Post Processor Required for CNC?

[CEN888]

I use Varicad which exports Autocad style dxf files, R13 - Autocad 2013 . Luban imports them as small 39 odd mm graphics . That I have to manually re-scale . I can create a 100mm square and give Luban the known dimensions and it turns out with the correct dimensions. Add a circle or arc on the outer edges , apply what should be the known outer dimensions and Luban seems to add buffer , preventing the correct arc or dimension. I can manually create tool path slices from dxf slices , but having to tweak every scale manually wastes so much time. Is there anything non proprietary that will create tool paths from an open standard like step or stl ? Or is there a way to have Luban recognize the dimension information correctly in dxf’s