Yes it was how I did it, I exported as 2d after Imported it again.(won’t work!)
I don’t know about other threads but I have done it! 
Basically as machinists we are trying to achieve a true cad arc with start,center,through,end points and one continuous curve. Sketchup doesn’t work this way of course but its a pain in the rear when you have to convert sketchup arcs to true cad arcs!
HOW I DID IT:
Drew some ideas in sketchup like something that would be cut on a cnc, flat to plane with no faces, the arcs have only 6 segments to highlight them, one of the arcs (right) is tangent.I then exported this as a 3d dxf.(do not import back in as I did)
Then opened up the dxf in draftsight and check it out, true arcs all round! This is exactly what I need to achieve, as you can see the arcs have only start,end,through,center points. This should import to cnc very well I hope. 
ADDED LATER!
Then imported into xilog cnc software and it still has the arcs see image below
Also check the code for the pgm below, XL2P is a LINE, XAR is an ARC. I have all the arcs showing as XAR commands meaning they have also been imported in machine code as true arcs.
Thanks guys, gotta say this will save me and others many an hour of frustration!
Ian