Extend the ends or edges of a curve or surface

Add to an existing curve or surface by extending from an endpoint or edge. You can extend straight out or continue the curvature at the endpoint or edge.

You can also extend a trimmed surface if the Merge option is turned off, and you select a boundary which is a surface isoparm (constant U or V). You cannot select a trim edge.

If Merge is off, selecting an interior isoparm on a surface will cause the extension to start from the selected isoparm. If Merge is on, the extension will start from the closest edge.

Extend a curve or surface by extrapolating its shape

Choose Object Edit > Extend.
Click near the endpoint of a curve, curve on surface, or an edge of a surface.
A double arrowhead manipulator (for curves) or thick green border with three double arrowhead manipulators (for surfaces) indicates which end or edge will be extended.

Note
You can select and extend several curves, curves-on-surface or edges simultaneoulsy. The only restriction is that all selected objects must be of the same type.
Do one of the following:
- For a curve, drag the mouse to change the extend length.
- For a surface, select the middle manipulator and drag to extend the surface proportionally. Or select one of the outer manipulators and drag to extend the surface non-proportionally.
- Instead of dragging, you can type a distance and press (Windows) or (Mac).
Note
Both ends must be extended in the same direction, either positive or negative. A label shows the extension distance while you’re dragging. The controls are turned on until you exit the tool.

Note
You can only extend periodic surfaces proportionally (one manipulator).

If using the Extrapolate type with Merge on, you can select two opposite edges of a surface and symmetrically extend both at the same time, as shown below.

In all other cases, you can only use non-proportional Extend when a single edge is selected. Consequently it will not work when Chain Select is on and several tangent continuous edges are selected automatically.
To snap to a curve, surface curve or trimmed edge while extending a surface, hold down the + (Windows) or + (Mac) keys and click down on the curve. Hold down (Windows) or (Mac) to snap to a grid intersection, or (Windows) or (Mac) to snap to a control point (CV, edit point).
If extending curves, snapping to another curve will intersect the extended curve with the snap curve in the current view only.

Note
The object you are snapping to must be within 300.0 cms of the curve or surface you are extending.
To undo an Extend operation, select Edit > Undo.
Note
Extending a curve-on-surface cannot be undone.

Add CVs or edit points to the beginning or end of a curve

Pick the first or last CV or edit point.
The type of point you pick (CV or edit point) is the type you will add.
Choose Curve Edit > Modify > Add Points.
Click to add the new points.
Note
In orthographic windows, the new points will be in the same plane as the previous point, unless you snap the points to existing geometry.

What if...?

The curve behaves differently after I add points?

Adding points to the beginning of a curve may affect tools that work differently depending on the direction of a curve.

The Add points tool does not actually add points to the beginning of a curve. If you have picked the first CV or edit point, the tool reverses the curve and then adds the new points to the end.

See Reverse the direction of a curve or surface.