Applying Dimensional Constraints
Dimensional constraints let you control distances or angles between 2D geometric objects or points on objects by applying dimensional constraints and specifying values. You can also set up equations that control distances and angles. For example, in the sample drawing, the radius of the outer arc on the right is 1.5 times the radius of the circle.
When you apply a dimensional constraint to an object, a constraint variable is automatically created for maintaining the constraint value. For example, you can see that the radius of the circle on the right is identified by the variable rad1.
You can also see that dimensional constraints have a little padlock icon adjacent to them so that you can easily differentiate them from dimensions.
You apply dimensional constraints and control their appearance using the tools in the Dimensional panel of the Parametric ribbon.
Dimensional constraints control the size and proportions of a design.
Linear distance constraints control the distances between objects or between points on objects. For example, when you change the distance of d1 to 7 units, the object immediately updates.
Angular constraints control the angle between objects or between points on objects. When you change the angle of ang1 to 90 degrees, the part immediately updates.
Diameter and radial dimensional constraints control the sizes of arcs and circles. When you change the radius value rad1 to 0.75, both the circle and its related concentric arc immediately update.
As you have just seen, if you change the value of a dimensional constraint, all of the constraints on the object are evaluated and the objects that are affected are updated automatically.
Of course, in order for this to work as intended, you must first establish the necessary geometric constraints and then apply dimensional constraints. If geometric constraints had not been applied, the lines, arcs, and circles would not have maintained their relationships to each other when the various dimensional constraint values were changed.
Dimensional constraints are different from dimension objects.
Dimensional constraints are used in the design phase of a drawing, whereas dimensions are typically created in the documentation phase.
Dimensional constraints drive the size and angle of objects; therefore, changing a dimensional constraint changes the size of the object. But dimensions are driven by objects. They update only when you change the size of an object.
By default, dimensional constraints are not objects. They display with a single style, maintain their size even when you zoom, and are typically not plotted.
If you do need to plot dimensional constraints, you can change the format of a dimensional constraint from dynamic to annotational.
Source: Autodesk
