Cutting from Cartoon

The cutting of glass directly over the cartoon without patterns is variously called trace cutting, English or European method. The advantages include a more direct process with fewer operations, making for less chance of inaccuracies.  These make this method quicker than using patterns or templates to draw or cut around. The disadvantages are that you still need to make patterns for opalescent or very dark glass, and there is no pattern to guide any grinding required.

To employ the method, use a strong contrast ink for drawing the lines of the cartoon. Draw these in the appropriate width - for copper foil (ca. 0.8mm).  This can be accomplished with a ball point pen or fine felt tip.  For lead, a thicker line (ca. 1.6mm) is required - a bullet tipped felt pen is usually appropriate, if it is not worn.

leadlightdesign.com

To cut, place the glass over the appropriate part of the cartoon and cut at the inside edge of the line. It is best to cut and break one line at a time.  Re-set the newly cut edge along the cutline and score the next line.  Break it and repeat the number of times required to cut out the whole shape.  Which line should be the first to be scored and broken is described here. 

Although the glass is normally only three millimetres thick, there is some possibility of a refraction of the light if you look from the side of the cutter.  As described elsewhere, you should be holding your cutter upright in the left to right plane and angled slightly back toward you so that you can look with your dominant eye along the barrel of the cutter and head.  This ensures you are directly above the cut line and do not have any refraction caused by the glass. 

Translucent glass may, and opalescent glass will, need a light box to assist in the scoring.  This increases the light coming through the cartoon and glass to enable a sharp image of the lines to be seen.  This means that if you intend using opalescent glass, your cartoon should be done on translucent paper to allow the maximum light through.

freepatternsforstainedglass.com

For black, dense and strongly opalescent glass, pattern pieces will need to be cut, as the insufficient light will pass through the glass to be able to see the cartoon accurately.

The reduction in the number of operations to guide the cutting of the glass also reduces the occasions for small errors to creep in.  It does increase the accuracy of cutting and speed of building a panel.

The Effect of Glass Temperature on Cutting

There are many opinions on how glass cuts when cold.  Some report cutting outdoors in sub-freezing temperatures, others that only warm glass cuts well.  I decided to see what scientific information there may be on this idea.

The Science

The scientific literature mostly concentrates on the effects at higher temperatures than we are concerned with.  However, there are some things that are applicable, and some of these effects of temperature are outlined below.

·         High humidity results in loss of strength. 

·         The strength of glass is reduced by 25% at 100°C compared to 0°C.

·         Glass needs several days to be at an even temperature throughout.

·         Variance in temperature across the glass causes unwanted breakages.

·         Colder glass becomes more brittle due to loss of elasticity.

·         Hardness of glass increases with decreasing temperature.

The terms of strength, hardness and brittleness have scientific definitions that are hard to apply to the everyday glass cutting that we do.  Strength may or may not have applicability to glass cutting.  Elasticity may or may not be an important factor in cutting.  Surface hardness may play a part in cutting while cold.

Applicability of the Science

However some things seem to apply. 

High humidity results in loss of strength.  This may be a factor in low temperature cutting.  The humidity in a relatively closed environment increases with the reduction in temperature.  Breaking glass is about the creation of a weakness in the glass along the score line.  In so far as strength is a factor in the break running along the score line, this may be an element in cold glass cutting.  If the whole glass is weaker, the difference in strength at the score line is less and so promotes unwanted breaks.

Variance of the temperature of the glass throughout the substance of the glass promotes unwanted breakages.  Perhaps the cold glass that is difficult to cut is not equally cold throughout.  Certainly a number of people report that they store their large glass outdoors and can still score and break the glass during the winter perfectly well before bringing it into the studio. 

Glass becomes more brittle with decreasing temperature, and it also becomes harder.  Perhaps these two elements are a factor in controlling breakages.  If the glass is both harder and more brittle, a different scoring method is required. 

The way in which glass at any temperature breaks is related to the force of the score, the speed of the score and the angle of the cutting wheel.  If the glass is both harder (at the surface) and more brittle it requires less scoring force or a blunter wheel angle.  The more blunt the wheel on a thicker (i.e. stronger) glass, the more vertical the stress lines are created in the glass.  So in a cold and harder glass, a blunter wheel angle seems appropriate, even though the glass is not thicker.

