I have made a few manually. I used the horizontal arbor in my mill and a dividing head. First I made a cutter that holds a piece of tool steel. Mounted the blanks I made then stepped out the teeth with the dividing head.
There are pulley tables you can get off the net that tell you the blank diameters you need to machine to before cutting the teeth.
I made these for a supercharger on a truck but I personally think it's cheaper to buy small ones rather than make them your self. If you wish to make them for fun then I have added some pictures of how I made my big ones.
Hope this has been helpful,