Gear geometry
Gear geometry data is available from PIC Design Inc. which is now part of RBC Bearings at the link:
http://pic-designcatalog.com/Images/pdfcat/section_12.pdf
Stock Drive Products provides an on-line Handbook of Gears at the website:
http://www.sdp-si.com/products/Gears/Index.php
The Gleason Gear has a lot of useful information:
The American Gear Manufacturers Association provides standards for sale on-line at the site: