Lesson Learned: Dont try to cut tempered glass

ajstoner21

ajstoner21

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Andrew
I was going to put this in the Lesson Learned forum, but since its not aviation related at all, I thought it might go better here.

I almost feel stupid now, after the fact :mad2:, but wow was that scary/cool.

I was at a friends house this afternoon. He has a ton of wood working equipment and was teaching me about the art of wood working. We were just fooling around, and decided to make a picture frame. Nothing complicated really, just some 45 degree cuts, and some wood glue.


We had this nice little frame put together and now needed a piece of glass. He had an old sliding glass door, that was apparently tempered (apparently our common sense was sleeping....). We were going to cut a piece of it to use in the picture frame. He had a neat little glass cutting tool. I have ZERO experience cutting any form of glass, which became very very obvious at this point. Neither did my buddy. Hindsight, should have used more common sense and tried to google it. This tool was like cutting drywall. In theory, you score it, and it'll snap in a nice clean line. Absolutely not so with tempered glass.

We scored both sides of this piece of glass, and could not get it to break at all. (We were both wearing goggles/gloves, safety equipment). He took a hammer and hit it a few times, and this glass did not break at all. He took a tile cutting blade, put it on a circular saw, and tried to cut it. It was starting to cut the glass. He stopped, and we just stood there looking at it.

About 5 seconds after he stopped (only a few inches in to the cut), the glass quite literally exploded. Glass pieces shot EVERYWHERE. on top of shelves 20 feet away. It scared the sh*t out of me to be standing near it, and see. But at the same time, it was quite an awesome sight. Neither of us got injured, looking back, out of pure dumb luck i'm guessing. I was surprised it didnt just crack or break locally, where we were trying to cut, but the entire sheet of glass almost shattered instantaneously.

Man, did I learn a lot today.


We ended up going to home depot and just buying a small piece of glass, and then his glass tool worked like a charm....
 
Pictures or it didn't happen!

Yeah - tempered glass doesn't cut so well. It's been treated in such a way that it has a lot of internal tension. Any nick in the surface will realease that tension almost explosively. The glass breaks into a brazillion small pieces instead of large shards. Your car windshield is annealed but the rest of the windows are tempered. If the windshied was tempered your first rock chip would 'splode it. Plus, since tempered glass is stronger, your melon would crack first if you weren't wearing your seatbelt in an accident.

By the way - I think building codes require tempered glass in doors just in case someone tries walking through them. Our back door opens inward and is in a corner in such a way that it swings towards a window. That window is also tempered but the window next to it is not. There may be an etched symbol in a corner that tells you it's tempered.
 
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Matthew said:
By the way - I think building codes require tempered glass in doors just in case someone tries walking through them.
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Yes they do.

And, if the door is in a storefront (or has sidelites), tempered glass is also required for the first few feet on either side of the door...4', I think.

And if the storefront run so the floor, tempered glass is required in the lower section...3', I think. This is why you see a horizontal mull at about 3' above the floor in full height storefronts. There's tempered glass below, "regular" above.
 
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Yep, in fact my glass shop I use regularly warns you to make sure that you have the measurements right when you buy tempered glass as it can't be cut afterwards. That's kind of the whole point, they stress it so it crumbles rather than turning into large shards.
Even glass that hasn't been tempered specifically still has enough stress in it so that you have to anneal it to relieve it enough to work with it otherwise it tends to spontaneously crack on you.


When visiting the Corning museum they had a shirt with a very stressed looking guy on one side and a more relaxed one marked "annealed" on the other.
 
I am surprised the scoring or (escpecially) the cutting did not make it explode right away. I've had the pleasure of doing a "controlled detonation" on a sliding glass door pane with just a tap to the corner with a hammer.

WHat a story. Glad no one was hurt.
 
Years ago I was driving my Mustang past NAS Brunswick toward Bailey Island. Suddenly, there was an explosion of glass shards throughout the front of the Ford. ????? I pulled over, stopped, and called the police. The officers were perplexed, looking for the cause. Finally, a hole was discovered in the metal area just outside the top right corner of the windshield. Bullet hole!

