
An instrument is only as honest as its calibration. Every CMM, profilometer and spectrometer in the lab carries a calibration record against a traceable standard, and a serious operation can show the certificate for the instrument that measured your part. The follow-up questions are the same as for the machines: is the equipment calibrated on a defined interval, and does the lab control temperature so the part and the reference are measured under the same conditions? A measurement without those two is a number, not evidence.
What process capability (Cpk) does the operation hold?
A machine can hold a tolerance once; a quality system holds it ten thousand times, and Cpk is the number that tells you which one you are dealing with. Cpk measures how well a process stays centered and within its tolerance band, not just whether one part happened to pass.
The standard here is Ppk ≥ 1.67 at the initial study on key characteristics and Cpk ≥ 1.33 on general characteristics. On a representative length characteristic of 76.1–76.5 mm, SPC data across 25 subgroups of 4 parts shows Cpk = 1.851 (one characteristic on one part, not a blanket capability claim) — exceeding the key-characteristic threshold. The point is not the single number; it is that the number exists and can be shown to you, with the control chart behind it. Ask for the chart, not the summary, and read the trend rather than the headline.
Reading Cpk takes one sentence: the higher the number, the more room the process leaves inside the tolerance band, and the less likely a normal shift is to push a part out of spec. The thresholds buyers actually use break down this way.
| Cpk value | What it tells you | When it applies |
|---|---|---|
| ≥ 1.33 | Process is capable for general characteristics | Everyday features with normal tolerance |
| ≥ 1.67 | Process is capable for key characteristics | Safety- and function-critical features |
| Below 1.00 | Process is not centered or not stable | Stop and investigate before production |
Which certifications back the quality system?
Certifications are the evidence that a quality system exists and is audited by someone outside the company. They are not a substitute for machines or measurement, but they are the cheapest pre-audit you can run, because a registrar has already walked the floor. Three matter for CNC work, each protecting against a different failure.
| Standard | Certificate number | Scope |
|---|---|---|
| ISO 9001:2015 | 116024/A/0001/UK/En | Machining of metal parts |
| IATF 16949:2016 | 131941/A/0001/SM/En | Manufacture of CNC metal machining parts (excludes product design, Clause 8.3) |
| ISO 14001:2015 | 116024/B/0001/UK/En | Environmental management related to machining of metal parts |
Verify, don't admire. The habit that matters is not asking "are you certified?" — every website says yes — but asking for the number and checking it against the issuing body and the legal name (Dongguan Zhuohang Ltd). A logo is decoration; a number you can verify is evidence.
How is incoming material verified?
The most expensive defect in machining is a perfect part made from the wrong material, and it is the one defect that no amount of dimensional inspection can catch, because the part measures right, it is just the wrong alloy. The prevention is at the door: every incoming lot is checked by XRF against its mill certificate before it goes on a machine.
This is not a sampling nicety; it is the difference between "the material you asked for is the material you got" and "we assumed the supplier labeled it correctly." For a stainless 316L part that must resist a specific chemical, or a 7075 part that must hold a specific strength, the alloy is a spec, not an assumption. XRF confirms it, and the result is documented on the lot record.
What documentation ships with every batch?
A quality system's output is a document, not a handshake. The deliverables that should ship with a quality-controlled batch are the CMM inspection report, the SPC control chart and the material certificate — the three records that turn a pile of parts into a traceable, accountable delivery.
Read the CMM report the way an engineer reads it: every critical dimension should carry a measured value, not a pass/fail flag. "OK" is an opinion; "10.0013 mm" is a measurement. When every critical feature has a number next to it, you can accept the batch on evidence rather than trust. When it has flags instead of numbers, you are accepting on faith, and paying for certainty you did not receive.
Is APQP and PPAP documentation available?
For automotive and regulated programs, first-article and pre-production documentation is not optional — it is the contract. This operation has delivered complete APQP/PPAP packages on customer projects, including process flow charts, control plans, SPC data, PFMEA and environmental control procedures.
