Drilling Holes in Glass & Cutting Bottles

by Steve Ackman
(built on Paul Wilson's original article)
Drilling Holes
For most glass craftsmen, the best method for drilling glass is the grinder method because most will already have the grinder and the cost of a bit is only around $15.00 or $20.00.
There are several small bits on the market, typically in 1/8" and 1/4" sizes that have diamond grit on both the circumference and the end of the bit. These can be used to do a "plunge grind" if kept adequately lubricated. Use a sopping wet sponge or acid brush against the back of the bit to keep it wet, or a spray bottle set to mist, while you lower your glass slowly onto the bit slowly drilling through the glass. Most bits are meant to sit high on the grinder shaft, in which case a "second story" or "grinder tower" attachment is sometimes helpful to provide support for the work.
Some pieces will be much easier with two people; one to keep the bit wet, the other to control the work. Since this type of bit is diamond-coated both on the end and on the circumference, you can easily plunge a bit-sized hole through and then enlarge it to whatever size you need, all in the same operation. The disadvantages to this method are that you're working upside-down, meaning that you can't see what you're doing on opaque glass, and again, it's harder to apply coolant.
Applicable to all rightside-up drilling methods, a good way to keep coolant and/or slurry where it's needed is to build up a small dam of clay, putty, or glazing compound around the area where the hole is to go, and fill the dam with coolant or abrasive slurry. There are many possibilities for coolant, ranging from plain water to light machine oil.
Recommended in the Machinery's Handbook for "holes of medium and large size," is the old copper pipe and abrasive slurry method.
Use a copper or brass pipe (or tubing), which has the same Outside Diameter as the desired hole size. Use 100 grit carborundum (obviously diamond lapping compound would work too) and light machine oil, and support the glass with a piece of felt or rubber not much larger than the hole to be drilled. If possible, drill halfway through, then flip the glass and complete the hole from the opposite side. The ideal speed for this method is 100 surface feet per minute.
RPM to get 100sfm for common sizes
1/4 inch 1528
1/2 inch 764
1 inch 382
2 inch 191

Halfway between the grinder bit and copper tube is the diamond core bit. Probably the best choice for doing production work or drilling into bottles and other non-flat objects... also probably the most expensive. Recommended speeds for core bits are faster than the copper/brass method, and differ according to manufacturer. About the smallest you can get is 1/2" though some manufacturers start at 1".
The other popular method for drilling a hole is to use a carbide spade drill bit made for glass and ceramics. You can pick these up at most glass, hardware, or building supplies stores. The recommended coolant here is kerosene and/or turpentine, or the same stuff you use to lube your glass cutter. A tip for success using these bits (for flat glass) is to put a piece of scrap glass underneath the piece you're drilling to prevent the spade from "breaking through" the back side, sometimes catastrophically. They generally range in size from about 1/8" to 1/2" in 1/16" increments.

Cutting Bottles
There are several methods for cutting bottles, the best of which, and the hardest to find, is the sixties vintage bottle cutter.

A good method for the do-it-yourselfer (you're reading this, aren't you?) is to cobble together a V-trough and use it in conjunction with a regular glass cutter. The fixture can be made by cutting two 45 degree cuts in a short piece of 4 X 6 so that you have a trough in the wood that a bottle can sit in. If you don't have a saw capable of this, you can alternately nail or screw a 2 X 4 and 2 X 6 together forming a right angle. You probably also want to add a block to one end of your trough to serve as a rest for the bottom of the bottle to ensure a straight score that starts and stops at the same place.
You then turn the bottle in the trough while holding the cutter against the side, scoring a line completely around the bottle. A few gentle taps around the inside the bottle along the score line should help break it in two.

After it's cut, then what? You have sharp edges which need to be dulled. The manual way to do that is to get some grey automotive silcon carbide "wet or dry" sandpaper. Place the paper on a smooth flat surface and wet it down. Invert your bottle-half and use a figure-eight motion to sand it smooth (be prepared to work at this for a bit as it doesn't happen quickly). After the edge is relatively smooth and flat, the corners will still be a bit on the sharp side. You can place the sand paper on something with some give, like a mouse pad, or your hand, and rotate the bottle-half to help round off those sharp corners. If you need a polished edge, you'll have to do a LOT of handwork, using gradually finer abrasives. A far better method is to fire polish the edge in a kiln.

There are a couple other methods that will also work after a fashion to make two halves out of one bottle, but which can be rather hazardous, and in my opinion aren't particularly neat, but for the sake of those adventurous and inventive souls looking for "field expedients," I'll mention the words "string and kerosene," and "nichrome wire and resistance heating."
Paul Wilson & Steve Ackman 1997,2000 ©
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