Adjusting Cut Running Pliers

Typical cut running pliers

Cut running pliers are very useful tools if used correctly.  The pliers must have the curve in a “frown” rather than a “smile” to operate properly.  The knurled screw at the top and the scored line on the top jaw help place the pliers the right way up. They must be placed directly in line with the score. They should be only a centimetre or so onto the glass.  Holding them at the end of the handles, apply gently increasing pressure until you hear a click or see the score running.  If it does not run completely, turn the glass around and apply the pliers to the other end of the score.

Use of the Adjustment Screw

It is important to make use of the adjustment screw to get the best from the pliers.  If this is not adjusted properly, it is possible to crush the glass, or at the other extreme, not run the score at all.

The jaws need to be adjusted for the thickness of the glass.  The method I use for this is to place the edge of the runners on a corner of the glass to be scored.  

Loosen the screw until the glass is gripped by the jaws.  

Gradually tighten the screw until it resists your gentle pressure on the handles.  This gives you the correct opening of the jaws for that piece of glass.

When the pliers are properly adjusted to the thickness of the glass, you will not crush the glass and it is easy to use the pliers without cushions.

Breaking Apart the Last Two Thin Strips

For multiple thin strips of even widths, score all the strips first. Then break all the scored strips off the remaining sheet as one piece. Start the breaking process by breaking the scored sheet in the middle, then in the middle again, until there are only two to break apart.

Cut running pliers are most useful until the last two thin strips are to be divided.

At that point use two breaking pliers to hold each side of the two pieces of glass. The noses of the pliers should almost touch on either side of the score line. Apply pressure in a downward pivoting motion to break the pieces apart.

Breaking Tapering Pieces

Breaking thin pieces of glass can be tricky, but there are a few things you can do to help direct the break the way you want it to go.

Relieving scores made alongside curved and tapering pieces make the breaking more certain. A relieving score is one that is in addition to the primary score. This additional score will allow you to break the thin or tapering piece from the larger sheet safely, and then go on to break out the delicate piece.

The object is to always be breaking away less glass than is retained. The use of two breaking/grozing pliers, one on each side of the narrow pieces gives more even pressure than fingers or cut running pliers with wide jaws.

When breaking tapering pieces of glass you should normally grasp the thin end in fingers or pliers and run the score toward the  thick end and ease the run of the score. When the score opens an initial distance, turn the glass end for end and run the score back to the opened one. 

Breaking Pieces from Large Sheets

Breaking a piece of glass from a large sheet is often a frightening prospect. It doesn't have to be. It is better to cut a straight line piece from your larger sheet than it is to try to cut a curve. This describes a straight line cut from a large sheet of glass.

Use a cutting square or other non-slip straight edge to guide the cutter. You can push as in normal stained glass cutting, or you can draw the cutter toward you as glaziers do. In either case, the pressure needs to be even and the speed consistent.

When moving large scored sheets, avoid pulling the sheet by one end. The score may run suddenly and not always along the line. Instead, move the sheet with support on both sides of the score. After the glass is scored, you have choices about how to run the score.

One easy way to break off large pieces is to move the sheet so the scored line is just inside the edge of the bench. The biggest piece will be on the bench and the smaller piece in your hands. Give a quick, sharp downward push with both hands on the overhanging glass. This action will separate the piece from the main sheet. Having the glass score inside the bench edge gives you a place for the broken off piece to rest, rather than pivoting toward the floor.

Or you can slide the straight edge under the glass on one side of the score, and press firmly, but not sharply on each side of the score. The glass will break evenly along the score line. This is a more gentle method of breaking the glass. A variation on this is to place a couple of matchsticks or glass painting brushes at each end of the score and apply the pressure.


If the glass sheet is of a size that you can hold it in both hands with the score between, you can draw it off the bench, let it hang vertically, and bring your knee up briskly to hit the score line, and it will break easily. This is a showman’s way of breaking glass sheets when the score line is approximately centred on the sheet.


Cut running pliers often do not work very well for long straight scores on large sheets of glass. However, if you use this method, tapping at the start and at the end the score line before squeezing the running pliers will help the score to run the way you intend. This is sometimes the only way to achieve the break of the score.  A note on the adjustment of cut running pliers. 

