Call the Parametrics! - AutoCAD 2012 - page 438

AutoCAD (and, to a very limited degree, in AutoCAD LT) might just be the most signific-
ant new feature ever.
If you know what I'm talking about, you're probably pretty interested in finding out more
about what you can do with parametrics in AutoCAD. If, on the other hand, you think
parametrics are the folks who show up when you dial 911, the following paragraphs
should straighten you out.
Maintaining Design Intent
Parametric (rule-based) drawing is by far the best way of enforcing design intent in 2D
drafting. Design intent in AutoCAD (or any other engineering software) means that when
drawings are edited — this part made wider, that hole made larger — all the attached or
related objects behave in a predictable way that honors the designer's intentions when
she created the drawing in the first place.
Before AutoCAD 2010, there was simply no way of maintaining the design concepts that
went into a drawing. You could use AutoCAD's drawing and editing commands to draw
accurate, precise plans, sections, and details, but as far as AutoCAD was concerned,
they were just a bunch of lines and circles.
Take, for example, that base-plate drawing example in Chapter 3. Maybe the engineer
has had a second look and determined that those 1 1⁄2-inch (38mm for the metric crowd)
bolts aren't quite up to the job — they need to be changed to 1 3⁄4 inch (44mm). To re-
vise the drawing using AutoCAD in the traditional way, you draw a new, larger circle for
the bolt and erase the old one. Now the nut is too small, and so is the hole in the plate
(maybe you can't see it, but you know and I know it's there). There's a whole lot of edit-
ing required to fix this drawing.
In AutoCAD 2012, you can add some intelligence to those lines and circles by applying
constraints to them. For example, you could apply a dimensional constraint to the bolt
circle and the hole circle such that the hole circle is always 1⁄16" (2mm) bigger than the
bolt circle. And while you're at it, you'd probably want to apply a concentric geometric
constraint between the circles so that whenever the bolt circle moved, the hole circle
moved with it.
Now that is intelligent design!
Defining terms