gmax is the cnc4free.org preferred 3D design application  by reason of it's functions, pedigree and ability to expand core features by use of plugins and scripts.  CNC specific tools are available for gmax in the form of the CNC_Toolkit MAXScript plugin.  No other FREE application will function with CNC_Toolkit.  

gmax has single floating-point precision for engineering work. At the same time gmax is also capable of many types of freeform modelling.  gmax is derivative of Autodesk's Autocad and 3D Studio, being essentially a restricted version of 3D Studio Max  V4. Click the image to access  the gmax download  via the turbosquid website. .