Metrologic DCS has outlined four practices for reducing disagreements over Geometric Dimensioning and Tolerancing (GD&T) as product manufacturing information (PMI) becomes more common in CAD files and standards continue to evolve. The metrology software supplier frames the problem as a communication gap linking design, production and inspection: a misread feature, reference or tolerance can send a part through the wrong measurement routine and create scrap or repeated exchanges between teams.
The guidance runs from interpreting the digital definition to reporting results on the shop floor. Metrologic DCS presents the practices as ways to make inspection preparation more repeatable; the time and scrap benefits described are the company’s own.
Start with the PMI rather than re-keying tolerances
The first step is to decode design intent from PMI: which feature is targeted, which references apply and which tolerance is specified. Metrologic DCS says this step is error-prone when handled manually, because a copied value or misunderstood reference can lead to inspection against the wrong requirement. It recommends software that takes PMI as its starting point instead of requiring users to re-enter tolerances, so features and evaluations are created from the part’s digital definition. The company says this avoids re-keying, reduces interpretation gaps and saves time at the start of program preparation.
Automate the datum reference frame
The Datum Reference Frame (DRF) defines where measurement begins. It consists of reference features A, B and C and determines which degrees of freedom are constrained for evaluation. According to Metrologic DCS, building the DRF in the wrong order or selecting degrees of freedom poorly can cause the same part to be declared conforming or non-conforming depending on the operator, making it a major source of GD&T misinterpretation. The company recommends automating the step so that the DRF and degrees of freedom follow the drawing definition rather than operator choice. In its Metrolog software, the DRF is created automatically when a GD&T is evaluated, with degrees of freedom selected accordingly.
Reuse imported DRFs and track annotation status
References are already defined in the CAD model, where labels for A, B and C are placed by the design office. Recreating them during program preparation wastes time, can introduce discrepancies and forces rework whenever the definition changes, Metrologic DCS notes. On parts with many annotations, it can also be difficult to distinguish those already handled from those still to be measured. The company advises starting from DRFs coming from the PMI and predefining GD&T from them while maintaining a clear view of where each annotation sits and where its measurement stands. In Metrolog, Scan GDT reads the decoded PMI and assigns a status so users can validate both decoding and measurement.
Tailor reports to the reader
A report limited to “pass” or “fail” does not tell the shop floor what action to take, according to the company. An operator who does not know the type of defect may adjust by trial and error, producing scrap and correction loops. Metrologic DCS recommends matching the report to its audience: a table of numerical values for quality control, a Go/No-Go report for a quick decision and a decomposition analysis for the operator. Metrolog splits the defect of an evaluated feature into four independent types—form, size, position and orientation—alongside the global defect. The company says this helps users see which type dominates and what to correct first, and that a good report can reduce scrap and speed corrective action.