I'd like to hear from the veterans here, some tricks and tips for drilling thick plate.

I recently had to drill 1/4" plate SS up to 1/2" hole that was serious to get through. I finally had to drill about 6 holes on each one, coming up a few sizes every time. The way I was taught, from my dad at least, was slow and oiled. That's the method I've used all my life and it's served me well. Maybe my issue was just this piece?, it sure was hard!

Here's a few pics: