Tapping holes

[magicniner]

You can knock most of the point off a spiral flute tap without affecting it's function. In this way you can get close enough for finishing off with a custom trimmed bottom tap with reduced lead-in to finish the thread with as much profile as possible as close as possible to the bottom of the hole, if you want more thread closer to the bottom trim the bottom tap further and run it to the bottom of all the holes again.
I Thread Mill down to M3 but I wouldn't want to do a shit-load that way ;-)