by cvoinescu » Mon Oct 06, 2014 9:15 pm
This is usually because the PLA remains very soft. Slowing down does not help, because the heat radiating from the hot end keeps the PLA from solidifying.
To fix this problem, I had to do two things: turn on "orbit" in Skeinforge, and add a fan blowing on the print.
"Orbit" does not slow down the printing, but, if a layer takes too little time to extrude, it adds one or more loops around the object, to give the last layer time to solidify without the hot end being right above it. I'm not sure whether there's an equivalent feature in other slicers.
I used a small DC brushless fan rated at 12 V, but powered from about 7 V. You can also turn it down from the firmware, but I did not have a spare MOSFET output at the time. You don't need a lot of air, just a gentle breeze in the general direction of the printed object. (And remember to turn it off when printing ABS.)