Graphics Programs Reference
In-Depth Information
Chapter 16
Making “Smart” Drawings with
Parametric Tools
Don't let the term
parametric drawing
scare you.
Parametric
is a word from mathematics, and in
the context of AutoCAD drawings, it means that you can define relationships between different
objects in a drawing. For example, you can set up a pair of individual lines to stay parallel or set
up two concentric circles to maintain an exact distance between each other no matter how they
may be edited.
Parametric drawing is also called
constraint-based modeling
, and you'll see the word
constraint
used in the Tool Sets palette as well as the menu bar to describe sets of tools. The term
constraint
is
a bit more descriptive of the tools you'll use to create parametric drawings because when you use
them, you are applying a constraint upon the objects in your drawing.
In this chapter, you'll see firsthand how the parametric drawing tools work and how you
might apply them to your needs.
In this chapter, you'll learn how to do the following:
Use parametric drawing tools
•u
Connect objects with geometric constraints
•u
Control sizes with dimensional constraints
•u
•u
Put constraints to use
Why Use Parametric Drawing Tools
If you're not familiar with parametric drawing, you may be wondering what purpose it serves.
With careful application of the parametric tools, you can create a drawing that you can quickly
modify with just a change of a dimension or two instead of actually editing the lines that make
up the drawing. Figure 16.1 shows a drawing that was set up so that the arcs and circles increase
in size to an exact proportion when the overall length dimension is increased. This can save a lot
of time if you're designing several parts that are similar with only a few dimensional changes.
You can also mimic the behavior of a mechanical assembly to test your ideas. The parametric
drawing tools let you create linkages between objects so that if one moves, the others maintain
their connection like a link in a chain. For example, you can create 3D AutoCAD models of a
crankshaft and piston assembly of a car motor (see Figure 16.2) or the parallel arms of a Luxo
lamp. If you move one part of the model, the other parts move in a way consistent with a real
motor or lamp.
