Imagine the first layer is well parametered and sticking perfectly.
But then the nozzle stops, lifts up and then accelerates fast towards its next destination on the bed.
The sudden movement rips off a few millimetres of most recently laid track which has not quite had enough time to settle in to the print surface.
This is a situation I know well and, if it keeps happening, sometimes I:
a) rearrange parts on the bed to change the direction in which the nozzle will move when it lifts up to move to the next part;
b) slow the first layer even more;
c) make the first layer tighter on the bed;
Are there not things that could be done by the slicer itself?
3 suggestions that would need to be validated experimentally:
1) dynamic speeds for first layers. Say that you set the first layer to 50% print speed with "dynamic speed control". As the extruder reaches the end of a track it SLOWS down (50%, 40%, 30%....) to allow the track maximum time to bake in to the print surface before lifting off and moving at high speed in another direction;
2) a "continue in same direction of travel after nozzle lift" feature which means that the nozzle will, after lifting from the bed, continue for say 10mm in the same direction that it has currently been laying a track. Thus, if the track lifts off, it will do so minimally. Then it will change direction and head directly to where it needs to be next.
3) "dip nozzle before lifting to X% of layer height". This feature would, perhaps just before the end of a track, move the nozzle closer the bed to both squish the plastic into the bed (increasing adhesion) and to pinch off the filament;
Might option (3) leave a visible artefact in the print? Yes, but it would be minimal compared to the appearance of a track that becomes detached and thence smeared across the base of the print. And if it serves to prevent small parts from detaching altogether, then in certain situations it would be more than worth it.
A reverse version of option (3) might be interesting for another moment in the Gcode which NEVER works well. That is the moment the very first track goes down. Invariably (despite a pre-extrusion in the dock and having set the first layer at an "ideal" height) the very first part of the very first track doesn't stick or curls up. If the nozzle were to start CLOSER to the bed for the first 1-2mm and then back off to the desired settings, my guess is that this would fix the problem.
Thanks (loving 4.0!)
