Luthier CNC

[Voicecoil]

The best taps I've found for through holes in ali are the blue ring spiral point types like this:

They're made specially for aluninium, the interrupted thread higher up seems to help with binding. Typically I've found you can tap a hole in 12mm plate in 3...4 seconds with one of these in a cordless drill with some cutting fluid. For blind holes as Mekanik said you need to use a spiral flute tap (to get the chips out), again I've found the blue ring types are marginally the best.