This link offers a set of books by David J. Gingery. They are NOT free, but worth paying for...
http://gingerybooks.com/The book store link is:
http://gingerybookstore.com/index.htmlThese are very good how-to books on engineering, building and using tools to build the things
which might no longer be available in a SHTF aftermath.
Consider some of the books for your basic library, even if you, personally, do not possess the
skill set to use them. Someone, in the future, might want this information.
I note that they offer a book sale on damaged books at 50% off. The next sale is May 1, 2016, so
make a bookmark and check back later.