Micro CNC Machining Quality Control

How is geometry verified for quality?

Hexagon GLOBAL S CMMs build the datum reference frame and measure position, cylindricity, and other geometric controls against it. A laser microscope and surface finish equipment support profile checks, so the measurement matches the control on the drawing. A caliper measures size; a CMM measures the geometry the GD&T calls out.

The verification is not a pass/fail stamp at the end of the line — it is the same class of measurement your own lab would run, produced at the machine. The CMM fits a plane for flatness, a cylinder for cylindricity, and an axis for position, then compares the result to the tolerance zone and reports the deviation against the datum structure.

That report is what makes quality transportable. You can read the measured deviation, reproduce it in their own lab, and get the same answer. A quality system that produces a number you can check is a quality system that can be trusted.

The instruments are calibrated on a schedule, because a CMM that has drifted writes confident wrong numbers. Calibration records are part of the quality file you can review, and they are the difference between a measurement you can trust and one you can only hope is right.

Why does the datum matter to measurement?

A geometric control without a datum has no origin, and a measurement without a datum has no meaning. The CMM builds its coordinate system from the datum, so the same part measured twice — or measured by your own lab — returns the same answer. That is what makes a tolerance verifiable. If your lab gets a different number, the disagreement is traceable to the datum definition, not to the machine.

The datum is also what keeps a quality check honest. A part can be measured from a convenient face instead of the drawing's datum and pass, while the same part measured from the correct datum fails. The quality system pins the datum first, so the measurement always starts from the reference the designer intended.

That is why a measurement you cannot reproduce is a measurement you cannot trust. The datum is what makes the number reproducible — at the shop, at your lab, or at a third-party auditor — and reproducibility is the whole test of whether a tolerance claim is real.

Which certifications back the quality system?

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

Honest scope note: IATF 16949 excludes product design under Clause 8.3. We are a build-to-print manufacturer — you own the design, and we own making it repeatably to your print.

A certificate is a pre-audit you get for free: a third party has already checked that the system is documented and running. The numbers are stated so you can confirm them with the registrar, which is the only way a certificate is worth more than the paper it is printed on.

What process capability does the shop prove?

A capability statement is worthless without a control chart. On a representative length characteristic (76.1–76.5 mm), our SPC shows Cpk 1.851 (one characteristic on one part, not a blanket capability claim) against an initial-study target of Ppk ≥ 1.67, with general characteristics held to Cpk ≥ 1.33. That is a measured result. A capability number without a control chart is a claim, not evidence.

Capability is the difference between a part that happens to pass and a process that reliably passes. Ppk ≥ 1.67 at the initial study on key characteristics means the process is centered and its spread sits well inside the tolerance zone, with margin to spare. The margin is the point: a process that just clears the band will ship a bad part the moment anything drifts; a process with margin absorbs the drift and keeps shipping good parts.

The control chart behind the number is the live record. Points plotted over the run show whether the process is centered, whether it is drifting, and whether the spread is stable. A process in control produces points that stay inside the control limits; a process going out of control shows a trend before a part fails, which is the whole point of charting in the first place.

How is a part inspected before it ships?

The inspection bench is the same class of equipment a buyer would use to audit us, and the results are documented.

• Hexagon GLOBAL S CMMs (2) for dimensional and geometric verification, plus a gear measuring center and vision measuring machines.
• KEYENCE VK-X3000 laser microscope and SURFCOM 1800D for surface finish and profile.
• XRF (iCHEQ) spectrometer for incoming material composition checks.
• HVS-1000A micro-Vickers hardness tester, Fischer coating gauge, salt spray and tensile testers.

The inspection happens at the machine, not in a distant lab, so a drifting feature is caught while the batch is still running. Every control on the drawing maps to an instrument, and the report names both the control and the method, so a position tolerance is proven by a CMM fit rather than an operator's feel.

The same CMM program written for the first article inspects the production run, so there is no re-baselining between prototype and volume. The validation carries forward, which is why the first article report matters: it fixes the measurement method for every part that follows.

How is material verified before it is cut?

Incoming bar is XRF-checked against its mill certificate so a mixed or mislabeled lot is caught at the door, and a material certificate with a heat number follows the batch through production. A wrong alloy defeats every geometric control downstream.

The XRF check reads composition, not just the paperwork, so a swapped lot is caught before it reaches a machine, where a certificate alone would not have stopped it. The heat number then links the finished part back to its raw stock, which is what lets a non-conformance be isolated to a specific lot instead of guessed at.

