I've been using this for a short while. Obviously designed specifically for easy design of machinable components, so has all the appropriate features for this kind of work. The demo videos are well worth watching, with some nifty techniques relevant to any drawing program... even pencil & paper! <img src=/S/free.gif border=0 alt=free width=30 height=15> - 6MB.
Online Machine Shop - Download Free CAD Software here