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Core Drill Bits
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Diamond drill bits come in many different sizes and shapes but are primarily of two basic styles, blunt nose bits and core drill bits. There are also two basic types of diamond drill bits relating to the application of the diamonds; bonded and sintered.
Blunt nose bits are solid at the tip and have diamonds on the tip and on the sides of the tip. This style of bit drills a complete hole by grinding a full hole the size of the tip. Core drill bits however, are hollow at the tip. They have diamonds along the edge of the tip and slightly up the sides of the tip, similar to a margarita glass that has been "rimmed" with salt. Diamond Core Drill Bits grind or saw a circle at the edge of the tip rather than the full diameter of the tip. A core drill results in a hole the size of the tip and a smaller "core" or "plug" that comes from the middle of the hole. Core drills are often called hole saws, since they grind or saw a circle to create a hole.
Since Blunt Nose bits drill out the complete hole, they are only effective for smaller holes. This style of diamond bit is only available in sizes up to about 3/8" and are used primarily on glass. Blunt Nose bits are not designed for extremely hard materials such as stone or ceramic and porcelain tile. Core drills only drill out a portion of the resulting hole, so they tend to drill much faster than blunt nose drills. Core drills can be used to drill large holes and can be used on most non-ferrous hard materials such as glass, stained glass, ceramic, porcelain and fiberglass, ceramic or porcelain tile, limestone, slate, marble, granite and other stone materials.
Bonded diamond drill bits have the diamonds bonded to the the edges of the drill bit tip, generally using an electroplate bonding process. These drill bits are generally slow-speed bits and are fairly inexpensive. During use, the diamonds eventually wear off of the bit due to the hardness and abrasiveness of the material being drilled. Bonded diamond drill bits must not be used on metal, concrete, or masonry and require proper speed and adequate water lubrication.
Sintered diamond bits have the diamonds mixed directly into or embedded in the steel tip. As the metal tip wears down, new diamonds come to the surface. Some 'sintered' diamond drill bits are designed for use on metal, concrete or masonry, however, the specific manufacturer's recommendations must be reviewed. Sintered diamond drills are generally high-speed bits and are somewhat long-lasting, however, they are also extremely expensive.
The life of any type of diamond drill bit depends upon the hardness, abrasiveness and thickness of the material being drilled and the specific drilling techniques used (drill speed, pressure and lubrication), however, the diamonds of a drill bit don't actually wear out as much as they wear off due to heat and friction caused by the extreme hardness and abrasiveness of the material drilled.
Drilling in glass, ceramic, marble, etc. is a slow process compared to softer materials such as wood or even metal. A fairly deep hole can be drilled in wood in just a few seconds, while it can take 20 or 30 seconds or longer to drill a hole in standard 1/8" thick glass. In some very hard stones and tiles, it may take 2 to 3 minutes to drill only 1/4" deep. Using diamond bits to drill in hard materials is not difficult, however, it takes time. A person should consider that they aren't 'drilling' a hole, as much as 'grinding' a hole.