Type "CLCAM" in Autodesk® AutoCAD® command prompt to launch the main form of the software. All other commands can be accessed thru button clicks from the main form. Refer to help file for more details.

Choose the POLYLINE --> choose the edge you want to be the CommonLine --> choose the CommonLine method --> Specify tool-diameter --> Click "Create CommonLine Path" button to get the output. 

The installer that ran when you downloaded this app/plug-in from Autodesk App Store will start installing the app/plug-in. OR, simply double-click the downloaded installer to install the app/plugin. You may need to restart the Autodesk product to activate the app/plug-in. To uninstall this plug-in, exit the Autodesk product if you are currently running it, simply rerun the installer, and select the "Uninstall" button. OR, click Control Panel > Programs > Programs and Features (Windows 7/8.1/10) and uninstall as you would any other application from your system.

WWW.AUTOCAM2D.COM

Works only on LWPOLYLINE objects in AutoCAD.