Before you even start on the fly cutter, find out if the hi/low gears in the head of the mini-mill are plastic, if they are plastic, you will soon mash them with a fly cutter and need to change them, don't bother asking how I know.

If the gears are plastic, you just better go buy the ally ones and replace the plastic crap, then once you've done that, then you can start to think about making a fly cutter for your mini-mill. :-)