I would not use a tap, requires too much power. I use thread mills. One part I build has a 1-8 threaded hole, 2 inches deep, 6061 aluminum. I do it in one pass with a 2HP spindle.
Like this one, but with a 1/2 shank https://www.amazon.com/Micro-100-TM-...ustrial&sr=1-2
Or a multi-cutter type