I could only make a hole and a half in glass tile before the chisel was pretty much up worn out the floor. I used a slow gear for the drill and moved fairly slowly, but progress slowed on hole number one and made no progress on hole number two. Time when I was halfway through the tiles. At this point, all I could do was say "Damn!" and continue with the smaller one to the end, then enlarge the hole as needed. When I finished, the second shot was screwed up. Revain was good to bring it back.