GDT:Form Overview
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| Symbol | Form Overview |
|---|---|
| Type | Form |
| Category | Form |
| Standard | ASME Y14.5 |
| Author | Admin |
| Datums | Not used for form controls |
| Modifiers | Varies by control and feature type |
| Tolerance zone | Varies by control |
| Image | GDT-Form-Overview.svg |
| Common mistakes | Referencing datums for form-only controls; choosing the wrong form control for the feature |
| Related |
Summary
Form controls limit the shape of individual features without reference to datums.
Definition
Form tolerances constrain the shape of a single feature (or a feature's surface elements) without establishing a datum reference frame. They answer: “Is this feature straight/flat/round/cylindrical enough?”
Scope
Use form controls when you need to control shape only, independent of orientation or location.
Controls in this category
Examples
- Use GDT:Straightness to control a shaft axis without datums.
- Use GDT:Flatness to ensure a sealing surface is sufficiently flat.
When to use it
Use form controls to ensure a feature is straight, flat, round, or cylindrical within a defined tolerance zone.
Common mistakes
- Referencing datums for form-only requirements.
- Using a location or orientation control when only form is needed.