When A CMM Beats Hand Tools
Complex geometry, GD&T callouts, tight positional tolerances, and first-article parts are where a CMM shines. It gives repeatable, documented results—and a clear map of which features pass or fail.
Send The Right Inputs
- Latest drawing (with revision) and, if available, STEP/IGES model
- Datum scheme and any customer-specific notes
- Tolerance strategy (critical features first)
- Special fixturing or clamping instructions
Alignment: The Usual Trap
A defensible report starts with a defensible alignment. Lock the datum structure as defined on the drawing, avoid “best-fit” unless the spec allows it, and state the method in the report. Temperature close to 20 °C, part stabilised, and consistent probing strategy—these basics prevent long email threads later.
Fixturing And Environment
Rigid, repeatable fixturing reduces measurement noise. Keep the part clean and thermally stable; avoid hands-on warming. For thin walls or elastomers, agree on probing force or optical strategy.
Reporting That People Can Use
- Feature list with nominal, measured, deviation, and tolerance
- Clear OK / Not OK status
- Notes for any non-measurable or ambiguous features
- Screenshots or simple plots for complex GD&T results
Common Pitfalls To Avoid
- Mixing CAD revisions in the same run
- Hidden datum re-definitions to make features “pass”
- Reporting only averages without min/max or form errors
- No record of probe qualification or environmental conditions
Checklist Before You Ship Parts To The Lab
Drawing ✓ · CAD file ✓ · Datum scheme ✓ · Quantity ✓ · Special fixturing ✓ · Due date ✓