2012

Table Of Contents
It is important to understand the chain of associativity because moving or
deleting one of the links in the chain can break the relationship between all
the objects.
NOTE
To modify the shape of a surface that is generated from a curve or spline, you
must select and modify the generating curve or spline, not the surface itself.
If you modify the surface itself, you will lose associativity.
When associativity is on, the DELOBJ system variable is ignored. If Surface
Associativity and NURBS Creation are both on, surface are created as NURBS
surfaces, not associative surfaces.
Save time by planning your model ahead; you cannot go back and add
associativity after the model has been created. Also, be careful not to
accidentally break associativity by dragging objects away from the group.
Create Geometric Relationships between Associ-
ative Surfaces
Use geometric constraints to constrain and restrict surfaces. And use
mathematical expressions to derive surface properties.
Use Geometric Constraints with Surface Profiles
Just as with 2D drafting, geometric constraints can be used to restrict the
movement of 3D surfaces. For example, you can specify that a surface remain
fixed in a perpendicular or parallel location to another object. In the example
below, an offset surface is locked in a parallel position to its original surface.
406 | Chapter 8 Work with 3D Models