Drilling Tips & Techniques

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How to Drill Glass, Tile & Stone
How To Use Diamond Drill Bits

Drill glass, ceramic, porcelain, wall tile, floor tile,
limestone, marble, slate, granite, stone, tile & fiberglass!

- Make a Selection or Scroll Down -

Materials for Diamond Drill Bit Use	Pilot Bits on Core Drills
Types of Diamond Drill Bits	Starting Bit with a Template
Material Hardness & Abrasiveness	Drilling Tempered Glass
Drilling Speeds	Deep Boring Beyond 1/2"
Lubrication	Ceramic & Porcelain Tile
Lubrication Tips & Techniques	Drilling Glass Bottle or Block
Drill Pressure	Drill Glass Aquarium
Balance Speed & Pressure	Drilling 'Blind" Holes (not thru material)
	Diamond Drill Bit Life

Carbide Tipped
Spear Point Drill Bit

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Materials for Diamond Drill Bit Use

Diamond drill bits are used on glass, stained glass, ceramics, ceramic tile, porcelain, porcelain tile, limestone, marble, granite, slate, stone and fiberglass.  Drills that are 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 merely cause heat build-up that burn up the bit and cause "heat fractures" in the material.

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

The sections below discuss the characteristics of various materials, the different types of diamond drill bits, and the special techniques for using diamond drill bits.  The most important factors are to use a good diamond bit, a slow drill speed (see speed tables below), low drill pressure (see pressure tables below), 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 charts).  Impact type "hammer drills" should never be used with diamond drills bits.

Top - Core Drill Bit
Bottom - Solid Tip Bit


Diamond Core Drill Bits
with Bonded Diamonds


Diamond Core Drill Bits
with Sintered Diamonds

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Types and Styles of Diamond Drill Bits

Diamond drill bits come in many different sizes and shapes but are primarily of two basic tip styles, solid tip bits and hollow core drill bits.  There are also two basic types of diamond bits relating to the application of the diamonds - bonded and sintered.

Solid tip drill bits have diamonds on the tip and 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 and are often called hole saws, since they grind or saw a circle to create the hole.  They have diamonds along the edge of the tip and slightly up the sides of the hollow 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.

Since solid tip bits will drill out the complete hole, they are only effective for smaller holes in hard materials.  This style of diamond bit is only available in sizes up to about 3/8" and are used primarily on glass, jewelry, soft stones or sea shells.  Solid tip bits are not designed for extremely hard materials such as very hard stone or porcelain tile or for drilling large holes.

Core drills only drill out a portion of the resulting hole, so they will drill much faster than solid tip drill bits.  Core drills can also 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, 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.  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 are used for drilling up to about 1/2" deep in glass, tile and stone.  They are not designed for drilling in metal, concrete, or masonry and require proper speed and adequate water lubrication.  All bonded diamond drill bits carried by Diamond Drill & Tool are Electroplate Bonded Bits.

Bonded Bit   Sintered Bit

Picture shows the thin-wall tip of a Bonded Diamond Bit next to the thick-wall tip of a heavy-duty Pro-Sintered diamond drill bit.  The bonded bits will drill much more quickly but are designed only for drilling in glass, tile and thin stone up to about 1/2" deep.

Sintered diamond bits have the diamonds embedded directly into the metal tip of the bit.  As the tip wears down, new diamonds come to the surface.  Sintered diamond drill bits are often designed for deep drilling in stone, concrete or masonry, however, the specific manufacturer's recommendations should be be reviewed.  Sintered diamond bits are more expensive and because they are heavy duty, they drill more slowly, but they last longer.  Depending upon the material being drilled and the drilling techniques used, Sintered diamond bits can last 30 to 50 times longer than a bonded diamond bit, sometimes even longer.

The life of any type of diamond drill depends upon the hardness, abrasiveness and thickness of the material being drilled and the specific drilling techniques used (drill speed, pressure and lubrication).  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.

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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 natural material is Diamond, with a Knoop measurement of 7,000.  Tungsten Carbide, used in carbide drill bits, is the second-hardest natural material.  However, with a measurement of 2,000, Tungsten Carbide is only 28% as hard as Diamond.

