Sometimes this question pops up on the internet: How do I drill a hole in tempered glass? That’s a legitimate question, but it is actually the wrong one. First of all, you should ask yourself: Can I drill a hole in tempered glass? Well, unfortunately for you, the answer is No. See the image above. That’s what happened to a guy who tried it. Yes, there are articles out there where they tell you to get a diamond drill bit, then clamp the glass down, and drill the glass after you positioned some clay around the area you are going to drill. You can try that, and get the result you see in the pic above.
Let me tell you clearly: if the glass is truly tempered, you can’t drill a hole in it. It may look fine at first, but at some point, it will completely shatter. The only thing you can do on tempered glass is edge work (which means, drilling a small amount on the surface).
That’s the quick answer for you. Now in the rest of the article we are gonna go through these points:
- What is tempered glass?
- How can you tell if the glass is tempered?
- Can you drill a hole in tempered glass? (I already gave you the answer, but I’m gonna go into detail)
- Can you drill annealed glass?
- How do you drill holes through glass?
What is tempered glass?
In short, tempered glass (or toughened glass) is what you call safety glass in everyday life. It is annealed glass that has been through thermal treatments to increase its strength. After tempering, the surfaces are put in compression, while there is a tension state inside the glass. These stresses are what cause the glass to shatter into small pieces when broken. They do this for safety reasons: the small chunks are less likely to cause an injury. For this reason, tempered glass is very used in public spaces, and cars.
Tempered glass has several applications due to its strength and safety: for example, shower doors, car windows, glass doors and tables, mobile phone screen protectors, plates, and cookware. It is also used as a component of bulletproof glass.
Tempered glass has many benefits, but there are also downsides. The biggest one is that it cannot be cut after tempering. All the cuts and holes must be done when the glass is still in the annealed state.
How can you tell if the glass is tempered?
Well, the easiest way to check this is to hit it with a hammer: if it shatters into tiny pieces then it’s definitely tempered! Jokes aside, there are a few legitimate ways to tell if your glass is tempered or not. Let’s get through them.
Look for watermarks
The first thing you should do is to check for watermarks. They are usually put in the glass’s corner, and contains the name of the manufacturer and the safety approval markings. Check all the corners, and look carefully because it could be faded, or hard to see if it’s located between glass layers.
Check the edges
If the edges of the glass are exposed, you should check if there are any chips there. If the edges are smooth, without chips, then the glass is tempered. In case you find any roughness along the edges, then the glass isn’t tempered.
Look for imperfections
Due to the heating process, tempered glass might contain dimples, bending, or warping. You should check the glass closely and you might spot one of those imperfections. Another thing to look for is impressions left by tongs. They are used for removing tempered glass from the heat. If you find any of them, then you have tempered glass in front of you.
Check the glass with polarized sunglasses
Put on a pair of polarized glasses and check your glass (you need to do this in sunlight). If the glass is tempered, you will see a pattern of dark lines forming a grid on the glass surface. This pattern indicates the variation of glass stress; it is formed during the cooling process of the glass. Another way to do this is to take a picture of the glass through a polarizing filter. You can get one of those for your camera on Amazon.
I still can’t tell if my glass is tempered or not…
Well, in this case, you should assume that your glass isn’t tempered, especially if you didn’t find any markings. If you need for example a small hole in a mirror to get some cables through, I would probably go for it. Don’t drill too close to the edges (take at least 3/4 of an inch of distance), and remember to wear safety gear (a mask and glasses for the dust, gloves to protect your hands).
Can you drill a hole in tempered glass?
It should be clear by now that you can’t drill a hole in tempered glass. If you want to have a tempered glass with a hole in it, you need to get the hole done when the glass is in annealed state, before the tempering process.
You can do edge work on tempered glass, but you need to be careful: if you remove too much glass, it will shatter. Also, you are weakening the glass by doing that. So be careful.
The only tempered glass you can drill successfully is the ultra-thin glass used for example in cell phones. That’s because it is chemical tempered glass, which is substantially different than heat-tempered glass. This kind of glass is only used in special applications, you don’t find it in cars, doors, etc.
Can you drill annealed glass?
“Annealed glass” is just another word for the standard glass you see all the time. Your mirror is probably made of annealed glass. It is a thermally treated glass that is then slowly cooled to release any internal stresses. You can distinguish it from tempered glass because it’s much cheaper, and when it breaks it form bigger chunks that can be very dangerous.
Can you drill this kind of glass? Absolutely. But you are going to need the right tools and the right procedure to do so. Check the following paragraph to learn more about it.
How to drill holes through glass
Basically, you can drill holes in whatever type of glass (excluding tempered glass). The first thing to do is to get the right drill bit. You need to use glass drill bits. These are carbide bits, and you can get them at your local hardware store or online. Another option is to use a diamond drill bit.
After you get the right drill bit, you need to prepare the glass for drilling. Since the surface is smooth, the bit might slip as you start drilling. To prevent this, you can either tape the glass or tape a piece of cardboard to the glass on the spot where you are making the hole. Remember not to drill too close to the edges, or the glass will shatter. Take at least 3/4″ off any edges.
Now, it’s time to drill. Take a variable speed drill, and begin at a very slow speed to create a dimple in the glass. This will prevent the drill to slip later on. After you did this, remove the tape or the cardboard and start drilling faster, at about 400 rpm.
Don’t drill faster than that, or you will get burn marks around the hole. To avoid this, you should apply a coolant before and during drilling: either water or oil is fine. Another thing you could do is placing a wet sponge under the glass to keep it cool if you don’t want to make a mess with water or oil. The coolant will also prevent the glass from cracking because of the hot temperature developed.
Don’t press too hard or you will break the glass! You need to apply only a little bit of pressure, and let the drill do the work. Make sure the glass backside is firmly supported.
So in conclusion, It should be clear by now that you can’t cut or make holes in tempered glass. There are no ways around it: you may read online that someone did it, but it probably wasn’t tempered. Apparently, you can “grind” a hole into tempered glass, (there are videos on Youtube about this) but I never tried it, and I wouldn’t suggest it. By doing that you are losing the integrity of the tempering process, and you might break the glass.
In the end, it might be worth the try only if you don’t mind seeing your glass shatter, and/ or the hole you want to make is small. If you are going to do this, remember to put some safety gear on first: a pair of glasses, some gloves to prevent cutting your hands, and a mask to avoid breathing the glass dust.
That’s it for today’s article, I hope you found the information you were looking for. See you in the next one!