How to cut off the threaded edges of a glass bottle

people have cut bottles for a variety of reasons. Blues guitarists have used bottlenecks to produce a sweet singing tone from their instruments. Thrifty people have cut the necks off to make tumblers. Artsy and crafty types have used various portions of bottles to fashion a variety of objects such as vases or decorative jars.

Before starting to cut glass bottles, it may be helpful to get a little (very little) physics lesson about the properties of the glass. Glass is actually a liquid in a frozen state. Unlike ice, however, glass’s melting point is over 2000 degrees. When you cut glass, you’re not really cutting it as much as performing a controlled break. For example, if a cut is desired on a flat sheet of glass, one simply scratches a line (scores) where the cut is to be. Then the glass is broken along this line. With a bottle, the same thing is done; however, the procedure is complicated by the curvature of the bottle.

There are a couple of methods that can be used to cut bottles, depending on how accurate of a cut you’re going for. Guitar players use the necks of wine bottles to make slides utilize the following method. Fill a suitable bottle to the desired cut point with oil, and then simply jab a hot poker into the oil, shearing the bottle at the cut line. Variations of this method include scoring the bottle where you want the cut, wrapping a piece of kerosene-soaked cotton string around the bottle at the scored line, then setting the string ablaze. The bottle should break at the line. You may have to put a few droplets of water onto the string after it goes out. Both these methods produce a rather rough cut that requires a lot of smoothing.

There are commercially available bottle cutters. Most are just a jig of some sort that holds or turns the bottle while a stylus scores the bottle. Then a rod is inserted to tap around the inside of the bottle at the scoreline until it breaks. Glass bottles can actually be cut with ordinary scissors. Hold the bottle underwater, and cut like you normally would. The edges will come out very rough. The tried and true method is to use an ordinary glass cutter available at any hardware store to score the bottle at the desired cut line, fashion a piece of a metal rod with a 90-degree angle near one end, use that rod to gently tap on the inside of the bottle at the scoreline until it cracks. Then smooth out any rough edges.

What ever method you choose to cut your bottle, the edges will have to be smoothed out. Emery cloth is a great choice for this task. Start with a rough grade, and then gradually progress to a lighter grade as the edges become smoother. Another method is to wrap the emery cloth on a piece of round dowelling. This helps to avoid a cut finger while the edges of the glass are still sharp.

What ever method

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