I rescued 22 panes of tempered glass from french doors that someone was discarding a few years back, and they’ve been sitting in my shop waiting for a project. Now I am planning a wall of built-in shelves over cabinets, and I want to use some of the glass in doors. Sort of a curio effect in the middle of the wall, which I’ll light too. My problem is that I am constrained to the size of the glass, which is not lending itself to the sizes of the doors/openings that naturally fit the project. I do not want to purchase new glass – that would defeat my goal of keeping this project within budget.
So … can I reduce the size of the panes? I tried scoring and breaking one pane a while back, and of course it scared the hell out of me with a loud bang and shattered into a zillion pieces. The glass was for exterior doors, so it may be photo treated as well, not sure. Is there some kind of nibbler that I can use along an edge to work it down slowly, and will that work on tempered glass? The edges will be buried in the door rails/styles so they will not be seen.
I’m open to suggestions –
Replies
If no one here has an answer, I would call a glass outfit. I don't know what they use to cut tempered glass (maybe some sort of machine with a diamond blade), but at least they will be able to tell you if it can be cut.
I suspect that glass is tempered after it is cut to size, so it may not even be possible to cut once it has been tempered. I don't know for sure, though.
You cannot cut tempered glass it is cut then tempered.Tempering is done by heating the glass and cooling it using air jets .This has the effect of shrinking the outer layers of glass holding the rest in compression, when you score the outer layer, bingo you release that energy .Result shrapnel.That is one good reason for being very careful with glass sizes!!Don't ask how I know
As Nikki suggested call a glass shop or at least try a glass forum rather than a wood forum. A quick search on google appears to have a general consnsus of "No, for cutting tempered glass"!
A quick search on google appears to have a general consnsus of "No, for cutting tempered glass"!
a consensus as well on this wood forum, at least among the responses that actually answered the question! Some things really are binary regardless of the amount of consultation we seek.
Jimbo, No Dice!
It will ruin your glass cutter and explode with just a nick with a center punch
I once walked into a restaurant/bar pulling a toolbox on wheels
The corner of the metal box nicked the Hurculite door and the whole panel of tempered glass (3/4" thick) popped and turned to snow. Fortunatly no one noticed as there was a ballgame on the TV being watched by a noiser crowd of construction workers on lunch break (Liquid Lunch)
If possible design your project to accomodate the size of the panes. Or else, buy some self adhesive sanding discs (Silicon Carbide) medium and fine
Cut to size and adhere to each side of a pane and TA DA! Sharpening surface for honing and sharpening chisels and plane irons
To cut the sanding disc stuff, don't ruin scissors or snips, but cut from the backs with a straight edge and a sheetrock knife.
Steinmetz.
Edited 12/29/2004 10:31 am ET by steinmetz
I was affraid of that, and I too learned first hand that I cannot score and break this stuff. But I was hoping that a hand-held nibbler would let me take little pieces off an edge without exploding the pane. Thanks for the idea for sharpening ... with 22 panes, that makes 44 sides covered in abrasive. I'll be set for a day or two.
Jimbo I MEANT to sell the product to toolnuts and use the money to buy the right sized panes. It's called,'Value Added'. Stein
ever notice how it keeps crackling , long after the initial shock wave explosion?I had "rice krispy" sounds in my van for a two day stint after an unplanned sliding glass door panel got interupted in it's being a flat pane of glass.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations.
You might be able to untemper the glass, then cut it. Wrap a pane in aluminum foil (in case it breaks) ,put it in a cold oven, turn the knob to 250* leave it one hour. Then turn the knob to 500* (or 550 if your oven goes that high) leave it 1 hr, then turn off the oven and let it cool w/o opening the door. Try cutting it, and if successful, you can do the rest all at once, but you have to sticker them 1/2" apart and do 2 hrs at the 250 and at the 500 settings.
Thanks Rob - I never fathomed trying to untemper the glass. I take it the nibbler is out of the question or you would have recommended it, so I wont go out and buy one of those. I will however try your suggestion. I even have a broken pane that I can use without wasting any.
If you have a broken pane that is not just crumbles, then it was not properly tempered, and is not a valid test.
The whole idea of tempered glass is that stresses are added so that it never breaks into large pieces that could cut someone, but rather that it will crumble if anything happens to it, destroying the glass but causing minimal damage to the person. ________________________Charlie Plesums Austin, Texashttp://www.plesums.com/wood
You make an interesting point ... . Maybe my premise was wrong from the start. The piece I tried to cut (scored with a glass cutter and bent over a sharp edge of my bench) completely shattered, but the broken pane lost a corner when I was knocking apart the french doors it had been in. I suppose that if the glass were tempered, that could not have happened. The pieces that the shattered pane broke into were shards, not little squares like auto glass. Does that shape of the pieces indicate anything to you?
You may have high strength annealed glass, and not fully tempered for ANSI specs. I have sucessfully cut "neo-ceram" a woodstove glass for hi temp..but it was dicey.If ya really want it that bad, it can be done, but the attrition rate is a moderate to high loss factor.play the flame from a propane or mapp torch over the cut line, and work fast. The support must not be a heat sink..IE a non absorbant stand off. lay the fire to it, score, and use a wood tapper to encourage the fault thus created.stand back and give it another good wallop, 7 times outta ten, it'll pop clean.
