
This turns your spline cage into a patch object mesh. However, it
causes a problem inside the mesh that you need to fix.
Step 4: Delete Any Unnecessary Geometry
Whenever a Surface modifier is applied to a spline cage it will create
a surface or skin where the line segments of the spline form a
three- or four-sided polygon. Since the circles themselves started
out as unique shapes and are four-sided, Surface thinks those cir
-
cles need a skin across their surface. In other words, additional
geometry was created inside the mesh, geometry you need to
delete.
The best way to get at these inner faces is to apply an Edit Mesh
modifier , rotate your view, use ...