Vertical surfaces are usually the only surfaces that need to be manually oriented. FeatureCAM tries to automatically flip surface normals so that they are consistent. For this automatic flipping to work on vertical surfaces, there must be some non-vertical surfaces nearby. For parts that have only vertical surfaces, FeatureCAM does not automatically flip any normals. That means that you must ensure that all surface normals point either in or out by manually flipping the normals to ensure a consistent cutting side.
For open surfaces with a floor, the normals are flipped to create a pocket shape and the insides are milled.
For open surfaces with a top, they are treated as a boss shape and the outsides of the surfaces are milled.
