AutoCAD® 2012 FOR DUMMIES®

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 ½-inch (38mm for the metric crowd) bolts aren't quite up to the job — they need to be changed to 1 ¾ inch (44mm). To revise 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 editing 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 ...