ABS extrusion Lagging

so I am trying to print a VERY small bridge...1.5cm
i have printed longer before but this particular file doesn't seem to want to print...

When I look closely it seems that what is happening is;
- as the nozzle beings the bridge there is very little extruded,
- as the nozzle is about half way over the bridge it begins extruding a lot heavier... the weight of this means the extruded material just remains on the nozzle tip until it reaches the edge and gets wiped off...

I have tried a slightly slower print, and a much slower print (Bridge print a 7mm/s).. still the same problem occurs.


Afterwards I tried just extruding the ABS manually. I can see the extruder gear turn but it takes about 1-2 seconds before any material comes out the nozzle. is this normal??

? could it be my nozzle is blocked? (once it's extruding it comes out fine and to the correct thickness..)
? could it be my nozzle temp isn't high enough? it's at 245°c



Sorry i don't have any images, I'm going to try the print again tonight and will get an image/video of the failure...

You probably have a very short "run up" to the bridge and it tries to print it just after a retraction/extrusion cycle. Several things to try:

1) Set the "Bridges" parameter under "Speed" ("Print Settings") in Slic3r to something very low (e.g. 10mm/s - you also need to check the "Detect bridging perimeters" box under "Layers and perimeters").
2) Rotate the part 90, 180 or 270 degrees in Slic3r ("Plater") and see whether that works (the bridge might then be printed from the opposite direction giving a longer "run up")
3) Check the "Only retract when crossing perimeters" box under "Infill" and maybe "Avoid crossing perimeters" under "Layers & perimeters" (though that makes the slicing ridiculously slow so ensure slicing has completed before using the G file) to try to avoid the preceding retraction.
4) If all else fails you could try reducing the retraction length or disabling retraction completely "Printer settings", "Extruder 1". You'll get horrible stringing, but that can usually be filed off.

Dave
(#108)