The Stovebolt Site Forums The Shop Area The HiPo Shop Cutting tempered glass when top chopping.

Back a while ago there was a thread on chopping tops and cutting the corner glass on the deluxe AD. This glass is tempered and there was discussion of if it was possible to cut it.

On another site there was a post by someone in the glass business that lays it all out. Here is a portion on the post pertaining to the subject. He is a little off on the "Except for the windshield, the remainder all automotive glass is tempered" He is referring to late models, an older car/truck with flat glass was safetyplate. Only the bent glass was tempered.

"Windshields are not tempered, and they can be cut; I'm aware of that. Like you said though, it is difficult to successfully do. Except for the windshield, the remainder all automotive glass is tempered and cannot be cut. Once glass is tempered, it can no longer be cut, or drilled, without it exploding. All "cutting", grinding and drilling is done before tempering. The tempering process puts a compressive stress on the perimeter of the glass and that's what keeps it from exploding on its own. If you remove that band of compressive stresses, nothing is holding it together. If the glass is not tempered correctly, and the compressive stresses are not distributed evenly, the glass can even explode, untouched, in a brand new car for no reason. I worked for an automotive glass mfgr and we had a little problem with that once...oops. When tempered glass "explodes", the chunks even have to be under a certain size per federal safety regulations... Ok, off the topic a little... On 99.9%+ of all modern cars, all glass is tempered except the windshield. I believe some of the very, very high end Mercedes cars use (or used at one time) laminated backglass for bulletproofing"

There is a way to cut the cab corner windows that are tempered. Tempered glass is glass that has been heated up to near melting then cooled very quickly, so that the outside of the glass becomes solid before the inside. The outer layer is squeezeing the inner with great pressure. The only way to releave the pressure is to slowly heat up the glass (which could cause the glass to burst anyway) to almost fluid then cool it off slowly. Once cooled it will no longer be tempered. You can then cut, drill, etch, the glass without problem. Then have the glass re-tempered. But the glass might break, because the older the glass the harder it is to work with. I have never done this but my frien, who is a professional glass guy passed along the info. He dumned it down to explane it to me, so the process could be slightly more complated, and is beyond most of us anyway.
Hope it helped

Jonathan,

The only problem with that approach is that most (I think about 99.9%?) glass is tempered in a chemical bath at elevated temperatures and it is not a thermal process that does the tempering but a chemical process, the elevated temps just speed the process up so it doesn't take weeks. Glass does go through a thermal process earlier in the manufacturing cycle, but this is annealling and it simply removes any residual stresses in the glass so it doesn't explode when touched.

It is the chemical infusion of "typically sodium" molecules that makes tempered glass non-recyclable AND places the outer layers of the glass into compression. Heating it may cause the sodium molecules to disperse back out of the glass if done in a sodium starved bath, but getting the chemistry right to do what you suggest would be difficult at best. I am not saying it can't be done, but lexan starts looking really good by the time you have busted your 4th or 5th corner cab window doing experiments. :rolleyes:

Nothing is better than being informed by someone that knows what the heck he is talking about. Man, I love the technical stuff.
Thanks, to both of you guys.

MARTINSR

Being informed by someone acknowledged about his job is the way to take the guesswork out of scene.
There is just no magic. Or You have the right info or have nothing.