HI Jason
I used a handmade cutter in a milling machine and a dividing head shown in the last pictures. For this application this worked just fine. If I wanted production gears I would use an involute gear cutter. The process of cutting gears is not that hard. There are formulas that give you the info needed like size of gear blank and how deep to cut the teeth (actually the space between the teeth). David Gingery has a series of book on how to make many things your-self.
http://www.lindsaybks.com/dgjp/index.html
And for aluminum casting
http://www.backyardmetalcasting.com/forums/
Or google the topic of your choice.
Great fun. If you want more info just post it.
Have fun
Tom