-Let’s take a look how to FILLET a closed polyline in few steps.

-Type in FILLET command and select the Radius option.

-Enter a new value according your design and press Enter.

-Now choose the Polyline option and click the 2D polyline.

-Notice all four corners of the polyline are rounded automatically.

-To restore the original polyline shape, execute Fillet command.

-Choose the Radius option, set the value to 0 and press Enter.

-Once again choose Polyline option and Click the polyline.

-When the fillet radius is set to 0, you can remove all arc segments from a 2D polyline.