Breaking glass with your fists

No, this is not about punching the glass – a dangerous approach. But it is a two-fisted approach to holding glass to break it.

For scores with significant, but not necessarily equal, amounts of glass on each side of the score this is a quick simple approach to breaking glass. After scoring, raise one edge of the glass and put your fingers under the glass on each side of the score. Curl you fingers into your palm, and put your thumbs on top of the glass. Turn your wrists outward and the glass will break cleanly.

With practice, the initial part of a curved score can be run by applying light pressure. Then you can turn the glass around and run the score from the other end to the opened score. This avoids lots of tapping and gives clean edges to the cut glass. It is just as simple as using cut running pliers and avoids the flare often associated with using cut running pliers.

This technique works best with glass that has at least 50mm each side of the score and on gently curved lines. For tight curves and narrow strips other methods need to be used.

Cutting Opalescent Glass

People often find cutting opalescent glass more difficult than transparent. My observation is that people exert too much pressure in scoring opalescent glass by listening for the creaking/scratching sound. 

Not all glass is made the same, even by the same manufacturer.  But all the same rules apply in scoring opalescent as transparent glass.  However, they sound different.

No more pressure should be put on opalescent glass than transparent.  Only about two kilograms (5 to 7 pounds) of pressure is required to score glass sufficiently to create the weakness that we exploit when running the score.

If you concentrate on keeping the pressure on both types of glass the same, you will hear different things.  On transparent glass you normally hear a creaking or light scratching sound and you do not get a whiteness along the score line.  If you hear same sound on opalescent glass, too much pressure is being applied. 

The same pressure (2 kilograms) on opalescent glass gives only a rumble of sound. No creaking or scratching is heard.  You can test this by placing a piece of glass on kitchen scales. Zero the scales with the transparent glass on it and score. Note the pressure you used.  Now zero the scales with a piece of opalescent glass on it. Ensure you score to the same pressure as on the transparent glass by looking at the readout on the scales.

Just as excessive pressure on transparent glass leads to erratic breaking of the glass, so it does on opalescent glass.  You will need some practice to stop listening for a sound and begin to feel the pressure you are applying to the glass. Once you do apply the same pressure to opalescent as to transparent glass, your success in scoring and breaking opalescent glass will increase greatly.

Scoring and breaking opalescent glass successfully is the same for both transparent and opalescent glass.  Use moderate pressure and don’t listen for the sound.

Feel the pressure. Ignore the sound.

Using Cut Running Pliers Without Cushions

Using Cut Running Pliers Without Cushions

There are a wide variety of cut running pliers for different purposes.  A description of some of them is here.

This post is to describe maintenance and use of this kind of cut runner.

The plastic covers that come with these cut runners eventually wear out.  The replacements are hard to find. There are things you can do other than buying a new pair just for the shields.

You can dip the jaws in tool coating compounds such as Plastidip.  This does not last as long as the plastic, but is easy to re-do.

You can wrap the jaws in tape.  Electrical tape, duct tape or even self-adhesive elastic bandage will do the job. Again, not long lasting, but easy to replace.

Or

You can use the cut running pliers without any covering on the jaws.  “You can’t do that. You will crush the glass!” is the response I hear.  You can use them bare. I do, and so can you.

The key is in the adjusting screw.  It is there not just to tell you which is the top of the pliers; it has a function too.  That screw adjusts the opening of the jaws to the thickness of the glass. 

A simple way to ensure you have the correct opening is to put one corner of the jaw on the edge of the glass with the jaw opening less than the glass is thick. Then tighten the screw until you feel the handles of the pliers begin to open.  Then you have the right opening for the thickness of the glass. 

It ensures you cannot crush the glass, as the jaws will not close at the centre to be less than the glass thickness. 

You also have a more direct feel of the glass without the spongy connection of the plastic. You can sense the glass beginning to bend just before the score runs due to the gentle pressure of the jaws of the cut runners on either side of the score.

Whether you use the cut runners with or without cushions on the jaws, it is important to keep the adjustment screw lubricated so you can adjust the width of the jaw opening for different thicknesses of glass.

Lubrication for cutters

You can cut glass without oil.  It has been done for a long time.  But it has been found that there are advantages to using oil on a score line.

The purpose of oil:

·        A minor element is to oil the cutter wheel.

