What a Real CMM Report Must Show
A genuine coordinate measuring machine (CMM) report is not a certificate that says pass. It lists five columns for every measured feature: characteristic name, nominal value, upper and lower tolerance limits, actual measured value, and deviation from nominal. If any of these columns is missing, the report does not prove anything.
Field-by-Field Breakdown
| Field | What It Means | How Hard to Fake |
|---|---|---|
| Report number | Unique ID linking to CMM machine log | Medium — numbers must match shop records |
| Part / drawing number | Identifies which revision was measured | Easy — but verify it matches your revision |
| Nominal value | Target dimension from the drawing | Easy |
| Upper / lower tolerance | Allowable deviation from nominal | Easy — must match the title block |
| Actual measured value | What the CMM probe recorded | Hard — real values show natural variation |
| Deviation | Difference between nominal and actual | Hard — should correlate with measured value |
| Pass / fail verdict | Whether the dimension is in tolerance | Easy — meaningless without measured values |
Three Signs That Are Hard to Fake
- A report number matching the CMM machine internal log with date and time stamp; ask for a photo of the CMM screen showing the run if you have doubts
- Measurement dates falling after machining completion and before shipment — a report dated before the parts were made is a red flag
- Deviation values with natural scatter; real machining produces small random variations, not perfectly centered values all reading 0.000
Three Follow-Up Questions for Your Supplier
- Which drawing revision does this report correspond to? The revision letter must match the drawing you released for production
- What CMM model was used, and when was it last calibrated? A current calibration certificate should be on file
- Can you show the raw point-cloud data or probe points for this dimension? Modern CMM software stores every touch point
When a Report Is Not Enough
A CMM report only covers dimensions programmed into the inspection routine; if a critical feature is absent, it was not measured. Review the ballooned drawing or inspection plan to confirm every critical dimension is included. TruPart Precision operates in Dongguan as an ISO 9001 certified shop and provides CMM reports with measured values on all tight-tolerance orders. Understanding how to read a report is the most direct way to verify that parts match the approved drawing.
Frequently Asked Questions
My supplier only sends a passed stamp without measurement data. Is that normal?
No. A pass/fail note without numerical values is not a CMM inspection report; it is a shipping label. Request actual measured values for every critical dimension.
Can a CMM report be edited?
Yes, a PDF can be altered, which is why cross-checking the report number against calibration records and asking for raw probe data matters for high-value orders.
Why does the measurement date matter?
If the report predates machining completion, it cannot be a genuine first-article or batch inspection; dates after shipment are equally suspicious.
Do I need a CMM report for every order?
For general commercial parts with ±0.1 mm tolerances, caliper checks may suffice; for any dimension under ±0.05 mm, a CMM report is standard practice.