I purchased a set of index plates for the Sherline lathe on eBay. The info in the smaller pamphlet is also contained in the larger book so no need to buy both. It covers almost everything one could think to ask about wheel and pinion cutting. The book by Malcolm Wild that was recommend is the best single reference that I have see.
HOW TO MAKE A MILLING ATTACHMENT FOR ATLAS LATHE HOW TO
Dave Creed also had written an article that documents how to make multi-tooth cutters. John Shadle has a web site that shows one method for making single point cutters. One of the more interesting aspects (and potentially expensive) of wheel/pinion cutting is cutters. dozens of contacts with guys (by email) that were doing wheel and pinion cutting. I probably spent a year or so studying before the first purchase. I didn't have an "in person" mentor available so I did what I had to do. The price of not quite understanding is wasted $$ on something you don't need or something that is not quite right.
I learned what I know of wheel cutting from books, videos, emails, and lots of study and reflection on the process. The more personal interaction you can get with experienced people, the better. This just touches the surface but other items include gear cutters, cutter arbors, gear blanks, and gear blank arbors. Indexes are commercially available for full-sized mills but then you wouldn't be using the lathe for gear cutting. Unfortunately, these must be custom made to fit an individual lathe.
That means you would need to rotate the index 40 times to complete one revolution of the head stock. "Practical Benchwork for Horologists" by Levin shows a universal index which attaches to the lathe and utilizes a 40:1 worm gear for accuracy. The index holds the head stock in a fixed position so the tooth can be cut and then allows the head stock to be rotated an exact amount. You wouldn't necessarily need all that if you have a full-size mill since it should be possible to mount your lathe bed on the mill (this is the setup I prefer). To power the milling attachment you will need a countershaft and idler pulleys which allow you to align the belt with the pulley on the milling attachment.
The milling attachment mounts on a cross slide and is used to spin the cutter. There are many different setups but the three basic needs for gear cutting with a lathe are.