I had a little play with R&P a couple of months ago whilst looking at all sorts of possibilities for making a small router. Have a look here it's a good place to design your own gears as they output the result as a DXF or DWG (can't remember which now!!)

Below is a small one I cut out of 6mm thick Acetal as a trial, I think with a 2mm end mill.

Click image for larger version. 

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