I have a Wanhao Duplicator I3, spent months performing modifications and improvements to it, one of the big ones being putting glass and PEI on the build plate. Everyone went on and on about how PEI is some wonder-material.... though I hear that while I was working on it something called Print Bite came out that's better but anyway...

So I finally used it for the first time yesterday.... and the only thing I have been able to successfully print are 20mm cubes.

I am using hatchbox PLA, not exactly an advanced or difficult material to print with, and from my understanding PLA doesn't even really require a heated bed, but I set mine to 45C anyway. I also reduced my acceleration to 800 and jerk to 3 as many people recommended to reduce ringing, and print at a fairly conservative speed of 50, with 45 for the outer/inner shell and 60 for the infill.

The Printer came with a OK-hand model used to test that the printer is working, and it never gets more than about 25 to 50% complete before it comes off the bed, and I even tried printing a 7 inch turntable.... basically a flat circle that takes up nearly the entire build plate... and not even THAT had enough surface area to stick to the PEI. I kept checking on it every few minutes and it was going fine... then I come back an hour later and it had completely come off the bed and was lying on the table.

Any suggestions what could be going wrong?