3D machining

Hi,

Can someone who is familiar with 3D machining on a cnc machine please tell
me what form the DXF file should take. I need to draw up some parts for a
project which I hope to be able to make on my little mill when it gets
finished but I can't decide whether I need to draw them as Autocad 'Solids'
or as 'extruded planes'. The reason I need to do it now is that the parts
will be based on an item which I have in for repair at the moment but which
will have to go back before my mill is up and running.
Thanks,

Ian
--
Ian W. Wright
Sheffield UK
www.iw63.freeserve.co.uk