It is not usual for people to have cutting wheels of different angles, so an easier, although more skilled, approach is to reduce the scoring force in cold conditions.  Reducing the force in scoring a hard and brittle glass causes the stress lines to be more vertical than increased forces do.  Increased forces cause lateral lines of stress to be created, leading to unwanted breakages.

Secondly, the glass being more brittle, less force in breaking stress is required.  As the glass becomes colder, the less elastic it is.  This elasticity is an important element in breaking the glass at room temperatures. The score needs to be run gently to counteract the loss of elasticity and the consequent increase in the brittle strength of the glass.

Conclusions

My conclusion, after the reading I’ve done, is that cold glass becomes slightly stronger and more brittle than room temperature glass, and so requires a slightly different method of cutting. This difference is to reduce the pressure of scoring and the force of breaking (applying stress to the glass).  

Of course you can warm the glass up before scoring it, but the research seems to indicate that significantly long times are required to equalise the temperature throughout.

Cutting Fused Glass

The same principles of glass cutting are applied to fused glass as to the glass used to make the fused piece.  The differences relate to thickness and variations in thickness.

You still score on the smooth side.  More pressure is not required.  For glass thicker than 6mm, you may wish to use a wheel with a more blunt angle. as shown in this illustration.

www.oaklanddiamondtools.com

The main reason that people may feel it is difficult to cut fused glass relates to the additional thickness.  Just as breaking 4mm glass requires more force than 2mm, breaking a 6mm piece requires more force than a 3mm piece.  

floridastainedglass.net

Properly adjusted metal cut running pliers can do the job, but a cut runner designed for thicker glass can be a boon.  They are designed to provide greater leverage and so more force to the glass breaking.  With these the glass breaks along the score line cleanly.

www.glass-tool.com

The breaking of glass that is uneven in surface levels, as in tack fused pieces, can be more difficult.  One is that running the cutter over glass with distinctly different thicknesses can be difficult.  Maintaining consistent pressure and speed over the bumps of the tack fused pieces is difficult.  The second is that the running of the score will not always follow the score line.  For example, if the score line runs close to the edge of a thick piece, the break is likely to skirt around the thick piece, and possibly off to the edge of the piece, rather than continuing to follow the score line. Planning the score line on tack fused glass is important to avoid trying to break near the edges of thick pieces.

One possibility is to score the glass on the shelf side.  This is certainly possible, even though the surface is rougher.  It does avoid scoring across different levels and makes the break along the score line more probable.

Score coated glass on the back - Kiln Forming Myths 16

Cut iridised glass on the back

The idea seems to be to get a more even score and avoid chipping of the iridised surface.

First, the iridised surface is almost microscopic in thickness.  It is put onto the surface as a mist of metallic oxides as it begins its run through the annealing lehr.  This thickness will not affect your scoring.

The back is usually rougher side of the glass and so will be more difficult to get a smooth, even score than the front iridised surface.

Chipping of the iridised surface is caused by too much pressure during the scoring.  Reduce your pressure and review your scoring practice.

Scoring the iridised surface with appropriate pressure will produce a clean break without chipping the surface.  These comments apply to dichroic and flashed glass too.

How Much Glass to Buy

Of course the answer is that you can never buy too much as you will use it for something later.  Still, economics comes into play sometimes and you need to consider how much glass is enough for a given project.

I find that the larger the pieces in the project, the more glass I need.  There is greater wastage with large pieces than in a project with many small pieces.  I always cut my large pieces first, as this leaves cullet for smaller pieces, thus reducing the wastage.

If you are using glass that has a definite pattern or flow to it, you need to plan on a greater wastage factor than if you are using plain glass or textured glass with no particular direction.

The stage you are at in your cutting will also have an effect on how much glass you need.  At earlier stages you will have more unexpected breaks than later on, so take that into account too.

Some people report that they can manage with one third more area than their project, others one half more.  I find that I usually need twice the area to have enough glass to complete the project.