The value of that capability is twofold. First, it proves the operation can run automotive-grade process planning, not just machining. Second, it means the same discipline — stated critical characteristics, sampling frequency, reaction plans — is available on your job, even if your program does not formally require a full PPAP. Ask for the quality planning behind the machining, not just the parts, and the answer tells you how the shop thinks.
How do you audit a supplier's quality system before ordering?
The quality audit is a short list of requests, and every item is answerable in one exchange. Run it before you send a drawing.
- Ask for the machine list and the CMM list — brands and counts, and confirmation the CMM is in-house.
- Ask for the certificate numbers — three numbers you check with the registrar against the legal name, not logos.
- Ask for a dimensional report on a similar part — measured values, not pass/fail flags.
- Ask for the SPC chart, not the Cpk summary — the trend tells you more than the headline number.
- Ask how incoming material is verified — XRF against the mill certificate, at the door.
A quality operation produces all of it on request; a pretender produces a brochure. The difference shows up in the first exchange, before you spend a dollar.
The audit closes the same way it opens — with a document you can file. When the supplier has answered the five requests above with the machine list, the certificate numbers, a dimensional report, an SPC chart and the material-verification record, you are holding a quality audit in five pages instead of a quality promise in five adjectives. That stack is what lets you accept a batch on evidence, and it is the same stack you will hand your own customer when they ask where the parts came from.
What this shop actually runs
Ask for capability evidence and the answer should be specific. The facility behind this guide runs 100+ CNC machines on a 6,800 m2 floor in Dongguan, China, with 100+ staff. The machine list, by category:
- 5-axis machining centres (10+) - Mazak VARIAXIS I-600 (510/910/510 mm travel, 12,000 rpm, 22 kW, 71.6 N·m, 30-tool BT40) and Mazak INTEGREX I-250H S (B-axis 0.0001°, 24 kW, 124 N·m, 38-tool HSK-A63). Chosen for compound-angle parts, single-setup multi-face prismatic work, and aerospace fittings where datum transfer loss is unacceptable.
- 3-axis / 4-axis machining centres (50+) - Brother SPEEDIO S500Z2N / S700Z2N (10,000 rpm, 14/21-tool ATC, 0.7 s tool-to-tool, Z-axis 2.2 G) and Mazak VCE-430A L / VCE-570C L (10,000 rpm, 118 N·m, 24-tool ATC). Chosen for prismatic parts, plates, brackets, housings.
- Swiss-type turning centres (10+) - Citizen Cincom A20-3F7 (Φ20 mm, 10,000 rpm), TSUGAMI B0206-III / B0205-III (Φ20 mm, 0.1 µm), STAR SR-32JII / SR-32J Type N (Φ32 mm, 8,000 rpm). Chosen for long, slender rotational parts at ±0.002 mm.
- CNC turning centres (20+) - HEADMAN T70M/1250 (720 mm swing, 117 mm bore, 3,000 rpm, BMT75 12-station turret). Chosen for shafts, bushings, flanges up to ±0.002 mm.
- Wire EDM (5+) - Sodick AQ535L (550/350/300 mm travel, ±20° taper, 800 kg workpiece). Chosen for hardened tool steel, internal splines, sharp internal corners that milling cannot reach.
- Inspection: Hexagon CMM + 20+ gauges - Hexagon CMM for coordinate measurement, plus vision system, profilometer, hardness tester, coating thickness gauge, XRF for material verification. The 10:1 rule (gauge 10x more accurate than the band) is applied to every feature.
- Machine highlights - VARIAXIS I-600: one-setup multi-face 5-axis + MAZA-CHECK auto-calibration; INTEGREX I-250H S: DONE-IN-ONE mill-turn, B-axis 0.0001° + Ai thermal shield; SPEEDIO S500Z2N / S700Z2N: Z-axis 2.2 G + 0.7 s ATC; Swiss-type: guide-bush switchable + 0.1 µm resolution.
