# Cutting Glass



## cabinetman (Jul 5, 2007)

You may be in a position needing to cut a piece of glass. It's not difficult. Following some simple procedures, you can cut glass up to ¼" thick without any real special technique.

Your first step would be to clean the glass so there is absolutely no debris near your line of cut. What actually determines the cut is a carbide wheel that rolls along the glass making a very fine score line.

You can use any flat table or bench top. It's best to have a low level loop carpet laid on the surface up to the edge. You could use any type of protector, even a U-Haul type pad will work. You just need to prevent any source of abrasion to the glass from positioning the piece.

I use a Plexiglas straightedge, I made like a "T" square, but it's actually an "L" square. The one in *this image* allows a cut of 50". I make a mark on the glass with a fine tip grease pencil. I set the edge of the straightedge next to the mark, and allow for the thickness of the width of the frame next to the cutting wheel. I prefer to use an oil filled cutter *like this one*. These cutters have replaceable cutter heads, and work very well. The oil can be any light oil, I use air tool oil thinned about 10% with mineral spirits.

When the straightedge is lined up, and the wheel is placed on the mark, I use the light oil and a soft brush to make an oil pass along the route that the wheel will take. This provides an excellent surface for the carbide wheel to score. I start at the top of the cut, and position the wheel on the top edge of the glass, and rock it back and forth a time or two just to get it to start at the top edge.

With a slight downward pressure, and a slight pressure against the straightedge make one single non stop pass all the way down, and off the glass. If the glass is thin, like ⅛", you could just take the two halves and snap them apart between your thumbs and fingers. Or, while laying flat, tap the underside of the score line where you came off the glass, and a split run up the score line will separate the glass. This also works on ¼" glass, using the metal tip on the handle, or the nose of a pliers. All it needs is a short sharp strike, about a ½" from the edge.

You could turn the glass, so the score line is lined up just beyond the edge of the table/bench, and lift it slightly and snap it down on the table. The piece should just break off cleanly. 

Cutting mirror is the same procedure for cutting on the face of the mirror. For smoothing the cut edge of clear plate glass, you can use 100x wet-or-dry silicone carbide sandpaper dry with a block. That will ease off the sharp edges. For the mirror, only ease the face edge. 

Mirror has a silvering done to the back. When the mirror is cut, the seal is broken between the back coating or silvering, which will allow oxidation to the silvering from the edge. This accounts for mirrors turning black or clear around the edges. 

Lay the mirror on some newspapers on a flat surface, backside up. Use an acrylic spray on the exposed edges all around. This will help prevent the oxidation.

















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## Gene Howe (Feb 28, 2009)

Good tips, C-Man.
Thanks.


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## cabinetman (Jul 5, 2007)

As an addendum, don't attempt to cut tempered glass. You can identify it by a small label in one of the corners. If you do, it will shatter in minute pieces. That could replicate an explosion. The breaking up in small pieces could take place in a few seconds, or last a few minutes or more.


















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## Doomi (Aug 5, 2013)

cabinetman said:


> As an addendum, don't attempt to cut tempered glass. You can identify it by a small label in one of the corners. If you do, it will shatter in minute pieces. That could replicate an explosion. The breaking up in small pieces could take place in a few seconds, or last a few minutes or more.



I've made this mistake on glass that wasn't labeled. One way to tell if it is tempered or not if it isn't labeled is to look through polarized sunglasses. If it is tempered you normally see a rainbow in the glass.


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## JohnnyG73 (Sep 10, 2013)

When I was just out of high school I worked in a window factory. All of the bad glass (wrong size or not needed) had to be broken. Some of the tempered sheets of glass could be hit with a hammer without breaking. All it took was a light tap on the edge though to break it. You could listen to the glass crackle for a while after it broke.


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## Sleeper (Mar 24, 2009)

Great information! Thanks for taking the the time to post


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