Ask HN:What are some great books, sites and blogs on hardware innovation?

Few days back I came across with a nice blog/site on "Guerrilla guide to CNC machining, mold making, and resin casting". Here is the link http://lcamtuf.coredump.cx/gcnc/. I would like to know what are some of the best resources out there where a person can develop some hands on skill on hardware/physical product development. I would n't mind starting as a hobby.