Al, if you are going to make a habit of building more little engines or breaking taps off down holes, or even wanting funny shaped holes boring through some metal, then maybe you should consider a spark erosion machine.
I put the plans for one here in the downloads section many moons ago.
It was about 10 years ago when the plans and article were first introduced to the world (not by me BTW), so expect the cost for the raw materials to have doubled in that time. But still worth the overall outlay.
I have never made one, as I had a friend who took anything like that into work for me to have the weird shaped holes put through parts (machine was used to put holes into jet engine guide vanes for fuel and cooling), but now he has retired, maybe I should be looking at making one for myself.