How To Use Diamond Core Drill Bits

Drill glass, ceramic, porcelain, wall tile, floor tile, limestone, marble, slate, granite, stone, tile & fiberglass!
By: Maurice Hon
Feb. 10, 2010 - PRLog -- 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 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 2,100, Tungsten Carbide is only 30% as hard as Diamond.

Drill Speeds
Diamond drill speeds vary depending upon the manufacturer and type of diamond drill.  Glastar Blunt Nose Diamond Drills, designed for use on glass, can be used at high speeds up to 10,000.  However, Diamond Core Drill Bits, for use on glass, stone and tile should be used at slow to very slow speeds, with the speed decreasing as the hardness and abrasiveness of the material increases.  Also, since the circumference of a bit increases as the bit diameter becomes larger, the drill rpm speed must be reduced on larger bits to offset the increased speed at which the outside cutting edge is moving.
The following table shows recommended drill speeds for Diamond Core Drill Bits.  Drill speeds considerably in excess of these speeds will quickly burn up the diamond bits.  Reduced drill speeds, low drill pressure and use of water for lubrication will extend drill bit life.

Since all materials vary in hardness and abrasiveness, it is impossible to determine exact drill speeds.  Additionally, as discussed below, lubrication and drill pressure must also be considered when determining the proper drill speed.  A faster drill speed or increased pressure may reduce the cutting time slightly, but it will also increase the friction significantly and heat up the bit, reducing the bit life considerably and increasing the risk of heat fractures and material breakage.  If used properly, a diamond drill bit should never be more than warm when touched after use.  If a drill bit develops yellow, brown, blue or black 'burn marks' around the tip, it is an indication of extreme heat and that the drill speed being used is too fast or the amount of pressure on the drill is too great.


Water or coolant must always be used to cool and lubricate the tip.  The lubrication reduces heat build-up, prolonging drill bit life and helps avoid heat fractures in the material.  Water is most often used as the lubricant, since it works very well and has no cost.  Oil based lubricants do not work well on diamond drill bits.

Good lubrication is critical.  Minimal lubrication will keep the bit from burning up, but very good lubrication techniques will extend bit life by a factor of 5 or even 10.
When drilling in fiberglass, a diamond drill bit can be used dry or with a very small amount of water.  When drilling in glass or ceramic, soft ceramic tile and porcelain, if properly lubricated, the dust from the cut should dissipate into the water.  The drill bit contact with the surface should always be wet and the drill bit tip should never be hot.  If the tip is ever more than just warm, it is generally an indication of too little lubrication (or possibly too much speed or pressure).

When drilling in hard, abrasive materials such as limestone, sandstone, hard ceramic and porcelain tiles, marble or granite, it is critical to have lots of lubrication.  With these hard materials, it is common to drill under water or to have a small amount of water constantly running over the drill bit and bore hole.  In either case, the "pumping" technique described below is needed to assure water reaches the very tip of the bit.

This discussion is presented only as a guide.  It is almost impossible to have 'too much' lubrication and the only down side risk is the mess from water being thrown off by the bit.  However, 'too little' lubrication will cause many problems.

Lubrication Tips & Techniques

Various kinds of very specialized industrial water feed equipment are available for industrial production type work.  But, when drilling with diamond bits, the primary concern is merely getting enough water lubrication on the cutting edge of the bit, no mater what method is used.

However, all lubrication methods are not equal.  Since good lubrication extends drill bit life considerably, we rated the various methods to help people understand the differences between the various methods.  As a rule of thumb, the relative rating also gives a general indication of the relative drill bit life under various lubrication methods.  For example, the clay dam lubrication method (8 rating) should provide a drill bit life of approximately 4 times that of using a squirt bottle (2 rating).

The most basic method is to use a small hose that runs water onto the surface near the hole and down into the bore hole.  To provide lubrication on a horizontal surface, one trick is to place a plastic jug or bottle with a small hole near the bottom of it, next to the drill hole.  The water leaks out of the bottle and provides continuous lubrication as you drill.  To allow lubrication to reach the drill tip, it is important to use a "pumping" technique described below.  Without the pumping technique, the water rarely reaches the very tip of the drill bit.

Another excellent lubrication technique is to build a "dam" around the drill hole using a small amount of modeling clay or a similar material.  This method is very effective, especially if the water extends above the side tip lubrication hole to allow water to flow into the bit providing good interior lubrication.  "Pumping" the drill will also increase the lubrication at the tip.  The clay can be used many times if it is stored in a plastic sandwich style zip-lock bag to keep it from drying out.

For low volume repetitive work, it is also possible to place the material into a short 'cake' style pan (place a thin plastic board underneath so you don't drill into the pan) and fill the pan with water so that it covers the surface of the material being drilled.  If possible, the water should cover the side lubrication hole on the tip of the diamond drill bit.

When drilling on vertical surfaces, about the only way to apply water is to use some type of hose.  If that is not possible, a marginally effective solution is to have someone constantly "squirting" water into the bore hole using a squirt bottle.  Squirting water will usually keep the bit from burning up, but unless a pumping action is used, the water rarely reaches the very tip of the drill. Formore information, please visit

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Gila Diamond Products's line of diamond tools are designed to provide the optimum performance for different cutting material types. The following items will be important in selecting the correct blade for your application.
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