Ditto previous suggestion of Machinery's Handbook. It is the bible for any serious machine designer. Not a lot of examples of finished machinery, but more detailed information than you will ever use about machining practices, procedures, and standards. Invest in one now.
Also, get your hands on all the old printed catalogs that you can. Items like cylinders, speed reducers, bearings, conveyors, power transmission devices. Most of the old school catalogs had engineering sections in the back with a lot of good information. And there's just something about a printed paper catalog for general browsing, learning, investigating...
I also learned a lot by studying, IN INTRICATE DETAIL, the drawings done by those that came before. A paper mill I worked at had drawings done in ink on linen from the 1800's. Real pieces of art. Those guys spared no effort to make a clear, easy to understand, fully detailed drawing.
When you're looking at an existing drawing, take some time to study it. Pick some small design detail, like a flange, or a hole, or a finished surface, and just start asking yourself questions - "Why did he do it that way? Wouldn't it have been simpler to do it some other way or not at all? What would happen if he had done it this other way?" Those questions will lead to answers that become lessons. And if you can't figure out the answer, ask someone older.
