How to Cut Glass

Intro: How to Cut Glass

Glass cutting is a fascinating skill that a lot of people try, but quickly gives up. Why is that? My thought is that most people go and buy glass for a certain project, and expect to get e decent result after a few tries. That might work for a handfull, but I would strongly recommend to find a local glass shop and ask for some scrap glass for free or strongly discounted with the soul purpose to practice on. Glass workshops always get a lot of long skinny pieces that is good for nothing but splitting up to short pieces to make them fit in the recycle bin.

I will show you the basic steps of cutting glass, and hopefully give some helpful hints, but the truth is: The most important thing to learn glass cutting is practice, practice and more practice!

STEP 1: What You Need

-Glass (obviously!) For practice I would recommend 3 or 4 mm thick glass., which is not hard to work with but also not to thin to break easily. 2mm is typical glass for picture frames, but can be a difficult thickness before you feel comfortable with how much pressure to put on the cutter. 5 mm and thicker gets harder to break, and can take some courage when it gets really thick. 8mm and up, you need to really put weight on the glass to break it open (I'm talking using your body mass to have enough oomph, and I'm 6'2" tall !, that's 190 cm for those outside the US ).

Glasscutter. The picture is showing three, but really just two different kinds. The wooden handled one is easy to find, has spare cutting wheels, but no oil compartment. The two others have oil compartments fitted with a valve at the cutting head that will open up as you push down the cutter to the glass and lets out a steady flow of oil as you cut. Most glassworkers would have both kinds at hand, but as you start I would recommend the wooden one because of price and a few uses the "fancy" ones does not have. (I'll get back to that)

I went online to look for different cutter, and discovered that it's not easy to find my kind of wood handle cutter now. ( I got mine a long time a go when I was still working at a glass shop.) Most the model have the ball head, used for hitting the glass to open up the score made in the glass, a method I try to avoid since in my mind the hands on method has a greater success rate.

Oil/lubricant. You do not want to do "dry cuts" on glass, which I will show in the next step, so you need some kind of lubricant. Glass shops normally has a thin clear oil specially made for cutting glass, but my experience is that they prefer to keep this for themselves. (mostly because it's inconvenient having several people coming by every day asking for a few "drops" for their puny projects) , You can find glass cutting oil on Amazon or other web stores. If you just need a few drops, and your wife has a sowing machine, you could beg her to give you some of the sowing machine oil. It's very similar to glass cutting oil, but gets a bit pricy if you want to do a lot of cutting. Since my wife has not been willing to share her sowing machine oil, and I am not able to purchase from Amazon ( I live in China), I've used WD-40. It works ok, but is not ideal. The bonus is that the long straw you can put on makes it easy to fill the oil compartment of the fancier cutters. You can also use vegetable oil or other oils found in the grocery shop, but they are most times too thick to put in the oil compartment cutters, and more messy and sticky.

Flat work surface. You want the glass to be totally flat, and have good support everywhere. Any bending and tension in the glass will result in the cut/score to run "off track" if you have not already broken the glass in the cutting process. The best surface should be firm and not too soft. you can work on a tile or smooth concrete surface, but it's easy to damage the glass scratching it and chipping it as you move it around on such a hard surface. The best is a wooden surface covered with felt or something like it. this gives the right firmness and good support, makes it easy to slide the glass around without scratching it, and is forgiving if you should be sloppy and bump the corner/edge of the glass into the work surface.

Measuring tape. Most glass jobs have little leeway, and you want to measure well before you cut. Unlike wood, you can't just sand/plane down the glass a tad (unless you happen to have a big glass polishing machine hidden behind the junk in your shop).

Straight/angle. If you want a straight cut, you need a straight! You might be steady on your hand and good at following lines, but if you want a true straight cut, get a straight that you can put your cutter up against. That means that the typical thin steal straight or angle will not work, since the wheel on the cutter will lift the glass cutters head too high up to lean on the straight. Ideally you want something between 1/8-1/4 inch thick.

There are many more things you can buy for working with glass, like circle cutter, suction cups, tongs etc. but we will not go there now, since it's not necessary for just plain cutting.

