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TIP: Safety glasses should always be worn when scoring and breaking glass to protect your eyes from possible glass slivers. It is also important to use a bench brush and dust pan to keep your work area clean and free of glass slivers. This will help eliminate bad breaks and the possibility of picking up glass slivers with your hands.
Determine which side of your glass is the front. The front is usually the smoothest or shiniest side. Lay it on your cutting surface, front side up. Place your pattern piece on the glass. If you are using patterned or textured glass, refer to the directional lines that are drawn on your pattern pieces. Holding the pattern in place, trace around it with a felt-tip pen. Remove the pattern and mark the corresponding piece number in the center of your glass piece.
Scoring your glass: Standing in a comfortable position, hold the cutter like you would a pencil and keep it perpendicular to the glass. Starting at the edge of the glass closest to you, place your cutter head on the glass approximately 1/8" away from the edge. Apply light, even pressure to the cutter. Guide the head across the surface of the glass on the inside edge of your traced line and off to the other side of the glass. One even score is all it takes; don't rescore over your line or move your cutter back and forth while scoring. This will result in a bad breaking score and it will also chip the wheel of your cutter.
The rule of thumb in cutting out glass pieces is to start with your most difficult cut first and finish with your easiest cuts. Inside curves are the hardest ones to score and break, followed by outside curves and then straight lines. Imagine that you are a sculptor making a masterpiece out of marble. In order to free your creation of the marble, it is necessary to chip away a little at a time until your creation emerges. This same principle applies to glass. The nature of glass is that a score wants to travel in a straight line to the nearest edge in order to relieve the inner pressure of the glass. So it's best to score and break tricky curves a little at a time instead of all at once. Once you have gained more experience and understand the limitations of the glass, you will be able to score and break more severe curves.
Look at your score line. Are there small flakes of glass popping up from the score line? If so, you are applying too much pressure on the cutter. With your next score, lighten up a little bit. Are you unable to see where your score line is? Not enough pressure is being applied, so try again pushing down a little harder.
After scoring your glass, you will need to break it. There are several different ways you can achieve this. You may use your hands, running pliers, or breaker/grozer pliers. Always remember to break each score line right away before making the next score. The fastest way to wear our your cutting wheel is by scoring over other score lines.
Severe inside curves are impossible to break out with just one score. Score along the pattern line, but don't break this score yet. To relieve the inner tension of the glass make a shallow score near the edge of the glass and parallel to the pattern line. Break it out using breaker/grozer pliers. Repeat this process until you have worked your way to your first score. If you have a bad break, retrace your pattern piece and try again.
Breaking glass with your hands: Form fists while holding the glass with your thumbs on top of the glass (score side up) holding it in position and with the knuckles of both hands touching under the glass. Position the end of the glass score so that it is centered between the knuckles of both hands. Hold the glass firmly, apply even pressure with your thumbs and break (bend) the score line away from the score. This is a quick, snapping motion. You are rolling your knuckles together beginning with your index fingers and ending with your little fingers and snapping the glass apart. This is all done by twisting your wrists.
Breaking glass with running pliers: Hold the glass with score side up. Position the pliers at the beginning of the score and match up the line on the top of the pliers with the score. Tighten the screw until it touches the lower jaws of the pliers, then loosen the screw a 1/4 turn. Gently squeeze the running pliers to run the score. If the score only runs part of the way, you can turn the glass and repeat the process from the other end.
Breaking glass with breaker/grozers: Hold your glass in the hand that won't be holding the pliers. (If you are right handed, hold the glass in your left hand or vice versa.) Form a fist with your thumb on the top of the glass and your fist under it. Your knuckles should be adjacent to the score line. Position the breaker/grozers (with the flat jaw on top) directly across from your knuckles and parallel to the score line. Hold the glass firmly and apply even pressure while snapping up and away. This is the same motion used in breaking glass with your hands.
If your score breaks unevenly, clean up the ragged edges with breaker/grozer pliers. With the flat jaw facing up, grasp small pieces with the pliers and snap them off. If the pieces are too small, hold the pliers at a 90° angle to the edge of the glass and drag the serrated jaw of the pliers across the edge. If you still have jagged edges on the glass, you can use a glass grinder to shape and smooth these edges.