What is a CMM report?

A printed or PDF record of each measured feature on a part, with its nominal size, tolerance, actual value and pass or fail. It proves the part matches the drawing.

Do all parts need CMM checking?

No. Simple sizes are checked with gauges, micrometers and height gauges. A CMM is used for complex parts, GD&T tolerances and first article or PPAP reports.

CMM (coordinate measuring machine): uses and accuracy

A CMM, or coordinate measuring machine, measures a part in three dimensions with a precise probe. It checks sizes, positions, angles and geometric tolerances against the drawing or 3D model and prints a report. Buyers in automotive, aerospace and precision engineering often ask for CMM reports on first articles.

Quick facts

Measures: Sizes, hole positions, flatness, roundness, profiles, GD&T
Typical accuracy: A few microns on good bridge machines
Types: Bridge, gantry, horizontal arm, portable arm
Probes: Touch-trigger, scanning and optical probes
Output: Inspection report against drawing or CAD model
Room: Needs a temperature-controlled room (about 20 °C) for best accuracy

When a CMM report is asked for

First article inspection (FAI) before a batch is approved
PPAP submissions for automotive buyers
Parts with position, profile or other GD&T tolerances
Complex parts where gauges are not practical

What a report shows

Each dimension's nominal value, tolerance and measured value
Pass or fail for each feature
Datums used for measurement
Optionally, a colour map against the 3D model

Good to know

Measure at a stable temperature; steel grows about 11 µm per metre per °C
Clean parts before measuring; burrs and chips give false readings
Agree datums with the buyer before measuring

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Questions

What is a CMM report?: A printed or PDF record of each measured feature on a part, with its nominal size, tolerance, actual value and pass or fail. It proves the part matches the drawing.
Do all parts need CMM checking?: No. Simple sizes are checked with gauges, micrometers and height gauges. A CMM is used for complex parts, GD&T tolerances and first article or PPAP reports.

The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 15 October 2026.