How would you cut tempered glass? The use case is a friend asking me to take tempered glass shelves from one mini fridge to make shorter to fit in another one.
I’ve never done any glass work so not even sure where to start.
literally impossible. the nature of tempered glass is a complete surface envelope of highly tensioned glass over a core. it’s very tough to crack or scratch, but any opening in the envelope will always shatter the entire piece into little cubes.
even a water jet won’t change this. tempered glass simply cannot exist with the surface envelope cut
companies like Binswanger will cut glass to shape and THEN temper that in their machine. i don’t know of any way to do tempering at home, or how to anneal the temper out of an existing piece.
if you need safety, then you can buy laminated safety glass and work that. laminated is actually two glass surfaces sandwiched over a core of acetate (plastic). your car windshield is always laminated but side and rear are usually tempered. tempered always shatters into cubes with any damage, laminated strongly wants to stay in one piece even with extreme damage. laminate is not easy to cut either- you can score both faces, break along the score, but the acetate core will still hold it together.
i was told some people do that double faced score and snap, then put alcohol into the seam and light it to melt the acetate core. a lot of work. a water jet will cut through all 3 layers at once cleanly, though
Danny explained it well. I found some reports of success cutting tempered glass with a wet saw but I’m skeptical (to put it mildly).
Otherwise, “how to cut tempered glass” results are all about annealing the glass in a kiln to de-temper it before you cut. More trouble than it’s worth unless you have a piece that’s very special for some reason.
There is an idiot in me who wants to try on a fiber laser engraver.
I’d be curious what that idiot finds out 
it’s possible to do a shallow engraving in the surface, but it is a high risk of shattering immediately on the bench and it is very susceptible to shattering on its own forever after that.
the high tension surface that makes it tempered glass means cutting it is basically like cutting a water balloon in half. it’s not a matter of HOW you cut it. you could put a water balloon in the freezer and cut it on a band saw, but the balloon is still popped and you won’t have half a water balloon in the end. and there’s no way I know of to even fulfill that analogy in tempered glass by freezing the glass.
the basic state of that high tension surface envelope being incomplete is not a sustainable condition.
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Does anyone have a small square or less of tempered glass?