I now have this file:
Skateboard Mold Sliced-Slice-3.zip (20.5 KB)
It’s the third layer, so only the edges need to be machined, the rest of the board is flat (and should stay that way). If I calculate the toolpath, it not only machines the edges but the whole board, making it need around 3 hours while that is not needed at all. How can I tell Estlcam to not do that? 
Use the STL Convert to 2D and then File > Edit drawing to save a mask DXF. For the STL Workspace select Mask and your saved file. Mask the whole board and then Unmask the ends.
Okay, sorry, I have to ask: What do your edit your file with? Mine is opening in AutoCAD. Or am I doing something wrong? Can you do it more slowly for someone that does not get it?
Figured it out now, but it’s everything but intuitive. Thanks for your help.
Glad you got it. The default Estlcam generated 2D usually works as is, I had to edit the one I posted down to a rectangle and two arcs to get a mask that didn’t have some odd masked lines on the slopes… no edit needed w/ < v12.119
…I should note that three (previously working… < v12.119) out of four 3D to 2D conversions I’ve done in v12.123 are missing a perimeter line and do not work as masks (Christian emailed).
