Not sure if you actually did anything yet, but I work for a countertop and tile company. If you have a quartz countertop, you need to drill TOP DOWN. Also, are you sure you need a 1/2" bit? We typically drill a 1-3/8" hole with a Dia Diamond Wet/Dry bit for a faucet hole. If you need to use a 1/2" core bit for a filtration faucet, same, buy a Dia bit. Need to use a Milwaukee Angle Grinder to operate; you'll burn out a regular drill. Lastly, get a large sponge, wet it, and cut a hole in the sponge and place the drill bit through the hole as you drill. Start the bit at a slight angle to the edge of the cut-out and then shift the grinder to a 90 degree angle to the countertop to finish.

Typically, the dual mount sinks are 18g sheet metal. Yes, use a metal bit to go through the flange, but my guys are lazy and use the Dia bits. Hope this helps.