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Drill Speeds

Drill speeds vary depending upon the manufacturer and type of diamond drill.  Glastar Blunt Nose Diamond Bits, designed for use on glass, can be used at high speeds up to 10,000.  However, DiamondSure 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. 

Since the circumference of a drill 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 DiamondSure 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.

DiamondSure
Bonded Diamond Drill Bits
Recommended Drill Speeds

DiamondSure - Bonded Bits	Recommended Drill Speed (rpm)
Material         Bit Size -->	1/2"	1"	2"	3"	4"
Fiberglass	1200	700	350	250	175
Glass, Ceramic & China	800	500	250	160	125
Limestone & Marble Stone	600	450	225	130	100
Ceramic Wall Tile	600	450	225	130	100
Porcelain Wall Tile	500	375	180	125	90
Porcelain Floor Tile	500	375	180	125	90
Granite Stone	400	300	150	100	75

Designed for materials to about 1/2" thick
(Not for use on Concrete, Masonry, or with Hammer Drills)



DiamondSure
Pro-Sintered Diamond Drill Bits
Recommended Drill Speeds

DiamondSure - Sintered Bits	Recommended Drill Speed (rpm)
Material         Bit Size -->	1/2"	1"	2"	3"	4"
Fiberglass	1600	800	400	300	200
Glass, Ceramic & China	Not recommended for Glass
Limestone & Marble Stone	1600	800	400	300	200
Concrete & Masonry	1600	800	400	300	200
Ceramic Wall Tile	1600	800	400	300	200
Porcelain Wall Tile	1200	600	300	225	150
Porcelain Floor Tile	1200	600	300	225	150
Granite Stone	1200	600	300	225	150

Designed for long-term use in materials up to 1-3/4" thick
(Not for use with Hammer Drills)

SPEED KILLS:

Reduced drill speeds, low drill pressure and increased use of water lubrication will extend drill bit life considerably.

LUBRICATION:

DiamondSure Bonded Diamond Drill Bits and DiamondSure Pro-Sintered Diamond Drill Bits require water lubrication.

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, the amount of pressure on the drill is too great, or water lubrication is inadequate.

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Diamond Drill Bits - Lubrication

Water must always be used to cool and lubricate the diamond drill 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 good lubrication techniques will extend bit considerably.

When drilling in fiberglass, a diamond 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 only a guide.  It is almost impossible to have 'too much' lubrication, however, 'too little' lubrication will cause many problems.

 
Core Drill Bits
Note side tip
lubrication hole


Using a clay dam
lubrication technique
to drill glass block.


Using a pan
lubrication technique
to drill a ceramic plate.

Water Swivel mounted
in drill press chuck.

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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 basic clay dam lubrication method (4 rating) should provide a drill bit life of approximately twice 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 very important to use a "pumping" technique described below.  Without the pumping technique, the water will not reach 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 can be 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 is also very important to increase the lubrication at the tip.  Without the pumping technique, the water will not reach the very tip of the drill bit.  The clay can be used many times if it is stored in a plastic zip-lock style bag to keep it from drying out.

For low volume repetitive work, it is also possible to place the material into a pan or plastic tub (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.  The water should cover the side lubrication hole on the tip of the diamond drill bit.

To allow lubrication to reach the drill tip, it is very important to use a "pumping" technique described below.  Without the pumping technique, the water will not reach the very tip of the drill bit even if the bit is under water.

When drilling on vertical surfaces, about the only way to apply water is to use some type of hose or water swivel, discussed below.  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 will not reach the very tip of the drill.

One of the most effective methods and the one used by most professionals is to use a Water Swivel, also know as Water Feed Swivels or a Water Feed System.  A Water Swivel injects water into the center hole of the drill bit shaft while it is drilling.  The Swivel "feeds" water lubrication directly into the center of the bit, the water escapes around the tip and bubbles up around the outside of the hole.  A Water Swivel Lubrication System forces water to the tip of the drill bit and also cools the inside and outside of the bit.  See also our Water Swivel page.

No matter what lubrication method is used, a periodic "pumping" action will significantly improve lubrication at the drill tip.  Because of the pressure on the drill tip, water has trouble reaching the very tip of the drill bit.  A "pumping" technique allows lubrication to reach the very tip.  While drilling, merely raise the drill up and down a fraction of an inch once in a while as you drill (maybe every 20 to 30 seconds).  This assures that water enters the drill tip area completely and fully lubricates the very tip.  Pumping the drill improves lubrication at the tip and will improve drill bit life considerably.