STEP 2: Getting Ready for the Cut

Measure, measure and measure. A lot of jobs I've done are down to the millimeter, so there is no room for failure. your project probably has some more leeway, but it never hurts to be accurate. Now you come to the first factor where practice makes a difference. How much does your cutter differ from the size you want on the glass. My experience is that most cutters are 2 mm from the middle of the wheel to the edge (left or right). My wooden handle one is different from each side, but I never cut with the thick side since that's where the nut for changing cutting wheels is placed.

Next is the lubricant. If you have a cutter with the oil tank in the handle it's just to fill up and go. If you have a more basic cutter you got two ways of applying the lubricant. With a short cut, it should be enough to put some on the cutter, or dip the cutter in some of whatever oil you use. For longer cuts the best would be to put some straight on the glass the whole way where you want to score the glass. Have some oil of choice in a cup, and use a little brush to tip in the oil and brush onto the glass. You dont need much, but be sure to have it on along the whole line. Putting on a lot will just give you extra mess to clean up after you're done cutting.

I did some cuts with and without oil, to show how they look. The single cut is all without oil. On the picture with three lines, you see one without oil, one with oil done by the wooden handle cutter and the last with my self lubricating cutter. The perfect cut should be close to invisible, but I'm a bit rusty.

If you do a dry cut on a thick glass, pressing down hard as you score, there will actually be this crackling sound from the score after you have done it. It's hard to record the sound though, so you'll just have to take my word for it or try yourself.

STEP 3: Cutting/scoring

This is it! you are now ready to cut/score the glass. I've always struggle to explain how hard to press the cutter on the glass, but I think I've found an OK way now. This do require a flatt digital scale preferably with a tare function (reset function), but can be done without the tare as long as you know your math.

I placed a practice piece of glass on the scale, and pushed the tare button to zero out the scale. (no tare function, just notice the weight on the glass and add on the desired pressure). The few cuts I did I ended up with a pressure between 90 and 110 OZ. Put the cutter on the glass and try to get a feel of how much pressure to use, as you cut, try to keep about the same pressure and speed the whole way.

Keep the cutter in a straight angle right/left and slightly tilted toward you.

Cut/score only once! If by any chance parts of the line was not scored, you can try to run over that part again., but ideally you should only need to do it all in one move.

Hopefully you now have a nice clean score in the glass and can move swiftly to the next step. I say swiftly, because the score will "harden up" again if you leave it for a couple of minutes.

STEP 4: "Breaking" the Glass

Now, you'll find out if you did all the things above right. A nice clean score should make the breaking easy, but for those who have never done it before it can be a little scary thinking: How is that little scratch going to make the glass break open in a perfect straight line?

There are three ways of doing this.

1. "The Shocker", hitting the glass on the opposite side of the score from one end to the other of the glass. This is the last method I would choose, unless the glass is to thick or in a position where the two other methods are not possible. ( I do not have any pictures of this method now, but can add later if someone want)

The disadvantage with this method is that every time you beat the glass you risk that the cut will start traveling to the left or right away from the score, especially if you're not good at hitting right under the score.

2. "The casual"

!!!! Do not try this on any glass thicker than 5 mm if you don't have some experience with this method !!!!!!

Only by the help of your hands, break open the score. Place your two pointer fingers on the underside of the glass one of each side of the score. Put your two thumbs on the top of the glass, one on each side of the score, and just break it open like you would break a chocolate bar.

The danger with this is your hands are surrounding the edge of the glass, and are more exposed to cuts if your not carefull, or have a little mishap.

3. "The Safe" , the safest and most controllable way of breaking the glass on most thicknesses of glass. This method was the one my teacher would always tell me to do during my classes unless it was not possible because of reasons mentioned earlier.

This is where the wooden handle cutter of mine come into great use. I place the end of the cutter centered straight under the beginning of the score. An alternative to the cutter can be any wooden or plastic piece 3-5mm / 1/8 inch thick, and 1 cm / 1/2 inch wide. Then place one palm on each side of the cutter, resting them flat and firm on the glass. Then, when ever you have built up enough guts, give the glass a good push straight down towards the surface and it should "pop" apart in the blink of an eye.

STEP 5: Thats It! Now, Practice, Practice and Practice!

That's how you cut glass. I hope this has been helpful to you and you have not had to break out any bandaids. When I was working with glass, my goal was always to start the weekend without any on my hands, which was many times dependent on what kinds of jobs I had at the end of the work week. I'm including a little video of me doing a wavy cut, just to show it's not hard when you have done it for a while.

