That’s correct. Flat to screen surface finishes do not have a directional annotation plane and do not support an extension line. You cannot drag surface finishes off the model surfaces that are created flat to screen.
In Creo, if the placement surface is planar, then you can drag surface finishes in the XY direction beyond the placement surface. An extension line is created in the XY-direction when you drag the surface finish off the reference surface as shown below
You can drag the surface finish in the Z-direction even when it is off the surface till the surface finish reaches a point where an extension line cannot intersect the placement surface.
Note: You can also drag the surface finish attached to a conic or cylindrical silhouette off the surface in the direction of the silhouette if –
- The current model orientation is the same as the annotation plane orientation of the selected surface finish
- The surface finish is attached to the silhouette of a conic or cylindrical surface
- The Annotation plane is parallel to the axis of the cone or cylinder.
This pic shows the movement of the surface finish along a cylindrical silhouette.
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Content Source: PTC