·        A major element is to oil the score line.  An oiled score line stays open longer than a dry one.  

·        An oiled score line reduces the amount of visible chipping from the score line.

The kind of oil

·        Mineral oil does not oxidise to gum up the scoring wheel.

·        Any light mineral oil from sewing machine oil to WD40 is acceptable. Some use very light oils such as turpentine or white spirits.

·        There are cutting oils that are synthetic and easier to clean than the standard oils and spirits, in that less residue is left when the oil is wiped off.

·        Vegetable oils might appear to be a good substitute.  But they oxidise and become sticky, attracting dust and other particles which soon block the turning of the scoring wheel.  This requires frequent checking and cleaning.  Avoid vegtable oils.

Methods of applying

·        The oil can be put into the cutters that have a reservoir.

·        The cutter can be dipped into a container of oil with or without an oil-soaked material.

·        The oil can be painted onto the glass before scoring.

  Any combination of the above will work.

Tapping Glass Scores

Many people tap the underside of the glass after scoring.  The purpose of this is to run the score.

However, this tapping is often unnecessary.  Running the score can be done in a variety of ways, some more suitable for one kind of score line than another.

Straight score lines can be run in several ways.

• ·        Move the line to the edge of the bench or cutting surface and use a controlled downward force on the glass off the edge while holding the remainder firm.  Works best if at least a third is being broken off.
• ·        You can place a small object, such as the end of your cutter or a match stick, directly under the score and place your hands on either side and press firmly, but not sharply, down on each side at the same time.  This is good for breaking pieces off from half to a quarter of the full sheet.
• ·        Make your hands into fists with the thumbs on top of the glass and the fingers below.  Turn your wrists outwards to run the score. Works best if the glass is approximately half to be kept and half to be broken off.
• ·        Take the glass off the cutting surface, hold in front of your knee at about 45 degrees and raise you knee quickly to the glass.  This will break the glass cleanly, but is only useful for moderate sized sheets and where you are breaking off about half of the sheet.
• ·        Use cut running pliers to run the score.  Be sure the jaws are adjusted for the thickness of the glass, and do not apply excessive pressure.  If the score does not run all the way, turn the glass around and run the score from the opposite end. Best where there are approximately equal thin parts to be broken away from each other and when the score line is no less than an oblique angle to the edge. It does not work very well for thin pieces or acute angles.
• ·        Use two grozing pliers nose to nose and flat side up at the score line and bend them down and away.  This works best on thin and or pointed pieces.
• ·        Breaking pliers can be used at intervals along the score. This is most useful on long thin pieces.

Curved score lines, of course require a bit more care but generally employ the same methods.

• ·        Gentle curves can be dealt with as though they are straight lines, although the breaking at the edge of the cutting surface is a bit risky. This means the two-fist, running pliers, two grozing pliers and breaking plier methods can be used.
• ·        Lines with multiple curves usually require cut running pliers to start the run at each end of the score.
• ·        Deep curved scores may require the running pliers whose angle can be adjusted to be at right angles to the score.  The ones I know are Silberschnitt, made by Bohle, although the ring pliers by Glastar work in the same way. This usually requires that the edge of the glass is not more than 5 cm from the score.  This blog gives information on a variety of cut running pliers. 

Tapping

After trying all these methods to run the score, sometimes the score is so complicated or deep into the glass that you cannot simply run the score.  Tapping may then be required, but it is a last resort.

Tapping, to be effective, must be accurately directed to places directly under the score line.  The tapping cannot be at random places under the glass. Each tap must be controlled – to be direct and to be firm. 

The impact needs to be directly under the score. 

• ·        Taps that are either side of the line will either not be effective, or will promote breakage other than along the score line. 
• ·        Tapping to either side of the score also promotes shells to either side of the score line.  These are not only dangerous when handling, but also require further work to remove these ledges of glass.

The impact also needs to be firm. Random impacts to the glass promotes breakage other than along the score line.

• ·        The taps need to be firm – neither light nor hard.
• ·        Each tap should be at the end of the run begun by the previous one.  This promotes a smoother run of the score with less opportunity to start a run off the score line. 
• ·        To avoid the incomplete running of the score that leaves parts of the score untouched you need care. As the glass begins to break along the score line, place the next impact at the end of that start to continue the run. 

