Best way to fix ABS corner curling on enclosed Prusa style printer with PEI heatbed? I'm trying to set up an enclosed (custom enclosure) Prusa i3 style printer for ABS, but having a fair amount of difficulty preventing the part corners from curling.



Detailed specs:


Geetech A10 (generic Prusa clone) w/ PEI heatbed
Custom enclosure
Slic3r software
ABS filament (obviously!)
247&nbsp;°C hotend temp
115&nbsp;°C heated bed first layer, 110&nbsp;°C for others
Fan on for layer 3 and above


Verified heatbed temperature with calibrated IR imager.

Thus far I have been unable to prevent parts from separating from the heatbed during print, primarily at the corners where stress is concentrated.  I've tried various heatbed temperatures from 90&nbsp;°C to 115&nbsp;°C, lower hotend temperatures (which just made the problem worse and caused complete print failure), cleaning the PEI surface with alcohol, etc. to no avail.  I'm even seeing this to some extent with Benchy, it shows up as a lift to the stern and bow (slight bend parallel to the keel) -- the print is otherwise basically perfect.

I've attached an image of the more extreme curling -- yes, I should probably be using mouse ears on a part like this, but I see the same thing on parts that shouldn't require mouse ears.

What is the best way to fix this particular problem?  Temperature adjustments, brims, rafts, something else?
Adding 20mm mouse ears was sufficient to resolve the problem using the original extrusion / heatbed settings.  I did not expect mouse ears to be required on the Benchy model, but given the lack of better advice it seems this may be a poorly documented "feature" of ABS.

Results on the original worst-case test model:



Note that the brims will not help if the bed is insufficiently leveled -- the brim has to actually merge with / melt into the base part layer, so the extruder height has to be perfect at the brim to part interface.

Example of extruder too far away from bed: