To Trace the Inner Contour of an Enclosed Area, Segment by Segment (AutoCAD Mechanical Toolset)

Click Home tabConstruction panel drop-downContour Trace. Find
At the Command prompt, select Inside.
Click in an area to define the boundaries of the contour you want to trace.
In the Message dialog box, click No.
The system traces the contour, pausing at each vertex to mark it.
Each time the system pauses type Y and press ENTER. Repeat until the entire contour is drawn.
Note:
To remove the vertex markers, type REDRAW at the command prompt and press ENTER.