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Diamond Drill Bits - Drill Pressure

When using normal drill bits on soft materials such as wood, increasing the pressure causes the bit to drill faster and has little affect upon friction or heat build-up on the bit.  When drilling in harder materials such as hardwoods, it is more important to reduce the pressure and let the bit "drill at its own speed".  Otherwise, friction will quickly burn up the bit.  When using diamond bits, the affect is similar to hardwood drilling, but it is magnified many times due to the extreme hardness and abrasiveness of the material being drilled.

When using diamond bits on glass, ceramic or porcelain tile, limestone, marble and granite, etc, it is very important to have only light to medium pressure on the drill and to let the bit "drill at its own speed".  Increasing pressure will not speed up the cutting noticeably, but it will increase the friction considerably and quickly cause the bit to overheat.  This not only burns up the bit, but it also heats up the surrounding surface and can cause heat fractures or breakage to occur.

If a drill bit develops yellow, brown, blue or black 'burn marks' around the tip, it is an indication of extreme heat caused by the excessive drill speed or by too much pressure on the drill.  Impact type "hammer drills" should never be used with diamond drills as they have no benefit and will cause the tip of the bit to mushroom or split.

If a hole is being drilled completely through a piece of material, it is also important to "lighten up" considerably on the pressure when the drill bit is near the back of the material.  This reduces chipping, splintering or fracturing on the back of the material when the bit emerges from the back.

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Balancing Cutting Speed,
Drill Speed, Pressure and Lubrication

The cutting speed and life of a diamond drill bit are affected by the hardness and abrasiveness of the material plus the drill speed, pressure and lubrication.  Experience with a specific material quickly allows a person to determine the optimum drill speed, pressure and lubrication to obtain the fastest cutting speed with the least affect upon bit life and risk of heat fractures or breakage.  However, lacking experience, it is best to start out with a very slow drill speed, very low pressure and lots of lubrication.  This starting point reduces risks to a minimum and extends bit life considerably.

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Pilot Bits on a Diamond Core Drill Bit

Pilot bits are often seen on standard metal core drill bits or hole saws designed for use on wood and other soft materials.  A pilot bit is a small drill bit located in the center of the hollow core drill bit, that keeps the bit centered while starting a hole.  Pilot bits are especially convenient when using a core drill bit in a hand drill.  When a pilot bit is not present, a core drill bit may tend to "walk" until it seats into a groove.

However, pilot bits are rarely used on diamond core drill bits since there are many drawbacks of a pilot bit with the diamond core drill bit design and drilling in very hard materials.

A template can easily be used to start a core drill that does not have a pilot bit.  This simple technique is discussed in the following section.

If an optional Center Pilot Bit is used to start the drill bit, it is important to remove the pilot bit as soon as possible after the bit has started drilling. The carbide pilot bits cause the diamond bit to drill very slowly and the pilot bit can wear out quickly when drilling in very hard materials.  Once the diamond bit has begun drilling, the center pilot bit should be removed before drilling the rest of the hole.

Starting template
made from plastic.

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Starting a Core Drill Bit by Using a Template

Core drill bits above 1/2" work best when used in a drill press rather than in a hand drill.  Starting a core drill bit when using a drill press is simple, since the drill press keeps the drill bit from moving about.  To reduce drill bit slippage or "walking" when using a hand drill, a template can be made to help start the drill bit if necessary.

A template is made by drilling a pilot hole in a piece of soft wood or plastic, using the diamond core drill bit or by cutting a "V" in the edge of a piece of wood or plastic or drilling a hole in it the size of the core drill.  The hole template works best, however, the "V" template is easier to make and can be used with many sizes of core drill bits. 

Templates are often made of 1/8" plexiglass, 1/8" pressed wood or even cardboard.  For repetitive drilling, a plastic or plexiglass template works best since water lubrication can be used immediately.  The template is placed on the surface of the material being drilled, with the pilot hole or "V" above the target hole area.  The template will hold the core drill bit in place as it starts.  After just a few revolutions of the drill bit, a groove is created and the template can be removed.