Cutting thin strips

Cutting thin strips of glass such as used in Mission Style patterns and precision fusing projects requires skill and assistance. For transparent and translucent glass you can arrange a right angle guide on a board and tape a piece of lined notepaper to the jig. Use a cutting square and move it right along the lines on the note paper making four or six scores at a time and then breaking on the last score first and then every other score, and then each one in half.

Another method is to use the edge of the bench as a guide. With a small adjustable carpenter’s square, you hammer in nails at the predetermined width (plus half the thickness of the cutter head). Align the glass to the edge of the bench between the nails. Place a straight edge against the nails and score. This gives strips of the same width every time, but works best with strips of 10mm (3/8”) or more. This is illustrated in the processes section.

The thinner the strips are to be cut, the more important it is to make the scores and then divide the sheet in half - the two halves in half each - the 4 quarters in to halves, etc, until you are down to the piece that only needs to be divided in two.

The thinnest strip that can be cut is a fraction wider than the thickness of the glass.  This is because the glass will always break toward the weakest area.  If the strip is thinner than the glass is thick, it will break within the strip.  The narrowest strip that can practically be cut is at least one or two millimetre wider than the glass is thick.  So, if you have 3mm glass, the narrowest you can cut is 4 or 5 mm.  Four millimetre wide strips can only be cut from really smooth consistent thickness of glass sheets.  It is much more practical with decorative glass to limit the width to twice the thickness of the glass you are cutting.

Cutting thick glass

Use the correct angle of cutter wheel for the thickness. 

Use a similar pressure to cutting 3 or 6 mm glass. It is natural to think that as the glass is thicker, you need to use more pressure. The different angle of the cutter wheel is designed to transfer the standard pressure more directly downward.

Use cut runners made for thick glass to help break the glass. Run score from both ends of the score, especially on curved scores.

Example of cut runners for thick glass

Alternatively, turn the over and use hammer and rounded screw driver to run the score (similar to tapping method for thinner glass). Place the screw driver blade directly over the score line and tap it with a hammer. This will start the run. Continue it by placing the screw driver over the score at the end of the open score and tap again to continue the run.

Orientation of Cutter Heads

In addition to the alignment of the cutter, you need to be sure you are moving the cutter forward in the way it was designed. If you look at the cutter from the side you will see two things. The most obvious one is that the angles of the cutaway on the head are shallower at the front and steeper at the back. In addition if you look carefully, the axel for the wheel is slightly forward of the centre line of the whole cutter.

Cutters aligned to score to the left

So it does not matter where the fixing screw on the head is. It may be at the front or at the back. What matters is the cutaway at the back which allows the cutter to be used with a shallower angle, than if reversed. This is most obvious on wide cutter heads.

Cutters arranged to score to the right

Repair of a Plastic Barrel Cutter

Generally, there are two parts that can break or be damaged – the wheel and the barrel.

Wheel

If the wheel is damaged or worn, you can replace the head. When considering that, look at the cost of the head and consider whether the small cost difference indicates you should buy a new cutter instead.

The most common damage is a flat spot on the wheel. You can check for this, immediately after dropping the cutter, by lightly moving the cutter across a smooth piece of glass. If you hear a regular ticking sound, the wheel is probably “flat spotted” and will need to be replaced.

A worn wheel is more difficult to detect and is also much less likely to occur. I have been using some of my cutters for 15 years without any sign of being worn.

Plastic barrel

Sometimes the plastic barrel cracks or breaks. This will mean that the oil in the cutter will leak out. So you can consider continuing to use the cutter without oil, or by dipping the head in an oil soaked bit of cotton wool or similar material before each cut.

If the break is at the threaded end and you want to continue to use the ball at the end for tapping purposes, you can glue the barrel back together with an epoxy resin. Make sure the pieces are free from oil. Then glue and allow to cure. After curing, sand down any excess resin to make the cutter comfortable to handle.

Then for additional strength you can wrap with dental floss or extremely fine wire. Start below the glued area and go to the end of the break and back again. You could coat this wrapping with epoxy again both to secure the wrapping and to further increase the strength.