Tolerances held: milling ±0.003 mm, turning ±0.002 mm, grinding and wire EDM ±0.002 mm. Capability: Ppk >= 1.67 initial and Cpk >= 1.33 in production on key characteristics.
Certifications: ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, clause 8.3 design excluded, disclosed openly) and ISO 14001:2015 (116024/B/0001/UK/En), issued to Dongguan Zhuohang Ltd, USCC 91441900MA4UWT6X39, established 2005.
Service area: Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa — built in China, shipped worldwide.
Contact: Felipe Iglesias, [email protected], +86 13126536955.
Want the evidence behind the quality claims?
Email [email protected] or call +86 13126536955 for a CMM report, SPC chart and certificate numbers you can verify.
Frequently Asked Questions
How do you prove the quality of your CNC machining?
In short, Quality is proven by measurement, not adjectives. Dimensional checks run on in-house Hexagon CMMs, surface finish on a profilometer, and material composition on XRF against the mill certificate.
What process capability do you hold?
In short, Key characteristics target Ppk ≥ 1.67 initial and general characteristics Cpk ≥ 1.33. On a representative length characteristic of 76.1–76.5 mm, SPC data across 25 subgroups of 4 shows Cpk = 1.851 (one characteristic on one part, not a blanket capability claim), which exceeds the key-characteristic threshold.
What metrology equipment does the quality lab own?
In short, The lab owns Hexagon GLOBAL S CMMs, a gear measuring center, vision measuring machines, a KEYENCE laser microscope, a SURFCOM profilometer, an XRF spectrometer, a micro-Vickers hardness tester, a coating thickness gauge, and salt spray and tensile testers.
Which quality standards are you certified to?
ISO 9001:2015 (No. 116024/A/0001/UK/En), IATF 16949:2016 (No. 131941/A/0001/SM/En) and ISO 14001:2015 (No. 116024/B/0001/UK/En). IATF 16949 scope excludes product design under Clause 8.3, so this is a build-to-print operation.
How do you verify incoming material?
Every incoming lot is checked by XRF against its mill certificate before it goes on a machine, so a mixed or mislabeled alloy is caught at the door. This prevents the most expensive defect in machining: a perfect part made from the wrong material.
What documentation ships with my parts?
CMM inspection reports, SPC control charts and material certificates ship with your parts. Each critical dimension carries a measured value rather than a pass/fail flag, giving you the evidence to accept the batch without a second guess.
Do you provide APQP and PPAP documentation?
In short, Yes — process flow charts, control plans, SPC data, PFMEA and environmental control procedures are available for automotive and regulated programs. A complete APQP/PPAP package has been delivered on customer projects, demonstrating automotive-grade quality planning and process control.
How do I verify your certifications are real?
In short, Ask for the certificate number and issuing body, then check that number with the registrar and confirm the legal name on the certificate matches Dongguan Zhuohang Ltd A number you can verify against the legal name is evidence; a logo is decoration.
What does Cpk tell a buyer that a pass/fail check does not?
In short, Cpk tells you whether the process stays centered and inside the tolerance band over time, not just whether one part passed. A pass/fail check answers "is this part good?"; a Cpk chart answers "will the next ten thousand parts be good too?" That is the question a production buyer is actually paying to have answered.
How often is the metrology equipment calibrated?
In short, Calibration runs on a defined interval against traceable standards, and the record for each instrument is available on request. Ask for the calibration certificate of the CMM that will measure your part — a serious lab produces it in the same exchange as the dimensional report.
CNC Machining Factory Quality — Related Pages
Continue reading: CNC Machining Factory · CNC Machining Factory Services · CNC Machining Factory
Standards referenced on this page
- ISO 14001 — Environmental management systems — Requirements with guidance for use
- IATF 16949:2016 — Automotive quality management system standard
- ASTM A582/A582M-12 — Standard Specification for Free-Machining Stainless Steel Bars