Glass Cutting

by D. Scott Williamson
May 15,2019

In this simple short tutorial I’ll cover the basics of cutting straight lines in glass and smoothing the edges.

Glass Cutting Materials
Glass Cutting Materials

Materials

  • Glass or mirror to cut
  • Glass cutter (like this one)
  • Household oil (3 in One is what we’re using)
  • Straight edge (optional, only needed for straight lines)
  • Ruler
  • Felt tip marker
  • Gloves – glass is very sharp and serious deep cuts can happen quickly
  • Eye protection
  • Newspaper (optional)

Additional materials for smoothing:

  • Water
  • Diamond whetstone or hone

Safety

Eye protection is recommended. Small glass slivers are created which can be sent up into the air either when breaking the scored glass or handling materials. These slivers are nearly invisible once in your eye making them extremely difficult to extract.

Gloves are recommended. Fresh cut glass is razor sharp, accidents happen quickly, and unprotected hands may be cut deeply. I recommend work gloves with leather or plastic work areas especially on the inside of the fingers, thumb and palm, but even fabric gloves will likely offer some protection.

Glass Cutting

Prepare your work area. Clear any debris from your work surface that may scratch the glass or prevent it from laying flat. Make sure you have enough area to move the glass around.

Cutting glass will create small glass splinters and shards that will need to be cleaned up. Laying newspaper down on your work surface first is recommended (though not pictured). When you are finished cleanup can be as simple as carefully folding up the newspaper containing any glass debris and placing it all in the trash. It’s safer too.

Mark the glass for your cuts. Using a ruler and a felt tip pen mark the line you wish to cut. I prefer to measure and mark the distance from edge opposite the cut in a few places and connect the marks with a line using the ruler.

Prepare to score the line. If you are artistic or if precision isn’t important you can score the line freehand, otherwise you will want to score along a straight edge. Finding the right strait edge can be tricky as common rulers may have raised markings, or may be too thin to reach the cutter side above the wheel. I prefer to use an 1/4″ scrap piece of oak trim – it’s thick enough and straight enough to be an excellent guide.

Whatever guide you choose, be sure to account for how far away the cutting wheel actually is from the edge when the glass cutter is held alongside it.

Oil the cutter. Oil isn’t strictly necessary but it helps the score run and lessens the work on the cutter prolonging its life. Place a few drops of household oil in a small container (I find water or soda bottle caps handy for this). Dip and roll your glass cutter’s cutting wheel in the oil. It doesn’t take much, but makes a difference.

Score the glass. Holding the cutter so that the wheel is away from you and the square notches are pointed upward you will score the glass along the line. You can grasp the body of the cutter as pictured or pinch the sides of the tip of the cutter, whatever is comfortable for you to control while providing firm pressure. Starting at the far edge of the glass, draw the cutter toward you in a single motion with even firm downward pressure completely over the near edge of the glass. If you are using a straight edge be sure to hold it firmly with your opposite hand while drawing the cutter straight and firmly against it and focusing on firm downward force. You should hear the scraping sound of the glass cutter as it scores the glass surface with a clear thump as the cutter rolls off the near edge. Do not go back and forth or make multiple cuts as each scratch will cause the glass to break differently.

Run the score.  (a.k.a. “breaking the glass”) Set your tools aside and carefully pick up the glass grasping the near edge firmly right on either side of the score line. Grasp it with your thumbs on top and your index fingers nearly beneath the score line at the edge, then apply a firm “tenting” pressure right at the edge with your fingertips (raising the center from below while lowering the outer portions with your thumbs). If everything went well you will hear a clean crack and the glass should have parted into two pieces right along your score line.

Glass Smoothing

Smoothing the edges (Optional). The edges of cut glass are razor sharp. If you are cutting glass for a window or picture frame the edges will probably be safely concealed in a frame or mounting, but if the glass is to be handled you may want to smooth the edges. For this I like to use diamond whetstones or hones. The diamond is harder than glass so can be used as an abrasive.

Wet the whetstone. It is crucial for quality and safety that you thoroughly wet the whetstone throughout the entire smoothing process. Grinding or sanding glass creates fine glass powder that can cause serious long term damage if breathed into the lungs. It may even be life threatening. In addition to cooling the glass and prolonging the life of the abrasive, wet sanding will capture the glass powder in the water which will appear milky when done. To wet my abrasive I either spray it with a mister or dip it in a cup of water every minute or so. This also helps keep the abrasive clear of debris and working efficiently.

Grind the glass edges. This may be the most important step to wear good gloves. The glass is razor sharp and and will be wet while you need to firmly grasp it to grind all the top and bottom edges and corners. There are 4 top , 4 bottom, and 4 corner edges to smooth plus the 8 corners themselves. Grind all the edges and corners with a smooth light circular or back and forth motion. There really isn’t a right or wrong technique here, just find what’s comfortable. Try to start at a 45 degree angle and work the entire edge to take the sharpness off, then you can work more angles to round over the edge or try to smooth the outer face. Don’t forget to round over the pointy corners too. Be careful not to let the abrasive block slip off the edge, because if it scrapes against the surface it will almost certainly scratch the glass leaving a visible mark. Work one edge at a time and smooth it completely before moving to the next edge. It is easy to lose track of what has been smoothed and what hasn’t while flipping and turning the glass, if uncertain it is harmless to regrind an edge.

Rinse and repeat. Rinse the glass and diamond whetstone under water and inspect the edges. The water is safe to pour down the drain. You may feel the edge with your finger but don’t run your finger along an edge to test it, a sharp spot is likely to cut you. Smoothed areas will look frosted due to the grinding. Depending on how much smoothing was done the entire side or just the edges will have the frosted appearance. An edge does not need to be completely ground for the glass to be safe to handle, sharp edges and corners are what causes cuts.

Clean up. Use the same care that you would use if you were cleaning up glass that was accidentally broken. If you worked on top of newspaper carefully fold it up and discard it. If not, carefully sweep up the glass slivers (and hopefully not broken glass pieces) from cutting. I don’t recommend using rag or towel to clean up because the cloth can capture glass slivers that can hurt someone later. If you have small glass cutoff waste, wrap it in newspaper or put it in a sturdy container like a box or sealed plastic bottle when you throw it away to prevent it from tearing the trash bag or hurting someone who may handle the trash. It is not a good idea to place cut glass in your recycling, glass may be manually sorted and the cut pieces could injure someone.

I hope this was helpful. Thanks to Workshop 88’s GailJo Kelly for demonstrating the process.  If you have any suggestions I’d love to hear about them, please comment or contact me at Workshop 88 (info@workshop88.com).

D. Scott Williamson
Compulsively Creative