Poll - Have you chipped your glass bed and wondered why?

I was wondering if others chipped their build plate (bed) the same way I did.
I believe I chipped mine because the work was taken off too soon and the bed didn't have a good cool down period. I used the paint scrapper that came with my printer.

 

Depends on the filament you're printing with.

Certain flavors of PET are notorious for pulling chunks of glass out of glass build plates if the bed is allowed to cool too rapidly after a print is finished (this is why Taulman recommends having a line in your ending Gcode to leave the bed at 35C until you get around to removing the print).

RichRap has multiple videos on the subject and a couple of experiments where he tried different protective coatings on glass and evaluated how well they worked.

EDIT: This assumes people aren't being given some of the older R1/refurbished R1s that had flawed glass beds that would simply crack and shatter over the course of several heating cycles.

 

mine chipped and i was under warranty so i got a replacement but i have used a glue stick to fill in the chip and not having any issues going to try some epoxy next time got some clear epoxy at auto store I would think it could handle temp it is made for glass

 

I pulled off some chunks after using too much Wolfbite to hold down my ABS. Robo gave me 1/2 off a replacement (warranty-ish) and I bought another spare just in case. Glad i did.

It seems best to brush on a small amount and apply while the bed is cool as it warms. Keep spreading until it dries to get a thin even coat. You shouldn't even notice the coating there but for the texture being slightly grippier when warm; kind of rubberyish.

After chipping my second bed, I now apply water to the warm[ing] bed in the same manner after the Wolfbite has dried to be doubly sure of a thin and even coat.

Between prints I just "refresh" the coating with another brushing of water, and don't reapply Wolfbite before a good "scrubbing" with water and paper towel, followed by Alcohol wipes. I have no idea if the alcohol wipes do anything more than the water, but I have a glut of them (I used to use hairspray on the bed) and it feels safer to use them than not.

 

I'd like to replace it, but apparently Robo stopped offering them a long time ago.

 

Have you called them?
Don't go by what they show online.

 

Ok, I didn't think to try that. I guess I will give that a shot.

 

Does Robo (or anyone else) anneal their glass? Any time you work glass you put stresses into it. Annealing makes the glass much stronger by allowing those stresses to relax. I am tempted to get a replacement bed made and have it annealed just as an experiment.

 

I work glass, specifically borosilicate.

The chipping problem is not temperature, it is stress. I can plunge boro straight into the torch without preheating, which is rather a bit more aggressive heating and cooling than you'll see on a robo.

Not knowing how these glass plates are made, beyond the standard float process, it's very unlikely that they were annealed.
That means that there will be regions of high internal stress. Not a problem for most float glass applications, but with a cooling part shrinking and pulling on the glass, the additional stress can cause chipping.

http://www.simax.com/en/section/32-simax-glass-mass.html
SIMAX Glass Annealing
Annealing represents a thermal process, the purpose of which is preventing the formation of undesirable and unadmissible high thermic stress inside glass, which could decrease the product resistance, and, eventually, removing the already formed stress.

Obviously not a native english speaker, but there it is. Removing the already formed stress from the initial work, allowing more margin for other stresses before fracture.

In better english from Wikipedia:
https://en.wikipedia.org/wiki/Annealing_(glass)

"Annealing of glass is critical to its durability. Glass that has not been properly annealed retains thermal stresses caused by quenching, which indefinitely decrease the strength and reliability of the product. Inadequately annealed glass is likely to crack or shatter when subjected to relatively small temperature changes or to mechanical shock or stress. It even may fail spontaneously."

I've seen spontaneous failures, even in a common shot glass. Sitting on the counter, I happened to be standing there. "Ping" and it's cracked in two pieces.

 

Pretty much the opposite of annealing:


Note that the high apparent strength is from the HUGE compressive forces caused by the internal stress from rapid cooling.

 

This is due to unequal thermal contraction between the filament material, your adhesive and the glass. Remove prints hot or put an interface like totem on 3m sticky or put down tape. These will eliminate this issue and then you can remove whenever you want. These printers should all come with a thermal management barrier but they don't.

 

I've got 2 big chunks out of mine, so if I print something big I get 2 warped spots. I just sand them down and use a slurry if I have to fill in gaps.
Now I would like to replace it, but I'm not sure with what. I debated about getting a piece of glass to put over the top of the old one, but I'm not sure what type and where to even go to get one. I thought about aluminum but I'm not sure if a thin sheet over the glass would work well or not.