Cutting glass circles

Have you ever watched a movie where the cat burglar breaks in through a window by cutting a hole in the glass? He scores a circle with something sharp and as quick as anything pops out the piece of glass. Well unfortunately, as with many things you see in the movies, it’s not the same in real life.

The thing with cutting a circle out of glass is you can’t have your cake and eat it too, you either get the hole or you get the circle. The reason for this peculiarity, that only occurs in glass, is that you can’t just cut straight through glass, you need to score the circular line first and then remove sections or else you risk the whole piece breaking. If done correctly the glass will break perfectly along the scored line, following the path of least resistance.

The reason the circle won’t just pop out, is that you’re not cutting all the way through, even if you did, the circular piece of glass would be the exact same size of the hole so it couldn’t be removed – there is no give, which is why you need to choose between either having the hole or the circle.

Image credit: By Hendrik Kueck from Vancouver, Canada (Flickr) [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons

So you want to cut a circle of glass

Cutting glass circles is by far the easier of the two options, however, whether you want a circle or a hole the process is mostly the same. Things you’ll need:

  1. A permanent marker
  2. A circle cutter (looks a bit like a compass – order online or look for at hardware stores)
  3. Spray lubricant oil (not essential but helps the cutting head glide along the glass)

If you need glass, go to my choosing the right glass page to make sure you are using the right glass for the right job.

Step 1:  First up mark the centre of the circle, making sure you leave at least an inch of glass around the outside of your circle, if you don’t the cut will run to the edge of the piece you’re working with.

Mark the centre point and circle

Mark the centre point and diameter

Step 2: The next thing you want to do is set the diameter, use the sizes on the circle cutter to set this. Circle cutters usually have four marks on the suction cup, use these marks to line up the spot you marked for the center of your circle. I usually use a permanent marker to mark my lines, this can be removed from the glass with a bit of metholated spirits after you have finished cutting. After attaching the suction cap you want to lightly roll your cutting head around, making sure you have left enough room around the circle. It’s also a good time to check that your cutter is set to the right diameter. After this, if you have it, spray the glass and cutting head with spray lubricant and lightly roll the cutter around again, now you’re ready to score the glass.

Step 3: Scoring the glass and finding the right pressure takes a bit of practice but it’s close to the pressure you use when writing with a ballpoint pen. You want to push the cutter head down at this pressure and complete one rotation making sure to stop when you reach the start of the cut, after this you need to open the cut.

Step 4: Opening up the cut can be done in a few different ways, the first option, and the way I do it is to turn the glass over and using your thumbs push down on the score mark, if you do this on a carpeted bench or a towel or something similar it will open up the score mark, this will be easy to see and if you move along the line, pushing as you go, you should see the score mark open up. Keep doing this until you get back to the start of the cut. It usually makes a click sound when it’s completely open.

The other way you can open the cut is by lightly tapping the line with a hammer on the opposite side from where you scored the glass, this can sometimes leave a rough saw tooth edge, it is, however, a good way to start a cut and I will usually use this technique on thicker glass.

Step 5: After completely opening the cut you want to turn the glass over and repeat the process on the other side. This makes sure the glass is completely separated, this can be done by pushing or tapping.

Step 6: The next step is to release the circle, this is done with a normal glass cutter, make four score marks in the waste glass in a cross shape and open the cuts in the same manner this will release the circle.

Score four lines out to each edge

Score four lines out to each edge

 

 

Tap out the unwanted pieces

Tap out the unwanted pieces

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