Scheme Options for Planar Surface Features (ASME)
Planar Surface features support the following scheme options:
Geometric Tolerance
This option requires that you to constrain the location of the plane with a
profile tolerance. You can apply additional
geometric tolerances to constrain the orientation or
form of the feature.
Size Dimension
A size dimension defines a condition in which the opposing planes (the constrained feature and the reference feature) form a
feature of size. The size dimension may impose a constrain form (due to
Rule #1) of that feature of size. Thus, a size dimension applies constraint not only on the constrained Planar Surface feature, but also imposes constraint on the form of the reference feature.
This scheme has the following requirements:
• Dimension:
◦ Normal to the Planar Surface.
◦ One endpoint is in the plane of the Planar Surface.
• Reference Feature:
◦ Planar Surface feature that:
▪ Is parallel to the selected feature.
▪ Passes through the other endpoint of the selected dimension.
▪ Has an opposing normal vector to the constrained Planar Surface.
▪ Has a projection onto a midplane that overlaps the projection of the constrained Planar Surface on the midplane.
If desired, you may also apply a geometric tolerance to the size dimension to constrain the location, orientation, or form of the feature of size that is defined by the two opposing Planar Surface features.
Offset Dimension
An offset dimension defines a
tolerance zone that is parallel to a reference plane. The constrained Planar Surface feature must lie completely within that zone. Thus, an offset dimension imposes constraint on the location, orientation, and form of the constrained feature.
This scheme has the following requirements:
• Dimension:
◦ Normal to the Planar Surface.
◦ One endpoint is in the plane of the Planar Surface.
• Reference Feature:
◦ Planar Surface feature that:
▪ Is parallel to the selected feature.
▪ Passes through the other endpoint of the selected dimension.
If desired, you may also apply geometric tolerances of orientation or form to the feature.
Although an offset dimension and a size dimension have a similar appearance in the model, they have different requirements and apply different constraint (as described above). Ideally, an offset dimension would be represented with a dimension origin symbol (
) to differentiate the dimension from a size dimension and to provide an indication of which is the constrained feature and which is the reference feature. However, dimension origin is not supported in this version of the application. Instead, GD&T Advisor adds an optional annotation (controlled by the Offset_Dim_Text application option) to all offset dimensions so that they can be differentiated from size dimensions. Note if desired, you can manually select the Origin option for one of the dimension endpoints.