Cutting Tempered Glass...Possible?

[EvilRufusKay]

Here is the jist. I am modifying my rear hatch and want to dramatically reduce the size of the window. I do not want to use Lexan unless I have to. My window already has the correct curvature so I would like to modify it. Can tempered glass be aneeled? Is there an alternative?

 

Thanks,

Rufus

[preith]

From the reading I've done, the glass must be annealed first, and then cut and tempered again after. They compared tempered glass to a balloon.

[Tony D]

nothing horrible about cutting it, you get a sandblaster, set up a template for the window size you want, duct tape it or glue it to the glass, and have at it at about 60psi using fine aluminum oxide or slag.

 

you will slice through the layers of glass and laminated plastic in short order. This is how shops cut down glass for chop-tops.

If you have a steady hand, and a fine point nozzle, you can get away with just ductaping whatever you don't want cut so you don';t make pitts in the glass and have at it, but I have always used a sheetmetal shield.

 

As for Lexan or Polycarbonate, you can easily get it to the "right curvature" using several industrial guns (I like the adjustable steinel) hooked to an extension cord blowing into a small "furnace" you make from bricks on your concrete driveway. Lay he polycarbonate sheet on an elevated piece of sheetmetal, and have theheat guns blowing across the bottom of the apparauts (indirect heat) to raise the internal temperature to around 300 degrees (just where the plastic will droop). Pull the cover and exhaust stack off the top, grab the oversized piece of sheetmetal and polycarbonate sheeting with some heavy gloves and slap the polycarbonate onto the back window---it will assume the same droop, and re-harden that way. Then all you do it cut it to size with a Zip Cutter like for drywall.

 

Far easier than sandblasting, and cleaner, too! You can control the heat guns on a multiple plug outlet strip, by running an extension cord through an electric oven thermostat that will maintain and regulate the heat in your makeshift "polycarbonate heating oven"!

 

Yeah, I had lots of time on my hands to experiment when I was younger!

[blueovalz]

When using the blasting method of cutting tempered glass, does the heat generated by such (at the edge of the tape) become an issue? The reason I ask is I am under the impression that a large heat gradiet can cause the tempered glass to pop as well.

[Guest Phil1934]

Won't work on tempered glass. He's referring to laminated windshield glass. Either find a windshield of the correct curvature and cut it to size or try a curved window like a '50 Ford that Vintage Glass sells. Just remember if it's close you have to work the metal to fit the glass as there's no bending of the glass.

[Guest 77vegasz]

Use Lexan, and get the protective film used by NASCAR for their Lexan windows. It goes on like contact paper, and when it is scratched or pitted, you peel it off and place a new one on, it keeps the Lexan clear and scratch free.

 

Jon

[EvilRufusKay]

Won't work on tempered glass. He's referring to laminated windshield glass. Either find a windshield of the correct curvature and cut it to size or try a curved window like a '50 Ford that Vintage Glass sells. Just remember if it's close you have to work the metal to fit the glass as there's no bending of the glass.

 

Windsheild glass is tempered. True its laminated but it is also tempered. Thanks for the info guys.

 

Tony,

 

I am having trouble visualizing what you mean by this furnace. Could you elaborate a little more on the construction? I really appreciate it!!

 

Rufus

[Guest Phil1934]

https://www.lynxservices.com/consumers/autoglassFAQ.htm

[EvilRufusKay]

I stand corrected. Thank you Phil!!

 

 

So in your opinion sandblating is not an option because the force applied will shatter the glass? I suppose I could try, and if it does break just go with the lexan and the sheets that 77vegasz recomended.

 

Anyone know at what temperature tempered glass needs to be taken to, and the duration at that temperature to become annealed?

[JMortensen]

I've never done it myself and I'm no expert, but I used to order glass on a weekly basis, and I thought that tempered glass could be cut with a water jet saw. That was the impression I got from the glass company anyway.

[EvilRufusKay]

I've never done it myself and I'm no expert, but I used to order glass on a weekly basis, and I thought that tempered glass could be cut with a water jet saw. That was the impression I got from the glass company anyway.

 

I wonder where I could get my hands on one? Hmmm.....

