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Analyzing Skirt Surface Options: Extension Directions

You can add or modify the direction that the skirt surface extends from the silhouette curve segments.
• Extension directions can significantly alter the shape of the skirt surface.
• Arrows denote direction at each segment vertex.
– Orange – Default direction
– Cyan – User-defined direction
– Red – Tangent direction
• Select location and direction reference.

Extension 2
Figure 2 – Viewing Default Extension Directions

Extension 1
Figure 1 – Completed Skirt Surface

Extension 3
Figure 3 – Viewing User-Defined Extension Directions
Analyzing Skirt Surface Options: Extension Directions
By default, when the skirt surface extends from a silhouette curve, it extends normal to the curve. The direction of extension is defined at every curve segment endpoint. If the directions at the curve endpoints overlap, the skirt surface will fail.
You can modify the direction of extension for the curve endpoints in the Extension Directions tab of the Extension Control dialog box. This enables you to significantly change the resulting shape of the skirt surface. For example, in Figure 1, the extension directions for the left side of the skirt surface have been modified, causing the resulting shape to be different.

When you select the Extension Directions tab, the extension directions for each of the curve segment endpoints displays in the graphics window.
Consider the following points regarding extension directions:
• Default extension directions display with orange arrows, as shown in Figure 2.
• Extension directions that you have modified or added display with cyan arrows, as shown in Figure 3.
• If you apply tangent conditions to curve segments for the skirt surface, the extension directions display with red arrows.
Modifying and Adding Extension Directions
You can modify extension directions as a means to solve a failing skirt surface, or you can modify them simply to modify the shape of the resulting parting surface. You can also add additional extension directions.
To modify or add an extension direction, you must specify the following:
• Location – You can either select an existing included extend curve endpoint or create a datum point at a new location where you want to add an extension direction.
• Direction reference – This specifies the direction in which the skirt surface will be extended. You can select any of the following references:
– Plane – The skirt surface is extended perpendicular to the plane. You can select either datum planes or planar surfaces.
– Curve, Edge, or Axis – The skirt surface is extended along the direction of the specified curve, edge, or axis.
– Coordinate System – The skirt surface is extended along the specified coordinate system axis, which you must specify.
Each added or modified extension direction displays in the Extension Directions tab as a point set. For each defined point set, you can perform the following operations:
• Remove – This enables you to remove the point set.
• Redefine – This enables you to select a different location for the point set.
• Direction – This enables you to select a different direction reference.
You can also add new point sets.

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