Tapping the glass under the score should be a last rather than first resort in running a score.

Diagnosis of Cutting

If your scoring and breaking of your glass is not going well, you need to diagnose the reasons.  There are always a lot of suggestions that warming the glass will solve the problem. Yes, warming glass may help. A discussion of the effect is here. But it will not overcome any faults in the basic skills of scoring.

A lot of images, shown on the internet, of straight line scores failing to break along the score, indicate some possible elements in scoring that lead to these unwanted break-outs. 

One possibility is you are using too much pressure. A discussion of the amount of pressure required is here.  You should be scoring to the pressure required, rather than any sound that may come from scoring.  This is emphasised when cutting opalescent glass.  The correct scoring pressure makes almost no sound or only a gentle rumble as it cutter moves over the undulations of the glass.  The most frequent reason for more difficulty in breaking opalescent glass is excessive pressure while attempting to get the same sound as from transparent glass.  There are even a few transparent glasses that make little or no sound when being scored with the correct pressure.

Another common problem in scoring is keeping an even pressure throughout the score.  It can be difficult to keep the pressure even on complicated cuts.  When the cartoon has multiple curves or deep concave lines, it can be difficult to keep the pressure even as you move your body around to follow the line.  One piece of advice I received early on in my learning was to rehearse the score allowing the cutter wheel to move along the score line with virtually no pressure.  This shows how the piece of glass needs to be oriented to ease your movement around the glass to make the score.

Slowing the cutting speed can help to keep the pressure evenly distributed along the score.  Straight lines are often scored quickly.  But, even on straight lines, slowing the speed can make the pressure more even throughout the score.  It can also avoid variable speed during the scoring, which leads to different forces being placed on the glass.  The pressure may be consistent, but the effective pressure is greater when slow than when fast scoring is used.  If the speed is variable, the effective pressure differs along the score line.

A fourth thing that may be happening on straight lines is that the cutter wheel is at an oblique angle to the direction of the score.  This will often be heard as a scratching sound as you move along the score line.  This can be overcome by a gentle pressure against the straight edge you are using to align your score.  Of course, the straight edge needs to be held firmly to avoid having it move.  Allowing the head of the cutter to have a little freedom of movement also helps keep it parallel to the straight edge.

All this is merely speculation about your scoring practice.

You need to get someone to observe you scoring.  They do not need to be experts, nor other glass artists.  They just need to be observant. Tell them what you are looking for in each of the four elements of scoring and have them observe only one thing at a time.

First get scales that you can zero when you have a small piece of glass on it. Score without touching the glass. Have the observer tell you if the pressure was consistent throughout the score, and if you are in USA, whether the pressure was above 7 pounds or below 4 pounds. (For the rest of the world 3kg to 1.8kg). Practice until you can score consistently at about 2.2kg (ca. 5 pounds).

Second, have the observer stand a little distance from you. Score toward the observer. They need to observe whether your cutter is perpendicular to the glass while scoring and if there is any variation.

Next, they need to tell you if your head was directly above the cutter all the way through the score. They will be able to see whether your eye is directly above the cutter

Is your body behind the cutter, or do you use your arm to direct the cutter?  The observer will be able to tell that when you are scoring curves. The most consistent speed and pressure is delivered when the cutter is steered from your torso, rather than your arm and wrist.  It slows the scoring action, gives smoother curves, and more even pressure.

The last element, you can do yourself.  Once you are doing all the things above, you will be able to hear any scratching noise, rather than the gentle creaking noise of an even score with adequate pressure.  If the scratching noise is intermittent or only at one point, the likelihood is that you are twisting the cutter head, so the wheel is not in line with the score line.

Glass Cutting Surfaces

There are several considerations about your surface for cutting glass.

Make sure you are putting the glass on a flat surface. If the surface is uneven, it will give difficulties in scoring and breaking.  This means that large sheet timber is an excellent surface.  These boards need to be securely screwed down to the bench structure to avoid any warping.

There is some advantage to having a slightly cushioned cutting surface. This will help accommodate glass with a lot of texture and those sheets that have slight curves in them. 

