Learning Resources
I try to encourage people to keep learning new processes, new things, because it keeps life interesting. In a pursuit of learning, you can always try to better yourself and improve your abilities and knowledge.
Below you can find books that will help for reference and resources to help expand your possibilities.
Machinery's Handbook
The Machinery's Handbook is a resource that you will run into in the machining/manufacturing world, but it could help people who want to get a little more scientific about what they make. It contains the science/math of many critical features like threads, gears, and making your own cams.
You won't be able to read the whole thing, but it will always have interesting knowedge and reference for you.
The Complete Metalsmith
I first ran into this one in my jewelry classes for studio art. It has a lot of things that would be great for aspiring metalsmiths, but there are things like chain mail patterns that would work well for cosplay people as well. It will teach you some basic metal working techniques to some elaborate ones.You can typically find this used for under $20 from eBay or other bookstores online.
The Colouring, Bronzing and Patination of Metals
This one was another gem from art school that I found. It has the chemical makeup of all the patinas to turn various metals more different colors than you can think of.