SolidWorks 2011 Parts Bible - Matt Lombard [261]
The word surfacing has often been used (and confused) to signify complex shapes. Not all surface work is done to create complex shapes, and many complex shapes can be made directly from solids. Many users think that because they do not make complex shapes, they never need to use surface features. This chapter shows mainly examples that do not require complex shapes, in situations where surfaces make it easier, more efficient, or simply possible to do the necessary tasks.
While some of the uses of surfaces may not be immediately obvious, by the end of this chapter you should have enough information and applications that you can start experimenting to increase your confidence in surfacing techniques.
Understanding Surfacing Terminology
When dealing with surfaces, you may hear different terminology than the terminology typically used with solid modeling. This special terminology also often exists for surfaces because of important conceptual differences between how solids and surfaces are handled.
These terms are fairly universal among all surfacing software. The underlying surface and solid construction concepts are generally uniform between the major solid and surface modeling packages. What varies from software to software is how the user interacts with the geometry through the software interface. You may never see some of these terms in the SolidWorks menus, Help files, training books, or elsewhere, but it becomes obvious as you use the software that the concepts are relevant.
Exploring the Knit function
Knit is analogous to the solid feature Combine in that it joins multiple surface bodies into a single surface body. Unlike Combine, Knit does not perform the subtract or intersect Boolean operations. It also has an option to create a solid if the resulting surface body meets the requirements (a fully enclosed volume without gaps or overlaps). However, unlike the solid bodies in Combine, which may overlap volumetrically, surface bodies must only intersect edge to edge, more like sketch entities that can only touch end to end.
Knit is also sometimes used in the same way that the zero-distance offset is used, to copy a set of solid faces to become a new surface body.
You can find one nice option that enables you to quickly see where the boundaries of a surface body lie by choosing Tools⇒Options⇒Display/Selection⇒Show Open Edges Of Surfaces In Different Color. By default, this color is a medium blue, and you can change it by choosing Tools⇒Options⇒Colors⇒Surfaces⇒Open Edges.
Using the Trim function
The Trim function in SolidWorks 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.
Using the Untrim function
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 19. Figure 20.1 shows how Untrim works.
FIGURE 20.1
Untrimming a surface
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