In this example the user has placed corrugated cardboard under the glass for cushioning, but with a hard surface underneath

Consider ease of cleaning.  As you score and break glass, small shards will be left on the cutting surface.  The tell-tale squeaks as you move the glass indicate there is other glass under the sheet. These shards and any other small almost invisible things under your glass can promote unwanted breaks. Also, if there is glass or other grit on the surface, it may scratch the glass. So make sure you brush the cutting surface clean frequently.

An example of a ready made cutting bench.  It has the advantage of being easy to clean and compact when not in use. 

Think about the size of sheets you will be cutting.  Large sheets often have minor imperfections in texture, or some bowing.  These benefit from a slightly cushioned surface. It also allows the sheets to be put down onto the surface with more confidence that it will not break in contact with the bench top.  But if you are cutting mostly smaller sheets, they benefit from a smooth hard surface to support the whole of the sheet especially when cutting long thin or curved pieces.

An example of a large cutting bench with composition board top surface

Some of the materials used are sheet boards (such as marine plywood, MDF, and other composition boards), short pile carpets,  thin rubber or foam sheets, dining table protectors and pin boards. 

All these are useful for cutting each with advantages and disadvantages.

• Carpets and foam can trap shards of glass, so have to be cleaned very carefully to avoid retaining sharp glass within the pile or foam.
• Smooth, wipe-able surfaces avoid trapping glass, but can be slippery. Choose one with a non-slip surface.
• A slightly cushioned surface is good for large sheets
• Smaller sheets of glass are best cut on smooth hard surfaces, providing support for all of the glass sheet.

You can also consider, as in the example above, the use of different cutting surfaces on top of the larger smooth and hard surface.  This allows adaptation to the needs of your glass without duplicating surfaces.

Before scoring, clean the glass on both sides, to ensure any sounds you hear when moving the glass relates to glass shrds on the bench rather than grit on the glass.  At the very least, clean along the cut line, as this makes the action of the cutter smoother. The grit on the glass actually interrupts the action of the wheel, so you get a staccato effect in the score line.

Cutting Hour Glass Shapes

Hour glass shapes, wasp waists, or those that are thinner along the length than the ends, should be avoided as much as possible.  They are difficult to break out from the score.  More importantly, they are an inherently weak shape. The longer the piece is with the narrow part along its length, the more likely it is to break; in cutting or in the long term, in the panel.  However, these shapes are sometimes unavoidable.

The principle to use in scoring and breaking out the glass is to remove less glass than that you are retaining at each stage of the process.

This has consequences: 

• ·         breaking the first score is the easiest
• ·         only a rough outline of the final piece should be scored and broken from the sheet
• ·         Relieving scores and breaks will be necessary.  The number will depend on the relative thickness of the thin and thick parts.
• 
  

You can make the first score and break of one side of the shape from the main piece of glass – usually with little difficulty or need for relieving scores. (1)

You then should score and break off the piece to be retained from the larger sheet.  Be sure to give a margin for the final piece. (2)

Now score the other part of the hour glass shape.  Do not tap the score. Begin gently to run of the score from each end.  Don’t worry if the runs do not meet up.  Do not tap to make them meet up. (3)

If running the score from both ends is not enough to make the run complete, you will need to use relieving scores.  These scores can be like onion rings – generally concentric curves running in the same sort of shape as the curve to be broken out.  

Or you can use the fish scale approach – overlapping crescents.  These are most useful for deeper inside curves.

Either way, each score needs to be planned.  Each relieving score should be smaller than the width of the piece to be retained.  In general, this means the outer relieving scores can be wider apart.  As you approach the final shape, the distance between the scores will need to be less and less. (4,5,6)

More information on scoring and breaking out concave curves can be found here:  http://glasstips.blogspot.co.uk/2008/08/cutting-concave-curves.html

Holding the Cutting Head

Many people hold their cutting head steady with a finger during the scoring process.  This is not necessary.

The axel of the cutting wheel is slightly forward of the centre line of the cutter.  In addition, the cutter is held slightly angled back toward the operator to be able to see the wheel and the cartoon (or marker) line.  Both of these act to ensure the wheel follows the movement of the arm or body in a forward motion. 

In cycling, the distance between the angle of the shaft of the cutter and the axel is called the “trail”.  The greater the amount of trail, the easier it is to keep the bicycle following a straight line. The same applies to the cutter. This trail is created by the extension of the angle of the cutter to the glass.  The axel of the wheel is behind that line. The cutting head has a sharper angle at the back than the front to accommodate this angle backwards. The resultant forward force is in front of the axel and so leads the wheel to follow the direction of the cutter without any need for stabilisation.