[Guest Phil1934]

There's a new polycarbonate call Martuff or something like that that will even stand up to windshield wiper abuse. I've got an article here somewhere so I'll look. Found it. It's a GE lexan with a thin coat on both sides as hard as glass. Try Percy's High Performance in MO 573.346.4409 They sell Speedglass which I think is precut windshields but they should have bulk or can cut to your template, which is the way I would go.

[Dan Juday]

You're not going to cut tempered glass. For the de-tempering/annealling the temperature at which you need to bring the glass to will cause it to slump. You need expensive specialized equipment to even consider this.

 

If you must have glass that is curved correctly you may find a custom glass shop that can slump a piece of laminate safety glass but this will not be cheap either. Go Lexan. This is a material you can manipulate yourself with some heat.

[Guest trickz]

I have thought about this alot ,just for chopping the top,my machinest saw a guy cut plastic, by putting tin foil over it and useing a palsma cutter.just an idea! now what about using laser or water jet on tempered glass.If you kept the glass cold /chilled could this work??? thanks trickZ 8)

[Dan Juday]

...now what about using laser or water jet on tempered glass. If you kept the glass cold /chilled could this work??? thanks trickZ 8)

 

Years ago I owned a glass shop.

You need to know what the tempering process does to the glass to understand why you can't cut it. In a post above it was mentioned that tempered glass is like a balloon. This is correct.

 

To temper glass you put your finished cut piece of glass in an oven and slowly raise the temperature. As the glass approaches a molten state the molecules in the glass begin to realign. At this point it is removed from the oven and cool air is blown over the surface. This flash cooling (annealing) freezes the molecules on the surface in their hot configuration. Then as the interior of the glass slowly cools to room temperature the molecules inside realign to the their cold configuration. This sets up tremendous tension between the glass on the surface and the glass on the inside. This internal tension is what makes the glass so strong.

 

FYI, the tempering process is very closely controlled. If the rate of heating and cooling are not precise and completely even over the entire surface of the glass it explodes from the tension. Even with high quality equipment and computer controls they still lose a certain percentage due to tiny unseen imperfections in the glass.

 

So now you can see that cutting tempered glass is impossible. It would be like trying to cut an inflated balloon in half and hoping you could get two rubber bowls out of it. Once the surface is cut through the whole thing collapses.

 

It is possible to scratch or etch the surface of tempered glass so long as you don't penetrate too far. I have sandblasted designs on 1/2" tempered glass as deep as about .060"

 

Hope this helps clear things up.

[Tony D]

1)lay some cinder blocks in a square on the concrete driveway.

2) knock out some holes so you can lay your heat guns on their sides, and blow into the center of the square---four guns could be used. I would think the $19 Harbor freight specials wouldn't be too bad a hit... Make these holes about halfway from each end of the square.

3) lay some conventional bricks like you were going to make an ornamental diamond inside the first square. The heat from the heat guns might just blow on those bricks. If you have fire bricks, use them here! Basically you just need four bricks or rocks to act as heat diffusers / buffers and supports. Failing in finding fire bricks, my first oven was made using tin cans as the supports!

3)lay some 3/4" plywood atop these four bricks. Use sheetmetal scraps to prevent the diffused heat from blowing directly on the plywood as it can be 1100 degrees, and make the wood smoulder

4)cover the cinderblocks with some more plywood with a hole in the center to let out heat. Use a sheetmetal scrap to open or colse the hole to help build heat faster...

 

I hope this isn't getting to obtuse---but are you getting the picture?

Basically you want to trap the heat discharged from the guns in as small an area as you need to heat the polycarbonate. You lay it on the shetmetal cover of the first piece of plywood set on the bricks. If you are daring, you can skip actually picking up the whole board from inside when it comes time to drape the plastic---you can pick it up with tongs at two opposite corners, and just drape it floppily over the buck.

 

This is how I made rear windows, side windows, and quarter windows out of 95% Light Blocking Greay Smoked Polycarbonate. It looked Bitchen, and NOBODY could break into my freakin Z again with a simple spring powered centerpunch or hammer---unless they went after the windshield, and wanted to crawl through broken glass.

 

(Theft of personal property is the mother of invention!)

 

Good Luck if you need further clarification ask, and I'll try to be more detailed.

