Datasheet

UnDerstanDIng ParametrIc DesIgn
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the same part, and you can copy the part file to create variations of the original part. In order
to assemble parts, you create geometric relationships called assembly constraints defining how
the parts go together. The constraints are parameters that can be defined and revised by you at
any time in the design process as well. Part models can be arranged into small assemblies, and
placed into larger assemblies, to create a fully realized subassembly structure that matches the
way your design will be built on the shop floor. Figure 1.4 shows the part model from the previ-
ous illustrations placed multiple times in a subassembly and then that subassembly placed in a
top-level assembly.
Making Changes
This process of creating parameter-based sketches, to define parameter-based features, to design
a parameter-driven part, to then be used in parameter-driven assemblies, is essentially paramet-
ric design. Of course, as with building anything, there are general rules and best practices to be
learned and followed in order to prevent your work from “falling apart.” For instance, what if
the pivot link used in the previous examples were to incur a design change that made one leg
of the link longer? How would the holes be affected? Should they stay in the same place? Or
should they stay at some defined distance from one end or the other?
Anticipating changes to the model is a large part of being successful with Inventor. Imagine,
for instance, that a simple design change required that the pivot link become 50mm longer on
one leg. This should be a simple revision that requires you only to locate the dimension con-
trolling that leg length and change the parameter value. Unfortunately, if you did not follow
the best-practices guidelines when creating the part originally, the change in the length might
displace the secondary features such as holes and material cuts and require you to stop and fix
each of those as well. This is one of the most frustrating parts of learning Inventor for any new
user who has not taken the time to learn or follow the known best practices of parametric mod-
eling. Fortunately for you, within the pages of this text you will learn how to create models that
are easy to update and do not “fall apart” during design changes.
Understanding History-Based Modeling
Inventor is often referred to as a history-based modeler, meaning that as you create sketches
and turn them into features, and then add more features and still more features, each addition
is based on a previous feature, and so the model is said to have history. This history is recorded
and tracked in the model browser. The model browser is a panel that displays on-screen and
Figure 1.4
A subassembly and
an assembly model
using the part
model
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