How are molds made for gears?

Question

I want to make my own gears, from absolute scratch. How are molds made for gears? My plan is to melt pennies with a blowtorch (since they're made from copper and/or zinc, both of which have a melting point lower than a blowtorch's temperature) but to do that I need to know how to make gear molds. Oh, and how can I prevent the liquefied pennies to bond to the mold as they cool down?

Answer 1

Gears aren't cast, at least the teeth aren't.  What gets stamped or cast is a gear blank, or disc of metal.  Then, the blank is put in a gear cutter and the teeth and shaft hole (if required), are machined into the disc.  See here for examples:

http://en.wikipedia.org/wiki/Gear_manufa...

Note that "casting" is not listed.  The reason is that casting can't produce accurate enough dimensions, and the little extra bits of metal leftover from the mold seams will prevent the gear from running true.  

So, cast the pennies into discs, then buy yourself a mill, and use the mill to cut the teeth into the disc.