i have to agree with Eric...for fast and efficient work on this, you should have a wet belt sander. once you get the production up and KNOW you want to do a lot more, you could even look into a diamond wheel. spendy, but it will last ya and you won't have to replace the wheel as often.

The 3M diamond pads I mentioned above will give you a much faster and far nicer finish than a Dremel ever will. If you're hoping to have people use these to drink from you owe it to your customers to give them as smooth a lip as possible...or their lips will pay the price. If you are going to use a Dremel (or any flex shaft or high rpm drill) clamp the drill and use as fine an emery drum as possible (they also have felts and corks for actual polishing but a bit of a pain at this scale; really designed for jewellery) and use two hands to rotate the glass against the drum. Much more control. Remember to keep your drum/glass wet. A sponge or drip feed will work but remember also to keep the water away from your Dremel with a splash shield of some kind; even a cut off plastic pop bottle will work. If you're using a flex shaft attachment for your Dremel (or have a Foredom) you don't need the same pecations as the motor is what you need to protect. That said, once done with any type, wipe it all dry with a towel and give it a light lube after to prevent rusting.