When I first got my UM2 a year ago I did a lot of experiments printing on glass. I have the HBK for my UMO and everything still applies:
PLA on glass
If you don't want to read it all... For maximum sticking you need the PLA to be hot enough on the bottom layer to flow onto the glass. This means heat. For 20C air, 220C nozzle, this means about 45C minimum. Colder than 45C means it won't stick well at all. From 45C to 70C it's all the same stickiness (no difference). But if you have colder air or colder nozzle you need warmer glass. So I recommend 50C or 60C to be safe. In fact I recommend you do a bunch of experiments and print something that takes under 3 minutes to print and find a way to measure the force of removing that object.
That was too much info. Anyway here is the trick for printing on glass (which is superior in every way to blue tape):
1) Get Elmer's wood glue (it's a pva glue like the glue stick- what country are you in?). Mix it 10 parts water to 1 part glue (this is not exact). Keep it in a glass jar with lid and shake well before each use. Use a cheap paint brush to spread onto the glass. Heat up the glass and don't print until the PVA is dry and so thin it is invisible.
2) Heated bed at 50C
3) Use brim option - extremely important
4) Bottom layer should be squished a bit. Consider moving the glass closer to the nozzle.
If you have very large prints that are still warping you *might* have to print at 75C to keep the part above glass temp on the lower layers. I have never had to do this. Make sure you let it cool to 50C before removing or you will destroy the part as it is still soft like clay at 75C.
Please update what country you are in on your settings.
For the ultimate in adhesion and warp-free printing I often print with blue painters tape on the heated bed @ 60-70 degrees, It works great. I used to have a custom heated bed but I switched to the kit and so far it has been perfect for me. I'm mostly just printing right on the glass with just a tiny bit of glue stick and I have not yet had any adhesion problems with that.
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