Cutting Circles in Stained Glass

Have you ever seen in the movies a cat burglar cut a circle in the window and pull it out with a suction cup? Us glass artists know that it’s impossible. But how do you go about doing it?

I use the Glastar Strip/Circle Cutter but there are many out there that are just as good. The circle cutter setup may be different but the cutting technique is the same.

1. Make sure your piece of glass is at least 1 inch larger than the circle you need.
2. Place circle cutter in center of piece of glass.
3. Do a test run around the circle to make sure you are comfortable pressing down all the way around the circle but do not press down on the cutter. Also make sure the cutter stays on the glass.
4. Press down on the circle cutter and score the glass in circle making sure to have the start and stop points of your score line match up. (Don’t let the center point of the circle cutter move)
5. Break your score line all the way around the circle by using the Morton M80, Morton Safety Break, or flip your glass over with score side down on short pile carpet or rubber pad and press on score line to run the break all the way around.
6. Make 4 relief cuts from your broken score line of the circle to the edge of the glass.
7. Break relief cuts and circle should come out in one piece.

Circles from 4” to 20” will typically break out clean with this technique. Smaller circles than this will usually have flares that will need to be ground. Larger circles are just harder to handle by yourself.

What kind of lightbox do you need for stained glass cutting?

There are many different lightboxes out there to choose from. There’s even a tablet available that will light up in different shades. You don’t need anything fancy just functional. In fact, the hardier and bulkier the better because that way you don’t freak out if you scratch it. It’s meant to be worked on. And you might even progress to the point where you will cut straight on top of the light box and not just use it for tracing the lines.

You will need a box that you can press down on. Wood and clear glass work the best.

If you have a box with plexiglass change it out for real glass, preferably ¼” thick and clear. The reason is because plexi flexes when you press on it. When you score glass you don’t want any bowing when you press down and glass won’t do that. If you were to use plexi it can cause uneven scoring and even cause your glass to break prematurely.

You can easily get a sheet of glass at your local window glass store. They will even cut it to your specifications and polish the edges for you.

The reason you want the glass to be clear is because your pattern paper will be your diffuser. Brightness is your friend when you want to see through the pattern and the glass. Some dense glass will be hard to see through if you don’t have intense enough light. Florescent lights are fine but if you have a choice I would get LED strip lights (as intense as possible) because then it won’t be so hot to work over.

What size lightbox do you need?

Well, I’m very spoiled, I have a very large 5’ x 7’ light table for any and all size panels I might build. But you really don’t need it. Simply have a small lightbox, slightly bigger than your biggest pattern piece around 12” x 12”.

When you use your lightbox have two full sized patterns, one for your lightbox and have the second pattern on a worktable nearby. As you cut out a stained glass piece put it on your worktable pattern. That way your cut pieces are out of the way and you can see your pieces fill your pattern. This will allow you to nearly eliminate piece numbering which can speed up your process as well.

What if I don’t have a lightbox?

You can make a lightbox out of anything that will hold glass above a light. Have an old glass top table? No, go down to your local recycle store and find one. All you need is the glass top table and a portable shop light, a table lamp (with shade removed), or even a strong flashlight under the glass. Be creative: coffee table, end table, dining room table, table with removable tiles (replace with glass).

How do I transfer my stained glass patterns to the glass?

There are many ways to transfer stained glass pattern to your glass, pattern shears, tracing paper etc. I don’t cut out my stained glass patterns at all.

A lightbox is, in my opinion, the most efficient method for stained glass cutting. You can trace your pattern pieces directly on the glass. This will save you loads of time by not cutting out and numbering your pattern pieces. Plus you can get a look at the direction and variations of the glass before you cut it. The only time you will have to cutout a pattern piece will be for extremely dense glass like black (or you can use tracing paper). This is how I use a lightbox:

• Put your pattern on the top of the lit lightbox.
• Put your glass on top of the pattern and position the glass with the variations (streaks, texture, color density…) where you like it to be.
• Trace the pattern on the glass that you want to cut out. (if you are having a hard time seeing the pattern, lift up the glass and trace the pattern line with a sharpie to make it darker)
• Score the glass (inside the line) and break out your piece. At this point you can position the glass however you need to get a good score line because the pattern line is on the glass.
• Place your cut piece on a second full sized pattern on your worktable.
• Repeat

When you really start to feel confident in this process, you won’t even have to trace the pattern on the glass you can cut directly on the glass with the pattern underneath to guide you.

Next week I’ll talk about what kind of lightbox you need. You might be surprised how simple they are?