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Depth of Bore

Bonded diamond core drill bits are designed to drill to depths of about 1/2".  We do not recommend drilling in materials beyond that depth.  However, it is often possible to push the bits beyond their design limits by drilling to a depth of about 1/2", then removing the core before drilling deeper.

The core can usually be removed easily on smaller holes by slipping a screwdriver down the drill slot and twisting.  On larger holes, you may need to chip out the center core 'plug' with a chisel before continuing to drill.  Removing the core reduces friction and heat build-up caused by the 'plug' and will usually allow drilling deeper holes if extremely good lubrication is used.

Drilling deep holes with bonded diamond drill bits is generally limited to about 1-1/4" in depth depending upon the specific material being drilled.  Even when removing the core periodically and using very good drilling techniques, the friction still increases considerably and limits deep boring.  For deeper holes, a sintered diamond drill is normally required.  The more expensive sintered bits have diamonds embedded directly into the metal tip and are most appropriate for deep drilling.

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Drilling 'Blind' Holes
with Diamond Tip Drill Bits

Most applications require a person to drill completely through the material, however some applications require drilling a 'blind' hole that does not go completely through the material.  Blind holes are simple with traditional drill bits that drill out the complete hole.  However, solid drill bits are not practical when drilling in extremely hard materials and solid tip diamond bits are rarely made.

A blind hole can be drilled using a hole saw style drill bit by drilling partially through the material and then removing the core or plug.  The core can usually be removed easily on smaller holes by slipping a small screwdriver down the drill slot and twisting.  The core will break off near the bottom of the hole and can be removed.  On larger holes, you may need to chip out the center core 'plug' with a chisel and very large holes may require drilling several smaller holes into the core to allow it to be chipped away and removed.

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Drill Ceramic Tile and Porcelain Tile

Ceramic and Porcelain tile, used on walls, counters and floors, has changed considerably over the years.  Ceramic tile was first developed with a heat-hardened vitrified glass finish on the top surface.  The inside of the Ceramic tile was still relatively soft.  Since the tile was easily scratched, manufacturers developed better manufacturing techniques to make the surface finish much harder.  The newer Ceramic tile now has an extremely hard surface that wears very well and the inside of the tile is also very hard.  While this is a distinct advantage from the stand point of wear, the newer Ceramic tile is often difficult to drill without a diamond drill bit.

Porcelain tile was originally developed as a harder alternative to Ceramic tile, for use in floor applications where usage and wear was more extreme.  Porcelain tile is made with various mixtures of materials, often including feldspar and quartz, which are two of the major components of natural Granite.  The use of Porcelain floor tile was generally limited to commercial applications, but by the late 1980's, Porcelain tile use expanded more into residential construction.

In the 1990's, tile manufacturers began to expand their Porcelain tile product lines to include many different styles and many that closely resembled natural stones.  Because of the natural stone look, Porcelain tile use on walls and counters became more popular.  Finally, in the late 1990's tile manufacturer's experimented with new manufacturing techniques that made the Porcelain tile significantly harder.  As with Ceramic tile, this was a major advancement resulting in reduced wear and very long life. 

Many Porcelain tiles are now as hard as Granite and some are even harder.  The newer type of high-quality, "super-hard", "Class V" Porcelain tile is now almost impossible to drill with the older "spear point" carbide drill bits and generally can only be drilled with a diamond bit.

When drilling in the newer super-hard tile, using a diamond bit is the only reasonable option.  However, even with diamond bits, the drilling process takes considerable time and the extremely hard material is not very forgiving if inappropriate drilling techniques are used.  It is critical that good drilling techniques be used.  Appropriate drill speeds, low drill pressure and good lubrication are critical.

Glass Block
Drilled to insert lights.

Frosted Wine Bottle
Drilled to insert lights.

Using a clay dam
lubrication technique
to drill glass block.

Purple LED lights with
purple wire in block
with bubbles and swirls.

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Drill Glass Bottle - Drill Glass Block

Drilling in glass block or bottles is basically no different than drilling in normal glass.  If you use the appropriate speed, use low drill pressure and plenty of water for lubrication, you won't have any problems.  Glass breakage with carbide bits is fairly common, but with a good diamond bit, it is extremely rare.  There are a few very important facts and tips that will helpful when drilling glass block or bottles.

