GDT:Datums Overview: Difference between revisions
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Created page with "{{Author Credit |author=Admin }} {{GDT Infobox |symbol=Datums Overview |type=Datums |category=Datums |standard=ASME Y14.5 |author=Admin |datums=Defines a datum reference frame from datum features |modifiers=Material condition modifiers and datum feature simulator rules |tolerance_zone=Datum-related tolerance zones and simulators |image=<!-- TODO: add diagram file name --> |mistakes=Unstable datum selection; missing datum order; mixing unrel..." |
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|modifiers=Material condition modifiers and datum feature simulator rules | |modifiers=Material condition modifiers and datum feature simulator rules | ||
|tolerance_zone=Datum-related tolerance zones and simulators | |tolerance_zone=Datum-related tolerance zones and simulators | ||
|image= | |image=GDT-Datums-Overview.svg | ||
|mistakes=Unstable datum selection; missing datum order; mixing unrelated datum features | |mistakes=Unstable datum selection; missing datum order; mixing unrelated datum features | ||
|related=[[GDT:Position]] | |related=[[GDT:Position]] | ||
Latest revision as of 19:27, 15 January 2026
| Symbol | Datums Overview |
|---|---|
| Type | Datums |
| Category | Datums |
| Standard | ASME Y14.5 |
| Author | Admin |
| Datums | Defines a datum reference frame from datum features |
| Modifiers | Material condition modifiers and datum feature simulator rules |
| Tolerance zone | Datum-related tolerance zones and simulators |
| Image | GDT-Datums-Overview.svg |
| Common mistakes | Unstable datum selection; missing datum order; mixing unrelated datum features |
| Related | GDT:Position |
Summary
Datums establish the reference frame used to locate and orient toleranced features.
Definition
A datum is a theoretically exact reference derived from a datum feature. Datum features are real surfaces or features on the part that are used to establish the datum reference frame.
When to use it
Use datums whenever a feature needs to be located or oriented relative to other features or functional interfaces.
Examples
Example: Primary, secondary, tertiary datums
A flat surface as datum A, a perpendicular face as datum B, and a hole axis as datum C.
Common mistakes
- Choosing unstable or non-functional datum features.
- Omitting datum order or mixing the order between segments.
- Using datum features that do not reflect assembly or inspection constraints.