Page 254 - Mastering SolidWorks

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226 CHAPTER 7 Modeling with PriMary Features

Using Entities in a Loft
For solid lofts, you can select faces, closed-loop 2D or 3D sketches, and surface bodies. You can
use sketch points as a profile on the end of a loft that comes to a point or rounded end. For
surface lofts, you can use open sketches and edges in addition to the entities that are used by
solid lofts, but you cannot combine open and closed contours.
Some special functionality becomes available to you if you put all the profiles and guide
curves together in a single 3D sketch. In order to select profiles made in this way, you must use
the SelectionManager, which is discussed later in this chapter.
The Sketch Tools panel of the Loft PropertyManager enables you to drag sketch entities of any
profile made in this way while you are editing or creating the Loft feature, without needing to
exit and edit a sketch.
I discuss 3D sketches in more detail in Chapter 6, “Getting More from Your Sketches.”

Comparing Lofts and Splines
The words loft and spline come from the shipbuilding trade. The word spline is actually defined as
the slats of wood that cover the ship, and the ribs of the hull very much resemble loft sections.
With the splines or slats bending at each rib, it is easy to see how the modern CAD analogy
came to be.
Lofts and splines are also governed by similar mathematics. You have seen how the two-point
spline and two-profile loft both create a straight-line transition. Next, a third profile is added to
the loft and a third point to the spline, which demonstrates how the math that governs splines
and lofts is also related to bending in elastic materials. Figure 7.9 shows how lofts and splines
react geometrically in the same way that bending a flexible steel rod would react (except that the
spline and the loft do not have a fixed length).
Figure 7.9
splines, lofts,
and bending
3 point spline, no end conditions

end reacts notice
tangency like a slight
changed pinned bulge,
joint just like a
real rod
in bending