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.

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.

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.