Bad glass or bad idea?

So I'm a newb. I was having issues getting ABS (a free spool that came with my kit) to stick to the glass on the heated bed. I was using ABS juice. It wasn't bad but not great. I roughed up the glass a bit with #320 SiC grit to give the part a little extra grab - I grind telescope optics so the stuff to do this was handy. Worked perfect! Was printing 245°C HE / 115°C HB for first layer then 240°C/110°C after that. FWIW there were other issues that made me suspect that it wasn't great filament.

I got some new filament from a local supplier that I'd only read good things about. I started printing with the same settings as above. After a dozen or so layers I noticed some strings in the print so I dropped the extruder temp to 235°C and that solved the problem. As you can see in the picture it grabbed onto the glass big time. The glass it still stuck to the parts and I can't get it off. This happened after the print was done and everything was cooling down. I'm going to assume this is a freak thing that doesn't happen often bud I'm wondering if it might have been just a bad piece of glass. I just did a print on a new piece of glass (with the lower ABS temps) and am getting the edges lifting. So I'm wondering if I rough up this glass again if I should expect the same thing to happen. Maybe try a finer grit?

Try putting the glass+print in the freezer for half an hour.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Just following up in case someone else comes across this thread that had the same idea as me. Conclusion is it was a bad idea. I tried it again with a new piece of glass and had a few bits of glass let go. I'd read that silicon carbide grit leaves micro subsurface fractures and that fits with whats happening here. I doubt a tougher glass like borosilicate would give any better results. Quartz/fused silica might, but I'm not going to guinea pig a piece of my quartz to test that theory! I tried using aluminum oxide grit that is supposed to be gentler on the glass and I didn't get any missing bits of glass, but it didn't help adhesion over plain float glass either so a waste of time.

Oh well. At least I learned something so it wasn't a total waste.... except the $4.50 in materials.

You definitely do not want to sand your glass. I've had glass chip out just from single fine scratch on the surface.