9

2-Rail Sweep Surface 1209
curves easier to see and improve per formance. Use
Ctrl+D (while the Keyboard Shor tcut Override
Toggle (page 3–872) is on) to toggle display of
dependent sub-objects, including sweeps.
Thesweepsurfacecandeviatefromthecurve
if you edit a curve in a sweep by increasing the
weight of the curve CVs. You can work around
this by refining the curve at the point where the
surface deviates.
2-R ail Sweep Sur face
SelectNURBSobject. >Modifypanel>CreateSurfaces
rollout > D ependent Surfaces group box > 2-Rail
Select NURBS object. > Modify panel > NURBS toolbox >
Create 2-R a il Sweep button
Sweep surfaces are constructed from curves. A
2-rail sweep surface uses at least t hree curves.
Two curves, the "rails," define the two edges of
the surface. The other cur ves define the surface’s
crosssections.A2-railsweepsurfaceissimilarto
a 1-rail sweep. The additional rail gives you more
control over the shape of the surface.
Sweep surface created with two rails
The c ross-sect ion curves should intersect the rail
curves. If the cross sections don’t intersect the
rails, the resulting surface is unpredictable. In
addition, the initial points of the rails and the
endpoints of the first cross-section curve must be
coinciden t. Use NURBS Snaps to accomplish this.
Automatic Cur ve Attachment
When you create a 2-rail sweep, you can select
curves that are not already sub-objects of the active
NURBS mo del. You can select another curve or
spline object (page 1–266) in the scene. When you
select that curve, it attaches to the current object as
if you had used the Attach button (page 1–1120).
Wa rn in g : If the curve you attach is a sub-object of
anotherNURBSmodel,theentiremodel(thatis,the
curve’s parent NURBS object) is attached as well.
Asyoumovethemouseoveracurvethatisnot
part of the active NURBS object, the cursor
changes shape to indicate that you can pick the
curve, but the curve is not highlighted in blue.
Procedures
To create a 2-rail sweep:
1.
Createthecurvesthatdefinethesurfaceyou
want to create.
2. Clicktoturnon2RailSweepinthe
toolbox or on the Create Surfaces rollout.
3. Clickthecurvetouseasthefirstrail,thenclick
the curve to use as the second rail. Click each of
the cross-section curves, and then right-click to
end creation.
The sweep is inter p olated smoothly between
the cross sections, following the outlines
defined by the two rails.
As you click curves, their names appear in
the lists on the 2 Rail Sweep Surface creation
rollout. The order in which you click the curves
can affect the shape of t he s weep surface.