I have seen this topic creep up a couple of times, and I would appreciate some help to get to the bottom of it.
I'm not sure why some people seem to have the issue, others dont, and that despite all (most) of us having the exact same printer.
This seems like a opportunity to try and find out whats different between people having PLA curl on overhangs, and those fortunate not to have it.
I'll add a picture of this model from thingiverse: http://www.thingiverse.com/thing:1709106
I printed the *coils and *circle version, and both exhibit the behaviour you can see below.
As you can see, the overhang on the side behind the nozzle curves up, while the front overhang (which is identical) doesn't.
If you print the long (snake coil) version, you will see the curling happening more on the right side of the printer, and less on the left, and more on the back side of the print, than at the front.
I have a similar issue with for example this print: http://www.thingiverse.com/thing:1563995
The fins of the rocket have overhangs until they meet the body of the rocket, and due to curling up and the small footprint, it they get knocked off the bed and the print fails.
Both models were sliced with slic3r, Prusa edition, RC2. With the default settings for PLA, 0.2mm and with Z-hop.
I didn't change anything in the settings.
I can get the snake to print, If I reduce the printing speed to 50% (during print, reduce speed with the dial on the printer)
I tied various other things, like higher and lower filament and bed temperatures. 100% fan speed, reducing extrusion modifier, etc.
The printer is in a room thats currently rather cold at about 12-15 degrees Celsius.
Could someone try to print the Snake_coil.stl from above link in PLA, and tell me if they can get it to print with default settings? Its no a very long print, and the curling shows up at about 30% into the print, maybe 30-40 minutes at default 0.2mm.
Any Ideas what I can do to get this under control?