Another solution is to cut the cracked end off and re-thread the remainder. It makes the cutter a little shorter, but will continue to hold oil and give good service.

Or, you could buy another cutter.

Space In Copper Foiled Projects

When cutting for copper foil projects it is important to leave a small gap between the pieces. This is both to allow for the thickness of the foil and for the solder to form a bridge to the other side of the panel.

I prepare the space in the cutting process by scoring at the edge of the pencil thin cartoon line. This leaves the thickness of the line between the pieces. I do not use pattern pieces unless I am using very dense opalescent glass. When I do use pattern pieces I cut them out with a scalpel knife so there is no space between the pattern pieces. I then draw around the pattern pieces and cut to the inside edge of the drawn lines. This also gives a margin for the foil.

Fitting the pieces is still required though. Some people foil one piece and then fit the next to it before foiling it. This is probably the most accurate way of getting a close fit. However, I save up my cut pieces which I have fitted to the cartoon and foil them while watching TV. My cutting and fitting is normally accurate enough that I do not have to take the foil off pieces, grind and re-foil.

While doing this fitting you need to be aware that an additional small gap between pieces is required to allow the solder to join both the front and back of the panel. This forms an “I” beam for strength. The adhesive of the foil is not enough to make a lasting and strong panel. The solder joining the two sides will give the panel the strength to last for a long time.

Cutting Small Diameter Circles

It is possible to cut regular, small diameter circles without buying a lens cutter. It can be done with the assistance of a Lazy Susan or cake decorating turntable.

Draw the circle of appropriate diameter on the turntable with a compass. Place the glass on top of the turntable, and position your cutter above the drawn circle. Press on the cutter with one hand and rotate the turntable with the glass on it, with the other.

Steady your hand with the cutter by keeping your elbow tight against your side. This enables you to make a very good, if not perfect, circle without buying an expensive small circle cutter.

If the glass is too dark or opalescent to see the line, make a template and put it onto the glass. Cut beside the template or use the template to mark the glass. Then place the marked glass on to the turntable and cut as with transparent glass.

You will not be able to run the score by turning the glass upside down and pressing as you can with larger circles. You will need to make a number of relieving cuts to the tangent of the circle and break them away one by one. Yes, this does leave a rough edge at various places around the circle, so grozing or grinding will be necessary.

Starting

“Where should I start cutting the glass from the inside or outside of the cartoon?”

Once the colour selections are made, you can start the cutting in what ever order suits you. Some cut colour by colour. Others cut the glass in the order that fits together. This usually means the main image is cut first and the pieces laid up on a glass easel to determine their interactions. When satisfied, the background or in-fill pieces are cut and fitted.

“Where should I start building a panel?”

When starting the assembly, begin at a lower corner. Whether left or right will depend on whether you are right or left handed and the way the panel fits together. Although sometimes it can be easiest to build from the top toward the bottom. Starting in a corner, together with battens or supports for the outer edge  will keep everything in place as you work.

When working on an oval or circle, you can use a multiplicity of nails around the outside edge to hold the glass pieces. An alternative is to cut the curve into a piece or pieces of float glass and fix this to the work board to hold the glass. If you do this use the outside of the cutline so that there is space for the heart of the perimeter lead.

Cut Running Pliers

Cut running pliers are intended to assist with the running of long straight or gently curving scores.  Sometimes they are referred to simply as running pliers.

There are a wide variety of these made for different purposes.  The following are illustrations of some of the styles.

This plastic cut runner is an economy version of the metal one below

 To use these cut runners, you align the raised line on pliers with the line of the score and squeeze gently.  The single line on the bottom jaw acts a fulcrum, allowing the two raised parts on the upper jaw to provide pressure to the score and run the break along the score line.

Metal cut running pliers

The metal cut runners are pliers with curved jaws. When looking at the pliers from the nose toward the handles you will see the curve like a down turned mouth. These assist the breaking of the score by putting tension on the glass.

Cut running pliers almost always are supplied with covered jaws. This are normally two pockets of flexible plastic that fit snugly onto the slightly flared, curved jaws. Keep these on. When worn they can be replaced by buying more, or by wrapping the jaws with tape using "liquid plastic" or sometimes even using them bare.

