I have CAD of a component, and i want to create a nest for that component (to 3D print the nest) how do i invert the cad so i am left with a block with the impression of the part in the block?  I only need half of the part indented into the block, i thought it would be easy to invert the CAD so was left with an impression of the part but not finding it easy, in fact not managing to do it at all, any help would be appreciated    step by step help for a novice    Just like pushing a penny into clay and the impression is left, that's what i want to do virtually with CAD.  Thanks