Font for inside and outside CNCing

Need to figure out how to get a font (or other shape) to CNC properly inside and out to fit into itself, i.e. method to know that shape has no radius smaller than the bit.

• downloaded CamBam to see if it can do such things
• testing Hershey Text - http://www.evilmadscientist.com/2011/hershey-text-an-inkscape-extension-for-engraving-fonts/
  • that provides nice single line engraving text, to a point solves the font's radius problem, but not the outside one...