I just added a PEI sheet on top of the glass of my UM2 (100% abs "fail" rate before PEI btw). Using stock ABS settings the corners warped >30% of the print's radius/length/width...size (xy plane). I raised the temp up to 99c and speed down to 80%, warping decreased to like ~10%. So I moved the bed ~1 turn of the leveling knobs closer after scouring every problematic PEI post and wet sanded lightly with 1500 grit. This helped but I still get 1-2mm of warping (zx plane and xy planes).
One thing I saw in PEI research was 110&50c seem to be the magic numbers for PEI, 110 being the temp where the surface adheres to abs and 50 where it rejects it.
This brings me to my issue, UM2 specs say 100c is max for the bed. The controls let you go above this, but prior experience with various brands, types, sizes, etc of heaters (and printers in general) have made me very apprehensive of going above a certain value (100 for most, 110 and 120 for a couple) since most seems to degrade in performance when pushed beyond that level.
So, whats the max "safe" temp for the UM2 bed, will it last at 110c? and I guess while we are at it who else still has issues with PEI after reading every other post that end at "wash with alcohol and run at a high bed temp, #goodluck"?!
ps PEI is pretty fricken sweet but at this point it's being out performed by failed-prints-melted-in-acetone-smeared-on-a-stock-SD4-bed :(
psps, the printer is mostly enclosed and I had a couple successes but the buildplate was even closer and the print wouldnt come off even after putting the plate in the freezer.