Use Surfaces > Rolled Edge > Tubular Offset 
to create a variable radius tube surface that uses free curves as a path.
- Choose Surfaces > Rolled Edge > Tubular Offset
. - In the control window, set Surface to Tube.
- Select a curve. If the Chain Select option is turned on, curves that are tangent continuous with the selected curve are also selected.
The curve is highlighted in green and a blue radius manipulator appears at the start of the curve.
If Auto Update is on, the tube surface is built automatically. Otherwise, click the Build button in the bottom right corner of the view.
- Adjust the radius by clicking and dragging on the blue circle, or by changing the Radius value in the control window.
- Hold the
key and click on the input curves to add radius manipulators that let you vary the radius of the tube along its length. - Do any of the following:
- Change the position of a manipulator by clicking and dragging the small circle at the center.
- Change the radius of a manipulator by clicking and dragging on the larger circle.
If Auto Update is not on, click the Update button to see the surface reflect these changes.
This tool maintains construction history. Modifying the curve updates the tube surface. Choosing Object Edit > Query Edit and selecting the surface lets you modify the radius manipulators and other options once again.
Note: The Tubular Offset tool can also be used to create tubes from curves-on-surface and isoparms, when the Surface option is set to Tube, or half tubes when Surface is set to Groove.