If you set Cross Section Orientation to 2D, the cross sections must be created in the Top View.  Entities created along the Y axis are translated along the Z axis. The X axis entities are translated perpendicular to the curve geometry. The cross sections are attached to the drive curve perpendicular to the curve geometry at the attachment point.

If you set Cross Section Orientation to 3D (the default), the cross sections should be connected to the drive curve in 3D space and oriented in the proper plane.

Example, Cross Section Orientation

In the illustration, "1" indicates Drive Curve, and "2" indicates the Cross Section

2D	3D
Top View	Isometric View

 

Result

 

Example, Cross Section Orientation

3D	2D

 

Result

Video, 3D Cross Section

Video, two different 3D cross sections

It is not necessary for the cross sections to be attached to the drive curve, just oriented properly.

Cross sections created in 3D space cannot be rotated or twisted with a directing curve (discussed later). When 3D construction is used, the surface is created through the existing cross sections.

Example, Cross section not normal to the curve

In the following illustration, the cross section is not oriented normal to the curve. The cross section is rotated 45º away from normal to the curve. The new surface maintains the angle.

The chaining direction of the drive curve determines the direction of the surface created when using 2D cross sections.

When 3D cross section geometry is used, the surface is constructed the same, regardless of the chaining direction.

SURFCAM orients the cross section based on the chaining direction. The positive X axis direction on the cross section will always be to the right of the chaining direction. This axis is based on SURFCAM’s WORLD axis.

The cross section geometry can be chained in either direction for 2D or 3D elements. The surface is created the same for either chaining direction.

Section chained counterclockwise	Result

 

 

Section chained clockwise	Result

SURFCAM creates the drive curve surface based on the cross section and drive curve attachment point. The cross sections are driven along the drive curve by this attachment point. This attachment point determines the cross section location relative to the drive curve.

2D cross section attachment points	Result

 

When using a 2D cross section, SURFCAM requires two locations to define the attachment point. The first is a location on the cross section itself. This is necessary in 2D since the section is not oriented in the proper plane and location relative to the curve. The second is the location on the drive curve to which the cross section should be connected.

 

The attachment point for the cross section does not have to be an actual location on the cross section itself. It can be a location relative to it such as a point in the center of an arc on the cross section.

3D cross section attachment point	Same Result

 

When using a 3D cross section, SURFCAM requires only one location to define the attachment point. As in 2D, a 3D attachment point does not have to be a location on the cross section itself. It can be a location relative to it such as a point in the interior of an arc on the cross section.

3D cross section attachment point	Result

A directing curve is an additional curve that can affect the tilt and rotation of the cross section. It acts as a “magnet.” The results will vary depending on whether the cross section orientation is 2D or 3D.

In the Create Surface Options dialog, set Directing Curve Selection to YES. After you select the "Drive curve" the prompt asks you to select the "Directing curve." After you select the cross sections, the Drive Curve Surface dialog appears. Set Tilt of Cross Section Planes to Directed or Normal. The following example shows the difference between Directed and Normal.

Example, Tilt of Cross Section Planes

Below, the first arrow indicates the selected "Directing curve."

Isometric View	Right Side View
Original Geometry
Tilt of Cross Section Planes = Normal Normal positions the cross section perpendicular to the drive curve to create the surface.
Shaded
Tilt of Cross Section Planes = Directed Directed uses the Directing Curve to position the cross section
Shaded

 

Example, Directing Curve in different plane
(Tilt of Cross Section Planes = Directed)

The arrow indicates the directing curve.

The directing curve acts as a "magnet" to create the surface.

In the Create Surface Options dialog, if you set Constant Between Similar Sections to YES, the surface maintains the shape consecutive identical cross sections. If you set Constant Between Similar Sections to NO, the surface blends the area identical cross sections shapes of the adjacent cross sections.

Example, Constant Between Similar Sections

Original Geometry

 

Constant Between Similar Sections = YES
The surface maintains the shape between the identical rectangular cross sections.

 

Constant Between Similar Sections = NO
The section between the identical rectangular cross sections blends with the adjacent arc cross sections.