Constraints
Constraints let you "fix" various dimensions that control the location and/or orientation of features on a solid. The Constrain Feature tool, in the Manipulate Feature toolbox, lets you add constraints to features.
For example, you could constrain holes in each corner of a slab to always be 25 mm from adjacent edges. The holes would remain correctly located no matter how you changed the dimensions of the slab. Without the constraints, changing the dimension of the slab leaves the holes static in their current locations.
Left: Original solid (slab) with holes offset 25 mm from adjacent edges in each corner. | Center: With holes unconstrained — changing the dimensions of the slab can leave the holes incorrectly positioned. | Right: With holes constrained — when the dimensions of the slab are modified, the holes remain correctly located 25 mm from adjacent edges of each corner.
Variables and Constraints
When adding a constraint to a feature, you can define the constraint using an existing global or local variable, either by itself or as part of an equation. When variables are used in this way, you can "redesign" the solid simply by changing the values of the variables. This results in the solid being regenerated with the new values applied to the constraints for the features.