There is a spacing screw on top which allows adjustment for different thickness of glass. It is intended that the jaws should not close completely – which can place excessive pressure on the glass – but be adjusted so that there is about 1mm less opening than the thickness of the glass. So when cutting 3mm glass there would be a 2 mm gap. On 4 mm glass the gap would be 3 mm, and so on. experience will show what relationship is best for you. The principle is that the pliers perform a gentle tensioning of the glass. Using your hands exerts more tension on the glass and cannot be so delicate.

Use

Align the centre of the top of the jaws - often the pliers have a centre line on the top to assist – along the direction of the score. Squeeze gently and the score will begin to run.

I have found my best success when using cut running pliers is to avoid trying to run the whole score from one end. With a bit of practice you get the feel for how much pressure you should be applying and so when to stop. Then turn the glass around and start the run from the other end. Usually the open ends of the score will meet and the break is completed. Occasionally the two runs will not meet. Then it depends on how complicated the curve is as to whether you use your hands to complete the break or start tapping the score line to finish the break.


More that one tool

There is a second variety of cut running pliers designed to run long scores near the edge of the glass.  These can be used in the same way as the cut runners pictured above.

The Ring Star cut runners

These cut runners made from plastic have a pad with a central raised point on the bottom jaw and a circular pad on the top jaw.  Placing the point directly under the score line will begin running the score.

 A more durable, but also more expensive version is the Silberschnitt cut runner.

Moveable pad oriented to run scores in line with the pliers orientation

The advantage of these is that the upper pad can be rotated to accommodate any angle, allowing shallow curves to be broken out.  If progressively deeper curves are scored, this too can assist in breaking out deep inside curves.

Pad oriented at about 60 degrees for running score at an angle to the plier's orientation

This allows a score to be run gently over a long distance. This is especially advantageous when the score is a curving one.  

Use
The upper pad is rotated so that it is at a right angle to the score.  The lower pad has a point to act as the  pressure point when the pliers are squeezed.  As you move along the score, you continue to adjust the upper pad to maintain a right angle to the score.  This is a much more gentle breaking action than the standard cut runners and runs the score in shorter distances.  However these short runs make it more certain to run the score successfully. 

Tools for Thick Glass

There are a variety of tools for breaking thick glass - usually 6mm and thicker.  Some examples are illustrated.

Note: these running pliers are pictured upside down.  The two plastic pads should be on the top of the glass.

These are used in the following fashion:

Adjusting cut running pliers for different thicknesses of glass.

Light Box

Light boxes are in many ways a development from the glass easel. These were used in studios to wax up the painted glass and display it as it would be seen in a window. Sometimes the glass painters painted across all the glass at once, so this method enabled them to see the results immediately.

Nowadays people tend to use back lighting for these and other purposes, so the light box has become more popular. Some of the uses are outlined here:

The light box is very useful when tracing or altering designs. The back lighting enables you to use other paper than tracing papers to transfer the design elements. You can fold the paper along the lines of symmetry to check on how the lines match, or to copy the lines from one side onto the other side at the designing and cartoon stages.

The light box can help select glass colours either initially or when the main pieces have already been established. The combination of the glass over light shows how they interact with each other. At later stages when the main glass is cut, it can help avoid unwanted bright or dull areas.

Possibly the most common use is in cutting dark or opalescent glass. The additional light allows you to see the cartoon through the glass and so cut directly from the cartoon. This can be enhanced by blanking out the excess light from around the glass or cartoon.

The light box enables the arrangement of the cut glass pieces to be assembled to view the colour balance and have a virtual view of how the panel or window will look as a finished piece. An additional step toward the result is gained if each piece is outlined in white-board markers – use black pens - to represent the lead or copper foil and their widths. This stops the light between the pieces from causing you pupils to contract, and gives a more accurate representation of the appearance of the final pane.  White-board markers can just be wiped off the glass without using spirits.

The light box is important in painting. The back lighting shows the effect of the painted line or level of shading immediately. This allows adjustments to be made quickly and accurately before firing,

Depending on how the light box is built, it also can be used as display lighting. This can be as up-lighting or backlighting.

