Dudley and Buckingham are my two immediate go-to's. Ironically, most of TheGoodStuff
® that I have ever found that was not in those two, was in pamphlets, papers, and historical data put out by the early manufacturers. AGMA used to be really good, ( even if you did have to sign up or be a member of a participating company ) but not so much any more it seems. It really just depends on how deep down the rabbit hole you want to actually go.
Frankly, the basics are covered by everyone and their brother and a few of the hobby level books are actually quite good. Older Machinery's Handbooks are choc full of data, too, if one bothers to look.
Fellows had some stuff, Barber Colman had some stuff, Gleason had some stuff, Cincinnati had some stuff, you get the idea... I even discovered some excellent resources in an operator's manual for a Koepfer at the time. ( basically every manufacturer had put out some manner of informational book or pamphlet )
If you want to get into the nitty gritty of exactly what makes a good gear and a bad gear, those are numerous, deep, dark rabbit holes covering materials, set ups, tooling, heat treating, surface treatments, tribology, etc...
Noise is its own little niche of study, too...
And then there all the white papers...
Don't forget Asymmetrical Tooth forms, either...!
Start with Ivan Law and see how far you want to go. May want to give member Dan from Oakland a ping and see if he's got time and inclination to assist. I know that I am happy that my Apprentice has interest in the niche. I've given him unrestrained access to my library and have arranged for more training to accommodate it. The knowledge base is shrinking quickly.
