How to Cut Glass Circles

Co-authored by wikiHow Staff

Last Updated: March 12, 2020

You've probably seen a movie where a burglar places a fancy glass cutting tool against a glass case or window, scores a perfect circle, taps it out, and makes a getaway with the jewels. Well, it's not quite that simple to cut a perfect glass circle, but with a circle cutter and the right technique you will soon enough be able to cut glass circles at home for stained glass or art projects. Start by scoring a circle in the glass, just like in the movies, then run the score, create relief scores in the corners, and apply gentle pressure to break the circle free.

Part 1

Part 1 of 2:

Scoring the Glass with a Circle Cutter

1
Put on safety glasses and protective gloves. Always wear protective eyewear when you are cutting glass; it only takes 1 sliver of glass to damage your eyesight forever. Use protective work gloves to protect your fingers from glass slivers.^{[1]
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- You will need a glass circle cutting tool to proceed with this method. Circle cutters consist of a suction cup for attaching the tool to the glass, an arm to hold the cutting wheel, and an adjustable cutting wheel that you can slide along the arm to set the size of the circle you want to cut.
2
Put a piece of glass on a flat work surface. Choose a piece of glass that is the diameter of your desired circle, plus at least 1 in (2.5 cm) more. You will be able to cut a circle out of glass that is up to about 25 mm with this method.^{[2]
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- If you are just starting out with glass cutting, then it is easier to see what you are doing with transparent glass. It's also a good idea to practice on some scrap pieces of glass to get the hang of it.
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3
Set the radius of the circle you want to cut on the circle cutter. Your glass cutter tool will have measurements written on the arm so you can place the cutting wheel at the desired radius. Remember that the radius is half the diameter of a circle, so your circle will be twice as wide as the radius you set.^{[3]
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- For example, if you want to cut a 6 in (15 cm) circle, then you need to set the radius on the cutter to 3 in (7.6 cm).
4
Put the suction cup of the circle cutter in the middle of the glass. Press the suction cup part of the tool firmly down with a thumb to secure it against the glass. Rotate the arm and cutting wheel around 360 degrees without applying any pressure to make sure there is at least ¹⁄₂ in (1.3 cm) of space between the edge of the circle and all sides.
- If you are having problems with the suction cup not sticking, then place some double-sided tape underneath it to help hold it in place.
5
Rotate the scoring arm 360 degrees with even pressure to score the circle. Place the thumb of your non-dominant hand down on the suction cup to hold it steady. Use your dominant hand to apply continuous pressure while rotating the cutting wheel arm 360 degrees around the piece of glass.^{[4]
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- Make sure you do a full 360-degree rotation without stopping or letting up pressure to create an even score line.
- You will hear a scratching noise as you rotate the cutter if you are applying enough pressure.
Tip: Starting the motion a bit to the left of the top center of the circle (if you are right handed) will make it more comfortable to complete the full rotation.
6
Remove the circle cutter from the piece of glass. Hold the glass piece down with 1 hand and use the other hand to disconnect the suction cup from the center of the glass carefully. Set aside the circle cutter as you will not need it anymore.^{[5]
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- The glass will be more delicate after you score it. Be careful when you handle the glass or the circle can break prematurely.

Part 2

Part 2 of 2:

Separating the Glass Circle

1
Turn the piece of glass over on a soft surface so the scored side is down. Flip over the scored glass on a soft surface like a towel. This will cushion it while you “run” the score line.
- ”Running” the score line means applying pressure to deepen it so that you can actually break the glass apart cleanly.
2
Press down gently with your thumb all along the backside of the score line. Start at the edge where you finished your score line. Place your thumb directly against the back of the score line and press down, then work your way around the whole score line to run it until you get back to where you started.
- If you use clear glass, then you will be able to see the score line running (the glass breaking along the line) more easily. If the glass is opaque or colored then you will have to look more carefully.
Tip: Smaller circles will require more pressure to run the score because they don't separate as easily from the rest of the glass.
3
Use a handheld glass scoring wheel to make relief scores in the sides. Turn the glass back over and make diagonal relief score lines from the edge of the circle to each of the 4 corners in the glass surrounding the circle. These score lines will release tension and make it much easier to separate your circle from the sides.
- Be careful not to let the circle drop out of the glass while you flip it over.
4
Apply downward pressure to each quarter of the sides to break them away. Pick up the glass so the scored side is facing you. Hold the circle with your non-dominant hand and use your dominant hand to carefully break away each outer section one-by-one.^{[6]
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- Do this above the towel and close to the work surface so that if you accidentally drop the glass there is less chance of it breaking.
- Use running pliers as an alternative to your hands if you have a pair. Running pliers are flat-headed pliers with rubber grips so that they won't break the glass.
- If you did everything properly to this point, then the sides will break away without much effort. Glass cutting takes patience and practice, so don't get discouraged if your first circle isn't perfect!