After more tests, its seems that the cut is consistently out by 2.85mm on a range of cuts 18mm, 20mm, 22mm, 24mm, 26mm, 28mm, 30mm, 32mm, 34mm and 36mm.
I have figured out that if I convert lines to either arcs or lines in rhino, then bring a DXF into VCarve that the kinks don't appear in the VCarve drawing but still appear in the CNC'd wood. Doesn't solve dimension problem, as this is a second problem, hope I don't confuse anyone.