 

Good Luck! You can get the polycarbonate in the right thickness to fit the stock rubber trim for the rear window from McMaster Carr. You cut it with a razor blade, and you can just "shrink" the stock sized hole porportionally, or turn it into a Triangle for that matter!

[EvilRufusKay]

Tony,

 

Thanks alot man I think I understand now. Where did you get the smoked poly?

 

 

Dan,

 

Thanks for the info.

 

 

Everbody,

 

Thanks for the ideas and help!!

 

Rufus

[Tony D]

here:

 

http://www.mcmaster.com

 

put "polycarbonate sheeting" in the search window, and start the search. You should find a 24X48" sheet is around $40 in the .188 thickness---which if I recall is the thickness of the factory glass.

 

These guys are probably not the cheapest place to get it, but they have one of just about EVERYTHING, you will be amazed at what they have in stock and what they offer in the way of anything...

 

The temperature resistance for this stuff is rated at 240 degrees maximum. From what I remember from when I did this last (around 1987) I would heat it to around 300Deg F or 320...

 

I would hook all the heat guns up on a circuit I made from an old oven timer that would simply swith them on and off from an outlet strip I made from a four plug outlet box and some 12 gauge SO4 extension Cord wire and hospital grade three-prong plugs I horked from work... This worked good enough to keep the "oven" temperature fairly constant.

 

When Atlas Copco bought me that Steinel Heat gun from Germany with the digital readout and variable temperature output and display I was thinking "If only I had this then..." Man, just set a single gun to 320, and walk away. Come back and check in an hour or so, and if it's ready, Pick and droop.

 

Another way to do this if you don'twant to droop the glass over another piece of glass is to lay your glass "outside down" and polish the inside with auto wax. Then pour in plaster of paris to a level to the edge of the glass (I ran duct tape around the edge, and let it set up thickly with a big lip on it so it had enough thickness to be handles gingerly.)

Then you simply carefully roll it back over, and separate the plaster fromthe glass (it should pop off) and then paint/po.lish and you have one heluva durable buck for drooping production quantities of glass over it!

The only drawback with plaster of paris is that it's easy to mar the buck, and it cracks eassily---hell it even cracks when it's drying! But it's cheap, and a couple of bags should do you just fine.

 

With some good release compound, you could lay fiberglass over it, and make a very neat looking filler plate---but some different procedures would apply to construction of the buck and for grafting it to make a solid hatch...

 

Good Luck. You will be amazed how easily it works once you heat this sheet to the right temperature. It will become flimsy like a big sheet of Lasagne! Just don't heat it over 320! (This was for the stuff I was using---the new stuff may have different characteristics) I was concerned about preserving the shatter-proof characteristics of the product, and from literature they sent me 320 rings a bell as a temperature you didn't want to exceed as it would start some crystalline changes that would weaken the product, or set up cracking or crazing or something like that. There is about a 60 degree range where you can work it with no degredation and it becomes very easy to form in this range. I was making vases by draping it over bowling balls and sitting them on a flat table top, all that kind of artsy hippie sh*te you do when you are in your early 20's!

 

Anyway, I'm sure "Lexan" put into google will return some meaty bits of information on thermoforming (then again "thermoforming lexan" might be a better search parameter for google) the product correctly. As I recall I recently (within the last two years) did a search and found a nice website that had all sorts of infomration on it that was helpful.

 

Anyway, the 60 degree working range was why I used an old salvaged oven timer---it seemed to handle the ampreage with no problem, and was relatively consistent in ti's operation when sat on the outlet hole just above the center of the sheet.

 

Again, Good Luck. Post back with how amazingly easy it was so more people start doing it!

[EvilRufusKay]

You said "Atlas bought me ......" Do you work for Atlas? I have 2 brand new Atlas machines. A T4000 and a T3000, don't tell me that you are a service rep!?!

[RB26powered74zcar]

Yes, forget about cutting temp glass. I do glass work now (since 1975, wow I'm old... ) and its next to impossible. As said above, its possible (although I'd have to see it to belive it) for it to be water jet cut, but I'm not sure...

 

I know it can be slowly sanded to remove size from it, but I have never known of anyone "cut" it with a glass cutter, without it exploding...