Editing Solids and Surfaces - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 207

Filleting and chamfering
Two frequent operations when modeling in 3D are rounding and chamfering edges.
Applying fillets
To round or to fillet edges, we have two commands. The first one is well known from
2D.
The FILLET command
The FILLET command (alias F ), besides filleting two linear objects in 2D, allows you
to fillet or round edges of solids and surfaces. When we select a solid or surface edge,
the command changes the usual prompts and adapts to fillet in 3D. The command
starts by displaying the information about the current settings, only important for 2D,
and prompts for the selection of the first object:
Command: FILLET
Current settings: Mode = TRIM, Radius = 0.0000
Select first object or [Undo/Polyline/Radius/
Trim/Multiple]: Edge selection
When we select a solid or surface edge, the command doesn't prompt for the second
object, instead it prompts for the radius:
Enter fillet radius or [Expression]: Value
After that, we click on all edges to be filleted, one-by-one, but only from the selected
solid or surface. The edge picked for the object selection already belongs to the se-
lection. After its selection, all edges are filleted and the command displays that inform-
ation:
Select an edge or [Chain/Loop/Radius]: Edge
selection
4 edge(s) selected for fillet.