There is no need to have your finger on the cutting head. It swivels for a reason. It will follow the direction you are pushing without any angle, so there is a clean score.  If you attempt to stabilise the cutter head you risk the wheel running at a slight angle to the direction of the score.  I talk about this as a skidding score. The result of this is to give a score with forces directed not only straight down but sideways too.   This gives the glass many more ways to break.  And not always along the line you want.

Also when you want to score a tight curve, the slight movement of the head allows the curve to be slightly smoothed again without any skidding.  This means there will be fewer pressure lines sideways to the score line.

Manufacturers have put the play into the cutter heads for a reason.  The above attempts to explain it.  The manufacturers would not include a feature that costs time and effort, as well as cost if it had no purpose.  It seems perverse of us to try to run counter to that by holding the head or even fixing it solid, so it is unable to pivot at all.

Adjusting Cut Runners

There are a number of types of cut running pliers.  These photos show some of them. 

The apparently most popular is this:

Cushions

It is frequently difficult to find replacements for the plastic cushions that come with a new pair of cut runners.  People resort to a number of means to provide a substitute.  Some wrap electrical tape around the jaws, others use fabric bandages (Elastoplast/band aids).  I have even used the liquid plastic that is designed for coating tool handles.

However, if you adjust the cut runners appropriately, you can use them to run your scores even without cushions.  The purpose of these cushions is only to compensate for too much pressure in running the score.

Use without covers

You can run the score without cushions by using the adjustment screw on the top jaw of the tool. Yes, it does tell you which is the top jaw without having to check the end of the runners, but it has a more important use.  It is not just a pretty cool way to tell which is up. 

Its purpose is to adjust the width of the opening so that it provides the appropriate amount of bending force no matter how much pressure you exert at the handles.  If you are running scores in three-millimetre glass, set the jaws to that width by turning the screw until the jaws are that width apart.

Place the jaws at right angles to the score, aligning the mark on the top jaw with the score line and squeeze the pliers.  As you squeeze, the curved jaws provide enough bending force to run the score without over stressing the glass.  It is the adjustment screw that limits the over-stressing of the glass during the running of the score. Yes, you may not be able to run the whole length of the score this way, but you can repeat from the other end and that is usually enough to complete the running of the score.

You can continue to use cushions of various sorts with this adjustment for thickness, but I found that these were not necessary when the runners were properly adjusted.  In fact, I found that soft cushioning made more difficulties than using them with the bare metal.  I discovered this during the period of using the liquid plastic coating as used for tool handles.  I dipped the jaws multiple times to give a cushioning effect and it worked fine.  The cut runners continued to work even after the tool handle coating had worn off.  It was then that I realised I could control the running pressure more directly than by having a cushion between the glass and the jaws.

Setting the spacing

An easy way to set the correct opening of the jaws is to test against the glass you are about to score and break.  Place one side of the jaws against the edge of the glass. Slide that corner just a few millimetres over the glass.  Turn the set screw on the top of the jaws anticlockwise until they are fitting the glass snugly.  Back off a half turn (clockwise) so the jaws move easily along the edge.  This is now set to run the score on this glass. 

Open the jaws and place the centre mark in line with the score.  Close them gently and you can observe the arc of the jaws above the score line. Squeeze the handles and the score will run along the line away from the cut runners.  As you have adjusted the opening, no matter how hard you squeeze the cut runners, you cannot add more pressure.  This means you avoid crushing the glass.

The principles

The curve of the jaws is designed to provide the bending force required to run the score.  The radius of the curve has been designed to provide the correct bending pressure for differing sizes of glass.  The most common ones are useful for glass up to, but not including, 6mm glass.  The screw adjustment provides compensation for differing thicknesses of glass.  Setting the width of the gap to match the thickness of the glass prevents the application of too much pressure.

Thicker glass

For thicker glass you need cut runners with wider jaws.  These usually are fitted with three points to apply the breaking pressure - one under the score and one each side of the score on the top.  Again, these are adjusted to be just less than snug to the glass before applying the pressure.

One example of  cut runners for thick glass.  There are a variety of others.