The next part gets in to Boolean operations extensively. See:
https://www.shapeoko.com/wiki/index.php/Carbide_Create_Basics#Boolean_Operations
for more information.
- select the joined rectangles, then control-click to add the rounded part to the selection — the joined rectangles should be solid, while the rounded part will be drawn with a dashed line:
- click on “Boolean Subtraction”


