Page 143 - Mastering SolidWorks

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112 CHAPTER 4 Creating Simple partS and drawingS

Using Symmetry
Symmetry is an important aspect of design intent. Taking advantage of symmetry can signifi-
cantly reduce the time needed to model the part. Symmetry can exist on several levels:
◆ Sketch symmetry

◆ Individual feature symmetry
◆ Whole-part symmetry
◆ Axial symmetry (a revolved part)
◆ “Almost” symmetry (the whole part is symmetrical, except for a few features)
◆ Left and right opposite hand (symmetrical) versions of the part

◆ Assembly symmetry
Determining Primary or Functional Features
This is probably the most important information to know. Primary or functional features include
how the part mounts or connects to other parts, motion that it needs to accommodate, and
additional structure to support loads.
Often, it is a good idea to create a special sketch as the first feature in the part that lays out the
functional features. This could be as simple as a straight line to denote the bottom and a circle to
represent the position and size of a mating part, or as complex as full outlines of parts and
features from all three standard planes. This technique is called creating a layout sketch, and it is
an important technique in both simple and complex parts. You can use layout sketches for
anything from simply drawing a size-reference bounding box to creating the one point of
reference for all sketched features in the part. You can use multiple layout sketches if a single
sketch on one plane is not sufficient.

Predicting Change
When the marketing department gets out of a meeting at 4:45 p.m., what changes do you need to
be prepared for so that you can still be out the door by 5:00 p.m.? No one expects you to be able
to tell the future, but you do need to model in such a way that your model easily adapts to future
changes. As you gain experience with the software and engineering design processes, keep this
idea in mind: you will develop some instincts for the type of modeling that you do.
I’ve talked a lot about what success looks like with a good design intent model, but let’s talk a
little bit about failure. Failure will turn out to be more motivating in practice. When design intent
fails, you get a feature tree full of errors, and you have to go through each feature, investigate
what’s wrong, and then fix it. The failures are generally due to errors in the parent/child
dependencies following the original change. Fixing errors like this can take up much more time
than creating a model in the first place. This is, in essence, the big weakness of history-based
modeling. There are a few ways to solve it:
◆ Be really careful. When this method fails, it is mostly due to the fact that you can’t predict
the future. (How will change happen?)
◆ Use a method like Resilient Modeling. This is a structured method where you keep track
of the parent/child connections, and only start new sketches on reference geometry with a
direct link back to something that will not change (origin or base planes).