If there is enough response, I will put in my best effort to post more instructables on glass cutting and other glass related instructables.

Untill next time, go break some glass! And remember the whole thing with bad luck breaking a mirror is just superstition! I would know after breaking thousands of them and having a wonderful family and exciting job.

Comments

[Adam Scott]

Make sure you cut on the correct side of the glass. Do not cut on the side of the glass that is coated with the UV coating. This is like conservatory glass.

[mickdp1]

Sewing machine oil is just mineral oil (or paraffin oil, depending on where you live) which can be bought at a hardware store cheaply and is very useful.

[vijithak321]

Many thanks for the useful article. The 'million dollar' advice is on how much pressure to put on the cutter when scoring, with the weighing scale etc., because this is an aspect i have never learnt from reading write-ups on the subject before!!!

[etmh]

Many thanks for taking the time to write this. I've needed to cut some thin glass (probably 2 or 3 mm) and eventually managed it, but I simply didn't know that I needed the oil (how would I know until someone takes the time to write a tutorial like this?)

[Duplo for Daddies]

I'm glad you like my instructable. I felt I ended up with a lot of writing and wondered if anyone would bother to read through it all. I wish I had a good way to make videos, but that has to be a future thing I guess. Good luck on any other glass projects you might encounter.

[SeanL59]

This is great for me, I prefer instructables that are written out rather than videos, so I'm always glad to find them on topics I need.

Thanks for the great synopsis and pleasant, conversational writing style!

[emews]

I too much prefer well written instructions to videos. I just seem to process the information better.

[chancylancer]

what are the notches for on the backside of the glass cutter and Thank You for the instructions

[MattP116]

I need to cut 4mm off an edge of a glass mirror. Does the method that you describe here work so close to the edge?

[Duplo for Daddies]

Hi Matt. Sorry for late answer. Busy times. If you have not already done the cut of the mirror, yes you can do it the same way, but you will need some plyers to get a hold of the thin piece of glass and break it off. It’s not an easy task, all dependent on how thick the glass is. I wish I could post something on it, but my schedule does not permit it at the moment. It would definitely be easier if you can cut off more of the mirror and compensate for the smaller size. I don’t know what you’re using it for so that makes it also hard to know what works best for you.

[anantyanta]

Thanks very much, I have a small project of cutting shelves for a cabinet, and of course checked Instructables first. :)
One question (hope you still see this after 3 years...) - you mention "the score will "harden up" again if you leave it for a couple of minutes." That sounds very strange to me - surely the scoring does not produce sufficient heat for softening up the glass, and glass is also not likely to oxydise after a cut? Could you please elaborate a bit on what this means, and what is happening during "hardening"? Many thanks! :)

[ascii]

There's a lot of mythology surrounding glass, mostly based on the idea that it's in some way liquid and flows. It's actually an amorphous solid, and does not.
When I first started cutting glass I was told that you had less than a minute to make the cut after scoring it, or less than thirty seconds, or less than an hour. I scored a scrap piece several times and put it aside for a week. Then I forgot it, and a month later when I found it I snapped it in each place with no trouble.
I was also told that glass more than a year old can't be cut, but the stuff I was using was easily a decade old.
I live in a house that's over a century old, and still has some original glass. I don't have the equipment necessary to accurately measure, but I can see no sign that it's thicker at the bottom. I'm told that the people running cathedrals used to take the windows out every few centuries and put them upside down for the same time.
Leaving aside that the frames are cut stone and weight several tons, that the cranes that could do this haven't been found and that the whole idea is ludicrous, glass doesn't flow, and an old window is exactly as it was made. If this wasn't so there's be at least one picture of glass which had slumped and torn open, and there isn't.
There's glass from Egyptian tombs made long before the pyramids, and it's not little puddles, or even distorted.
I've seen a picture of carefully made glass rods which were bent by thirty degrees - you can do this if you polish the surface so there's nowhere a crack can start - and left that way for forty years. When released they sprang back, unbent.
My son just asked, "If it flows after a few seconds, does that mean you can hold the edges together and let it melt back into a single sheet?" Sadly, you can't.
I don't like to nitpick, but this weird legend scares off novices, and there's no reason.
Aside from that, this is an excellent instructable.

