Glass supplier for large print bed in US.

I have started building a large printer 750mm X axis, 1200mm Y axis, 1000mm Z axis, I started looking at 0.250" cast aluminum jig plate because it is very flat, but $300 was a little higher than I wanted for this build. I thought about glass and knew it needed to be able to withstand at least 250C and plain glass will not work.

This company has a tempered glass that is good to 470C and can be used on a fireplace without any problem, I ordered a piece 30"x48"x0.250" with a pencil edge for $89, the shipping was high but for a total cost of $149 I was happy.

[www.onedayglass.com]

Is it flat enough?

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

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the_digital_dentist
Is it flat enough?

From what I've been told float glass is typically within a few waves of green light of being flat if properly supported (FWIW I'm into making optics for telescopes). However, a sheet that size has no chance on holding that kind of tolerance on its own especially at only 0.25" thick. So support will need to be well thought out.