📐 Geometric Dimensioning & Tolerancing (GD&T) – Control Summary 🧭
GD&T provides a precise language to define allowable variation in form, orientation, location, and runout—ensuring functional fit and interchangeability.
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🔹 FORM CONTROLS
(Control the shape of a feature — no datum reference allowed)
🔲 Flatness
Controls the flatness of a surface.
📏 Straightness
Controls straightness of a surface element or an axis.
⭕ Circularity (Roundness)
Controls roundness of a circular feature.
🛢️ Cylindricity
Controls the overall form of a cylindrical surface.
➡️ Combines circularity + straightness.
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🔹 ORIENTATION CONTROLS
(Control the tilt or orientation relative to a datum)
⟂ Perpendicularity
Controls 90° orientation of surfaces, axes, or median planes.
∥ Parallelism
Controls parallel orientation between features.
📐 Angularity
Controls orientation at a specified angle (other than 90°).
📌 Datum reference is required.
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🔹 LOCATION CONTROLS
(Locate features relative to datums)
🎯 Position
Locates center points, axes, or median planes of size features.
➡️ Also controls orientation.
🔵 Concentricity
Locates the derived median points of a feature relative to a datum axis.
⚠️ Rarely recommended—consider Position, Runout, or Profile instead.
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🔹 PROFILE CONTROLS
🌊 Profile of a Surface
Controls the shape and location of a surface.
➡️ Can control form, orientation, location, and size.
〰️ Profile of a Line
Controls the shape of individual cross-sections.
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🔹 RUNOUT CONTROLS
🔄 Circular Runout
Controls circular variation during rotation.
🌀 Total Runout
Controls overall surface variation, including:
✔️ Form
✔️ Coaxiality
✔️ Orientation
🎯 Key Insight
Selecting the right GD&T control simplifies inspection, improves manufacturability, and ensures functional performance—without over-constraining the design.
source : Six Sigma Manufacturing
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