i use a dremel rotary tool, the kind that plugs into the wall, not the rechargeable one-
i also have a princess auto rotary tool set, that cost about 20$ and works just as good.
then you need a diamond cutting wheel for it- like this-
http://www.drillspot.com/products/42..._Cutting_Wheel
canadian tire wants like 25$ for it- but again, i got a set of 4 at princess auto for about 4$.
you want to be outside, or in your basement or garage, as glass will fly a bit- tiny fragments like.
i use my bathtub lol.
also i wear leather gloves n safety glasses-
i pick a bottle that is the right size- i like the mastro brand ballsamic vinagar bottle from the grocery store- first i cut the end off, where the cap screws on-
i wind the rotary tool up to a good speed, and begin to lightly score the bottle, slowly spinning the bottle, while holding the cutting tool as firmly and straight as i can.
once ive gone around once, i follow my initial cut, only applying a bit more force- after a few turns of the bottle you will cut through at some point, when this happens itll crack along the length of your cut, and the end falls off.
i then take a rough measurement against my finger to estimate the needed length- doesnt need to be perfect- and begin the same cutting process at the desired point on the neck of the bottle.
i hold the bottle in my left hand and spin it slowly, while holding the cutter rigid, i dont try to go too deep, again once you are through at one point, the rest just breaks off.
then i use a knife sharpening stone, rubbing the jagged ends back and forth on it to kinda wear it down to a uniform level. once its relatively even i then fine tune it-
ill usually sit and watch a hockey game or something, just spinning the edges of the new slide first on emery cloth, then finer grades of sandpaper until the ends are nice and smooth.
the glass that flies around during the cutting process is very fine, like little grains of sand- after the first time i did one, i started wrapping a hankerchief around my face, because i could taste it for 2 days- probably not good for ya lol.
its really pretty easy- ive made 4 in this exact fashion, and havent broken a bottle yet- but i err on the side of caution, going real slow n easy with the cutting tool.
before i figured out this method i tried all the traditional approaches, and all where failures.
ive had such good results that people want them, and ive given 2 away- i thought id like to make a bunch and market them cheaply, but its hard to find decent bottles- now that the beer store takes empty wine bottles-
i asked the little girl who works at the beer store for some, explaining why i wanted them, the manager told her it was a liability issue and i couldnt have them.
then i found the basamic vinegar- i just dump it out, costs me 3$
i hope ive made some sense, at least enough for you to follow- its really easy. if you have any questions ask away-
remember, the silicants in coloured glass are different than those in clear glass- ive read that green and blue glass sound better, in my experience it is true, i made a clear one, and it didnt sound as good as the two you see in my pic- and of those two- the black one sounds best- but that maybe just to my ears
good luck