I tried using the Skeinforge Cool plugin in order to print the first layer at a higher temperature than the bulk of the object, with an eye toward improving the first layer’s adhesion to the build platform. Even with Reverse sucking back the filament before Cool begins, the nozzle dribbles little snots as it passes around the object’s perimeter:
The nozzle orbits at exactly the top of the just-extruded layer, so the least little bit of ooze from the nozzle sticks to the layer. The spacing between snots shows that the nozzle fills up on a regular basis, even with the Extruder motor turned off.
Running the extruder motor backwards for a bit would introduce an actual air bubble inside the nozzle, but then the plastic would ooze to the bottom, the air bubble would rise, and the nozzle would fart after starting the next layer. Not a desirable outcome.
These tweaks to the cool_start.gcode and cool_end.gcode routines lift the nozzle during the cooling orbit and lower it at the end:
(cool_start.gcode) M106 (fan on) G91 (incremental mode) G0 Z1 (up a little bit) G90 (absolute mode) --------------- (cool_end.gcode) M107 (fan off) G91 (incremental mode) G0 Z-1 (down to object) G90 (absolute mode)
Alas, Skeinforge inserts those files at every layer change, which means the nozzle jumps up-and-down at the same spot on every layer… and that introduces a major blemish at what used to be a minor seam.
Worse, if you’re building multiple copies of the same object, the G-Code file finishes a layer on the last object, does a little hop, returns to the first object, does a little hop, and then begins the cool-down orbit. Maybe that could be fixed by moving Cool after Multiply, but it’s starting to look like a hackfest instead of Just Working.