There are numerous different types and styles of glass block made by many different manufacturers.  Most have some type of design or pattern, however, for drilling purposes, there are two important characteristics to be aware of.  Glass block can vary significantly as to the thickness of the glass wall and some glass block is tempered.  This information is rarely disclosed on the block itself, but should be considered when buying glass block for crafting purposes.

If you are drilling glass block that has been installed in a wall, you don't have much choice but to drill whatever is there.  However, for craft projects, it is good to be selective.  If the glass block is 3/8" thick, it will take three times as long to drill compared to block with a 1/8" thick wall.  Additionally, it will triple the drill bit wear per hole, causing the bit life to be only one-third as long.  Some glass block and bottles are tempered to increase the strength of the glass.  Tempered glass should be avoided if reasonably possible.

Experienced crafters who work with glass block and bottles learn to search for different types and styles to test.  After drilling a sample of each, it is obvious which has a thin wall and if any are tempered.  Also, crafters who are drilling lots of glass blocks or bottles, normally develop some type of "clay dam" or pan drilling method, so that it can be drilled under water to improve lubrication and extend drill bit life. 

The "clay dam" method of lubrication is very effective for drilling in glass block and is simple to use.  Under water pan drilling works best for bottles.  "Pumping" the drill is also very important since even under water, the tip of the bit will go dry after drilling about 1/8" deep.  Water lubrication techniques are discussed in more detail in the Lubrication Tips & Tricks section.

Glass block normally has a vacuum inside.  Some of the water and glass dust will always be sucked inside when the hole breaks through.  However, it is easy to rinse out the inside of the block with water as long as the dirty water inside is not allowed to dry out.  The plug from the hole will sometimes be pulled into the block - it will usually drop out easily when the inside is rinsed.  However, if too much pressure was placed on the drill as the hole breaks through, it can cause the plug to have a flair from the splintering on the rear of the hole.  Normally, you can remove the plug with a pair of needle nose pliers, but the best solution is to reduce the drill pressure when nearing the back of the glass to avoid splintering as the drill breaks through.

A piece of wire from a regular coat hanger or a small wooden dowel work great for inserting into the hole to "push" the lights around inside the block, so that all the corners are filled with lights.

A hand drill works fine using a starting template and a clay dam - for a few glass blocks.  However, an inexpensive drill press is well worth the cost if you are making lots of blocks.  There are many very nice, inexpensive drill presses available these days and they make glass block drilling fast and easy compared to a hand drill.

The most popular diamond drill bit for glass block drilling seems to be the 1/2" size since it is about the right size for light strings.  We prefer a 5/8" sized bit because the slightly larger hole gives a little extra room when inserting the lights or when pushing them around and allows easy remove of the lights if you change your mind or need to change a bulb.

Glass blocks sometimes have a white or cream paint coating around the outside edge to give better adhesion for building mortar or caulk.  Most people remove the paint, but some just hide it under a ribbon.  If the paint is hard to remove, soaking the block in hot water usually softens the paint and allows easy removal with a common kitchen dish scratcher.

Glass blocks come in many sizes, shapes and surface textures.  The ones with a heavy surface textures tend to work best since they diffuse the light and hide the light string wires better. Our research has shown that there are at least 15 different surface textures available (there are probably far more), so a little searching can result in finding some unusual patterns that make very nice light blocks.

Most people seem to use the standard 8"x8"x3" blocks, maybe because they are easily available.  We have found that the smaller 6"x6"x3" blocks and even some of the odd shaped triangular, brick shaped and corner blocks are are also especially nice because of their unique sizes and shapes.  There are no limits to the artistic possibilities, so don't be afraid to try something different.

A hot glue gun with clear glue works very well to attach ribbons and bows, or ribbons can be tied as if you were wrapping a package.   Most people tend to start out with the multi-colored lights then quickly learn that the white and single colored lights are also beautiful.  The non-multi colored lights are especially nice for light blocks that can be used all year round.  Light strings also come with various colored wire, so experiment with the white lights with white wire or the red lights with red wire, etc to see what you like.

