Metrologic DCS has published four practical steps for reducing misinterpretation of Geometric Dimensioning and Tolerancing (GD&T) as product manufacturing information (PMI) becomes more common in CAD files and standards continue to change.
The first recommendation is to begin with the PMI rather than re-entering tolerances. The company says the PMI must be decoded to establish which feature is targeted, which references apply and which tolerance is specified. Manual copying or misreading a reference, it notes, can lead to inspection against the wrong requirement.
Datum frames and reused references
Second, Metrologic DCS advises against rebuilding datum reference frames (DRFs) by hand. A DRF is made up of reference features A, B and C and determines which degrees of freedom are constrained. If the DRF is built in the wrong order or the degrees of freedom are poorly selected, the company says the same part may be judged conforming or non-conforming depending on the operator.
Third, the article recommends reusing DRFs imported from the CAD model. The design office has already placed labels on references A, B and C, and recreating them can waste time, introduce discrepancies and require rework when the definition changes. Keeping track of which annotations have been handled and which still need measurement is also presented as a practical need.
Reports for the shop floor
Fourth, Metrologic DCS argues that a pass/fail result alone does not tell machine operators what to correct. It suggests reports tailored to the reader: numerical tables for quality control, go/no-go reports for quick decisions and decomposition analysis for operators.
According to the company, its Metrolog software creates the DRF automatically when a GD&T is evaluated, selects the corresponding degrees of freedom, and lets Scan GDT read decoded PMI and assign a status. Metrolog also splits a feature's defect into form, size, position and orientation, alongside the global defect. These are vendor-described capabilities; the article does not present independent verification or user results.