Chapter 27: Working with Surfaces
An example of a competitive system to NURBS surface modeling is point mesh data. This comes from
systems such as 3DSMax, which create a set of points that are joined together in triangular facets, and
can be represented in SolidWorks as an STL (stereolithography) or VRML (virtual reality markup lan-
guage) file. When displayed in SolidWorks, this data looks very facetted or tessellated into small, flat
triangles, but when viewed in software that is meant to work with these kinds of meshes, it looks
smooth. Many advantages come with this type of data, especially when it comes to applying colors
and motion. However, the main disadvantage is that the geometrical accuracy is not very good. Point
mesh data is typically used by 3D graphic artists, animators, and game developers.
By using a SolidWorks add-in such as ScanTo3D (available only in SolidWorks Premium), it is possi-
ble to take point mesh data and create a NURBS mesh over it. This is not a push-button solution, but
it offers capabilities where none previously existed. ScanTo3D is beyond the scope of this book, but
you should find it useful if you are interested enough to read about NURBS and point meshes.
Developable surface
Developable surfaces are surfaces that can be flattened without stretching the material. They are
also surfaces that you can extend easily in one or both directions. These include planar, cylindrical,
and conical shapes. It is not a coincidence that these are the types of shapes that can be flattened
by the Sheet Metal tools.
Ruled surface
Developable surfaces are a special type of a broader range of surface called ruled surfaces.
SolidWorks has a special tool for the creation of ruled surfaces that is described in detail in the
next section. Ruled surfaces are defined as surfaces on which a straight line can be drawn at every
point. A corollary to this is that ruled surfaces may have curvature in only one direction. Ruled
surfaces are far less limited than developable surfaces, but are not as easily flattened.
Ruled surfaces are used frequently in plastic parts and plastic mold design where draft and parting
surfaces from 3D parting lines are needed.
Gaussian curvature
Gaussian curvature is not referred to directly in SolidWorks software, but you may hear the term
used in more general CAD or engineering discussions. It can be defined simply as curvature in two
directions. As a result, a sphere would have Gaussian curvature, but a cylinder would not.
Existing Surface Tools
Surface feature equivalents are available for most solid features such as extrude, revolve, sweep,
loft, fillet, and so on. Some solid features do not have an equivalent, such as the Hole Wizard,
shell, and others. Several surface functions do not have solid equivalents, such as trim, Untrim,
Extend, Thicken, Offset, Radiate, Ruled, and Fill.