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How To Use Diamond Core Drill Bits,Drill glass, ceramic, porcelain, wall tile, floor tile, limestone, marble, slate, granite, stone, tile & fiberglass

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.

Material
Wood - Pine
Copper
Limestone
Marble
Slate
Porcelain Fixtures & China
Glass & Ceramic
Ceramic/Porcelain Wall Tile
Marble Style Floor Tile
Granite Style Floor Tile
Granite
Quartz
Tungsten Carbide
Diamond

Knoop
Hardness Scale
10
120
125 - 150
140 - 180
140 - 250
400 - 500
450 - 600
450 - 650
500 - 650
500 - 650
550 - 650
820
2,100
7,000

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.

Recommended Drill Speeds

Diamond Core Drill Bits

Recommended Drill Speed (rpm)

Material         Bit Size -->

1/2"

1"

2"

3"

4"

Fiberglass

1200

700

350

250

175

Limestone & Marble Stone

900

550

275

180

140

Glass, Ceramic & Porcelain China

800

500

250

160

125

Ceramic/Porcelain Wall Tile

600

450

225

130

100

Stone Style Porcelain Floor Tile

500

375

180

125

90

Granite Stone

400

300

150

100

750

(Not for use on Concrete or Masonry, or with Hammer Drills)

SPEED KILLS:

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

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.

Lubrication

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).

Drill Bit
Lubrication Method
Squirt Bottle
Hose
Clay Dam
Under Water
Water Feed
Pumping Action

Rating
(1 poor - 10 good)
2
4
8
10
10
10

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.

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 or so).  This assures that water enters the drill tip area completely and fully lubricates the very tip

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 drill 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 drills 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.

Recommended Drill Head Pressure

Diamond Core Drill Bits

Material

Recommended Drill Head
Pressure (lbs.) *

Fiberglass

10 to 15 lbs.

Limestone & Marble Stone

12 to 18 lbs.

Glass, Ceramic & Porcelain China

12 to 18 lbs.

Ceramic/Porcelain Wall Tile

15 to 20 lbs.

Stone Style Porcelain Floor Tile

18 to 30 lbs.

Granite Stone

18 to 30 lbs.

* WARNING:

Drill press arms leverage hand pressure by a factor of about
6 to 8.  So 2 lbs. of hand pressure on the drill press arm will apply about 14 lbs of pressure to the drill head.

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 or fracturing on the back of the material when the bit emerges from the back

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, when experience is lacking, 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

Pilot Bits on Core Drills

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 diamond pilot bit adds significant cost to the already expensive diamond core drill bits.
• The diamond pilot bit often wears out before the main core bit.
• Drilling times can be considerable when drilling in very hard materials and a pilot bit increases the drilling time even more.
• A pilot bit eliminates the shaft water-feed lubrication hole and does not allow the use of center water-feed equipment.

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.

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 ther 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.

Depth of Bore

Bonded diamond core drill bits are designed to drill to depths of about 1/2".  When drilling with core drills in material over 1/2" thick (such as slab marble or stone), it is generally best to drill to a depth of about 1/2", then carefully chip out the center 'plug' with a chisel or screwdriver before continuing to drill.  This process reduces friction and heat build-up caused by the 'plug' and will actually reduce the cutting time and increase the life of the bit.

When drilling large diameter holes (say 2" wide and larger) in some hard materials such as marble or granite, it is sometimes difficult to break-out the plug without drilling several smaller holes into the plug so that it can be removed in sections.

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

Ceramic and Porcelain Tile

1. 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 an 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.  However, 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 drill bit.

When drilling in the newer super-hard tile, using a diamond drill bit is the only reasonable option.  However, even with a diamond drill bit, 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 Drilling

Drilling in glass block is basically no different than drilling in normal glass.  If you keep the speed down, use low drill pressure and plenty of water for lubrication, you won't have any problems.  However, there are a few very important facts and tips that will help people in their task.

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 very important characteristics to be aware.  Glass block varies significantly in the thickness of the glass wall and also by how tempered the glass is.  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 very 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.

Tempered glass is sometimes used in glass block to increase the load bearing capability of the block.  Tempered glass has differing degrees of temper, and while it can be drilled, it should be avoided if reasonably possible.  Tempered glass block can increase drilling times by 200% to 500% or even more, when compared to standard untempered glass.  Additionally, depending upon the degree of glass temper, drill bit life can be reduced by 75% to as much as 90%.

Experienced crafters who work with glass block eventually learn to search for different types and styles of glass block to test.  After drilling a sample of each block, it is obvious which block has a thin wall and which block is untempered.  Also, crafters who are drilling lots of glass blocks, normally develop some type of pan drilling method, so that the block can be drilled under water to improve lubrication and extend drill bit life.  The "clay dam" method of lubrication is also very effective for drilling in glass block.  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 you break through.  But, it is easy to rinse out the inside of the block with water as long as the dirty water is not allowed to dry out.  The plug from the hole will sometimes be pulled into the block, but 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 to avoid splintering as the drill breaks through.

A Few Final Glass Block Tips

A piece of wire from a regular coat hanger works 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.

A 1/2" diamond core drill bit works well, is about the right size and seems to be the most popular size for glass block drilling.  However, we prefer a 5/8" bit, since the slightly larger hole gives a little extra room when inserting the lights, pushing them around or to easily remove them if you change your mind (or need to change a bulb).

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, last nearly forever and most importantly - they usually have a "special" random blinking pattern that blinks & twinkles & strobes, etc.  The special lighting affect is really worth the additional cost.

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, an electroplated 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.

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

About the Author

A Tender Record: Marjory Wilkins, Early Black & White photographs
Opening reception A TENDER RECORD Marjory Wilkins, Early Black & White photographs, 6-8pm The show is free and opens Saturday May 1 Exhibit runs thru May 27,

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