A new world opens up for many craftsmen when they discover ways of drilling in hard material. Suddenly, a variety of new projects are possible as more materials become available for the craftsman's use.
By using specialized drills and techniques, says Popular Mechanics, it is spossible to drill into hard material such as glass, porcelain, hardened steel, petrified wood, quartz, turquoise and various other stonelike substances.
Abrasive-grit drilling: An inexpensive method of making a hole in glass, china or similar material is to grind through it with abrasive particles, preferably on a drill press. The bits are made from rods of aluminum, copper, brass or even a headless nail. As these bits have tubular cutting ends, they are known as core-type bits. The desired diameter is milled on a lathe from a rod, then center-bored to form a recess in which cores develop from the material being drilled.
Granular abrasive is used between the material and the rotating drill bit. It's the abrasive that does the actual cutting. Abrasive is usually aluminum-oxide or silicon-carbide grains of 80 to 120-grit size. Types of abrasive include loose grains produced by abrasvie manufacturers, valve-grinding compound (such as permatex water-mixed), aluminum-oxide or silicon-carbide grains from sandpaper. Grain type and size are printed on the paper backing. Wet the sandpaper with lacquer thinner and scrape off the grains with a putty knife. Whatever the abrasvie source, it's then mixed with water to form a 'soup.'
Set the drill press at low speed when using core-type bits. Raise the bit every 10 seconds to permit fresh soup to flow over the cutting area. When the hole is almost through, control the feed pressure carefully to prevent chipping the underside.
Carbide-alloy drills: A typical masonry drill consists of a steel shank tipped with a flat piece of tungsten carbide. These bits have two cutting edges at a broad angle to each other. So-called glass drills are of similar construction, but the carbide pieces are sharper and more arrowhead shaped.
Such glass bits are particularly suitable for a drill press and can cut through glass and ceramics easily. When using carbide-alloy bits, support the glass on a firm surface, such as wood or hardboard, and clamp it securely. Keep the carbide cutter lubricated with a few drops of turpentine. Run the drill at moderate speed and feed the bit carefully to prevent overheating. Although the bit passes easily through the glass, there's a chance that it will cause chipping around the hole as it emerges. To decrease this possibility, turn the glass over as soon as the drill tip emerges (set the depth stop first) and finish drilling from the other side.
Diamond bits: For drilling small, hard gemstones, diamond-studded bits are recommended. These bits consist of tiny diamond grains bonded to lengths of hardened steel wire. Diamond bits are used wet, with the workpiece totally immersed in water or a special drilling fluid.
A small, variable-speed hand grinder is suitable for driving diamond bits, such as a Dremel Moto-Tool mounted in its drill press stand. When drills are hand-held it's difficult to drill in small, hard objects.
To master the technique of using diamond bits, apply pressure carefully to the workpiece until the bit bites. Then the bit won't jump or crawl sideways. Increase drilling pressure until the bit starts cutting, as indicated by the appearance of cloudiness in the fluid. Be careful not to apply too much pressure. If the motor slows down, release pressure at once. Prolonged pressure will overheat and damage the drill bit. Back the bit out every 10 seconds so fluid can refill the hole to cool the tip and clear away debris.
Make sure the workpiece is supported firmly enough to keep it from shifting, tilting or being grabbed by the drill bit. Secure stones firmly in place with caulking material if necessary.
As in all shop work, take precautions -- wear safety glasses while drilling and gloves while handling glass and glass particles.