Beyond the tree line to my left was a gravel pit where target practicing was common. Something went astray; it was estimated a bullet came through my left door's window and passed about six inches in front of my face. I was shaking for a while. Inexplicable is how tiny bits of glass got into my pockets, even inside the bill compartment of my hip pocket wallet(discovered when I needed to display my driver's license).
 
Lawreston said:
Years ago I was driving my Mustang past NAS Brunswick toward Bailey Island. Suddenly, there was an explosion of glass shards throughout the front of the Ford. ????? I pulled over, stopped, and called the police. The officers were perplexed, looking for the cause. Finally, a hole was discovered in the metal area just outside the top right corner of the windshield. Bullet hole!

Beyond the tree line to my left was a gravel pit where target practicing was common. Something went astray; it was estimated a bullet came through my left door's window and passed about six inches in front of my face. I was shaking for a while. Inexplicable is how tiny bits of glass got into my pockets, even inside the bill compartment of my hip pocket wallet(discovered when I needed to display my driver's license).
Click to expand...

Yikes! :eek:
 
You can trim tempered glass with a sand blaster. What I do is tape the inside line with a couple of layers of duct tape then use some cardboard inside of that to protect the glass I don't want to affect, then start going at it with a sand blaster. This also works on laminated glass. This is the method we used when chopping tops on cars.
 
I once tried to modify a VW window with a dremel tool, that did not turn out well either.
 
Glass is cheap, especially single strength picture framing glass. If you go to any busy frame shop, they will more than likely just give you a small piece of scrap if you are going to cut it yourself. If they cut it, a few dollars in cash will probably do it.

I used to throw away several hundred pounds of glass a month just to get it out of the way.

Never score both sides, don't run your cutter over top of a score you just made, unless you don't care about the cutter.

Those movies you see where the sneaky guy cuts a circle in a glass window by scoring it with a cutter is Hollywood B.S., it won't work. The glass has to snap away from the score.

-John
 
John Baker said:
Those movies you see where the sneaky guy cuts a circle in a glass window by scoring it with a cutter is Hollywood B.S., it won't work. The glass has to snap away from the score.
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OMG!! Say it isn't so!!!!

I used to drive a 1959 Sunbeam Alpine complete with a Lucas starter and generator and...

Now, to be fair, I should point out that I had found a source of junked Lucas hardware that I could cannibalize so I never actually bought new parts when I repaired the starter or generator. On the other hand, it did have a hand crank which should say something about the expected reliability of the electrics.

But in any case, getting it started in cold weather was always a process - at best. The best way was to simply to push start it. And, it was light enough that I could push from outside the drivers door (by myself), get it rolling, hop in, put it in gear and pop the clutch. That usually worked.

One day, the usual routine, battery cranked to nothing, get out, push it down the street, as I hop in I snag the window with my chin. Suddenly I'm sitting in the drivers seat amongst a sea of broken glass. Oops. As noted by others, the glass was everywhere.

On the bright side, I also had an extra set of doors with intact glass so it didn't cost anything to fix it.

Eventually, I concluded that a 1950's British sports car was probably not the most reliable choice for a daily driver and sold it along with all of the "extras".
 
timwinters said:
Yes they do.

And, if the door is in a storefront (or has sidelites), tempered glass is also required for the first few feet on either side of the door...4', I think.

And if the storefront run so the floor, tempered glass is required in the lower section...3', I think. This is why you see a horizontal mull at about 3' above the floor in full height storefronts. There's tempered glass below, "regular" above.
Click to expand...

I think the new rules require laminated glass,as opposed to tempered as ,laminated glass doesn't shatter.
 
frfly172 said:
I think the new rules require laminated glass,as opposed to tempered as ,laminated glass doesn't shatter.
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They would be best to require both. As a person who has gone through a windshield, I can attest they do shatter with sharp, jagged edges. Tempered glass 'pebbles' with rounded edges due to the extra tension. Tempered glass is also stronger and more resistant to being broken.
 
John Baker said:
Those movies you see where the sneaky guy cuts a circle in a glass window by scoring it with a cutter is Hollywood B.S., it won't work. The glass has to snap away from the score.

-John
Click to expand...

