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I have tried to print that thing: http://forum.seemecnc.com/viewtopic.php?f=35&t=5639.
PEI, 90 Celsius build plate, without aluminium/copper plate under glass. Every corner has been warped up, and looks like one of them has been warped more than others, and catch the nozzle. I was not wathing all printing process (it was 8 hours), just first 20 minutes, thats result:

Not sure why you are having these results. I print things that have many more sharp corners and have 100% success. Try the sanding technique and cleaning with isopropyl alcohol. You should be ab;e to do much better than that!

mhackney wrote:Not sure why you are having these results. I print things that have many more sharp corners and have 100% success. Try the sanding technique and cleaning with isopropyl alcohol. You should be ab;e to do much better than that!

Thank you, i will try sanding. I have isopropyl alcohol used. Maybe I need set nozzle lower when calibrating

You should have Z set to get a nice squished bead on the 1st layer. But if you have it too close you will have a lot of difficulty getting the parts off the PEI.

mhackney wrote:You should have Z set to get a nice squished bead on the 1st layer. But if you have it too close you will have a lot of difficulty getting the parts off the PEI.

I think my calibration is pretty ok, but I also think that refrigerating PEI to remove printed part is better than part warping every time. But at first I'll try sanding

Are you sure that your bed temperature is not too low? I print ABS on PEI and donot have this problem although at times there are signs that the corners are raising for 1mm to 2mm in.

I like to run my bed at 100C to 105C MEASURED on the bed surface for ABS and 70C for PLA regardless or what the thermistor says. There will always be heat loss resulting in a variance between the embedded thermistor and the surface.

PEI has made more difference in printing that any other single change I have made. There is just no mess with glues, sprays, tapes and the air around the printer stays less blue from my language.

Also I have learned to preheat the bed manually and allow 5 minutes or so to let temperatures soak and stabilize before starting. Left to start automatically the printer will start as soon as the embedded thermistor sees the correct temperature and the surface may be too cool. If the first pass is cool and does not establish a good grip, things will never improve as the bed heats up.

I also sand with 1500 or 2000 grit paper every twenty prints or so or when the bed starts leaving am image of the last printed part on the interface and wipe down with Acetone between prints.

Hope this helps.

nitewatchman

I'd get a heat spreader and make sure the temp on top of the PEI is the bed temp you're printing at. You will need to run the bed thermistor hotter. For ABS I run at 105 and the PEI will be at 100 or so. Without the heat spreader you will have a large difference in temp from center to edge and your print will peel off. I have no idea how people got it to print properly without a heat spreader.

Once the print is done, I don't even need to get the bed cold. Once it gets down to about 75-80, I can just pop it off. PEI is the best printing surface, period. No fuss, No muss.

Thanks for postin btw. My PEI bed has not arrived yet. But when it does i am sure that this thread will be usefull.