by Lloyd Sullivan – Harmony Stained Glass

Did you know that glass can tell you which cutter it likes the best AND how hard to press while scoring? It can. Most people think a glass cutter is a glass cutter and other than shape and color they are all alike. Nothing could be further from the truth when it comes to glass cutting . Different manufacturers grind their carbide cutting wheels at different angles and use different qualities of carbide. This will greatly affect the way glass will respond to the cutter's score. Yes, it is true that all cutters will score glass but not all glass will respond favorably to all cutters at your normal score pressure. If you only have one glass cutter you only need to do the “How hard should my score pressure be?” test below. If you have cutters from different manufacturers**  you should do the “Which cutter should I use?” test first, then do the “How hard should my score pressure be?” test. If you are having a problem breaking a certain piece of glass these testing procedures should be run on a couple of scraps of the problem glass and should help to reduce the breakage.

Which cutter should I use?

1. If you only have one cutter, go to the “How hard should my score pressure be?” test below.
2. If you have cutters from different manufacturers** line them up.
3. Cut two strips of the problem glass about ¾” wide and about 4” or 5” long.
4. Make a score using your normal pressure about 1/8” apart and in the same order that you lined up your cutters. Try to keep the group of scores fairly close to the middle of the strip.
5. You should now have as many scores as you have cutters from different manufactures**.
6. Hold the strip by each end and pull as you bend. The glass will break on the score made by the cutter that works best with the combination of your cutter, your pressure and that particular piece of glass.
7. Use this cutter in the “How Hard Should My Pressure Be?” test below.
8. If you change glass or if another person is doing the cutting, these tests will need to be done again. Just because a piece of glass likes a combination of your cutter with your pressure doesn’t mean the glass will like the same cutter with another’s pressure.

** If you have a Toyo Custom Grip cutter, it counts as another cutter even though you have other Toyo cutters because it has Tap Wheel Technology. This head is usually only on the Toyo Custom Grip Glass cutter.

How hard should my score pressure be?

1. Use the second strip of the problem glass from above and do the following.
2. Use the cutter the glass told you it liked the best from the test above.
3. In the middle of the strip, make a score using your normal pressure.
4. Move about 1/8” to the left of this normal pressure score and make a score using lighter pressure than normal.
5. Move about 1/8” to the right of the normal pressure score and make a score using heavier pressure than normal.
6. You should now have three scores, lighter than normal, normal, heavier than normal from left to right.
7. Hold the strip by each end and pull as you bend. The glass will break on the score that was made with its preferred score pressure. Use the pressure you used to score the score that the glass broke on and breakage will be reduced.

I have seen cases where these two tests made a remarkable reduction in glass breakage. All you have to know is how to ask the glass which cutter to use and how hard to press when scoring the glass. Now you do!