by Bob Beranek
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The biggest difference between cutting annealed glass and laminated glass is the way the score is broken. Annealed glass is relatively simple; if the scoring procedure was completed properly, you just initiate the break on one of the edges and the break propagates and separates from the main stock. However, breaking the score on laminated glass takes a little more creativity because the opposite sheet of glass is causing resistance.

There are a couple ways of running the score; pressure break, tweak break, table break, tap break and pliers break. Each type of break is determined by how far away from the edge the score is.

 A pressure break is one that is accomplished by turning the glass over so the score is facing the table top. Starting at one edge of the glass, place your thumbs on either side of the score and apply pressure until the break begins. Then continue to apply pressure along the score until the break progresses the entire length of the glass piece. This type of break procedure is recommended when the score is more than 12 inches from the glass edge.

BobsblogMarch7formattedThe tweak break is using your hands to tweak the glass at the score line causing it to begin the break.  hen, use the finger tips to propagate the break along the score line. Place the index finger directly under and on the opposite side of the score. Place the fleshy part of the lower thumb on the glass edge and tweak the glass to begin the break. This type of break procedure is recommended when the score is more than 4 inches and less than 6 inches from the glass edge. Once the break is begun on the edge, use the finger tips to propagate the break along the score.

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The table edge break is accomplished when the score is placed directly over the table’s edge facing up and the glass is dropped about an inch in height off the table’s surface. There must be enough weight on the protruding glass to cause the break to occur. This is recommended only when there is at least 12 to 18 inches protruding from the glass edge to the score.

The tap break is used when the score is close to the glass edge or if the score is difficult to start. It is accomplished with the use of drop jaw pliers or glass pliers. These are special pliers that have square, smooth jaws for running breaks without chipping the glass. The drop jaw of the pliers is tapped on the underside of the score causing the break to travel the length of the score.  This type of break does cause a scalloping effect on the glass edge and may be unacceptable to the customer unless extensive edge finishing is used.

The pliers break is one that is used when the score is less than 1-1/2 inches from the glass edge. Place the edge of the jaws directly on the score and squeeze with a slight downward pressure. Don’t forget to watch the break from a slight angled sightline. Turn the glass over and repeat the process on the other side. This type of break can also cause scalloping and takes a little practice and touch with the pliers.

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Now that both glass pieces are cut, the next step is to separate the lamination without damage to the glass edge. As you will notice, the glass cut from the stock piece is now somewhat floppy which will allow for the easy separation of the PVB. There are two basic methods to separate the lamination, melting it and cutting it. When it comes to melting, there is a safe way to do it and a relatively dangerous way.

For years, many glaziers used denatured alcohol to melt the polyvinyl butyral (PVB) between the two layers of glass. They would apply the alcohol along the break and light it to melt the PVB. However, this has proven to be a very dangerous method of separation. Denatured alcohol burns very pure and in the right light is almost invisible. If the cutter drizzles more alcohol on the glass the fluid will ignite, potentially cause the container to explode resulting in very serious injury. I do not recommend igniting denatured alcohol for the purposes of lamination separation, nor do I recommend its use at all.  

The safer way to melt the PVB is by the use of a heat gun. A heat gun produces heat without an open flame. Some heat guns have an attachment that can concentrate the heated air to a specific point, which aids in a more effective separation. To effectively use a heat gun, slightly bend the loose piece of glass in a downward angle and apply the heat evenly along the entire length of the break. Move the glass up and down until the lamination separates.

The preferred method of lamination separation is cutting. Cutting the PVB can be accomplished with the use of a single-edged razor blade or the use of a length of tape measure blade. The razor blade is the most common method but the tape measure blade has gained popularity.  The razor blade is thicker than a tape measure blade and requires the bending of the lamination to the point of possibly chipping the stock piece edge. The tape measure blade is more flexible and can be used around radius corners with the minimum separation of the two pieces of glass.  The tape measure blade is also self sharpening. If a new edge is desired, simply double over the blade and it snaps off.

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To use the razor blade or tape measure blade effectively, bend the waste piece slightly until the tip of the blade reaches the lamination layer. Then use several strokes to “score” and then cut the PVB. If a tape measure blade is used, place your thumb into the curvature of the blade when cutting the PVB. This provides stability and comfort during the cut. Once the lamination is cut sufficiently bend the waste piece away from the stock piece and remove.

Next week I will discuss radius corners.

Comment (1)

  1. Dennis Krawchuk said on 14-08-2018

    I am in the process of cutting down a curved windshield for n older pickup truck. My question is what to when I’m running my score and the score stops running? I started at the other end, but the score stops running about 3″ from the other score. The scores are on the same side of the glass I haven’t turned it over to score the other side yet. I’m afraid to hit the glass any harder with my pliers. What should I do?

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