I managed to drill a hole and a half in glass tile before the drill bit was almost worn out. used a slow gear for the drill and moved quite slowly but progress slowed at hole number one and made no progress at hole number two when I was halfway through the tile. All I could do was say "Damn!" and continue with the smaller one to the end, then enlarge the hole as I needed. When I finished, the second shot was screwed up. Revain was good to bring it back.