I know there are lots of these instructables on here, but this is a quick method that doesn't use thermal shocking.
I've tried thermal shocking, and the results are often messy, with occasional shards flying off. I've wanted to make one of these for a while, but I couldn't get the results that I wanted.
Step 1: You Will Need...
1, A 12oz bottle. In this case, a beer bottle
2, A tile saw
3, A scrap of wood
Step 2: Select Your Bottle.
I decided to use a Heineken bottle because of the shape of the back. I thought it'd make a nice drinking glass, even once the labels are gone.
Step 3: Cut the Bottle.
Add some water to the tile saw reservoir, and measure where you want the cut to be on the bottle. With the bottle in place, put the scrap of wood where the bottom of the bottle will be at the correct distance from the cutting wheel.
turn on the saw, and slowly roll the bottle keeping it in contact with the wheel, but not pushing hard. Very little force is needed here, just enough to take the vibration out of the wheel. Too much pressure will cause the bottle to break, and it wont follow the line.
What you're looking for is a shallow score along where you want the bottle to cut, and make 3, or 4 passes/rotations. By your 4th pass you should be through the bottle, and have a straight cut around the bottle. If you have a jagged edge it may be because you went too fast, but that's why we sand.
Step 4: Remove the Labels If You Want, and Sand.
I liked the glass of this bottle, so I decided to take the plastic labels off, then I sanded.
You could go through different grit densities here, but I just grabbed whatever sandpaper was trashed on my bench, and used it. I think it was a P100.
Sand until there are no sharp edges that might cut a drinker's mouth.
Step 5: Wash the Tumbler
Typically a quick rinse here will suffice, but my bottle had sticker residue on it. Mu best trick for removing sticker residue is to get it wet, and then cake it in baking soda (Bicarbonate of soda/sodium bicarbonate). The mild abrasive works well without scratching the glass, and as the glue comes away, the baking soda sticks to it, and washes away. Sometimes I use steel wool, but this didn't take much effort for a single glass. Had I been doing more than one, I would likely have used steel wool.