As most of you know by now I make molds for a pretty small niche market. Most of those molds are two piece (sometimes with inserts and other things) that are placed together and held with clamping screws (or bar clamps).
I also make some for gravity casting that are hinged with handles. For the most part they are small enough I can drill the holes or spiral interpolate for hinge pins on one of the CNC machines. Once in a while I make one that is to big to set under a drill on any of the machines except the drill press. My drill press is NOT a precision machine. I made a steel jig that fits over the hinge boss of those molds. It gets clamped in place, and a hand held drill is used to drill the hinge pin holes. Its not great, but its better than the "big" drill press in the shop. I know I need a decent drill press (or preferrably a taller mill), but for now that's the solution. It has worked, and I don't have to do it very often. Not often enough to spend the money on a better quality drill press or bigger milling machine.
Well.... I have another tall hinged mold on the mill right now. 18.5 inches. I'm actually roughing the blank on one machine, and machining the cavity on another due to speed and envelope limitations. It actually took me a little while to get happy with my order of operations, and I still have to hand drill the damned hinge pin holes. I sure would like a better process for that.
Than I had an "aha" moment. My thoughts about gun drilling on the lathe hold the answer. I have an MT4 adapter sleeve for the spindle, and an MT4 ER32 collet chuck. Its time to develop my method for holding and positioning stock on the carriage. For a one off I can probably just use some of my assortment of right angle plates.