Datasheet

18 CHAPTER 1 INVENTOR DESIGN PHILOSOPHY

Let’s start on familiar territory with software that most of us have used in the past: AutoCAD.

When you created a design in AutoCAD, that design was not much different from creating the

same design on a drawing board. In AutoCAD you can draw precise lines, arcs, circles, and other

objects, placed precisely and with accurate dimensions reﬂecting your design, in a way that you

cannot do by hand. When a design requires modiﬁcation, you erase, move, copy, stretch, and

otherwise manipulate the existing geometry more quickly than you can by hand as well. But other

than those gains in speed and accuracy, the workﬂow is much the same as working on a drafting

board. In short, AutoCAD automates drafting tasks but does less to speed up the design process.

AutoCAD 2010

With the release of AutoCAD 2010, you can create 2D parametric dimensions and constraints just like

Inventor.

Standard dimensions in AutoCAD are what we call driven or reference dimensions. A driven

dimension is controlled by the geometry, and it reﬂects the actual value of the geometry that is

referenced by the dimension. If you stretch a line, for example, the dimension that is attached to

the line will update to the new value. If you think about it, the only reason for a dimension on a

2D drawing is to convey the value of a feature or part to a person who is going to build it. If you

import that 2D ﬁle into a CAM package, no dimensions are needed because the line work contains

all the information about the part.

The workﬂow in a 3D model is substantially different from in 2D modeling. In a 3D model, you

create sketches in 2D and then add geometric constraints such as horizontal, vertical, parallel, and

so on. Adding the geometric constraints allows line work to adjust in a predictable and desired

manner and helps control the overall shape of the sketch. Once geometric constraints are in place,

you add parametric (driving) dimensions to the sketch geometry. By changing the value of the

dimension, you change the size of the sketch object. As you can see, the Inventor dimension is far

more powerful than the standard AutoCAD dimension because it not only conveys the value of

a feature or part but also serves as a design parameter, allowing you to change the dimension to

change the design.

Parametric feature-based modeling relies on the creation of numerous features within the

model. By creating a number of features within the model, you are able to independently change

or modify a feature without rebuilding the entire model. An example of editing a feature would

be changing the radius of an edge ﬁllet.

Parametric model features are typically either dependent or independent of one another. A

dependent feature is dependent upon the existence or position of a previously created feature. If

that previously created feature is deleted, then the dependent feature either will also be deleted or

will become an independent feature. An independent parametric feature is normally based upon an

origin feature such as a work plane, work axis, or work point or is referenced off the original base

feature.

Drawing in AutoCAD Becomes Sketching in Inventor

The fundamental difference between traditional AutoCAD and Inventor is that in AutoCAD you draw

and in Inventor you sketch. The difference sounds subtle but is very important. In AutoCAD you likely

construct lines precisely to speciﬁc dimensions to form the geometry that is required. In Inventor