Curves, tapping method
The tapping (knocking) method is handy in a few, but very important situations:
  • Curvy score lines
  • Glass that tends to run off the score
  • Textured glass
  • Capricious ring mottles
  • Long scores on expensive glass
When glass combines "expensive" with "unpredictable" you might find that tapping scores as short as 2 inches will save you both money and aggravation. When tapping score lines this short, be aware that the glass might spontaneously separate after the first or second tap.

In the example, a long, curving score is tapped to best help you understand how it works. STEP 1:
After scoring the glass, hold the glass vertically as shown. With your left hand (if you are a rightie), hold the glass across the score line. This is for safety reasons. Should the glass pieces separate prematurely, it is good to be able to prevent them from falling.

The score should be facing you. Hold the glass cutter behind the glass.

With the steel ball at the non-cutting end of your glass cutter, and beginning with the top edge of the score line, tap firmly along the lenght of the score. You will notice that the appearance of the score line changes if the tap is successful. You can see that it becomes brighter - this is internal cracking along the score.

Continue until you have tapped along the entire length of the score line.

Hold the glass similar to the normal handbreak. One hand on each side of the score line. One side of the glass which is perpendicular to the score should lay on the table. The other side of the glass which is perpendicular to the score should be elevated, and is the side that the hands hold. Place the thumbs parallel to the score, above the glass, and the other fingers curled under the thumbs, beneath the glass.

First, gently attempt to fold up and down along the score, to release some of the cohesion that comes from small irregularities in the score acting like the pieces of a puzzle.

Second, turn the sheet 180 degrees, and repeat. Do this a few times until you beging to feel that the pieces are loosening up. Third, break off the pieces with the normal downward motion. Note that a curve sometimes requires more force than a straight score under similar condition, and once the glass breaks off, you will have to hold back your motion with more force as well. Other times, the pieces will spontaneously separate as you tap.

Troubleshooting tip
If the microscopic break line runs off the score as you tap, which happens very rarely unless attempting to score challenging glass, stop. Turn around, and start tapping from the other end until the break line meets the one that runs off. There will be a nick, but you'll avert losing your piece! If the piece is small enough to break with pliers, make sure that the pliers are held where the two break opposing break lines meet, rather than the center. How To Cut Glass

page 1
page 2
page 3
page 4
page 5
page 6
page 7 (how to cut glass, by manufacturer)