Originally Posted by
MichaelHenry
Maybe I missed it, but what sort of tap are you using? For through holes you'd probably want spiral point taps (aka gun taps). Form taps might be a good option, as others have pointed out, but mind the hole size, which is larger than the hole for standard taps.
Also, you may find that your flood or mist coolant doesn't work as well with tapping as it does with cutting, especially in aluminum. I have much better luck by manually applying a few drops of Tap Magic Aluminum than I did with Hangsterfer S-500 or Qualichem 251C flood or mist coolant.