Float glass and toughened glass

[Brian Deakin]

I have read that ideally a thick piece of float glass should be used as a flat surface

My question
I have access to a free piece of toughened glass about 1/4 thick, 18 inches wide and 30 inches long would this be flat enough to use a a surface for flattening plane soles and plane blades

regards Brian

[Ron Kellison]

I don't see why not. Get 2 or 3 4x24" sanding belts, cut them open, glue them down with double-sided tape and you're in business!

Regards,

Ron

[Peter Quinn]

That's what I use. It's called " tempered" glass", it's been heated and cooled to give it additional impact strength, but it's still pretty darn flat. I believe mine is 1/4" as well. I bought remnants from a glass shop I do business's with for next to nothing.

[Gene Howe]

I use 1/4 glass, also. Wet/dry paper will stick to wet glass until evaporation overcomes the water's surface tension. Usually long enough for several plane soles and, it's easier to change grits.

[Steve Baumgartner]

That's what I use. It's called " tempered" glass", it's been heated and cooled to give it additional impact strength, but it's still pretty darn flat. I believe mine is 1/4" as well. I bought remnants from a glass shop I do business's with for next to nothing.
I don't think tempering should affect the flatness, but it does affect other properties that you should be aware of. Although tempered glass is stronger than regular glass, the purpose of tempering is not so much to increase strength as to provide safety. Tempered glass is "case hardened", meaning that the surface is under tension compared to the core. This causes the glass to crumble when it breaks instead of forming dangerous sharp fangs. Tempering is done after the glass is cut to size - you can't cut it yourself because it will crumble. It also doesn't stand up well to surface damage such as scratches. I'd think it would be fine for attaching sandpaper so long as you take care not to scratch it, but I wouldn't use it for lapping with abrasive paste.