You can attach GD&T datum and tolerancing symbols to a 3D model. Creo Elements/Direct Modeling aids you in the process in an advisory role which ensures that correct and meaningful GD&T symbols are created.
Geometric dimensioning and tolerancing (GD&T) is the ASME and ISO engineering standard used to describe the form, fit, and function of the features comprising a part. The relationships between features are represented as tolerances either between a feature and another feature on the same part, or between a feature and another part.
This page describes how to apply Creo Elements/Direct Modeling symbols to your models. It is not intended to cover all the concepts and possibilities of GD&T itself. For detailed information about the GD&T standard, see Dimensioning and Tolerancing, ASME Y14.5M - 1994. For information about the individual GD&T symbols, see the Symbol Library .
If you are using the Creo Elements/Direct Annotation module, you can transfer GD&T symbols to your drawing using the Transfer Annos command.
Part-level and assembly-level GD&T
Datums and tolerances can be "owned" by either a single part or a single assembly. GD&T features at the part level must contain only elements from the owning part. GD&T at the assembly level can contain elements from any parts under that assembly. Therefore, multiple GD&T can be on the same element, but because they are at different levels, they do not violate the GD&T rules. You can use the Structure Browser to help visualize the hierarchy of GD&T features.
For example, consider the hierarchy a1 : a2 : p1. You can put a Datum A on the same face of p1 at the two assembly levels and also at the part level. Note, however, that the GD&T exists separately at each level, although there appears to be three Datum A's on one face.
The GD&T owner context can be controlled to display only those symbols belonging to a given owner.
A note on assembly-level GD&T
When GD&T tolerances are applied at an assembly level, no transformations that occur on the assembly will be communicated to tolerances or custom features that are owned by the given assembly. The impact of this restriction is noticeable in the following two events:
• Scaling the assembly: When an assembly is scaled in Creo Elements/Direct Modeling, each of the bodies within the assembly is individually scaled. This means that assembly level features (such as GD&T) do not get notified that a scale operation has occurred. For GD&T, this has the specific impact that the tolerance zone will not be automatically scaled by the same factor used to scale the assembly. This situation is not consistent with GD&T tolerances attached to parts, as they are properly notified of scaling events and will update their values if the part is scaled.
• Moving/rotating the assembly: When repositioning an assembly, GD&T tolerances (and also custom features) owned by that assembly do not get notified that a transformation has occurred. For GD&T, this has the specific impact that directions (like zone direction) associated with a tolerance will not be automatically updated when rotating an assembly. This situation is not consistent with GD&T tolerances attached to parts, as they are properly notified of such events and will update their values if the parts are repositioned.
The above applies, in general, to all custom features. If a custom feature is created whose owner is an assembly (or more generally, a parcel), then those features will not be properly notified of transformation events and their internal values will not be automatically updated. This situation does not apply to custom features attached to parts (in general, bodies). They are properly notified of transformation events and will update their variable values automatically if the part is repositioned or scaled.