[Duplo for Daddies]

Thanks for you comment Ascii. After I wrote my comment on glass being some kind of solid liquid, I found a new article on the matter that talks about the term liquid is not correct about glass, and the thicker bottom than top on old glass is not because of gravity over long periods. So I was wrong about that. There is no good explanation on the thin top thick bottom, but I guess esthetically/logically it would make sense to put the thicker part down if it was not an even glass. (the way they made glass before the big factories always gave uneven glass, but that a whole other lesson)
About the score, I have always felt that it's better to break it as soon as it is done. Can you break it after a while/a year? Of course, because the score you have made will always be a weakness in the surface. I can not prove that time makes a difference other than what I feel.
I have never heard about the age of the glass being an issue when it comes to cutting unless it's so old that it was made with the old techniques. The way they made glass before left a lot more uneven tension/surface in the glass, and made it more prone for the breaking of the glass to run of the scored line. You can still get glass made with the old techniques, but it's expensive, and especially targeted towards companies who do maintenance on antique and protected architecture built before they had the "perfect" glass we use now. I once did a job on a protected building with the old kind of glass and it was very interesting to look at the old pieces of glass. I had to cut a few new pieces to some of the windows, and I notice a big difference in cutting the old style glass and new kind. I would love to share, more, but I got an appointment to run to. Thanks for all comments!

[Duplo for Daddies]

Hi! Glad my instructable is still read by people. Glass is considered a solid fluid. Meaning it still moves and changes over time. If you have an air bubble in a piece of glass standing vertically, the air bubble will actually move upwards over a period of many years. Another neat thing is if you find an old window ( I don’t know how many years), the glass will be slightly thicker in the bottom than top because it is “sagging” (don’t know a better term for it). So when you score the glass, think about it has cutting through the surface of water. When you have just run over it , the surface area is weak and unbalanced and easy to break open, but as you leave the score alone without opening it, the tension in the surface will become balanced again, and just leave an ugly line. This naturally leaves some weakness in the glass, but not to a degree where you can do a controlled opening/splitting of it. I hope that gives a decent explanation.

[anantyanta]

Thanks mate, that was a great explanation, thank you very much indeed!
By the way, being the noob in glass-cutting that I am, I tried with a glass pane I got from a neighbor (they put it out on the street to be collected). Tough luck - imagine my face when I realised that was security glass, and splintered in millions of pieces when I tried to break it at the cut. :D
Used >1 hour to clean up my workspace again. Now I'll have to see where I can get glass again for my project...
Mind you, I'm not blaming you, at all! Was my own stupidity.

[RicardoVerdi]

Thank you. Shame that the 23 second video would not play - it said
An error occurred. Please try again later. (Playback ID: Ob5GhiNhZkKqBVAZ)
Learn More

It was recommended to me to score both sides of the glass. Do you have any comments please?
We have a window company nearby, they install new windows into homes and discard the old ones. They are happy for us to collect glass from their rubbish skip. We went recently and they had just broken up lots of bits the previous day! We took what they had and ruined a few but got one good piece for a cupboard door insert, now we just need one more piece to cut. They are closed for holidays so I hope they open as planned next week - with new covid restrictions some companies may not open for a while here in Ireland.

[adejinleseyi]

Thanks for the information, it is very useful.

[RobertC436]

A big thank you for the information I have two of the cutters that have oil containers built in similar to the ones you showed I have 3mm and some 5mm glass and need to cut a piece of the 5mm for a friend's shop window so any tips are greatly appreciated.

cheers

Robert.

[Duplo for Daddies]

Glad I could help. Have you done the cutting yet? Please let me know how it went.

[misterxp]

wow. Wish I had seen this before I cut some glass a few weeks ago.

I also have the wooden handle cutter, like yours, but I bought it years ago. I tried to cut glass then with bad results and it was left in a drawer. I only used it now because I needed to cut some glass for a pictue.

I didn't think to look at instructables. I did a dry cut and passed over the line 4-5 times. I was able to cut the glass OK but the edge was terrible. Now I know why I got that horrible sound. I will try again with following your instructable! Thanks for sharing!

I will also try and cut some shapes like you did too!