Strength of glass

[TheStu]

I know that glass is a bit of a general word, and am not sure if this is the right place... but here we go.

I am designing a shelf for a new computer desk and want to use glass for it (instead of the wood that I usually work with). The shelf will be supported by four 5/8" steel threaded rods, and will need to support a standard PC tower (call it... 30-40lb to be safe), there will be another shelf above it but it will only need to support 10lb or so, but if it can also support the same as the tower shelf, that's fine.

So, first of all, is this the right place?
Next, how thick a piece of glass would I need to accomplish this?

 

[nboy22]

I was just watching this TV show called James May's 20th Century (BBC Show)

It was showing how glass on skyscrapers is much, much stronger than regular glass.

They took a mini cooper car, and dropped it from 10 feet up in the air onto a sheet of this glass and it didn't break. They were saying that they have a special hardening process where they heat it up to 600 degrees celcius and then place it in a cool area, and supposedly that increases the strength of the glass.

This leads me to believe it wouldn't matter the thickness if you've got a nice, strong piece of glass. The problem is just how to obtain that glass.

 

[Howard]

That's tempered glass.

 

[TheStu]

I neglected to mention that it would be a piece 18"*30"

 

[CycloWizard]

Yes, this is the right place. There are lots of types of glass, though I think the kind you want is generally called "S-glass." I don't have my books at home to look up the properties, but a quick check online gave the following:

Tensile Strength (Mpa) ............. E-glass 3450 / S-glass 4300
tensile modulus ( Gpa)............... E-glass 72.4 / S-glass 86.9
Strain to failure........................ E-glass 4.8% / S-glass 5.0%

It's too late for me to try to think about the design now, but I can do it tomorrow without much trouble I think. Off the top of my head, I would say that 1/4-3/8" should probably be plenty.

 

[The Boston Dangler]

the tempered glass on my tv stand is about 1cm thick and holds over 80 pounds.

 

[TheStu]

the tempered glass on my tv stand is about 1cm thick and holds over 80 pounds.

Well, that seems to hold with what CycloWizard wrote, I will have to see if the local glass place here carries something like that, and will make the alterations that I need. I don't think that I have on hand what I need to cut, shape and drill glass.

 

[AndroidVageta]

I admit that I am no expert or anything...but if the glass is going to be supported underneath...and it isnt sugar glass (lol) the simply holding a computer tower shouldn't be an issue at all...Im thinking even non-tempered glass would work. You arent using the glass for your actual work area (thinking table/desk top) so any glass should work, especially more common store bought types.

Just my 2 cents, but I think its logical!

 

[TheStu]

I admit that I am no expert or anything...but if the glass is going to be supported underneath...and it isnt sugar glass (lol) the simply holding a computer tower shouldn't be an issue at all...Im thinking even non-tempered glass would work. You arent using the glass for your actual work area (thinking table/desk top) so any glass should work, especially more common store bought types.

Just my 2 cents, but I think its logical!

It is going to be supported on the corners. 5/8" steel threaded rods, holes drilled 2" in from each corner, nuts placed on either side (probably with rubber gaskets/washers between glass and nuts). So, yes it will be supported but with a sheet that size, a large amount of weight is going to be moved to the middle of the sheet.

At least, that is what I can figure from Physics and Engineering courses that I took 5-6 years ago.

 

[The Boston Dangler]

i applaud your aggression in building a glass flexi-rack! glass and stainless should look killer. good luck working with the glass, it's way out of my league.

edit:
you can't cut tempered glass. i found this place at random on google:
http://www.onedayglass.com/

 

[Mark R]

You should only use tempered glass for furniture.

Aside from the increased strength of tempered glass, tempered glass a safety advantage. Conventional glass when broken, cracks into sharp edged pieces. Tempered glass, if you do manage to break it, disintegrates into tiny round pieces. If you've seen the glass pieces after a car wreck , or a break-in, you'll know what I mean.

 

[William Gaatjes]

I remember you can also buy laminated glass. Even if it would crack it would hold together. That should prevent any possible hazard...

