A symbolic language on engineering drawings that defines allowable variation in form, orientation, location, and runout of part features.
GD&T uses feature control frames referencing datums. Key categories: Form (flatness, circularity, cylindricity, straightness), Orientation (perpendicularity, angularity, parallelism), Location (position, concentricity, symmetry), Runout (circular, total). Standard: ASME Y14.5-2018 or ISO 1101.
In AM, GD&T helps communicate which surfaces are functional vs. aesthetic. Mark datum faces that will be machined post-print. Use position tolerance (⊕) to specify axis location of holes, not just diameter tolerances. Critical for hybrid manufacturing workflows.
FDM cannot achieve IT6 or better without post-machining. Avoid specifying form tolerances (flatness, straightness) below 0.3 mm on printed surfaces. Use GD&T to communicate intent, but verify achievability on the actual machine.
Related terms: Tolerance, Surface Roughness, Dimensional Accuracy
| Field | engineering |
|---|---|
| Also called | GDT, geometric tolerancing, ASME Y14.5 |
| Source | EDi Brain: rules-core |
Engineer, author of The Big Book of 3D Printing and additive manufacturing expert