Metrologic DCS has outlined four practices intended to reduce Geometric Dimensioning and Tolerancing (GD&T) interpretation gaps as Product Manufacturing Information (PMI) becomes more common in CAD files and standards continue to evolve. Misinterpretation, the company says, can lead to conflicting measurements, scrap and costly back-and-forth between design, production and metrology teams.
Start from PMI
The first step is to decode the design intent carried by PMI: which feature is targeted, which references apply and which tolerance is specified. Metrologic DCS notes that manual re-entry is error-prone, because a copied value or misunderstood reference can send a part through inspection against the wrong requirement. The company recommends software that uses PMI as its starting point and creates features and evaluations from the part’s digital definition, reducing re-keying and interpretation gaps.
Automate the datum reference frame
A Datum Reference Frame (DRF) defines where measurements begin. 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 poor selection of degrees of freedom can make the same part appear conforming or non-conforming depending on the operator. Automating DRF and degree-of-freedom selection from the drawing definition is presented as a way to make results repeatable across operators, machines and sites. In the company’s Metrolog software, the DRF is created automatically when a GD&T is evaluated.
Reuse imported DRFs
Because references A, B and C are already labelled in the CAD model, recreating them during program preparation wastes time and can introduce discrepancies, especially when definitions change, according to the company. Reusing DRFs imported from PMI allows GD&T to be predefined from them, while a progress view shows where each annotation sits and how its measurement stands. Metrologic DCS says its Scan GDT function reads decoded PMI and assigns a status so users can validate both decoding and measurement.
Tailor reports to the reader
Metrologic DCS argues that a report limited to “pass” or “fail” does not tell the shop floor what to correct. It recommends different views for different readers: a table of numerical values for quality control, a Go/No-Go report for quick decisions and a decomposition analysis for the machine operator. In Metrolog, the defect of an evaluated feature is split into four independent categories—form, size, position and orientation—alongside the global defect, so the dominant type can be identified first. The company says a good report reduces scrap and speeds corrective action.