Toughened (T) - toughened by a heat treatment. It disintegrates into small, granular pieces, which are not sharp, and reduces the risk of injury. Small pieces will still be dangerous to children so ensure they are kept away in the event of breakage.
Laminated (L) - 2 or more sheets of ordinary glass attached together by a plastic interlayer. On impact any broken glass will remain attached to the plastic reducing the risk of injury
Wired glass (W) - Has a network or mesh of wires embedded in it.

An alternative, less expensive option is stick-on safety film, which helps prevent glass splintering.

Below are some further points to consider:
Transfers or sticker can highlight dangerous glass areas to children.
Children may trip on loose rugs or mats, so keep them away from glass doors and windows
Low-level glass areas can be screened with plants or furniture
When buying furniture with glass doors or tops, look for approval to BS 7376 and BS 7449
Keep glassed areas well lit

http://www.safekids.co.uk/GlassDoorWindowSafetyChild.html

http://en.wikipedia.org/wiki/Laminated_glass

 

[Mark R]

Wired glass (W) - Has a network or mesh of wires embedded in it.

It's a little misleading to call wired glass a safety glass.

It really has very little safety benefit. The wire doesn't add strength, and doesn't stop the glass breaking into razor sharp shards. Indeed, because the wires hold the shards together, it can be more dangerous than simple plate glass, e.g. if an arm is pushed through such a window.

It's only real use is as a low-cost fire-resistant glass. The wire simply keeps most of the glass fragments in place, so when the glass breaks due to heating by fire, it doesn't fall out of the window, and helps prevent smoke from spreading. The wire also provides a secondary benefit in that it conducts heat from one part of the glass to the other, and helps reduce 'hot spots' which cause uneven thermal expansion and subsequent glass cracking. However, modern alternatives such as borosilicate glass tend to give better performance - better heat insulation, better resistance to breaking and better phsyical strength. They also don't have the butt-ugly prison-style appearance.

Laminated glass is an alternative to tempered glass for furniture - but may be more expensive. However, it is the preferred option when maximum physical strength is required, as it is potentially significantly stronger than tempered glass.

 

[TheStu]

i applaud your aggression in building a glass flexi-rack! glass and stainless should look killer. good luck working with the glass, it's way out of my league.

edit:
you can't cut tempered glass. i found this place at random on google:
http://www.onedayglass.com/

That is a great site, and gives me an idea of how much it will cost me. Apparently, for rounded corners and holes drills, it will run close to $100 a piece, and I need 4-6 pieces... so I might have to wait a while.

The whole thing will be a combination of stained wood, steel rods and glass plates. Should look pretty good when I am done, whenever I can get started of course!

 

[alfa147x]

Keep us updated! I'm looking forward to seeing how this turns out

 

[DrPizza]

You could also take your piece of glass and submerge it in a potassium bath (probably heat up some potassium nitrate until it is molten around your glass. The sodium atoms/ions within the glass can migrate out & be replaced with potassium, which is a larger atom. The result of this is that the outer layer of your glass will be under compression, which will close up a lot of imperfections, making your glass far far stronger; sometimes referred to as "unbreakable glass."

I believe that the bodies on epi-pens are strengthened this way. My former professor who owns/owned the company that makes the epi-pens (I believe all glass bodies for epi-pens are made by that company) now has a company that can strengthen all sorts of glass pieces by this process.

You could make a plate of glass this way & let us know how it works.

 

[Modelworks]

Remember to use some sort of rubber between the supports and the glass so that the load is evenly distributed through the glass and onto the supports. Any glass will break if you put too much force on small areas. Ice pick + window = shatter , and all you have to do is press down on the ice pick .

 

[narzy]

the thing that would concern me the most would be the vibrations caused by the fans and hard drive of a glass built case. Oh this is for furniture not a computer case. I'm probably wrong about the vibrations anyway but it was a thought I had .

 

[jimhsu]

i applaud your aggression in building a glass flexi-rack! glass and stainless should look killer. good luck working with the glass, it's way out of my league.

edit:
you can't cut tempered glass. i found this place at random on google:
http://www.onedayglass.com/

For why you can't cut tempered glass, look up Prince Rupert's Drops. Essentially, tempered glass is a very VERY strained piece of glass, held together by tensile stresses in the inside and compressive stresses on the outside. Disturb one of these two components, and boom. Even scratching a piece of tempered glass enough has the same effect. This relates to the sporadic occurrences of glass windows "spontaneously disintegrating" in places like backyard patios and Apple stores.