Additional notes:
Light box requirements
Flexibility
Top surfaces
Lighting

Scoring Glass

Cutting glass is done by “scoring” the surface of the glass with a glass cutter, then breaking it along the score line. The break you make will always follow the path of least resistance, so you want to be sure that the score you make becomes that easy path and glass breaks the way you want it to.

Holding the Cutter
Generally, you use the cutter by moving it away from you, so you can see the cartoon lines as you score. When using a straight edge such as a cork-backed ruler to guide your cutter, you can pull the cutter toward you, or push it away as suits you. The cutter should always be held at a 90 degree angle (left to right). You can determine this by looking down the cutter to the wheel and to the cartoon line below.

It is important that the work be done from the forearm rather than the fingers or the wrist. The forearm should be held closely to the body. This reduces the freedom of movement, giving clean flowing score lines. It also reduces the actions that can lead to repetitive stress injuries. Any turning required by tight curves can be done by turning the body from the hips or shuffling around the bench with the glass at a corner.  Of course, for long cuts your arm will have to extend from you body in a parallel direction with the score line.

Scoring Pressure
The second and very important element in scoring glass is the amount of pressure used.  Very little pressure is required.  You should hear no more than a quiet hiss on transparent glass and almost no sound on opalescent glass.  However some manufacturer's transparent glass has almost no sound either.  So the important element is the pressure, not the sound.   Most people start with applying far too much pressure. Tests have shown that only about 2 kg of pressure is required for a clean score.

You can test the effect of this amount of pressure on a bathroom scale.  Place a piece of clear glass on the scale and without touching the glass with your other hand, score it noticing how much weight is being recorded.  Keep trying until you are at the 2 kg area of pressure.  Try breaking the glass.  Score a curve with the original amount of pressure and break the glass.  Then using the same curve score the glass with the 2 kg pressure and break the glass.  You will see and feel the lesser pressure provides a clean break.

Excessive pressure leads to breaks showing significant stress marks on the edge of the glass.  Too little pressure has no effect on the glass, making it impossible to break along the score line.  The correct pressure (ca. 2 kg.) leads to almost vertical stresses being put into the glass which assists the breaking along the score line.  Too heavy pressure creates stress marks which are at increasingly large angles with the increasing pressure.  This will still break cleanly on straight lines, but when working around curves the glass can follow one of the lateral stress marks away from the score line.  Excessive pressure is often the cause of glass breaking away from the score line on a curve, especially a tight one.

Scoring Opalescent Glass

Cutting opalescent glass often gives difficulties in getting clean breaks along the score line. You need to remember that the opals do not make much if any sound when cut with the correct pressure. If you are scoring so that you hear the ziiip sound, you probably are pressing too hard. When the score is too hard, the opals do not break easily or truly. Only the same pressure as used on transparents is required. Feel the pressure rather than listen for the sound.

Cutting Flashed Glass

Some recommend cutting flashed glass on the clear or non-flashed side. This is based on the idea that the flash is only laminated to the main body of glass. My view is that flashed glass has proved to be very stable over many centuries, and so is firmly a part of the whole sheet.

What is more important is to observe that flashed glass often has a bow. If you place the glass on the bench, you may find that it rocks or sits up from the bench. If you cut the glass on the convex side, that is the side which is not resting on the bench except at the edges, you may find that you break the glass during the scoring, unless you are using the lightest of pressures. It is more certain to get a good break if you score the glass on the concave side - that is where the edges are slightly raised from the bench. So the important element in deciding which side to cut is to score the concave side whether that has the flashed colour or not.

This does not occur with all flashed glasses, and is more important on large sheets than small ones. On the small ones, the curvature is so small as to be immaterial.

Cutting Bottles

Cutting bottles seems to have a fascination for many people. There seem to be three methods – heat and cold, scoring, sawing.

There are various ways to apply heat and cold to assist with breaking the bottles.

- A string tied around the bottle and soaked in a flammable liquid is a common way to apply heat. As soon as the flame has gone out, you immerse the bottle in cold water; the temperature differential should crack the glass where the string was.