Finally, if you ever get a chance to try the "LED" or "Tiny Lights", give them a try - especially the big strings of 60 or 100 (it takes a few more lights because they are so small).  Yes, they cost more, but they create almost no heat and bulbs last nearly forever.  Most importantly, some LED light strings have a light function controller that gives a special random blinking pattern that blinks, twinkles and strobes, etc.  If you can find the type with the light controller, the LED strings with the special lighting affect is really worth the additional cost.  Our experience is that most people who try the LED lights with the controllers rarely go back to the standard bulb lights.

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Drilling Tempered Glass - Not Recommended

Tempered glass can be drilled, however, breakage may run as high as 80% to 90% depending upon the degree of temper in the glass.  We do not recommend trying to drill tempered glass.

The manufacturing process of making tempered glass places the molecules of the glass under stress.  The stress points might look much like a piece of wood containing lots of "knots", however, there is no outward appearance to indicate the hidden stress.  Highly tempered glass will often crack at the stress points near the hole.    Since the amount of hidden stress increases with the degree of temper, the success rate of drilling tempered glass reduces with the increase in glass temper.

When trying to drill highly tempered glass, the diamond drill will take several minutes to drill what would normally take only seconds in regular untempered glass.  Normally, about half-way through the glass, it will suddenly make a very loud "pop" and the glass will crack or shatter into many pieces.  If the glass is very highly tempered, the "pop" may be more like an "explosion" with the glass shattering into many small pieces.

There is no way to know the amount of temper in a piece of tempered glass, so there is no way to evaluate the amount of risk involved in trying to drill it.  Therefore, we DO NOT RECOMMEND attempting to drill tempered glass.

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Drill Glass Aquarium

Aquariums are often drilled to allow for installation of side-entry filter systems rather that standard top-mount systems.  The side-entry systems also provide better flow-through water movement where that is a special factor.  To drill a glass aquarium is not difficult - it is basically the same as drilling normal glass.  However, additional precaution should be taken when drilling aquariums compared to normal glass.

There is always a small risk of causing a break when drilling any glass.  While the risk is extremely small if proper drilling techniques are used, this small risk is always there.  If a break would occur when drilling in regular glass, it is frustrating, but not a major loss.  However, the loss of an aquarium is much more significant, so reasonable care should be taken. 

As additional 'comfort', we offer that the structural integrity of glass increases significantly as it becomes thicker.  So, the small risk of a drilling problem actually reduces significantly as the size (and cost) of the aquarium increases.  Based upon our testing and our customer contact, we offer the following suggestions for aquarium drilling.

Take proper care:  You don't need to be an expert at drilling glass or aquariums.  No matter if it is a 20 gallon tank or 2,000 gallons.  Take your time, use proper drilling speeds, low drill pressure, good water lubrication and follow a few basic cautions relative to aquarium drilling.

Be sure you have the right sized drill bit:  Pipe is measured as an inside diameter.  So 1-1/2" pipe or a 1-1/2" fitting will have an 'inside diameter' of 1-1/2".  However, the outside diameter can vary depending upon the type of pipe or fitting used and the specific manufacturer.  Be sure to measure the outside diameter properly so that you drill the correct size hole.  This may sound rather basic, but we assure you that it is a common mistake.

Avoid drilling in the bottom of the tank:  The bottom of a tank is most often tempered glass, but it is rare for the sides to be tempered.  Also, the water weight on the bottom is significantly greater than on the sides of a tank.  Anytime glass is cut or drilled, micro fractures always occur along the cut, plus a hole reduces the structural strength of the glass.  While tanks are generally "over engineered" to be much stronger than actually needed for their capacity, the bottom is the "weakest link" and should generally be avoided.

Drill at least 1" from the sides of the glass:  All glass contains minor imperfections and flaws.  Micro fractures also occur along the edge of glass when it is cut.  To avoid placing any additional stress on those weak spots, we recommend staying at least 1" away from any glass edge.

Use proper lubrication techniques:  Basic lubrication techniques are discussed above in Lubrication Tips & Techniques <Click Here>.  The best lubrication method for tank drilling is to position the surface horizontally and use a dam made of clay or similar material around the drill area.  The method as discussed in the above section, is very simple and also very effective.  If a large stationary tank is being drilled in the vertical position, use the 'spray method' and take care to get as much of the spray into the drill slot as possible.

