SolidWorks 2010 Bible

Part VI: Using Advanced Techniques

Solid modeling tends to limit you to a type of parts with square ends or a flat bottom because solids

are creating all sides of an object at once. For example, think about an extrusion: regardless of the

shape of the sketch, you have two flat ends. Even lofts and sweeps typically end up with one or two

flat ends because the section sketches are often planar. Surfaces enable you to create one side at a

time. Another way of looking at it is that using surfaces requires you to create one side at a time.

You will find times when, even with prismatic modeling, surfacing functions are extremely useful,

if not completely indispensable. I do not propose that you dive into pure surface modeling just to

benefit from a few of the advantages, but I do recommend that you consider using surface tech-

niques to help define your solids. This hybrid approach is sensible and opens up a whole new

world of capabilities. I have heard people say after taking a SolidWorks surfacing class that they

would never look at the software in the same way again.

Non Uniform Rational B Spline

NURBS stands for Non Uniform Rational B Spline. NURBS is the technology that most modern

mechanical design modelers use to create 3D geometry. NURBS surfaces are defined by curves in per-

pendicular directions, referred to as U and V directions, which form a mesh. The fact that perpendic-

ular directions are used means that the surfaces have a tendency to be four-sided. Of course

exceptions exist, such as three-sided or even two-sided patches. Geometry of this kind is referred to

as degenerate because one or more of the sides has been reduced to zero length. Degenerate geometry

is often, but not always, the source of geometrical errors in SolidWorks and other CAD packages.

Figure 27.2 shows some surfaces with the mesh displayed on them. You can create the mesh with

the Face Curves sketch tool.

FIGURE 27.2

Meshes created with the Face Curves sketch tool

Degenerate point