- Filling the bottle with water to the level where the break is wanted and then applying gentle heat with a torch flame at that level should promote a crack.

- Alternatively, the bottle can be scored and put into the freezer for a while and then into hot water.

Scoring is the common method to start a crack.

- This is followed by tapping from inside the bottle with tools from a purchased kit or home-made tappers – a metal ball on the end of a curved piece of metal.

- The score line can also be the preliminary step in the application of heat or cold.

These provide the cleanest edges to the cuts. However there is quite a high failure rate using these methods.

Sawing is method that provides a higher success rate, but is wet, and leaves rough edges to the cut, requiring further cold work.

- Band saws designed for glass can be used, but usually do not have a high enough throat to allow the thickness of the bottle to pass through.

- Most tile saws cut from underneath, so rotating the bottle can lead to a cut completely around. This requires a lot of skill to do free hand, so you need a jig to keep the bottle at right angles to the blade and the bottom the same distance from the blade while rotating the bottle all the way around.

Preventing Chipping When Using a Tile Saw to Cut Glass

One of the most common problems in using a tile saw to cut glass is the tendency for the saw to chip the edge of the glass as it completes the cut. This occurs when the blade of the saw has less glass to cut through. Excessive and uneven pressure and the lack of support cause this break-out.

It's possible to improve the quality of the cut by slowing down and pushing the glass through the blade more gently, but this seldom solves the problem completely. Pushing equally on both sides of the cut is also important to minimise the break-out.

One solution that does work is to provide support for the end of the bar. This adopts a woodworking method for preventing splintering at the ends of cuts.
Use a scrap length of pattern bar or other thick glass. Place it against the glass being cut. As the blade emerges from the glass being cut, hold the two pieces firmly together and continue cutting. The blade should immediately engage the second piece of glass. Once the saw blade entirely clears the first piece, you can turn off the saw and remove a chip-free slice from the pattern bar.

You'll need to trim off the ends of the scrap piece from time to time, but you can use the scrap over and over until it becomes too small to do the job.

This works best with a tile saw where the blade is below the cutting surface. When you use an overhead saw, the breakout is much rarer.

Drilling Glass, 2

Using a Drill Press

It is best to have a drill press if you are doing a lot of drilling. It provides a stable drilling action and the pressure on the bit can be controlled.  It is important to ensure the bit is running true without wobble. The drill press should have instructions to help correct any untrue running of the chuck.  Make sure the drill bit is secured firmly.  Core drill bits are easier to keep true, as they normally have a threaded fixing.

With a drill press, you can drill continually until the hole is completed, or until a white paste or dust begins to appear. This indicates the drilling is being done dry and will in a few moments heat up the glass too much. When the white paste appears, back out of the bottom of the hole a little to allow water to flush the glass out. Then continue.

Keep a firm grip on the glass being drilled. Maintain its position, especially if you are intending to back off intermittently to allow water to the bottom of the hole. This enables you to get back into the hole without scratches.

If possible, submerge the piece. But if that isn’t possible, just squeeze a little puddle of water on the surface and watch it swirl around. You can see if it is pulling ground glass out of the hole by watching the circulation. Placing a plasticine or clay dam around the drill area will keep the water confined.

Don't push down any harder than you comfortably can with the tips of your fingers. Keep it steady. Listen for the sound of diamond grinding glass

If the core gets stuck in the bit, knock it out with some stiff wire or a nail. Always remove each core right after drilling. They are very difficult to remove if there is more than one in there.

Every diameter drill bit has an optimum drill speed. The smaller they are the faster the speed required. Based on what the manufacturers recommend, a Dremel running at top speed is way too fast. When using a Dremel for drilling glass, slow it down with the speed control. Drill presses do tend to be on the slow side for glass drilling so it takes a bit longer, but there are big advantages in other respects.

For other tips on glass drilling see:

Keeping things wet
Using a drill press
Drilling with a Flushing Head
Avoiding chipping
Drilling holes with copper tube and grit
Drilling tools
Drilling glass without a drill press
Hole Placement
Drilling speeds for diamond bits in glass