Assure adequate lubrication:  While drilling, it helps to raise the drill up and down a fraction of an inch once in a while as you drill (about every minute or so).  This assures that water enters the drill hole completely and fully lubricates the very tip of the bit .  The technique is especially helpful when drilling larger tanks with thick walls.

Ease off when you are nearly through:  As a drill breaks through the back side of any material, it will cause some splintering.  Due to the brittle fragile nature of glass and your desire to retain structural integrity, you want to minimize the splintering.  Merely reduce the drill pressure as you near the back of the glass.  This is one of those rare instances where time is your friend.  If it takes you 3 minutes to drill 3/4 of the way through, back off and use another 3 minutes to go most of the the the remaining 1/4.  The final 1/32" to 1/16" is the most delicate, so again take your time and ease up on the pressure.

If your hole ends up being a little too tight:  You don't want the hole to be any larger than you actually need, but sometimes people cut it a little too close.  Since the pipe fittings are normally plastic, an easy solution is to use fine sand paper to reduce the outside diameter of the fitting slightly.  If your hole is a little too large, the gasket on the fitting normally provides extra room and should provide an adequate seal.

Finally:  Drilling holes in any glass reduces the structural integrity of the glass and reduces the safety levels that were engineered into an aquarium. 

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Diamond Drill Bit Life

The life span of all types of drill bits is affected by the hardness and abrasiveness of the material being drilled, the thickness of the material, plus the speed of the power drill, the amount of pressure used and the use of adequate lubrication.  The hardness and abrasiveness of materials can vary significantly.  Even materials which appear similar have varying degrees of hardness and abrasiveness.  Each individual's drill speed, pressure and amount of lubrication also varies significantly.  As a result it is nearly impossible to estimate the life of a diamond bit.

For example:  On standard 1/8" glass, a bonded diamond bit under 3/4" may last for 200 to 300 holes, or more, depending upon the specific glass and specific drilling techniques used.  Larger bits tend to run about half as long due to a slightly different type of cutting action.  Drilling in 1/4" glass, being twice as thick, will normally produce only half as many holes over a drill bit's life, if the glass hardness and drilling techniques are the same.  Tempered glass has differing degrees of temper, and will reduce drill bit life by 75% to more than 90%, compared to standard glass. 

Lubrication has a significant affect upon drill bit life.  Using a center water feel lubrication device or drilling under water with the water level above the side tip lubrication hole gives the best lubrication and the best drill bit life.  Using a clay type "dam" gives fairly good lubrication but since the water normally does not reach the side tip lubrication hole, the lubrication inside of the bit is much more limited. As a result, using a dam lubrication method will often reduce drill bit life by 25% to 40%.  Finally, spraying or splashing water onto the bit for lubrication works, but lubrication is very limited and drill bit life can easily be reduced by 40% to 60% compared to using a good water bath.

On the extremely hard and abrasive materials, such as granite or the newer "super-hard" porcelain floor tiles, a bonded diamond bit may only produce 6 to 12 holes in 3/8" material.  However, the same bit may produce as many as 20 or more holes, all depending upon the specific material, the thickness and the specific drilling techniques used.  Tests on some of the less hard, class III floor tiles have ranged from 40 to 60 holes or more.  Wall tile is often less hard (but not always).  However, being only about 1/8" to 3/16" thick, the results in wall tile are normally two to three times greater than drilling in the same material that is 3/8" thick, all while using the same drilling techniques.

Sintered diamond bits have the diamonds embedded directly into the metal tip of the bit.  As the tip wears down, new diamonds come to the surface.  Sintered diamond bits are often designed for deep drilling in stone, concrete or masonry, however, the specific manufacturer's recommendations should be be reviewed.  Sintered diamond drills are more expensive and because they are heavy duty, they drill more slowly, but they last longer.  Depending upon the material being drilled and the drilling techniques used, Sintered diamond bits can last 30 to 50 times longer than a bonded diamond bit, sometimes even longer.

These examples are are all based upon extensive testing in different materials using proper drill speeds, drill head pressure, and lubrication.  Test results were much less, using poor drilling techniques, and extreme tests using improper drilling techniques often resulted in a bit "burning up" after only one or two holes.

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