Carbide Tipped
Spear Point Drill Bit

Return to top

Materials for Diamond Drill Bit Use

Bonded Diamond Drill Bits are used on glass, stained glass, ceramics, ceramic tile, porcelain, porcelain tile, limestone, marble, granite, slate, stone and fiberglass.  Drills used on wood or metal have a sharp metal tip or teeth, that cut into the material.  These types of drills do not work on glass, marble, etc. as the tips do not "bite" into the extremely hard material, and cause heat build-up that burns up the bit and causes "heat fractures" in the material.

Carbide tipped Spear Point drills are sometimes used on the "softer" types of hard materials - like untempered glass, sandstone and marble and some of the less hard ceramic and porcelain tiles.  While they sometimes work, they tend to chip the hard surface very badly, leaving a rough hole and often cause breakage due to fractures from the chipping and heat.  Diamond drill bits are designed differently - they have diamond tips that "grind" into the extremely hard materials.

An extensive detailed listing of specific materials and specific applications for using electroplated diamond drill bits is shown in the Drill Bit Uses section of our web site.  Diamond Drill Bit Uses: <Click Here>

While diamond drill bits are designed for drilling in extremely hard materials, Electroplated Diamond Drill Bits are NOT designed for use on metal, concrete or masonry materials.  For drilling in concrete, masonry, and metals such as iron, cast iron and steel, a carbide tipped drill bit must be used.  Do not use Electroplated Diamond Drill Bits on concrete, masonry or metal.

The sections below discuss the characteristics of various materials and the special techniques for using diamond drill bits on those materials.  The most important factors are to use a slow to very slow drill speed, low drill pressure, and plenty of water for lubrication.  Variable speed drills work best since the proper speed can be selected  Some fixed-speed drills have a minimum speed of 600 or 800 rpm, that may be too fast for many diamond drill applications (see speed chart).  Impact type "hammer drills" should never be used with diamond drills bits.

Top - Core Drill Bit
Bottom - Blunt Nose Bit

Core Drill Bits

.Return to top

Types and Styles of Diamond Drill Bits

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.

.Return to top

Material Hardness & Abrasiveness

Materials have varying degrees of hardness and abrasiveness.  Additionally, specific man-made and natural materials can differ greatly depending upon the exact physical composition.  For example, glass varies in hardness depending upon color and type, since various metals and minerals are added to achieve the different types and colors.  Glass also has differing degrees of "temper" depending upon the specific manufacturing methods used.  Ceramics, ceramic tile, porcelain and porcelain tile are various forms of vitrified glass like material.  They also have differing hardness and abrasiveness depending upon the type, composition, manufacturer and manufacturing methods used. 

The hardness and abrasiveness of natural materials, such as stone, vary by type, but they also vary significantly within a specific type.  Most stones are not pure - they are mixtures of various types of rock.  Granite, for example, contains various combinations of primarily quartz, feldspar, black mica and hornblende.  Therefore, a specific stone type such as granite or marble, will vary significantly in hardness and abrasiveness depending upon the exact mineral composition that varies by quarry location.

Below is a table of the hardness of various materials.  The table uses the standard Knoop Hardness Scale (kg/mm2).  The Knoop scale is a linear scale, so a rating of 100 means the material is twice as hard as something rated as a 50.  The hardest known material is Diamond, with a Knoop measurement of 7,000.  Tungsten Carbide, used in carbide drill bits, is the hardest natural material next to Diamond.  However, with a measurement of 2,000, Tungsten Carbide is only 30% as hard as Diamond.

.Return to top

Relative Hardness of Drill Bits vs Materials

Most people are very familiar with drilling in common wood such as fir or pine.  When a good steel drill bit is used to drill wood, the bit is about 80 times as hard as the wood.  Carbide is considerably harder than steel and if a carbide bit is used in wood, the hardness ratio is about '200 to 1'.

By comparison, when using a carbide bit to drill in hard porcelain tile, a carbide drill bit is only about 3 times as hard as the material being drilled.  The low hardness ratio of only about '3 to 1' helps a person understand the extreme hardness of today's porcelain tile.

The highest grade of porcelain tile is now as hard as granite.  In fact, it is basically man-made granite.  The low hardness ratio for a carbide bit explains why the newer porcelain tiles can't be drilled with a carbide bit.  Or if they can be drilled, bit life is calculated not as the "number of holes per bit", but rather the "number of bits per hole".

Diamond bits are the only solution for drilling in today's super-hard porcelain tile.  Diamond is the hardest known natural material and is nearly 4 times as hard as tungsten carbide.

Yet, even with even when using a diamond bit on drill today's porcelain tile, the bit is still only about 12 to 14 times as hard as the material being drilled.  Compared to the wood example of an '80 to 1' or '200 to 1' hardness ratio, shows why even diamond drill bits require good drilling techniques and have a limited life when drilling in today's hard materials.