Editing Solids and Surfaces - Autodesk AutoCAD 2013 Practical 3D Drafting and Design - page 211

Applying chamfers
Instead of rounded edges, it is also common to find cut edges in engineering or ar-
chitecture. There are two commands for this task, the first well known from 2D.
The CHAMFER command
The CHAMFER command (alias CHA ), besides its application in 2D, allows chamfering
edges of solids and surfaces. The effect is the same as applying a diagonal cut. In-
stead of a radius when filleting, here we must specify two distances that may be dif-
ferent. Due to this, in 3D we must select a base surface to which the first distance is
applied, and can only chamfer edges on that surface.
When selecting an edge of a solid or surface, the command displays different op-
tions, starting with the selection of the base surface:
Command: CHAMFER
(TRIM mode) Current chamfer Dist1 = 0.0000,
Dist2 = 0.0000
Select first line or [Undo/Polyline/Distance/
Angle/Trim/mEthod/Multiple]: Selection
Base surface selection...
As the selected edge is shared by two surfaces, we have to specify which the base
surface is, using the Next or OK options:
Enter surface selection option [Next/OK
(current)] <OK>: Next
Enter surface selection option [Next/OK
(current)] <OK>: Enter
We specify the chamfer distance measured along the base surface:
Specify base surface chamfer distance or
[Expression]: Value