Context

A CMM plan is not a checklist. It is a measurement strategy tied to datums, risk, and functional intent.

A real CMM inspection plan prioritizes critical dimensions, defines sampling cadence, and documents measurement uncertainty for audits.

The Trap

The trap is measuring everything equally. That wastes time and still misses the high-risk features. Without datum strategy, your CMM report is just numbers with no meaning.

The Geppetto Take

We build CMM plans around functional datums. Critical features get scanning and tight uncertainty control. Low-risk features get sampling or attribute checks.

Evidence / Data

  • Datum drift is the number one reason CMM reports do not match assembly behavior.
  • Scanning on critical seats catches form error that touch points miss.

Control Actions

  • Define primary datum from functional bearing or interface.
  • Use scanning for critical bores and seats.
  • Tier tolerances into critical / important / reference.
  • Document uncertainty for each critical measurement.

Checklist

  • Datum scheme aligned with functional assembly.
  • Critical features set for scanning or full profile.
  • Sampling rules defined for low-risk features.
  • Calibration status recorded per session.

What to Send

Send the datum scheme, tolerance map, and any functional performance requirements.

FAQ

Do we need to scan every feature?

No. Scan only the features that drive fit or performance.

Why do touch points fail on roundness?

They can miss lobing and form error between points.

How do you set sample rates?

Based on risk: critical features get 100%, others get statistical sampling.

CTA

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