Wednesday, 12 September 2018

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


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.

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