Autodesk ALIAS 2010 - Control Button Revolved Surface

Now you will create an arc for the center of the button.
5 Choose Curves > Keypoint Curve Toolbox, then Keypoint Curve Tools >
Arcs > Arc Tangent to Curve . You are prompted to
Select curve at location to make arc tangent to.
Click the first line, and without releasing the mouse button drag the start
of the arc to the end of the line at the origin.
You are prompted to enter the end point of the arc. Use the Point Snap
(Ctrl (Windows) or Control (Mac) key) to place the end point of the arc on
the top keypoint of the angled line.
466 | Chapter 7 Modeling an MP3 Player