Overview

Often it is easier to model a complex shape with several surfaces, rather than one large surface.

However, these kinds of composite surfaces cannot be used in some circumstances. You may want to use a tool that only works on single surfaces, or your manufacturing system may require a single surface.

The Combine Surfaces tool allows you to combine several surfaces into one surface. It has the following limitations:

• The combined outer boundary of all the surfaces must have exactly four sides.
• Combine surfaces does not work on trimmed surfaces.

To combine several surfaces into one new surface

1. Click the Combine Surfaces icon, or choose Surfaces > Combine Surfaces from the tool palette.
2. Pick the surfaces you want to combine.
   • As you add surfaces, the surface boundaries change color. Green means the current group of surfaces has a four-sided boundary and can be combined. Yellow means they cannot be combined.
   • When the surfaces can be combined, an arrow appears showing the normal of the new surface. Click the arrow to reverse the normal of the new surface.
3. When you have picked all the surfaces you want to combine and the boundary is green, click Go.
4. The system prompts you to click the edges that must be continuous with adjacent surfaces.
   • Click a green boundary line to mark it for tangency with adjacent surfaces. A label appears on the boundary.
   • Click the label to change the continuity type. Each click cycles through positional (pos), tangent (tan), and curvature (cur).
5. Click Go.

How the function works

1. Combine Surfaces fits four curves to each of the four outer boundaries of the set of surfaces you selected.
2. Then, it places a simple surface, of the degree you selected in the option box, within those four curves.
3. The function samples the interior of all the selected surfaces and modifies the surface to match those samples.
4. If the surface doesn’t match well enough, Combine Surfaces inserts knot isoparametric curves into the simple surface to allow for finer adjustments to the shape.
5. If you selected continuity with boundary surfaces, Combine Surfaces samples those surfaces as well, and increases the samples along the outer boundaries of the original surfaces.

Tips and notes

• Using very tight tolerances does not guarantee that the resulting surface will match the original surfaces with higher accuracy.

  Combine Surfaces tries to achieve tighter tolerances by:

  • increasing sampling, and
  • inserting more knot isoparametric curves for finer control.

  The result is often a surface with more complexity than you need.

• This tool can often achieve good fits with relatively loose tolerances. If you relax the tolerances, it also reduces the time it takes to create the new surface.

  Try using loose tolerances to begin with, and increase them if you are not achieving the accuracy you need.

Combine Surfaces Control

Tolerance

Controls the fit distance of the combined surface to the original surfaces.

Angle Tolerance

Controls the fit angle of the surface normals at sample points.

Iterate to Tolerance

Increases samples and insert more isoparametric curves until the tolerances are reached.