Geometric Dimensioning and Tolerancing (GD&T) connects design, production and metrology, but misinterpretation can lead to conflicting measurements, scrap and repeated exchanges between teams. Metrologic DCS says the risk is growing as Product Manufacturing Information (PMI) is increasingly embedded in CAD files and standards continue to evolve. In an article, the company outlines four measures intended to make inspection workflows more reliable, from reading design intent to delivering reports to the shop floor.
Start with PMI
Metrologic DCS recommends using software that takes PMI as its starting point instead of requiring users to re-enter tolerances. The company says manual decoding is error-prone: a copied value or misunderstood reference can cause a part to be inspected against the wrong requirement. When features and evaluations are created from the part’s digital definition, the company says, re-keying is avoided, interpretation gaps are fewer and program preparation time is reduced.
Automate DRF construction
The Datum Reference Frame (DRF) defines where measurement begins. It is built from reference features A, B and C and determines which degrees of freedom are constrained. Metrologic DCS warns that an incorrect build order or poorly selected degrees of freedom can lead the same part to be declared conforming or non-conforming depending on the operator. The company advocates automating the step so the DRF and degrees of freedom follow the drawing definition. In Metrolog, it says, the DRF is created automatically when a GD&T is evaluated.
Reuse imported DRFs
The references are already defined in the CAD model with labels placed by the design office, the company notes. Recreating them during program preparation wastes time and can introduce discrepancies, while parts with many annotations make it difficult to track which items have been handled. Metrologic DCS recommends starting from PMI-derived DRFs and predefining GD&T from them. Its Scan GDT function reads decoded PMI and assigns a status so users can validate both decoding and measurement, according to the company.
Tailor reports to readers
A report limited to “pass” or “fail” does not tell the shop floor what to correct, Metrologic DCS says. The company recommends different formats for different readers: numerical tables for quality control, a go/no-go report for quick decisions and a decomposition analysis for the operator. Metrolog splits an evaluated feature’s defect into four independent types—form, size, position and orientation—alongside the global defect, so users can see which type dominates and decide what to correct first. Metrologic DCS says a good report reduces scrap and speeds corrective action.