So, I will tell you the easiest ways to cut the neck of a glass bottle.
Method 1 - use a glass cutter
Here you will need a glass cutter. You can use the factory model or make it yourself. The design of a home-made device can be different: the main thing is that the bottle and the cutting element are securely fixed, but the bottle rotates freely.
Important! When cutting, you need to make one pass: this will provide the most even edge.
Next, you need to prepare hot (boiling water) and cold (you can with ice) water. First, pour along the cutting line with hot water so that the glass warms up well.
After that - immediately pour a bottle of cold water.
Glass should break from temperature reduction along the preliminary cut line. If this does not happen, the procedure must be repeated (first pour hot and then cold water).
Method 2 - candle flame
For this method, you need a candle and a piece of ice (you can use a container with very cold water). To break the neck, a straight line is drawn on the bottle with a marker, along which the glass warms up well above the candle.
Then the cutting line is cooled with ice, after which the glass breaks with a light tapping.
Method 3 - nargev from friction
Another way to break a bottleneck is to use glass heating due to friction. To do this, two plastic ties are put on the bottle, which serve as stoppers. Between them, three turns of twine are wound, after which the twine for its free ends begins to move forward / backward.
After 2-3 minutes, when the glass is sufficiently heated, the bottle is placed in cold water, and with a slight tapping, a break occurs along the heating line.
If you make a small incision before rubbing the twine on the bottle with a glass cutter, then you do not need to use cold water: the glass will crack when heated by itself.
Method 4 - installation with filament
This method will require a transformer, for example, from a microwave oven with the secondary winding removed, instead of which three turns of a powerful power cable are installed.
The free ends of the wire are closed through a thick wire. The support (base) must be heat-resistant and dielectric.
The next step is to connect the transformer to the mains. When the transformer is turned on, the thread becomes hot: a bottle is attached to it and gradually rotates. When the glass is heated, the neck will disconnect along the heating line, so you need to make sure that the heating is uniform and along one line.
Method 5 - the burning rope
This method will require natural twine and some refined gasoline for lighters. A piece of twine is cut off with the length required to turn around the bottle at least 3 times. Then this stretch of twine is soaked in gasoline so that it is completely saturated.
Soaked in gasoline twine is wound on a bottle in the place where it is necessary to chip and set on fire.
When the gasoline almost burns out, the bottle is lowered into cold water, where from the temperature difference the glass bursts along the heating line.
Method 6 - use specialized equipment
This method is to use an electric tile cutting machine. The diamond blade cuts thick glass well and evenly. It is recommended to work with gloves, a protective mask and glasses, since glass dust is very dangerous. The advantage of using a cutter is the ability to cut the bottle into small washers, which is not available with other methods.
Also, for cutting, you can use an electric multitool with a rotating working head. But when working with this tool, you need to securely fix the bottle so that the cut is smooth.
In conclusion, I would like to add that not all the methods discussed are safe. When trying to repeat safety precautions and use protective equipment (gloves and glasses).