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Waguespack c01.tex V2 - 08/30/2008 1:44pm Page 16

16 CHAPTER 1 INVENTOR DESIGN PHILOSOPHY

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 than 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 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 quantity 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 will either also be deleted

or become an independent feature, unless it is made dependent on a different preexisting feature

within the model. 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.

Sean Says: Drawing in AutoCAD Becomes Sketching in Inventor

The fundamental difference between 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 construct

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

lines and geometry that reﬂect the general form and function of the feature and then use constraints

and dimensions to massage it into the desired shape. This is probably the single biggest stumbling

block that AutoCAD users face when starting to use Inventor.

Understanding Functional Design

Functional design is an Autodesk term for a knowledge content tool that moves the user from

creating geometrical descriptions to capturing knowledge. Engineers and designers can use func-

tional design to analyze the function and solve the design problems, rather than spending time on

modeling a solution needed to create 3D representations.

The V-belts Generator

An example of functional design and its beneﬁt is the use of the Inventor’s V-belts Generator. Tradi-

tionally, to design a pulley system you would lay out the pulleys in positions as required by the design

and then choose a belt that met the design requirements and came as close as possible to ﬁtting the

pulley spacing. The result oftentimes is that no common belt size ﬁts the pulley spacing. The func-

tional design approach to this task allows you to specify the belt from a standard catalog of belt sizes

at the same time that you are creating the rest of the system. In this way, you know from the outset

that the design is indeed functional and will work in the real world.