# Blend Curve

Create a free-form curve that blends into one or more existing curves, surfaces, or edges.

Unlike a NURBS curve, a blend curve passes through the points.

Blend points can be attached to objects so that when the source object is updated, the blend curve is updated as well.

1. On the Geometry ribbon, select the Blend tool.

Note: The tool may be hidden in a dropdown menu. To access the dropdown menu, you can do one of the following:
• Click and hold the currently displayed tool (NURBS, Helix Curve, Extend Curve, Face Curve, or Divide).
• Select at the lower right corner of the currently displayed tool (NURBS, Helix Curve, Extend Curve, Face Curve, or Divide).
2. Optional: In the guide bar, select a curve degree. This controls the placement of the points to determine the shape of the blend curve.
• Cubic (3): Create a degree 3 curve.
• Quintic (5): Create a degree 5 curve. In general, select this option to produce a smoother curve.
3. In the modeling window, click to place the blend points.
Tip:
• To snap a blend point to an object, hover near the object before clicking.
• To unsnap a blend point from the object, move the mouse cursor far away from the object until the blend point detaches from the object and coincides with the mouse cursor.
• To force the blend point to snap to a surface or curve while editing a curve, hold down Ctrl while clicking.
• To force positional (G0) continuity, hold down Shift while clicking.
4. Edit the blend curve.
To Do this
Reposition a point
• Drag the point.
• Click the point, click the chevron, and then enter the x, y, and z coordinates.
1. Hover midway between two points, or at either end of the curve.
2. Click to add a point. Or drag to add a point in a different position.
Delete a point Click the point, and then press Delete.
Change the curve degree The curve degree controls the placement of the points to determine the shape of the blend curve.

In the guide bar, select one of the following options:

• Cubic (3): Create a degree 3 curve.
• Quintic (5): Create a degree 5 curve. In general, select this option to produce a smoother curve.
Change the continuity The continuity is used to constrain the shape of the curve at a selected point.

Click a point, and then select one of the following Continuity options:

• Positional (G0) (default): The blend curve is merely attached to the curve or surface at the blend point.
• Tangent (G1): The blend curve is made tangent to the curve or surface at the blend point.
• Curvature (G2): The blend curve follows the curvature of the attached curve or surface. The curvature is the same on both sides across the blend curve's boundaries.
• Double curvature (G3): Only available if you selected Quintic (5) for the Degree. The blend curve follows the curvature of the attached curve or surface. The curvature's rate of change is the same on both sides across the blend curve's boundaries.
Change the tangent direction of a point Click a point, click the chevron, and then select one of the following Tangent options:
• Auto (default): Automatically calculate the best tangent direction.
• Custom UV: You can define the custom tangent direction by clicking the four yellow dots on either side of the point.
• Free 3D: No tangent direction. You need to enter the 3D tangent direction coordinates. The continuity is automatically set to Positional.
Change the tangent magnitude of a point
• Drag the blue square handles.
• Click a point, click the chevron, and then enter a Tangent magnitude value.
Trim at a start or end point
• Click the start or end point, click the chevron, and then select Trim here.
• In the Control Panel, select Trim at start, Trim at end, or both.
Invert the trim at a start or end point
• Click the start or end point, click the chevron, and then select Invert trim side.
• In the Control Panel, select Invert start or Invert end.
Change the curve tension This controls the smoothness of the curve.

In the Control Panel, enter a Curve tension value. You need to choose a value from 0.01 to 1. Higher values correspond to smoother curves.

5. Right-click and mouse through the check mark to exit, or double-right-click.