All CNC Machined Parts Must Pass a Full Inspection

Inspection starts at goods-in. We check the mill certificate against the alloy you specified, confirm heat or lot numbers, and measure a coupon for hardness where the drawing calls it out. For 17-4PH, 7075, or Ti-6Al-4V, a wrong heat treat condition will not show up until the part fails in service, so the check happens before chips fly.

Setup is the second gate. The first-off part is measured against every dimension that the program can affect: datums, bolt patterns, wall thickness, bore size. If a feature is out of tolerance on the first-off, we correct the offset or the fixture and run another first-off. Production does not continue until that part passes.

This stage catches the errors that are cheap to fix. A wrong tool offset found at first-off costs a few minutes. The same error found after 500 parts costs a full run.

Once a run is stable, we monitor the features that drift. Tool wear moves a bore diameter or a shoulder height over a few hundred parts, so the operator checks those at a set interval and adjusts the offset. Temperature matters on long parts: a 4,000 mm aluminum extrusion can grow enough between morning and afternoon to close a ±0.005 mm window if the shop floor swings several degrees.

For tight-tolerance work, the probe on the machine does a quick check without breaking the setup. That is a screening step, not the final word. Probe results tell us whether to keep cutting or stop and re-measure on the CMM.

In-process data also feeds back into the program. If one feature keeps drifting in the same direction across three runs, the issue is usually the fixture or the toolpath, not the operator.

• 1
  First-off inspectionFull dimensional check before any production parts are made.
• 2
  Interval checksSet part counts for features that wear with tool life.
• 3
  Probe screeningFast in-machine check to decide continue or stop.
• 4
  Trend reviewRepeat drift across runs points to fixture or program.

Before shipment, every part is inspected. For simple parts that means a dimensional check against the drawing with calipers, micrometers, pin gauges, and thread gauges. For complex geometry we use a CMM with a touch probe and report the actual value for each controlled dimension, not just pass or fail.

A useful report lists the drawing dimension, the tolerance band, the measured value, and the instrument used. If a feature is measured on the CMM, the report should state the datum setup, because a bore measured from a different datum can read differently by more than the tolerance.

Cosmetic and functional checks sit alongside dimensions: surface finish measured in Ra, deburred edges, thread depth, and a visual pass under defined lighting. Anodized and plated parts get a color and thickness check against the finish spec. We can issue reports on request, and for medical or automotive programs the report format is agreed before the first run.

Start with the tolerance band, not the measured number. A bore at 10.002 mm is fine for a ±0.02 mm callout and scrap for a ±0.005 mm callout. Engineers who read the report against the drawing catch problems that a simple pass stamp hides.

Check the instrument for each feature. A 0.001 mm micrometer reading on a rubber-mounted part can move with hand pressure. A pin gauge tells you go or no-go and nothing about the actual size. The instrument should match the tolerance it is verifying.

Look at the spread across the lot, not just one part. If part one is at the low end and part 500 is at the high end, the process is drifting and the next run will likely miss. A stable process holds values in the middle of the band.

Finally, match the report to what you will do with the part. A fixture plate that locates on two dowel holes needs those holes verified on every part. A cosmetic enclosure panel needs finish and flatness verified. Inspection effort should follow function.

• 1
  Read against the drawingSame number can pass or fail depending on the callout.
• 2
  Match instrument to toleranceDo not verify a 0.005 mm feature with a caliper.
• 3
  Watch drift across the lotTrend matters more than any single reading.

Our quality system is certified to ISO 9001:2015, the base framework for process control and corrective action. For automotive and engine hardware work, IATF 16949:2016 adds production-part approval, control plans, and capability requirements on top of that base. Automotive buyers should expect a PPAP package, not just a dimensional report.

Medical device work runs under ISO 13485:2016, which requires documented design transfer, traceability, and validation of processes including inspection. If your part touches a patient, the inspection records become part of the device history file.

Information security runs under ISO 27001:2022. That matters when your drawings and CAD files are the sensitive asset. Uploads are handled as confidential, and we sign an NDA on request before files move.

We work to ±0.005 mm (±0.0002 in) on features the process can control, with surface finish from Ra 0.2–0.8 μm on fine work and Ra 0.8–1.6 μm on standard machined surfaces. Those numbers assume a rigid setup, a stable alloy, and a feature the tool can reach without long overhang.

The answer changes with geometry. A deep bore in 316 stainless will deflect a small boring bar, and the achievable tolerance loosens. A thin wall in aluminum can move when the vise releases. A 4,000 mm part can grow or shrink with shop temperature. When a drawing asks for a tolerance the geometry cannot hold, we flag it during DFM review rather than quote it and miss.

Material choice sets the floor too. Titanium and Inconel cut hotter and wear tools faster, so surface finish and tool life need more attention. Plastics like POM and PEEK move after machining as they relax, which means the inspection timing matters as much as the measurement.

If your drawing has a tight tolerance on a difficult feature, send it with the quote request. We run a free DFM analysis within 12 hours and tell you what the process can realistically hold.