The material gate is where quality starts, because a geometric control only means something if the part is made from the material the drawing specified. A tolerance held in the wrong alloy is a tolerance that will fail in service, and no CMM can catch that after the fact.

The heat number is the thread that ties the part back to its raw stock. When a lot is traced end to end — raw material source, process parameters, machine, operator, and inspection results — a non-conformance can be isolated to the exact lot and contained, instead of replacing an entire order. Traceability is cheap insurance against the costliest kind of failure: the one where you cannot prove which parts are bad.

Can the shop provide a PPAP package?

For automotive and regulated buyers, a PPAP package proves the process is under control. Our APQP/PPAP evidence includes process flow charts, control plans, SPC charts, and PFMEA — the same discipline an IATF 16949 audit looks for.

If you ask for a PPAP and the shop hesitates, that hesitation is the answer. A build-to-print manufacturer should produce this evidence on request, because the control plan and the SPC chart are the paper trail behind the tolerance. A shop that has never written a control plan has never proven its process is stable, and stability is the whole point of a PPAP.

The package is not automotive-only. Any buyer can ask for the same evidence — the control plan that names the characteristics, the SPC chart that shows the spread, and the PFMEA that lists what could go wrong. The discipline transfers to any part, because a stable process is a stable process regardless of the industry.

The control plan is the quiet centerpiece. It names each characteristic, its tolerance, the method that measures it, and the frequency of the check, so nothing important is left to memory. A process without a control plan is a process where the quality depends on who happened to be on shift, and that is not a quality system, it is a lottery.

How do you read a Cpk number without being misled?

A Cpk number is only as good as the chart behind it. Cpk 1.851 (one characteristic on one part, not a blanket capability claim) on a representative length characteristic means the process is centered and its spread sits well inside the tolerance zone. The two things to check are the characteristic it was measured on and the sample it was drawn from — a capability number on an easy dimension says nothing about a tight one.

Cpk value	What it tells you	Where it applies
1.851 (one characteristic on one part, not a blanket capability claim)	Demonstrated capability on a representative characteristic	Length, 76.1–76.5 mm
≥ 1.67	Key-characteristic target	Dimensions that matter most
≥ 1.33	General-characteristic target	Remaining controlled dimensions

The rule for you is to ask for the chart, not the number. A chart shows the spread, the centering, and the sample, and it either supports the number or exposes it. A supplier that will not share the chart is asking you to trust a number it will not let you see.

A second distinction matters to anyone reading capability: Cpk measures short-term capability from a stable run, while Ppk measures longer-term performance including drift and tool wear. A shop that reports only Cpk is showing you its best stretch; a shop that also shows Ppk is showing you what you will actually receive across a whole order. Ask for both, and read them together.

What should a buyer ask about a machining quality system?

• Ask for the certificate numbers and confirm them with the registrar — a stated number is checkable.
• Ask for a Cpk chart, not just a Cpk value, and check which characteristic it covers.
• Ask how incoming material is verified, and whether a heat number follows the batch through production.
• Ask whether the inspection bench is the same class of CMM your own lab would use.
• Ask for the PPAP evidence — process flow charts, control plans, SPC charts, and PFMEA — if the part is automotive or regulated.
• Ask whether the datum is pinned before the measurement starts, so the number is reproducible.

What this shop actually runs

If you ask for capability evidence, you deserve a specific answer. This facility operates 100+ CNC machines across 6,800 m2 in Dongguan, China, staffed by 100+ people. The machines, listed 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.

Tolerance bands: ±0.003 mm milled, ±0.002 mm turned, ±0.002 mm ground or wire-cut. Capability indices: Ppk >= 1.67 at the initial study; Cpk >= 1.33 ongoing in production.

Certifications: ISO 9001:2015 (116024/A/0001/UK/En) · IATF 16949:2016 (131941/A/0001/SM/En, design clause 8.3 excluded) · ISO 14001:2015 (116024/B/0001/UK/En), held by Dongguan Zhuohang Ltd (USCC 91441900MA4UWT6X39, since 2005).

Service area: we supply 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, with worldwide delivery from China.

Contact: Felipe Iglesias, [email protected], +86 13126536955.

Frequently Asked Questions

Standards referenced on this page

• IATF 16949:2016 — Automotive quality management system standard
• ASTM A582/A582M-12 — Standard Specification for Free-Machining Stainless Steel Bars
• ISO 14001 — Environmental management systems — Requirements with guidance for use