"Practice safe eating, use condiments"
Sorry for Roscoe's and my off topic nonsense.
Back to topic, I have seen many bad drill jobs, and almost all were due to impatience or too much pressure. Just keep thinging of it as mildly polishing away bits of the glass with little diamonds and you will get it. Yes, you can apply pressure and grind away, but never quite know when the last part will BLOW through with fractures. It is a very easy and rewarding activety if you take your time and pay attention. Wear goggles.