PEI Bed Burnt, Cracked, & Peeled

Ok after seeing the T-800 print from another thread, and having a lot of success with my current setup (after moving) I decided to give it a shot. I also wanted to try my hand with a print from sd card for gcode I create from Cura.

Well, the print went well mostly. 48 hours. .15 layer height, abs, 228 nozzle temp, 100 print bed, 20% infill.

The print was good. Some Z banding (which I’ve never been able to get rid of entirely). I had a small Z shift half way up. The main issue I had where cracking at various layers, so I thought. After removing the print I tore the pei right off, which was burnt along with the bottom of the abs. Im guessing 100 was too high. (I now recall an updated recommendation of 85 degree for ABS).

Images attached

My big question now - how do I repair the printer bed? Is this just a matter of pealing the rest off, cleaning the glass, and replacing the sheet? Are there instructions available (haven’t looked yet)? Do I need to be concerned with any other possible damage?

PS Taz 5 printer.

The temperature was a little too high for the grey plastic, but it should have been fine for the PEI sheet. That looks like it was up closer to 120. The main reason the PEI probably failed was due to removal technique. Grey ABS tends to discolor above 235 or 95 on the bed. It’s cosmetic, and you can generally ignore it or sand it off. To remove that part properly though, you need to use a careful wedgeing action around all edges at approximatly 60 degrees. Fully cool parts are actually harder to remove. The removal tool of choice varies, many people use paint scrapers. I personally use this cheese slicer: with the slicy part taped over with heavy gorilla tape. The thin leading edge which is dull at the front, but thin enough to get under almost any part, and reinforced at the sides is basically the ideal 3d printer part removal tool. I keep trying to get someone to make them without the cheese slicer part, but so far no luck.

As far as replacing the PEI, you’re in luck, it’s a fairly easy process with two paths you can take. 1. you can remove the existing PEI and adhesive and replace it for $45 . The process to do that involves freezing the entire build plate for an hour or so to cause the adhesive to relax, carefully removing the remaining PEI, using a citrus based adhesive remover (such as goof off) to remove just the PEI adhesive from the PEI side of the glass (and being extra careful to keep it away from the heater side), then cleaning the glass very well twice with glass cleaner and adhering the new sheet.

You can also just buy a new bed heater and glass PEI sandwich assembly: the blemished ones go for $49 or so.

To properly remove a part, wait for the bed temperature to lower to 60, or reheat it to 60, then starting at a corner, work your removal tool under the brim or part edge, being careful to not gauge the bed. then slowly work your way around the edges and towards the center, striving to wedge the part away rather than pull it up off the bed. If you end up with a discolored white spot under the part, thats an air bubble and it means you didn’t do it correctly. Next time you print that will act as an insulator, and either make things not stick correctly, or trap heat and cook your PEI. You may also have been slightly too close to the bed, though for a tall print like that it’s better to err on closer.

edit: you shouldn’t be too worried about other damage. You’ll want to check the bed for level/tram once you reinstall things, and maybe look to see if a rod looks visibly bent or anything like that, but that would be rare.

Hope that helps!

Thanks Piercet! Very helpful.

I actually have been using that exact cheese slicer. The bed temp was about low to mid 50s when I was removing it. I had removed it as you described but must admit I started to get a little impatient and used more force than normal after getting it half way off. That said, the PEI sheet was definitely “cooked” and chances are I had some air bubbles from the past that may have helped contribute to this as you alluded. Next time I will be more patient and set/wait for bed temp to 60 for removal.

Bed temp during print was def set at 100. Is it possible bed temp is greatly higher than LCD states? I took a pic of the LCD during print. It’s attached.

I’m not too worried about the discolored filament if it’s just color (and not something to be concerned with - like fire).

I happen to have a spare sheet of the PEI laying around (purchased a little while ago when I thought it was something that should be replaced regularly - I later learned that wasn’t true but held onto it). I will give it a go.

Thanks again.

Yes, it can very well be an incorrect temperature if the thermistor is failing or has become disattached. You will want to verify the temperature with an inexpensive infrared point and shoot thermometer such as found at your local hardware or automotive tool supply store (around $35), and if it appears to be off on the high side, check the underside of the bed where the electrical wires are attached and see if the thermistor flap seems to be pulling away from the bed for some reason. If it is off, the fix is generally to replace the bed heater unfortunatly as there isn’t an easy way to get to that sensor. But failure on them is also quite rare.