Likely I am being dense but I am having a heck of a time deciphering the gear section in the Machinery's Handbook. What I would like to do is cut some simple spur gears out of aluminum using a vertical CNC mill. I'm not looking for super precise gears... this is a hobby for me. Looks like it should be pretty straight forward as gears are a circular pattern of a feature pair (the tooth and the valley) but I missing something. Would someone point me to a layman's explanation of gear design or a freebie program that can at least provide the necessary parameters or preferably export a DXF profile?

Thanks