SolidWorks 2010 Bible

Chapter 27: Working with Surfaces ............................................................................................

Trim

The Trim function is analogous to the solid Cut. You can use sketches, planes, or other surface
bodies to trim a surface body. The underlying surface is defined by a two-dimensional mesh, and
for this reason, it is usually four-sided, but may be other shapes. When the underlying surface is
trimmed, the software still remembers the underlying shape, but combines it with the new boundary,
which is typically how face shapes (especially non-four-sided shapes) are created.

Untrim

Untrim is predictably the opposite of Trim. It removes the boundary from a surface. It can
remove the boundary selectively (one edge at a time, interior edges only, and so on) or remove
all the edges at once. Untrim even works on imported geometry, as described in the tutorial in
Chapter 26. Figure 27.1 shows how Untrim works.

FIGURE 27.1

Untrimming a surface

Surface created native

in SolidWorks by

lofting

Surface trimmed by a

sketch, trimmed away

portion shown as

transparent

Trimmed surface with

an Untrim feature

applied to it

Untrim works on native and imported geometry. It is not truly like feature history in imported

geometry, but it does help to uncover the underlying original shape of the face.

Hybrid modeling

Modeling software has long divided itself along Solid/Surface lines with products such as Rhino

(strictly surface modeling) and early versions of SolidWorks (strictly solid modeling). However, in

the last several years, modelers increasingly enabled both methods and allowed them to interact.

This hybrid modeling is a combination of solid and surface modeling. These days, it is much more

common to mix methods than it was even five years ago. Surface modeling is slow because you

model each face individually, and then manually trim and knit. Cutting a hole in a surface model is

much more involved than cutting a hole in a solid. Solid modeling is faster because it is essentially

highly automated surface modeling; however, as any software user knows, automation almost

always comes at the expense of flexibility, and this situation is no different. Surface modeling puts

the compromised power back into your hands.