SolidWorks 2010 Bible

Part II: Building Intelligence into Your Parts

FIGURE 7.17

The effects of the Pierce relation

Sketched sweep profile

Guide curve Pierce relation forces contact

Figure 7.17 shows what is happening behind the scenes in a sweep feature. The sweep re-creates

the original profile at various points along the path. The guide curve in this case forces the profile

to rebuild with a different shape. Pierce constraints are not required in simple sweeps, but when

you start using guide curves, you should also use a pierce.

Tip
If you feel that you need more profile control, but still want to create a sweep-like feature, try a centerline loft.
The centerline acts like a sweep path that doesn’t touch the profiles, but unlike a sweep, you can use multiple
profiles with it.n

Figure 7.18 shows a more complicated 3D sweep, where both the path and the guide curve are 3D

curves. I cover 3D curves toward the end of this chapter; you can refer to these sections to under-

stand how this part is made.

On the CD-ROM
The part shown in Figure 7.18 is on the CD-ROM with the filename Chapter 7 3D Sweep.sldprt.n

This part is created by making a pair of tapered helices, with the profile sketch plane perpendicular

to the end of one of the curves. The taper on the outer helix is greater than on the inner one, which

causes the twist to become larger in diameter as it goes up.

To make the circle follow both helices, you must create two pierce relations, one between the cen-

ter of the circle and a helix, and the other between a sketch point that is placed on the circumfer-

ence of the circle and the other helix. This means that the difference in taper angles between the

two helices is what drives the change in diameter of the sweep.