Yes DXF drawing with draftsight is all you need. There used to be plugins for sketchup which made DXF files from any sketch but I gave up on sketchup a while ago. I have used SVG also, when converting drawings or images off the web, using Inkscape. Estlcam rocks! Shhhhh!!, it's the perfect price! Gary
DraftSight works great for flat 2D cuts. If you want 2.5 / 3D, it gets complicated. Sketchup's modeling tools are amazing - it'd just be nice if it would play well with, say, anything else ever.
I have a lot of old files on Sketchup that I wish could be easily converted to DXF. A lot of the simple ones, I just quickly re-drew in Fusion 360. I have yet to try to use a .stl in Estlcam. I may have to give that a shot one of these days.
