I've tried a few methods:
- scoring with a glass cutting tool - didn't work well on round necks.
- scoring with a triangular file - this works much better. It's very important that your scored line be straight, that you don't have multiple start & stop overlapping areas, etc. So, it's a little tricky to do right on a bottle neck.
- I heat the scored neck over a candle flame until one side of the line is covered in soot, then hold under cold water. The neck breaks clean about 50% of the time, depending on how well I did the scoring.
- I like clean lines on the slide - so that means two cuts on a bottle neck to eliminate the top lip. That means about 4 bottles to get one good slide.
- it might be worthwhile to tap the inside of the neck with a small steel. That may break things more cleanly.
- One string willie gave better suggestions than I can, but let me mention a few points:
- first off - eye & respiratory protection are important
- secondly, you can use the side of the dremmel diamond blade to polish the edges pretty nicely. Afterwards, I typically just rub the slide edge on sand paper. That gets it looking pretty good.
- this is a pretty reliable method. But less fun than cutting & burning, and probably more expensive - since the dremmel diamond-coated blades are $15-20.
- i've never used them, but heard that they are great.
- I've tried creating some jigs to make it easier to work with a file, but so far it hasn't worked out well, but there's some light at the end of the tunnel.
- go to a cafe that serves wine. They can give you armfuls of free empty bottles. More than you'll ever use, unless you're picky and just want the neat blue-glass vodka bottles.
The standard "reinforced" cutting wheels work just fine. The non-reinforced ones (the cheap ones...) tend to flex and shatter.
I've done this too, works pretty well. Just score around the neck in a nice clean circle and tap... The sharp edges can be removed by judicious use of the same wheel.
I have found that I can get really good cuts using my Dremel tool on a slow speed using a diamond wheel (Lowes had a pack of them for around $10.00). You can actually cut all the way through the neck without cracking it. The cut at the base of the neck can be tapped to remove it after you made a good cut. If you try to cut the lip around the top of the bottle neck, you'll have to either cut it all the way through or cut really deep to remove it. I haven't tried using hot water yet. I have successfully cut and made 2 slides so far using this method without any problems. I'm sure a tile saw with a diamond blade would probably work even better. This method doesn't really take very long to do either.