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Type of glass on the build plate?

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No it's not. It's tempered glass. But I'm pretty sure you can use any glass. Boroscilicate glass (aka pyrex) has a very low temperature expansion coefficient so that would be better than regular glass. But more expensive. Because the heated bed heats up slowly and evenly and because the clips allow the glass to expand and contract, regular glass is fine. More important is the thickness of the glass (4mm?).

Anyway go to your local glass store and have them cut you up a piece of the right dimensions. It's very inexpensive. Maybe $10 to have it cut to dimension and ground smooth? Maybe buy 2. More money if tempered glass. Let us know how much they charge you.


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But I'm pretty sure you can use any glass.


Yes, you can. But the adhesion is not the same on every type of glass.

For instance, I use a mirror glass tile from IKEA on my custom heated bed on the UMO. And PLA sticks like welded to the glass. I recently had to put a mirror tile with the print on it for three days :!: into the fridge until it came of.

The standard glass on the UM2 has - well- acceptable adhesion when heated to the very same temperature (60°C). I also have the impression that the UM2 glass (where you can see some interferences) is not as even as the mirror tile which has to be perfectly even as you would see this in the mirror...

At the moment I don't know yet what the exact difference between the two glass types is but I'm working on it...


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I don't think thermal expansion counts at all. Printing is achieved at rather constant bed temperature. Well, first layer may be at higher, but normally just 10 degrees, and contraction from say 65C to 55C will be something like 0.01 mm per 100 mm.

I had a similar concern for a quite big ceramic plate (ca. 500x500 mm) on an X400 from GermanRepRap. But when I measured the variance between 20C and 110C, it was practically zero.

"Adhesion" may definitely differ. I think there are two kinds of "adhesion", when you do not use any kind of "glue".

1. By normal air pressure - this is obtained if the surface is as of... glass (glass, kapton, PET). On such a surface, if the plastic is laid down correctly, leaving (near to) no air underside, the atmospheric air pressure will keep the part on the bed. This is why, in such a case, you can detach the part by hitting it laterally, making it to slide on the surface and get some air that will actually make it... fly :)

2. Through porosity - these apply to such surfaces, as in the case of blue tape, BuildTak. There are also some "profi" machines that uses intentionally porous bed materials in different forms.

One interesting point is about the bed temp. Basically, the rule says that first layer should be above glass transition temp, say 5C, while the rest should be just slightly below, also 5C just for simplicity :) The only issue is that not always the actual value is known or is exactly the one stated by the manufacturer, but is a good starting point. To calibrate, one should try to find the temperature where the plastic become hard from soft and/or the other way around.


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