Heat that glass with a hot air gun, and touch the circle with an ice cube that round hole will drop out.
 
Matthew said:
Pictures or it didn't happen!

Yeah - tempered glass doesn't cut so well. It's been treated in such a way that it has a lot of internal tension. Any nick in the surface will realease that tension almost explosively. The glass breaks into a brazillion small pieces instead of large shards. Your car windshield is annealed but the rest of the windows are tempered. If the windshied was tempered your first rock chip would 'splode it. Plus, since tempered glass is stronger, your melon would crack first if you weren't wearing your seatbelt in an accident.

By the way - I think building codes require tempered glass in doors just in case someone tries walking through them. Our back door opens inward and is in a corner in such a way that it swings towards a window. That window is also tempered but the window next to it is not. There may be an etched symbol in a corner that tells you it's tempered.
Click to expand...


Yeah, I accidentally put a drill bit through a car window once. It instantly turned into glass pebbles. Kind of pretty, but didn't keep the wind out worth at ....
 
I made that mistake, trying to cut tempered glass. It wouldn't break when I bent it after scoring. I finally whacked it with a rubber mallet and got the explosion. The glass was the front window out of an old television; they used to use it to protect the big CRT (picture tube) that was a bomb waiting to implode if something struck it hard enough.

Dan
 
The tempering of automotive glass allows for those nifty spring loaded punch devices for rescue. Pop, bang. Window gone. ;)
 
denverpilot said:
The tempering of automotive glass allows for those nifty spring loaded punch devices for rescue. Pop, bang. Window gone. ;)
Click to expand...


I started in the EMS world and knew them as window punches. It wasn't until I went to A&P school and learned they are actually automatic center punches.

And if they quit snapping, you can usually clean them up on a grinder so it snaps again.
 
Yeah, back in the day, pops decided to try to repair a rear quarter window on the car by drilling a hole through the glass with a carbide dremel bit, and screwing it to the previously glued closing clamp.

Neither one of us saw it coming. Blammo.
 
Tom-D said:
Heat that glass with a hot air gun, and touch the circle with an ice cube that round hole will drop out.
Click to expand...

I'm going to have to try that. Never heard of that before. Are you talking about double strength window glass, tempered glass in a sliding door, or single strength glass?

-John
 
Lawreston said:
Years ago I was driving my Mustang past NAS Brunswick toward Bailey Island. Suddenly, there was an explosion of glass shards throughout the front of the Ford. ????? I pulled over, stopped, and called the police. The officers were perplexed, looking for the cause. Finally, a hole was discovered in the metal area just outside the top right corner of the windshield. Bullet hole!

Beyond the tree line to my left was a gravel pit where target practicing was common. Something went astray; it was estimated a bullet came through my left door's window and passed about six inches in front of my face. I was shaking for a while. Inexplicable is how tiny bits of glass got into my pockets, even inside the bill compartment of my hip pocket wallet(discovered when I needed to display my driver's license).
Click to expand...

Now see.... This makes no sense... Automobile windshields AREN'T tempered.. They are safety glass, with an adhesive/plastic layer between two layers of glass... whereas the doors and back glass are tempered.

If the windshield was tempered it would shatter with a rock chip.
 
I was in the fire department, we just used the pointy end of a small ex (extendable pry axe) which we carried on both the engines and the ambulance.

If you wanted to get really fancy, you'd take wide adhesive tape off the ambulance and cover the window with it. Smack the corner with the axe and then the whole thing came loose as a flexible glass on tape assembly.
 
Hell, I had a rear window shatter just from tightening the contacts on the high level stoplight that was mounted on the glass.
 
My mother presented us a set of Czech glass tableware that exploded like that. Unfortunately the little piece were irregular shape, some very small, and Americans unfortunately use carpets in their houses, making the cleanup a big problem.
 
John Baker said:
I'm going to have to try that. Never heard of that before. Are you talking about double strength window glass, tempered glass in a sliding door, or single strength glass?

-John
Click to expand...
No, never try that with tempered safety glass, you'll not get as far as the ice cube. and it doesn't work on laminated safety glass either. simple old single layer glass sheet it will work.
 
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