 

[SphinxnihpS]

For why you can't cut tempered glass, look up Prince Rupert's Drops. Essentially, tempered glass is a very VERY strained piece of glass, held together by tensile stresses in the inside and compressive stresses on the outside. Disturb one of these two components, and boom. Even scratching a piece of tempered glass enough has the same effect. This relates to the sporadic occurrences of glass windows "spontaneously disintegrating" in places like backyard patios and Apple stores.

...and my car window. I was not moving and nothing hit me. It just popped and spit one piece at me hard enough to stick in my cheek. Round my ass! Tiny cubes with 12 sharp edges.

Shop around. You get a raw piece of glass machined how you want, and then tempered. $100 is too expensive for 4 rounded corners, 4 bullnosed edges, and 4 holes per piece. You really only need 5mm stuff, not 10mm. It's quite strong.

Safety glass is better though, as tempered only requires one nick on the edge and you are out a computer monitor. The other problem is that when they temper the glass, it can shrink and warp very slightly. No fun if your mountings have to be precisely where you drilled them before the tempering.

I'd look into other means of attaching the glass to the desk. Drilling holes in glass presents all kinds of problems.

I also find that glass furniture's wow factor wears off quite quickly.

 

[TheStu]

...and my car window. I was not moving and nothing hit me. It just popped and spit one piece at me hard enough to stick in my cheek. Round my ass! Tiny cubes with 12 sharp edges.

Shop around. You get a raw piece of glass machined how you want, and then tempered. $100 is too expensive for 4 rounded corners, 4 bullnosed edges, and 4 holes per piece. You really only need 5mm stuff, not 10mm. It's quite strong.

Safety glass is better though, as tempered only requires one nick on the edge and you are out a computer monitor. The other problem is that when they temper the glass, it can shrink and warp very slightly. No fun if your mountings have to be precisely where you drilled them before the tempering.

I'd look into other means of attaching the glass to the desk. Drilling holes in glass presents all kinds of problems.

I also find that glass furniture's wow factor wears off quite quickly.

The whole thing is not going to be glass, the side shelves, and maybe the monitor stand are all the glass used. The largest part of the desk, the actual desktop, will be wood. And I am still messing around with the design, and waiting until I have the funds to build it, paying back student loans makes that tricky

 

[beginner99]

I was just watching this TV show called James May's 20th Century (BBC Show)

It was showing how glass on skyscrapers is much, much stronger than regular glass.

They took a mini cooper car, and dropped it from 10 feet up in the air onto a sheet of this glass and it didn't break.

That's why I always have to laugh in movies when they jump through skyscrapper-windows...often attached to a rope coming in from the outside.

 

[Leros]

the tempered glass on my tv stand is about 1cm thick and holds over 80 pounds.

My dad has a pretty heavy 40"+ CRT tv on a glass tv stand. I put the tv stand together for him, it was about 1/4" thick glass. We were barely able to lift the tv together, so I'd estimate 150 lbs or more.

 

[Modelworks]

The whole thing is not going to be glass, the side shelves, and maybe the monitor stand are all the glass used. The largest part of the desk, the actual desktop, will be wood. And I am still messing around with the design, and waiting until I have the funds to build it, paying back student loans makes that tricky

You also might consider acrylics. They give the look of glass and come in colors but can be shaped into any form you desire and are near impossible to break.
http://www.usplastic.com/catalog/default.aspx?catid=442

 

[Leros]

You also might consider acrylics. They give the look of glass and come in colors but can be shaped into any form you desire and are near impossible to break.
http://www.usplastic.com/catalog/default.aspx?catid=442

Acrylic is also a little bit easier to cut than glass.

For thicker acrylic you can cut it with a table saw, sand it down, and then polish the edges with a torch.

Thinner acrylics you score and snap, similar to cutting glass.