Graphics Programs Reference
In-Depth Information
ADDING CONSTRAINTS AS YOU DRAW
In the first part of this chapter, you saw that you can add constraints to an existing drawing using
the Autoconstrain command. You can also set up AutoCAD to add constraints as you draw. This
feature is called Infer Constraints. You can turn Infer Constraints on or off using the Infer Constraints
tool in the status bar.
If you use Infer Constraints to draw a series of lines, at the very least it will apply the coincident
constraint at the end of each line segment. If you use osnaps and polar tracking, other constraints
like parallel and perpendicular may be applied to objects as you draw.
Controlling Sizes with Dimensional Constraints
Perhaps the heart of the AutoCAD parametric tools is the dimensional constraints. These con-
straints allow you to set and adjust the dimension of an assembly of parts, thereby giving you
an easy way to adjust the size and even the shape of a set of objects.
For example, suppose you have a set of parts that you are drafting, each of which is just
slightly different in one dimension or another. You can add geometric constraints and then add
dimensional constraints, which will let you easily modify your part just by changing the value
of a dimension. To see firsthand how this works, try the following exercises.
Adding and Editing a Dimensional Constraint
In this first dimensional-constraint exercise, you'll add a horizontal dimension to the drawing
you've already been working on. The drawing already has some geometric constraints that you
are familiar with, so you can see how the dimensional constraints interact with the geometric
constraints.
Start by adding a dimensional constraint between the two arcs:
1.
Click the Aligned tool in the Tool Sets palette, or you can choose Parametrics
Dimensional Constraints
Aligned from the menu bar.
2.
Right-click on the drawing and select Snap Overrides
Center Option from
the shortcut menu.
3.
Place the cursor on the arc on the left side of the drawing so that the Center Osnap marker
appears for the arc (Figure 16.11). Notice that the arc is highlighted as you select the center.
4.
Right-click, and select Snap Overrides
Center Osnap Option as you did in step 2.
5.
Click the arc on the right side of the drawing (Figure 16.12).
FIGURE 16.11
Use the Center
Osnap to select the
center of the arc.
The Center
Osnap marker appears.
Place the cursor
on the arc.