Spheramid Enterprises Architectural Woodworks
Repairs, Remodeling, Restorations.
I have read about tempered glass many times, but have never seen the tempering process. The picture in my mind goes like this: Get the glass very hot all over, then blow jets of cold air on the surface in a grid pattern. I visualize a jet of air every inch in each direction so an 8 x 10 inch piece of glass would have 50-60 jets providing fast cooling on those spots, creating huge internal tensions in the glass, but in an even pattern so nothing breaks. Add an uneven tension, like hitting the glass, scratching it, etc., and all the tension shatters the glass into little pieces, not big shards to decapitate someone.
How could you have a corner broken off? One thing might be that the pane of glass was replaced with non-tempered glass. Another might be that the tempering was rushed a little - not heated enough, not blasted with enough cold air, some of the air nozzles plugged, or whatever. To me that means that the glass wasn't tempered - or at least wasn't tempered right. But do you want to make the same bet for all the other pieces of glass? If they are really tempered, the only practical solution is to save them for a project that needs that size... If you are not sure whether they are properly tempered or not, they could be used in an application that does not require tempered glass - like a high window or picture frame. ________________________Charlie Plesums Austin, Texashttp://www.plesums.com/wood
I don't know what kind of glass you have. If it's soda-lime-silica, it should anneal quickly at 900*F. Since your oven won't go that high, I suggested 1 hr. There is some function of time and temperature to predict how long it takes to anneal a given glass, but I don't know what it is..
If the broken glass looks like the side or rear windows in a vehicle,when they brake into hundreds of similar size pieces, that's tempered. Thee windshield is safety, glass in and outside with a plastic sheet in between. If the doors are more than 50 years old there more than likely NOT tempered, The quality standards on older glass is not of a very uniform quality. Some glass is just harder than others, Fletcher-Terry makes glass cutters with at least 4 different angled wheels just for such differences.You can't untemper tempered glass. You can bring it up to a near soft stage and cool it to the glasses formula. And then theres no way of knowing the glass formula. 1800*-2200*F.
I'm an engineer for a glass company. I've worked on some specialty tempering but don't have expert knowledge in the whole field. Here are some comments on the topic.
Tempered glass is impossible to cut, drill, or nibble in any way without shattering it.
If you cracked a window without it dicing (instantly fracturing into cube-like pieces) it was not tempered.
Tempered and annealed are opposite conditions. In tempered glass the entire exterior surface is under compressive stress, and the core is under tensile stress. In annealed glass the stress has been reduced to as near zero as practical.
Tempered glass can be annealed to remove the stress. In order to anneal glass the temperature to which is has to be subjected softens the glass, so it will sag and loose its perfectly flat shape. So annealing is not practical without proper jigs unless warping does not matter. The glass I worked with was not the common soda-lime glass, so I don't know the annealing temperature, but I suspect its much higher than a home oven can achieve.
Most wood stove windows are not glass, but glass-ceramic. Glass ceramics are glass materials within which controlled growth of microscopic crystals has occurred. With the right combination of ingredients and treatment, the desired properties can be obtained, in this case, resistance to temperature and thermal shock. If the crystals are smaller than a wavelength of light, the material is transparent, such as in Visions cookware. If the crystals are larger than a wavelength of light, the material is opaque, as in Corningware. It's possible to make materials in which the crystals form or disappear repeatedly in response to ultraviolet light. Photo sensitive eyeglass lenses are an example; the ones that darken in sunlight and lighten indoors. Glass ceramic wood stove windows are not stressed like tempered glass, so can sometimes be cut. They have stresses from other factors so are unpredictable.
Tempering of window glass is done with air. The glass is heated to a precise temperature then subjected to a blast of air from an array of nozzles spaced every few inches. The array oscillates to provide as even a blast as possible. Control of all the conditions is critical, or else the glass can warp, temper unevenly, temper too much or too little. You can even produce an "oil can" effect in which the glass is warped concave, but can be "popped" to be concave in the other direction.
Thermal tempering is the most common tempering method, but tempering can also be accomplished by chemical alteration of the surface and by lamination of glasses with different properties.
you had me at "I'm an engineer for a glass company."!
Hopefully that last word on cutting tempered glass.
Happy New Year
I'll concur with the "binary decision" that tempered glass can't be cut once it has been properly tempered.
Tempered glass starts out as regular single- or double-strength glass, is cut to the correct size and then annealed in an oven so as to temper it.
Any significant disturbance in the surface tension of the glass and it shatters into billions of pieces...to prevent serious injury to the small child or ardent adult woodworker who breaks it (smile).
I'd use it for another purpose or make your piece fit the glass.
BTW, I'm a "glass guy"..see my website.. http://www.kesslercraftsman.com
I can tell you that nibblers, cutters and even diamond grinders won't work...
lp
Thanks Larry the glass guy ... especially for helping me rule out the nibbler idea which I was having a hard time letting go.
Tempered glass can be cut via two methods. The first is to anneal the glass. This requires a kiln that the glass will fit in. The second method is to cut the tempered glass with a laser used to cut glass. Glass cutting by laser should be done by a professional glass cutter. The issue of glass thickness and the type of laser required precludes doing it yourself at home.
How does annealing cut glass ?
Annealing tempered glass causes the tempered layer over the glass surface to loosen enabling it to be cut without shattering.
Odds are good he's done with his project... his post was from 2004.
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